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COMPARISON OF TWO VISUAL ACUITY ASSESSMENT TESTS IN THREE TO SIX YEAR OLD CHILDREN
DISSERTATION SUBMITTED AS PART OF FULFILMENT FOR THE MS BRANCH III (OPHTHALMOLOGY) EXAMINATION
DEGREE EXAMINATION OF THE TAMIL NADU DR.M.G.R MEDICAL UNIVERSITY, TO BE HELD IN APRIL 2016
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BONAFIDE CERTIFICATE
This is to certify that this dissertation entitled “Comparison of two visual acuity assessment tests in three to six year old children” done towards fulfillments of the requirements of the Tamil Nadu Dr M.G.R Medical University, Chennai, for the MS Branch III (Ophthalmology) examination to be conducted in April 2016, is a bonafide work of Dr Rutika S. Dodeja, post graduate student in the Department of
Ophthalmology, Christian Medical College, Vellore.
Dr Andrew David Braganza,
Professor, Head of the Department, Department of Ophthalmology, Christian Medical College, Vellore 632001
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BONAFIDE CERTIFICATE
This is to certify that this dissertation entitled “Comparison of two visual acuity assessment tests in three to six year old children” done towards fulfillments of the requirements of the Tamil Nadu Dr M.G.R Medical University, Chennai, for the MS Branch III (Ophthalmology) examination to be conducted in April 2016, is a bonafide work of Dr Rutika S. Dodeja, post graduate student in the Department of
Ophthalmology, Christian Medical College, Vellore.
Dr Smitha Jasper,
Associate Professor,
Department of Ophthalmology, Christian Medical College, Vellore
Dr Swetha Sara Philip,
Assistant Professor,
Department of Ophthalmology, Christian Medical College, Vellore
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BONAFIDE CERTIFICATE
This is to certify that this dissertation entitled “Comparison of two visual acuity assessment tests in three to six year old children” done towards fulfillments of the requirements of the Tamil Nadu Dr M.G.R Medical University, Chennai, for the MS Branch III (Ophthalmology) examination to be conducted in April 2016, is a bonafide work of me, Dr Rutika S. Dodeja, post graduate student in the Department of
Ophthalmology, Christian Medical College, Vellore.
Dr Rutika S Dodeja,
Post graduate resident,
Department of Ophthalmology, Christian Medical College, Vellore 632001
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ACKNOWLEDGEMENTS
I feel absolutely grateful and truly fortunate at being given the opportunity to be a part of the institution that is Christian Medical College. This institution has made me the doctor that I am today and has amplified my love and interest in the field of
Ophthalmology manifold. I cherish the days I have spent here in learning the art and science of the subject.
I am indebted to all the parents and children who consented to participate in the study.
Without them, this work would not have been possible, nor would this education.
I am highly obliged to have had Dr Smitha Jasper as my guide. From her, I have learnt how important being methodical and thorough is. Every step of the way, she made an effort to refine my work and to steer it in a direction that would make it more
productive and meaningful. I am thankful for all the effort that she has put in to make this dissertation come together.
I thank Dr Swetha Sara Philip, my co-guide, for inspiring me to steer towards paediatric ophthalmology. It has been thanks to her interaction with children that I believed that this was possible. I am also grateful for her patience with me, despite all my inadequacies.
I specially thank Mrs Mahasampath Gowri, my statistician, who helped throw light on aspects of the thesis that were otherwise so bleak and scary. I would also like to thank Mr Prakash and Mr Madhan for all their help and guidance through the process of data entry and analysis.
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I am very grateful to Dr Andrew Braganza for his objective criticism, his rational approach and factual assessment of every situation presented to him. The way he always finds a sound solution to every problem is admirable.
I also thank Dr Sarada David, Dr Thomas Kuriakose, Dr Lekha Mary Abraham, Dr Pushpa Jacob, Dr Arathi Simha, Dr Sanita Korah, Dr Sheeja Susan John, Dr Padma Paul, Dr Deepa John, Dr Saban Horo, Dr Anupriya Arthur, Dr Jeyanth Rose, Dr Anika Amritanand and Dr Satheesh Solomon T Selvin for their kind words, nudges of
encouragement and constant support through these years, not just through this thesis, but also through my training.
I am indebted to my colleagues for remembering to help me achieve my sample size and being so pro- active in sending me patients through the course of my study. I am also thankful to them for all the laughter that we share while we work together, despite our differences.
This dissertation would not have been possible without the support of the staff of the hospital, and it is to them that I would like to dedicate this piece of work. Mr
Deenadayalan, Mr Maydhinaselvan, Mrs Joy Rathinammal, Mr Gideon, Mr Bhushan, Mrs Jayanthi, Mrs Sarojini, Mr Vijayarangan and Mr Mohan deserve a heartfelt thank you for their warmth, support and kindness.
Miss Chris Elsa, Miss Haseena Ruhi, Miss Nancy Priyanka were there every step of the way in making this work come together, whether it was finding patients, collecting and entering data and even wiping a few tears. They made this process joyful and egged me on further. I am very thankful to them for their dedication and sincerity
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towards this work. Here, I would also like to thank Mr Dinesh, Mr Bilto, Mr Ringsar, Miss Jennifer, Miss Shreya, Miss Tanya, Miss Shilpa, Miss Mahiba, Miss Abhriya and Mr Milton for their help through the process.
I would like to thank my family for their unwavering support through my education and for their constant belief that I can do better.
My husband, Dr Varun Hathiramani, deserves a special mention. I am forever
indebted to him for believing in me even when I did not and for making me wager on, even though I would have rather packed up and left. I am thankful, for everything that he has been, all through.
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ORIGINALITY REPORT
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TABLE OF CONTENTS
INTRODUCTION ... 1
REVIEW OF LITERATURE ... 8
MATERIALS AND METHODS ... 41
ANALYSIS AND RESULTS ... 52
DISCUSSION ... 70
CONCLUSIONS ... 75
BIBLIOGRAPHY ... 78
ANNEXURES ... i
ANNEXURE 1: IRB APPROVAL LETTER ... ii
ANNEXURE 2: INFORMATION SHEETS AND CONSENT FORMS ... v
ANNEXURE 3: DATA COLLECTION PROFORMA ... xxii
ANNEXURE 4: PICTURES ON THE STANDARD AND MODIFIED KAY PICTURE TESTS ... xxv
ANNEXURE 5: ILLUSTRATIONS OF THE TESTING PROTOCOL ... xxvii
ANNEXURE 6: EXCEL DATA SHEET ... xxix
1
INTRODUCTION
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The assessment of vision is the first step of examination in Ophthalmology. The assessment of vision helps us to quantify visual potential and to differentiate normal from abnormal. This then helps us to decide on whether or not treatment is required.
This is particularly important in children. This is because the period of visual development has been proved to be up to the age of seven years and therefore, the early detection of visual impairment will help in early management and thus, prevent blindness from preventable causes. (1, 2, 3, 4, 5)
Amblyopia is a very common and easily undetected cause of decreased vision in children, which is treatable if detected early. Assessment of vision in children is aimed at early recognition of amblyopia and its timely management. (1, 5)
The important thing in the assessment of visual acuity in children is to consider the phenomenon of crowding. It has been shown that uncrowded visual acuity charts over-estimate visual acuity in children compared to crowded ones. This may be disastrous in the diagnosis of amblyopia, and therefore in its management. (6, 7, 8, 9, 10)
However, the assessment of vision in children is painstakingly challenging. It requires diligence and patience. Children may not understand the test that is administered, are easily distracted, may resent occlusion of the better eye and may not follow
instructions. This makes it difficult for the examiner to carry out the tests that are normally done for adults. In order to circumvent this difficulty, many child friendly tests have been designed. These tests include pictures and toys, which help hold the child’s interest and thus help in carrying out the test easily.
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Among the tests used in the assessment of visual acuity, there are tests based on detection, resolution and recognition acuity. (8, 11)
Detection acuity is only to identify whether or not a target is present. It is a crude assessment and does not help in quantification of vision. (8, 11)
Resolution acuity is the identification of a particular target in contrast to its
background. The targets are variable and there are various tests of different designs available. Among these, one commonly used test is the Cardiff acuity cards. These cards include single pictures in a white outline against a grey background. The test is designed such that there are different pictures at different acuity levels and thus, visual acuity can be quantified and measured. This is an easy to carry out and is quick. This test is however, uncrowded. (8, 12)
Recognition acuity involves the resolution of the target and its identification.
Recognition acuity tests are the ones that are used for adults. They can also be easily administered to children above the age of six years. These include the Snellen’s chart and the Bailey Lovie visual acuity chart, which are used most commonly in adults.
The Kay picture test is also a recognition acuity test. It uses child friendly pictures like duck, house, clock, cup, boot, fish, truck and apple. The test involves the child
identifying and naming each picture at every acuity level. It is administered from a book and visual acuity quantified depending upon the child’s ability to identify and name the pictures at different acuity levels. This test is available in crowded and uncrowded formats. (8, 13, 14)
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There is yet to be a gold standard for the testing of visual acuity in children between the ages of 3 and 6 years. A variety of tests are used all over the world. Most of these tests are not standardised. We use Cardiff acuity cards in our routine clinical practice to assess vision in children who cannot recognize the Snellen’s chart.
Cardiff acuity test is a resolution acuity test while the crowded Kay picture test is a recognition visual acuity test. It is known that resolution acuity tests over-estimate visual acuity when compared to recognition acuity tests. Recognition visual acuity is the best measure of assessment of visual acuity in children between the ages of 3 and 6 years.(5, 6, 7, 10,15, 16) The crowded Kay picture test is based on the construction principles of the ‘gold standard’ Bailey-Lovie charts. The crowded Kay picture test is an acceptable practice for assessment of visual acuity in 3 to 6 year olds. (16)
To our knowledge, we have not found any study comparing the Cardiff acuity test and the standard crowded Kay picture test in 3 to 6 year old children. Our aim was to compare visual acuity assessment by the Cardiff acuity test and the crowded standard Kay picture test.
The Kay picture test was designed in the United Kingdom. In our clinical setting, we found that children find it difficult to recognise some pictures on the standard Kay picture test. The standard Kay picture test was therefore, modified to include more familiar pictures using standard principles of optotype size and contrast. The modified pictures include star,
spectacles, cup and saucer and toffee in addition to the original pictures that are duck, clock, fish and house. Therefore, we also assessed if pictures in the modified Kay picture test were more easily identified by children as compared to pictures of the standard Kay picture test. In
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order to do this, we compared time taken by the children to identify each picture in the two tests.
We also assessed various factors that we thought would influence visual acuity testing in children in the age group of 3 to 6 years. This included parental age and education, order of the child in the family, number of siblings, education of the siblings, current schooling of the child and the existence of co-morbidities in the child, parents or siblings.
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AIMS AND OBJECTIVES
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Aim of the study-
To compare the visual acuity assessment using Cardiff acuity cards and the Kay picture test in 3 to 6 year old children
Objectives of the study-
1. To compare assessment of visual acuity using the Cardiff visual acuity cards and the crowded standard Kay picture test in children between the ages of 3 and 6 years
2. To compare picture identification in the modified Kay picture test with the standard Kay picture test in children between the ages of 3 and 6 years
Hypothesis-
1. There is no difference in the visual acuity assessed between the Cardiff acuity cards and the standard crowded Kay picture test in children between the ages of 3 and 6 years
2. There is no difference in the identification of pictures between the standard Kay and the modified Kay visual acuity pictures in children between the ages of 3 and 6 years in our clinical setting
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REVIEW OF LITERATURE
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Visual function is an amalgamation of several simultaneous optical and neurological processes. (2, 11, 17, 18) It is the ability to survey a scene, recognise an object of interest, move towards it and pick it up, and requires a number of cognitive higher visual pathways.
(19) It is a composite of the ability of the eye to identify objects and discern details. Intact visual function is responsible for our ability to move accurately through visual space, handle visual scenes and help in recognition of different aspects of the world. (2, 11, 17, 18, 19) It comprises of visual acuity, contrast sensitivity, colour vision and visual field. In addition to these, there are other aspects of visual function that include stereo-acuity, reading fluency and reading comprehension. Visual acuity is one of the most important components of visual function. Visual acuity assessment is the most commonly used tool in ophthalmic practice in order to measure visual function. (2, 5, 11, 17, 18)
What is visual acuity?
Visual acuity is a description of the acuteness or the sharpness of vision. It is a function of the dioptric apparatus of the eye along with the retina, the nervous pathways and the central nervous system. (20)
Resolution is the ability of the eye to discriminate two targets separated in space. Limit of resolution or resolving power is the smallest angle of separation that allows the optical system to discern two separate images. It is important to be able to measure this resolving power of the eye. Measurement of this resolving power, or threshold of discrimination, is termed as visual acuity. (18)
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Visual acuity is determined by the smallest retinal image whose form can be appreciated. (20) It is dependent on the minimum visible, minimum legible, minimum separable and Vernier acuity. (21) The ability to differentiate progressively smaller letters is called the minimum legible threshold. The minimum visible threshold is a measure of the minimum brightness of a target required to distinguish it from its background. The minimum separable threshold is the smallest visual angle at which two separate objects can be discriminated. Vernier acuity is the smallest detectable amount of misalignment of two line segments. (20, 21)
The components of visual acuity include detection acuity, resolution acuity and recognition acuity. (8) Detection is the ability to determine whether or not a stimulus is present.
Resolution is the ability to be able to differentiate an object from its surroundings and recognition is the ability to identify the object. Recognition requires a greater cognitive function than detection or resolution. (8, 11) Recognition of an object requires comparison of the visual input with the ‘image libraries’ in the temporal lobe (19)
Visual acuity is important for the following: (22)
1. As a tool to help the clinician to verify the optimal correction of refractive errors 2. As a screening device to suggest the presence or absence of ocular abnormalities 3. To monitor the effects of disease, its course and treatment
4. To help determine the visual aids required for tasks with individuals of normal and subnormal vision
To help estimate a person’s ability to perform certain tasks (issuing a driving licence, assessment of colour vision)
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Visual development:
The visual system comprises of the retina, optic nerves and the visual cortex. The visual system is immature at birth and begins to mature in the first few weeks of life. (23) The basic visual capacity is established soon after birth and improves rapidly during the first year of life. (24) Normal visual development is achieved in progressive steps after birth. (25)
Structural development of the eyeball:
Emmetropisation is a normal physiological process of eye growth. It involves axial elongation of the eyeball in response to the normal hyperopia of the neonatal eye. This process occurs soon after birth and is completed in about 82% of infants by the age of one year. (26)
At birth, the axial length of the eyeball is about 17 mm. It enlarges to 20 mm by the end of the first year and rapidly grows up to 2 years, and then slowly increases up to 24 mm by adulthood. The keratometry at birth is about 52 D, and by adulthood it is 42-44 D. The crystalline lens at birth is of very high power. It is about 34 D, which changes to about 20 D by adulthood. As the cornea flattens, the lens also thins and flattens. This is accompanied by simultaneous axial elongation. There is a co-ordination of growth between the three optical components. (27) A pathway has been postulated that directs this growth and change during the first few years of life. The growth of the eye and emmetropisation are not just pre- programmed automatically, they also require a visual stimulus for their normal development.
(27) The rate of the eyeball growth is linked to child growth and thus, the process of emmetropisation occurs as a part of the entire growth process. (28)
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The fovea is responsible for central vision and has the sharpest visual acuity. The macular retinal layers are responsible for colour vision, contrast sensitivity, precision of visual acuity and stereoscopic vision. (29) The peripheral retinal is mature at birth. However, the fovea and the macula begin to develop at the age of 6 weeks post-natally and their development continues until 8 months of age. (29).The fovea reaches full maturity approximately at the age of 4 years. (29) Much of the improvement in visual acuity in the first few years of life is attributable to the development of the retina. The density of the photoreceptors in the centre of the retina increases, while that in the peripheral retina decreases. This is what accounts for the sharpest acuity at the centre. (30)
Structural development and maturation of the central nervous system components:
The development of visual function is dependent on the development of visual pathways in the eye along with those that are located in the visual cortex in the occipital lobe, the lateral geniculate nucleus in the thalamus and the development of the synaptic neurons that link the eyes with the lateral geniculate nucleus and the visual cortex. (31) Myelination of the optic nerve and optic tract is incomplete at birth and increase until the age of 2 years post natally.
(32) The lateral geniculate nucleus is immature at birth and there is a rapid growth in the post synaptic surfaces that are noted for the first few months after birth, which then slow down by the age of 2 years. The development of the visual cortex occurs during the first two years of life. (33) The retina and the lateral genticulate body mature at 2 to 3 years, and at this time, the VEP acuity is similar to that of adults (30). The development of synapses in the visual cortex is rapid after birth and stabilises by the age of 11 years. The maximum density of synapses is seen at 8 to 9 months of age. Following this period, there is a loss of synapses, which stabilises by the age of 11 years. (31) This stabilisation of synapses is thought to be
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because of the maturation of the nervous system and relates to the reduction in the plasticity of the central nervous system. (31)
The critical period of development is the period of visual maturation in which the visual system is affected by outside influences. (34) Visual stimuli are critical to the development of normal vision. The normal development of the visual pathways in the CNS requires the brain to receive clear and focussed images from both eyes. (34) When there is an inhibition of these neurological pathways due to any cause, there are anatomical changes in the visual pathway and the occipital cortex. (5) These areas are noted to be reduced in volume. (5) With appropriate stimulation, reassignment of the pathways from the affected to the fellow eye is known to occur, due to plasticity in the neurological structures. (5) This is however, possible only in the critical period of visual development, which is a sensitive time from birth to 6 to 8 years of age. (1, 3, 4, 5) This critical period is until the age of 8 years, as till then, the neuronal systems are plastic and allow for alterations in the visual system. (5) Various ocular processes that interfere with, or inhibit the development of the visual pathways may lead to amblyopia. (35)
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The description of normal visual behaviour in the first year of life proceeds as follows: (2, 40) Table 1: Normal visual behaviour in the first year of life (2, 40)
Function Age
Intermittent visual fixation , turns eyes and head to look at light sources, horizontal tracking
Birth
Fixation on a nearby human face, eye contact, vertical and circular tracking
2-3 months
Smooth following movements of nearby objects, watches own hands, reaches towards hanging objects
3 months
Fixation on distant objects, widening of sphere of Attention
6 months
Interest in pictures, recognition of partially hidden objects, grasps small objects
7-10 months
Visual orientation at home, looking through windows, recognises people and pictures
11-12 months
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Visual behaviour and performance:
Visual behaviour and performance evolve with the maturation of the visual system. The primary fixation reflex is present at birth and helps achieve foveal fixation in either eye. (36, 37) The re-fixation reflex allows foveal re-fixation from target to target and allows the maintenance of foveal fixation on a moving target. This develops from 6 to 8 weeks of age.
(36, 37) Most neonates are able to locate and briefly fix on a moving target. The conjugate fixation reflex develops from 2 to 3 weeks of age. Following this reflex, the two eyes can fix on an object together and follow it over a considerable range for a few seconds. (36, 37) Colour vision and smooth pursuit eye movements develop from 2 months. (37) Accommodation develops from 2 to 3 months and approaches the same levels of accuracy as adults. (37) By the age of 6 months, the conjugate movements of binocular vision are accurate and convergence is well developed. (36, 37) Stereopsis and binocular visual function develop between the ages of 3 to 7 months. (38) Visual acuity usually reaches the adult level of 6/6 by the age of 3 to 5 years. (2, 39)
Importance of assessment of visual acuity in children:
There is a need for reliable and accurate measurement of visual acuity in children in order to detect and manage paediatric eye disease. (2) There are many inaccuracies in the subjective assessment of visual acuity in children due to their insufficient concentration, co-operation and intelligence. It is important to hold the child’s interest through the period of the test, along with being able to provide a reasonably accurate assessment of vision. (13) In addition to this, children do not often complain about visual acuity disorders.
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The assessment of visual acuity in children is challenging, but of utmost importance for the detection of many ocular disorders including strabismus, refractive errors and amblyopia. (2, 11) Among these, the most important is amblyopia. It is said that at the heart of paediatric ophthalmology, lies, amblyopia.
“Amblyopia is the unilateral, or rarely bilateral, decrease in best corrected visual acuity caused by form sense deprivation and/or abnormal binocular interaction, for which there is no identifiable pathology of the eye or the visual pathway”.(3) In this disorder, there is a dysfunction of the processing of visual information. (1) There is inhibition of the neuronal signals in the visual pathway of the amblyopic eye by the fellow eye during visual development and this causes anatomical changes in the visual pathway, as outlined above.
For amblyopia to set in, there has to be a disparity in vision in either eye. (1, 5)
Amblyopia is usually evident as the reduction in recognition visual acuity.(1) Clinically, it is identified as a two line difference or a >1 log unit in the best corrected visual acuity in between two eyes.(3) For the early recognition of amblyopia, the American Academy of Paediatrics, American Association for Paediatric Ophthalmology and Strabismus, and American Academy of Ophthalmology have recommended referral of children between 3 and 5 years of age, who have a two line or greater inter-ocular difference or a visual acuity worse than 20/40, to eye care providers. (41)
The reported incidence of amblyopia in the United States is 1-4% in pre- school children.
(42), while another reports it as 1-3.5% in developed countries. (5) In a study done on 4029 school children in a south India (43) to determine the causes of visual impairment, 1.1% of the population was found to have amblyopia. Two studies from India, looking into the
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prevalence of refractive errors, in urban and rural setting showed an incidence of amblyopia as 4.4% (44) and 12% (45) respectively.
However, most amblyopic visual loss is potentially reversible with timely detection and appropriate intervention. If treated in the critical phase of visual development, vision can be restored to the amblyopic eye. The options for treatment of amblyopia include patching of the better eye and penalisation. (1, 3, 5, 46) Prior to this treatment, any refractive error, media opacity or strabismus has to be corrected. The Amblyopia Treatment showed that amblyopia treatment is highly successful and approximately 75% of children less than 7 years achieve resolution with either atropine or patching (5).
Visual acuity testing:
The resolving power refers to the smallest angle of separation between two points which allows for the formation of two discernable images by the optical system. (18) This is determined by the smallest retinal image whose form can be appreciated. This is the minimal separable angle, with a threshold of 2 to 10 seconds of arc. (19) It is measured by the smallest object that can clearly be seen at a particular distance. The minimal visible angle is produced at the nodal point of the eye with a threshold of 1 minute of an arc. This represents the diameter of a cone, which is nearly 0.004mm. Thus, the theory is that the smallest object that can be resolved by the eye subtends the same visual angle at the nodal point of the eye as a cone phoropter. (18, 19)
For two separate points to be distinguished, it is imperative that their images be formed on cones that are not adjacent to each other, but are separated by an unstimulated cone. (18)
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In order for this to happen, the object of fixation must subtend a visual angle of 1 minute of an arc at the nodal point of the eye. This is the minimum visual angle of the normal eye or the minimal resolvable angle. (18) Spatial resolution is the ability of the eye to discern two objects that are separated in space. (2, 11, 18, 19)
The assessment of visual acuity is performed in a variety of ways. Tests may require: (8, 11) 1. A judgement of whether or not a target is present (detection acuity), for example-
visually evoked potential (VEP).
This is a measure of the minimum detectable resolution. That means that it shows the ability of the eye to identify an object against its background. It is a task of contrast discrimination.
2. Evidence that the spatial detail contained within a target has been fully resolved (resolution acuity), for example- grating acuity tests, Cardiff acuity cards.
This is a measure of the minimum separable resolution. This is the least separation between two points, lines or objects which is required for them to be seen as separate.
3. The identification of the target (recognition acuity), for example- Kay picture test, Snellen’s acuity test, ETDRS chart
This is a measurement of recognition resolution.
Most of these tests make use of ‘optotypes’. An optotype is a symbol, the identification of which corresponds to a certain level of visual acuity. In order to maximise contrast, all tests employ black letters or symbols or pictures on an opaque or retroilluminated background. The recognition of optotypes depends on the cognitive ability of the individual. (18)
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Principles and methods of assessment of visual acuity:
Several standardised charts are available for measuring recognition acuity in adults. The most widely used charts are the ETDRS chart and the Snellen’s chart. The Illiterate E or the Tumbling E chart, the Landolt’s C test, numerical charts and charts in regional languages are also available for visual acuity assessment in adults. These tests are based on the theory that is described above.
The ETDRS chart is based on the Bailey- Lovie chart construction principles. It is considered to be one of the more accurate forms of assessment of visual acuity. The Bailey- Lovie charts are made such that there is a logarithmic progression in size of the optotypes, there are the same numbers of optotypes at each level, the spacing between the letters and between rows is proportional to letter size and there is equal average legibility for the optotypes at each size level. The advantage is that size is the only significant variable when changing from one size level to the next. The proportional layout with equal number of letters on each line has the advantage that relative crowding and contour interaction remain the same for all lines, while only the magnification varies. Along with the chart design principles, the clinical scoring of visual acuity in logMAR units as a method for giving additional credit for each letter read correctly was also described.(11) The ETDRS chart is designed to be read at 6 metres and is scored in logMAR units. The range of visual acuity is from 6/60 to 6/3, with the log unit for 6/60 being 1.0 and for 6/6 being 0.0. Each letter on the chart is equal to 0.02 logMAR. The Bailey- Lovie chart construction principles are followed in the construction of most of the tests used for assessment of visual acuity worldwide. Despite the ETDRS charts being shown to be more accurate, they are not a popular routine clinical tool as the testing time is longer,
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they require specialised lanes and are more difficult to administer than the Snellen chart. (19, 47, 48, 49)
The Snellen chart, on the other hand is readily available, quick and easy to perform. The chart has letters of different sizes arranged from largest at the top to smallest at the bottom, which are read, one eye at a time, at a distance of 6 metres. Each letter on the chart subtends an angle of 5 minutes of arc at the appropriate testing distance, and each letter part subtends an angle of 1 minute of arc. The bars and spaces of each letter subtend an angle of one minute of an arc. It is thus, designed to measure acuity in angular terms. Snellen acuities are expressed as a fraction, with the numerator equal to the distance from the chart and the denominator being the size of the smallest line that can be read. The reciprocal of the fraction equals the angle, in minutes of arc, that the stroke of the letter subtends on the patient’s eye and is called the minimal angle of resolution(MAR). The test chart is normally read from 6 metres (20 feet). This, a person who identifies the letter on the 18 line from a distance of 6 metres, has a visual acuity of 6/18. Normal visual acuity is 6/6, though young adults may sometimes be able to achieve 6/4 visual acuity. (18, 50) The disadvantage of the Snellen chart is that it has variable letter size and there are variable letters per line. There is no standardised progression between lines and this makes statistical analysis difficult. Also, the letters on a Snellen chart are not always of the same legibility, some letters are easier to read than others. The distance between the letters and rows is not standardised and contour interactions vary throughout the Snellen chart. (47, 48, 49)
The Landolt ‘C’ or the Landolt ring is an interrupted circle whose stroke width and gap width are one fifth of its outer diameter. The two borders of the break are parallel.
It can be used as a four position or an eight position test. (22)
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The illiterate ‘E’, also called tumbling ‘E’ chart is also commonly used. It is based on a five- by- five grid. The E is presented in different orientations at each acuity level and the patient’s task is to identify the direction to which the limbs of the E point. This too can be used either as a four position or an eight position test. (11)
Many other optotypes are available and may be numerical or in different regional languages.
Details of assessment of visual acuity in children:
The effect of crowding:
In the assessment of visual acuity in children, the phenomenon of crowding (also referred to as ‘contour interaction’) has to be taken into consideration. It is easier to recognise a single optotype than it is to identify a row of optotypes. (51)Crowding is suggested to be a part of normal visual development, but is exaggerated in amblyopia. Various studies have proved that the assessment of visual acuity is over-estimated in the absence of crowding and this can be detrimental to the diagnosis and treatment of amblyopia. (52, 53)In a study done by Norgett et al to investigate the effect of test design (crowding) and age on visual acuity in a sample of young children, the conclusion drawn was that measured acuity is affected by the amount of contour interaction induced by the type of optotype and by inter-optotype separation. They found that maturation of line acuity continues to take place from 4 to 9 years.Therefore, crowded visual acuity tests are better in the assessment of visual acuity in children. (54) In another study, it was shown that visual acuity testing done using a single line gives better results, but the results may be misleading. They showed that visual acuity improved when the full chart was substituted by a single line and also when the single line
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was substituted by single optotypes. They also noted that visual acuity improved more significantly in eyes with amblyopia than in control subjects. (55) Crowding in visual acuity tests can be achieved by presenting many optotypes of the same size in a single line or by placing crowding bars around optotypes. (53) The crowding bars form a rectangle around the row of optotypes or a square around a single optotype. The thickness of the crowding bars is standardised.
Description of the various available tests:
Assessment of vision must ideally be performed in a room with minimal distractions. The assessment begins as soon as the child enters the room of the examiner. The child’s ability to see the examiner, visually track the examiner and to respond to the examiner’s smile must be noted (39)
Children with normal developmental milestones can generally be divided into three groups with respect to visual acuity testing: birth to three years, 3 to 6 years and 6 years and older.
(2) In children younger than 3 years of age, visual behaviour (as in table 1), rather than visual acuity is assessed. The goal is to determine whether the visual behaviour is normal for age and whether it is the same in both eyes. Children start following the instructions required for testing around the age of 3 to 4 years and an accurate assessment of visual acuity can be made in nearly all verbal co-operative children (39)
Infants up to the age of 3 years and children with developmental delay are generally unable to accomplish recognition acuity tests. (2) In these situations, objective visual acuity tests are
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employed. They include the fixation reflex, preferential looking test, visually evoked response (VEP) and the optokinetic nystagmus(OKN).(2)
The fixation reflex is developed at birth and it is a good marker of visual function, especially in pre-verbal children (56) In order to document this reflex, either of the CSM (central- steady- maintained) or the F+F (Fix and follow) notation may be used. (2, 39)
The VEP test is a recording of electrical activity of the visual cortex by stimulating the visual pathway. (3) In OKN, a white drum with vertical black stripes is rotated before the eyes. The patient follows the stripe in slow motion and as it disappears, switches suddenly back to pick up a new stripe. By varying the breadth of the stripes or the distance of the patient from the drum, an assessment of the acuity can be made, particularly in uncooperative and malingering patients. (57)
In preferential looking vision testing, a child, when presented with two different patterns, will tend to fixate the most novel or complex stimulus. (58) The principle behind this method of visual acuity assessment is that when infants and children are simultaneously presented with a patterned target and a blank target of equal luminance, they will preferentially look toward the patterned target. (6, 9) The stimulus may be presented by a card or by a monitor.
The adult is positioned out of the infant’s sight during the presentation, either behind the card or a screen. The adult views the child through a peephole positioned in between the uniform and patterned field. As the adult is not aware of the position of either field, there is no bias in testing. The adult tries to use any aspect of the infant’s behaviour to identify the infant’s response. The infant may either turn his head in the direction of the patterned stimulus, or may spend more time looking in the direction of the patterned stimulus.
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The responses of the infant may be variable and the observer does a few trials before administering the test completely. The responses are verified before proceeding further. If the infant appears to look towards the patterned stimulus on most occasions, it indicates that the pattern is resolved by the infant and that further implies that the visual pathway is functioning. If, however, the infant shows no response to the pattern, there may be three possibilities. First, the infant is bored or preoccupied and is therefore inattentive. Second, it may be a genuine inability to resolve the target and may indicate a malfunctioning of the visual pathway. Third, it may be possible that the visual pathway is functioning well, but the region of the brain responsible for the appropriate behavioural response is immature. (9) As the infants grow, they become interested in their environments and then a simple stimulus may be enough to maintain their attention. (9) The most commonly used preferential looking tests include Keller acuity cards, Teller acuity cards and the Cardiff acuity cards. These tests are easy to perform, they are fast and accurate but do not take into account the phenomenon of crowding. These tests may, therefore, not be ideal in the detection of amblyopia. (6, 9) The accuracy of these tests depends on the examiner’s skill level and these test results are affected by lack of co-operation and altered visual fields. (59, 60)
By the age of 3 years up to 6 years, most children can complete a recognition acuity test that requires naming or matching of optotypes. (2, 8) Usually, symbol acuity is feasible from about 3 years of age and letter acuity from about 5 years. (8) The advantage of these is that children find these more interesting in comparison to the preferential looking tests. A variety of tests have been described including the Allen cards, the Wright figures, Lea symbols, the Patti Pics test, the Kay picture test, the Sheridian Gardiner test, the crowded Keeler logMAR test, the Landolt C test, the Sheridian STYCAR test and a modification that uses only the
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HOTV letters and the ‘tumbling’ or ‘illiterate’ E test.(2, 8) The factors limiting recognition acuity are that not all optotypes are equally recognisable and this measure is dependent on the observer’s cognitive ability and communication skills. (8) This is of particular importance when testing children. As these tests require cognition and communication skills, they are a more complex task in comparison to the preferential looking procedures. If these skills are not good, there may be an underestimation of visual acuity. (8, 9) The recognition of picture optotypes depends upon the child’s familiarity with the pictures and the results may be affected by social and cultural factors. (61) Most of these tests take into account the phenomenon of crowding.
The picture recognition tests are described as follows. The Allen cards and the Wright figures are not standardised in the construction and details of the pictures and also in the acceptable names that the children may use to identify the pictures. These tests are therefore not used. (8) Lea symbols were developed using the same principles of the Bailey- Lovie logMAR chart. The test has four figures, square, circle, apple/heart and house. The Lea symbols are 1.5 times larger than the equivalent Snellen E optotype. (8) The Patti Pics test is a variation of the Lea symbols and contains a star optotype in addition to all the others. The Kay picture test consists of 8 familiar pictures that the child can identify or name. It is available in both crowded and uncrowded formats and is based on Bailey- Lovie construction principles. (8)
The letter identification tests include the Sheridian- Gardiner STYCAR (screening test for young children and retardes) test. This test has widely been used in vision screening programmes, but is not very reliable. It includes seven letters (X, A, U, T, H, O, V). The letters are presented singly or in rows, and the patient is required to match the letters on a key
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card. The HOTV test is a modification of the STYCAR test and includes selected letters with vertical symmetry. Glasgow acuity cards (Crowded Keeler logMAR) consist of six letters (X, V, O, H, U, Y). These letters have approximately equal eligibility and have a progression of 0.1 log unit between lines. Four letters make up a line and each line is surrounded by a crowding box. (2, 8, 19)
Normative visual acuity in children:
The normal visual acuity using various tests in children as per age group is as follows: (4) Table 2: Normal visual acuity as per age (4)
Age in years Vision test used Normal
0-2 Visually evoked potential,
Preferential looking
20/30
0-2 Fixation behaviour CSM
2-5 Allen pictures, HOTV, E-games 20/40-20/20
5+ Snellen 20/30 to 20/20
A study was done by Drover et al to collect data on normative visual acuity. Visual acuity was assessed in 373 children between the ages of 3 to 10 years. The protocol established by the Amblyopia Treatment Study (ATS) was followed for the assessment of vision.
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The results showed that normative mean visual acuity in 3 year olds was 0.08 +/- 0.21 logMAR, 4 year olds was 0.08+/- 0.17 logMAR, 5 year olds was 0.03+-/0.19 logMAR and 6 year olds was -0.03+/-0.18 logMAR. This study also showed an improvement in visual acuity with increase in age. It showed that visual acuity showed significant improvement from 3 years of age to adulthood. (62)
A study done by the Multi Ethnic Pediatric Eye Disease Study (MEPEDS), looked at visual acuity in normal pre-school children with no ocular causes for abnormal visual acuity. (63) The normative visual acuity measured by this study is shown in the table below
Table 3: Normative visual acuity in 3 to 6 year old children (63)
Age
in months
Number Mean visual acuity In logMAR
(Males)
Mean visual acuity In logMAR
(Females)
Standard Deviation
36- 47 460 0.16 0.18 0.17
48-59 567 0.07 0.10 0.08
60-72 595 0.01 0.03 0.02
This study showed that mean logMAR visual acuity steadily improved with increasing age.
They also concluded that the existing guidelines for visual acuity assessment may be too strict for 3 year olds and too lax for 5 year olds. (63)
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Assessment of visual acuity in children with special needs:
The assessment of visual acuity in mentally challenged children (like those with developmental delay, cerebral palsy and other neurological conditions) is particularly challenging. It is usually done by testing pupillary responses, examination of light perception, optokinetic nystagmus and the ability to fixate and track using small brightly coloured toys.(64) Visual grating acuity testing may be performed using the Lea grating paddles, which are based on the preferential looking technique. In a grating acuity test, the patient detects the presence of parallel lines of decreasing width. This task is much simpler than the recognition of an optotype. (65) The Lea grating acuity test requires discrimination of the direction of long lines and is a more demanding task than the Teller acuity cards. (66)
Cardiff acuity cards:
The Cardiff acuity test (4740R Cardiff acuity test, Richmond products, 4400 Silver Ave SE Albuquerque, NM 87108) was designed by Dr J Margaret Woodhouse. It is a selection of preferential looking pictures designed to measure visual acuity in toddlers aged one to three years and in older individuals with intellectual impairment. The Cardiff acuity test was introduced with the intention of providing a more engaging stimulus for older infants and young children. The test consists of simple, recognisable shapes (fish, car, boat, train, house and duck). The shapes are on A4 size cards (21x29.5cm). The principle of the target design is that of a vanishing optotype. The targets have a white band bordered by two black bands.
The width of each black band is half the width of the white band. All objects are on a neutral grey background. Thus, the average luminance of the target is equal to that of the grey
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background. If the target lies beyond the subject’s resolution limit, it merges with the grey background, and then simply becomes invisible. Thus, this test brings together resolution, detection and recognition acuity. The pictures are all of the same size, but the width of the black and white bands progressively decreases. The acuity is given by the narrowest band for which the target is visible. The Cardiff test ranges from visual acuities of 6/6 to 6/60 (20/20 to 20/200), at a viewing distance of one metre, progressing in 0.1 log steps. There are eleven visual acuity levels, with three cards at each level, with a total of 33 cards. There is a picture at the top of the first card, another at the bottom of the second card, and the third card has the picture placed either at the top or bottom. (7, 8, 12, 67)
The examiner presents the cards, starting with the largest picture, at a distance of either one metre or 50 centimetres. The examiner presents the first card at the patient’s eye level and then watches the child’s eye movement. Depending on whether the eye movement is up or down, an estimation of the direction of gaze is made. A mental note is made and the second card is then presented. The examiner observes the movement of the child’s eye again. The examiner then checks the cards to verify whether both estimations are correct. If the estimations are correct, the next set of cards is presented similarly. If the direction of estimation is wrong, or there is no definite fixation observed, then the previous set of cards is again presented, using all three cards. The end point is when two of the three cards are consistently seen correctly. (7, 8, 12, 67)
For the Cardiff test, in case of toddlers, the total testing time is shorter, and the test procedure is interesting. The children see the process as a kind of a game, where they have to search for the hidden picture. The Cardiff acuity test is also useful in children with developmental delay (68), patients with neurological conditions (69) and in the deaf blind population. (70)
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When the Cardiff test was compared with both the Teller acuity test and the Snellen tests, the Cardiff test gave significantly higher acuities. (67)A preferential looking procedure which has a chance factor of 1 in 2 for each single presentation would be expected to indicate a higher acuity than a letter matching (1 in 5) and a letter naming (1 in 27) task. In a study comparing Cardiff acuity test to Bailey- Lovie Chart, it was found that the assessment of visual acuity with Cardiff acuity test alone will under-diagnose reduced acuity caused by refractive errors. (7) Certain visual disorders, including amblyopia, are often more difficult to detect with resolution than with recognition acuity tests. Therefore, any test that measures recognition acuity may be less than ideal as a method for assessing infant vision. (6)
The Kay picture test:
The Kay picture test (copyright Kay pictures Ltd) was created to provide recognition based visual acuity measurement for use in children aged two to three years. The Kay pictures test is based on the presentation of eight familiar pictures (clock, house, duck, boot, apple, fish, cup, truck) that a child can match or name. It comes in both uncrowded and crowded formats. The test incorporates the Bailey-Lovie chart construction principles, using a logarithmic progression of acuity levels, an equal number of optotypes (four) on all but the first two rows and a constant level of crowding between lines. The symbols used in the Kay pictures chart are based on Snellen sizing, with a stroke width that is the same as the equivalent Snellen letter. The picture spacing is equal to 0.5 picture diameter. A crowding bar surrounds the four pictures at each acuity level, the width of which is equal to the stroke
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width of the picture. The distance of the crowding bar from the pictures is equal to 0.5 picture diameter. (13, 14, 71)
The Kay picture test is designed to make visual acuity testing a fun, quick and easy process for young children. All the acuity sizes are in one book, with a choice of four pictures at each acuity size. This keeps the child interested during the test. The crowded Kay picture test has two complete sets with a different picture arrangement for each eye. Before performing the test, one has to make the child name all the pictures and accept what they say and repeat all possible names back as confirmation. If the child gets a picture completely wrong, that is acceptable. The parents may have an explanation for why the child refers to the picture differently, or the parent may correct the child themselves. If the child does not name the picture, the parent must be involved in asking. Sometimes, one may need to offer suggestions. Some children may be very shy or reluctant. It is very important to provide encouragement through the testing procedure. (14)
The test is performed at a distance of 3 metres. Occluding glasses are used to close the other eye while testing. To perform the test, the book has to be opened from the front and the examiner’s thumb chooses the picture size from the tab index on the right. The examiner flips the page to face the child and asks the child to name one picture at a time. The test is repeated with smaller sizes till the child’s threshold acuity is reached. At that point, the child is asked to name all the pictures at that acuity level plus one size above and below if possible. The single and crowded logMAR test books have eleven acuity sizes in both logMAR and Snellen’s notations. (13, 14, 72)
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A study was done to compare the Kay picture test and the logMAR crowded test. This study was done in children between the ages of 2.5 and 16 years. The study assessed whether the visual acuity results were comparable between the two tests, whether there was any difference in the visual acuity score between the two tests and whether there was any difference in the ability of children to be able to perform the two tests. It was found that the Kay crowded picture test was comparable with the logMAR crowded letter test. It was also found that the Kay picture test was easier to perform than the logMAR crowded letter test in children aged less than 5 years. (71)
Another study was done to compare the level of visual acuity with crowded and uncrowded versions of the logMAR acuity test and the Kay picture test in amblyopia. It was found that the logMAR crowded Kay picture test provides visual acuity more comparable with the gold standard crowded logMAR acuity test than the uncrowded logMAR acuity test. There was no difference in the levels of acuity with the two crowded tests for the group of amblyopic patients as a whole, but a slight overestimation was noted by the crowded Kay test when the participants with mild amblyopia were excluded. (73)
A study was done to validate the printed crowded Kay picture and the computerised crowded Kay picture logMAR test acuity measurements against the gold standard ETDRS letter chart scores. It showed that all three tests were similarly replicable and computerised Kay pictures appeared to be a valid alternative to hard copy Kay pictures. Kay picture acuity measurements were systematically biased producing better acuity when compared with the gold standard ETDRS.(74)Thus, the Kay picture test has been validated for use as it is comparable to the crowded logMAR test and the gold standard ETDRS chart.
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Recommendations for vision testing in children:
As per the International Visual Acuity Chart Guidelines, a standard visual acuity chart should have the following (8, 22)
1. Optotypes must be black on a white background 2. Crowding elements must be incorporated in the test 3. Optotypes should be of approximately equal legibility
4. The horizontal distance between adjacent optotypes must not be less than one optotype 5. The vertical distance between optotypes must not be less than the height of the larger of
the two lines of the optotypes
6. Atleast 5 optotypes must be displayed on each line
7. The optotype sizes should have a geometrical progression of step sizes of 0.1 logMAR units per line
The Amblyopia Treatment Study visual acuity testing protocol was developed in order to standardise visual acuity testing in children. In this protocol, aimed at testing normal children, the optotypes are presented in a logMAR progression, in a crowded manner. The protocol used a single letter surrounded by crowding bars for the assessment and recording of visual acuity. This protocol showed good testability in 3-7 year olds and had good test- retest reliability. It showed an excellent test- retest reliability with 93% of the eyes within 0.1 logMAR of the initial test score, which is similar to the adult values on the ETDRS chart.
This protocol was used in the multicentric Amblyopia Treatment Study. (75)
Monocular visual acuity testing is considered as the best practice vision screening method for children between the ages of 3 and 6 years. The recommended practice guidelines by the
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National Expert Panel to the National centre for Children’s vision and Eye Health, United States suggest the use of appropriately scaled (logMAR) single crowded HOTV letters or Lea symbols surrounded by crowding bars at a 1.5 metre test distance with the child matching or reading the optotypes aloud. A passing acuity score is the correct identification of three of three or three of four optotypes with each eye at the 20/50 level for children from 36 to 47 months and at the 20/40 level for children aged 48 to younger than 72 months. Acceptable practices are to use the HOTV or LEA symbols calibrated for a 3 metre test distance or to use a single line of these optotypes surrounded by a rectangular crowding bar on all four sides.
(16)
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Comparison of Cardiff acuity cards and Kay pictures as per above recommendations for 3 to 6 years old children (8, 22, 67, 72)
There are no published studies comparing the Cardiff acuity cards and the Kay pictures test.
Based on the review of literature as above, on comparison of the two tests, we found the differences as outlined in table 4 among them.
Table 4: Comparison of Cardiff acuity cards and Kay pictures
Characteristics Cardiff acuity cards Kay pictures
Principle Resolution acuity Recognition acuity
Black optotype on white background √
Crowding elements incorporated √
Optotype legibility √
Horizontal distance specification √
Vertical distance specification √
Geometric progression of optotypes √
Ease of administration √
Speed √
Use in patients withdevelopmental delay, uncooperative and
malingering patients, deaf and dumb populations
√
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Thus, the Kay picture test is an acceptable practice as per the above mentioned guidelines for the assessment of visual acuity in 3 to 6 year old children. To our knowledge, we have not found any study comparing the Cardiff acuity test and the standard crowded Kay picture test in 3 to 6 year old children.
Standard Kay and Modified Kay pictures:
The Kay picture test is a recognition acuity test. (2, 8, 72) In our clinical setting, we have found that children find it difficult to recognise the pictures on the standard Kay picture test.
The pictures on the standard Kay picture test include house, clock, duck, truck, fish, apple, cup and boot (Annexure 4; Picture 1). The standard Kay picture test has therefore, been modified to include more familiar pictures using standard principles of optotype size and contrast. This is hereforth referred to as the modified Kay picture test. The pictures on the modified Kay picture test include house, clock, duck, toffee, cup and saucer, fish, spectacles and star (Annexure 4; Picture 2). As there is no available data in literature comparing the standard and the modified Kay picture charts, a pilot study was conducted in the Department of Ophthalmology, Christian Medical College, Vellore, the details of which are as follows.
Details of the pilot study: (unpublished data)
A pilot study was conducted in the Department of Ophthalmology, Christian Medical College, between 05.12.2014 to 18.12.2014. The study was done to compare time taken by children between the ages of 3 and 6 years to identify pictures on the standard Kay and the
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modified Kay picture charts. The sample size for the pilot study was 25 children based on a study done by Mody KH et al (76) comparing Lea gratings with Cardiff acuity cards for assessment of visual acuity in preverbal children. As per the data in the study, a sample size of 25 subjects was required to detect a difference of 8.1 seconds with a standard deviation of 10 with 80% power and 5% error based on the formula
n= [2(Z1-α/2 + Z1-β)2 x SD2]/ (mean difference)2, where α= 5% and β= 80%
The inclusion criterion was all children between the ages of 3 and 6 years coming to the Department of Ophthalmology.
The exclusion criteria were all children who could not identify the first optotype on the Kay picture test with either eye or those who could not participate in the test due to physical debility.
Methodology-
Informed consent was obtained from all the parents using a consent form. After obtaining informed consent from the parent or guardian, the picture identification was performed using the standard Kay and the modified Kay picture test. This was done at a distance of 5 metres.
The children who wore glasses continued to wear glasses throughout the test. We performed the test on the right eye of the children, occluding the other eye with an occluder, except in the situation that they could not identify the first optotype on the Kay picture test or had an abnormality in the right eye.
The child was first shown the uncrowded standard Kay picture visual acuity chart followed by the uncrowded modified Kay picture visual acuity chart. The time taken to identify and
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name each picture was noted with the help of a stopwatch. The total number of pictures identified on each chart was also noted. The age of the children, their schooling status, visual and ocular complaints and co-morbidities were also noted.
Results-
Among the 25 children whose parents were willing for them to participate in the study, only 24 children were included in the study as 1 child was 6 years and 7 months of age.
Of the 24 children, 5 were between 3 to 4 years of age, 6 were between 4 to 5 years of age and 13 were between 5 to 6 years of age. 22 of the 24 children were attending school. Two of the children were not attending school, as one child was only 3 years old and not admitted yet, and the other, though 4 years of age was not admitted.
Of the 24 children, 4 had allergic conjunctivitis, 1 had undergone enucleation of the left eye for retinoblastoma and was on follow up, 3 were wearing glasses for refractive errors, 2 were amblyopic, one child had surgical aphakia and one child was pseudophakic following surgery for an open globe injury followed by secondary intraocular lens implantation.
None of the children had any systemic co-morbidities.
The overall difference in average total time taken to identify the standard Kay pictures and the modified Kay pictures was 8.06 seconds.
The minimum difference between the average times taken to identify two similar pictures (duck-duck) was found to be 0.19 seconds and the maximum difference between the average times taken to identify two similar pictures (clock-clock) was found to be 2.22 seconds. An age-wise subgroup analysis was done for 3-4 year olds, 4-5 year olds and 5-6 year olds.
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For all the sub-groups, the maximum difference in time was 2-3 seconds and the minimum difference in time was 1 second.
Limitations of the pilot study-
The optotype sizes of the corresponding pictures on the standard Kay picture chart and the modified Kay picture chart were not of the same optotype size (one-line difference).
The children were given only one attempt at picture identification.
The test was performed at a distance of 5 metres, when the recommended distance is 3 metres.
Conclusions-
When the average time taken to identify individual pictures were compared, children took lesser time to identify pictures in the modified Kay picture test as compared to the standard Kay picture test in 3 of the 4 pictures presented to the children.
The average overall time taken to identify the pictures on the modified Kay picture test was lesser than that taken to identify the pictures on the standard Kay picture test.
25 children participated in the study. The study showed that there was a difference of 8.06 seconds in the overall difference in the average time taken to identify the 8 pictures on the standard and the modified Kay picture charts. The minimum difference between the average times taken to identify two similar pictures (duck-duck) was found to be 0.19 seconds and the maximum difference between the average times taken to identify two similar pictures (clock- clock) was found to be 2.22 seconds. A subgroup analysis was done age-wise for 3-4 year olds, 4-5 year olds and 5-6 year olds. For all the sub-groups, the maximum difference in time
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was 2-3 seconds and the minimum difference in time was 1 second. Using data from this study, the study was then designed.
Thus, in this study, we assessed if pictures in the modified Kay picture test are more easily identified by children as compared to pictures of the standard Kay picture test using time taken to recognise the picture as a measure.
We also assessed factors that may influence visual acuity testing in children in the age group of 3 to 6 years. We studied parental age and education, order of the child in the family, number of siblings, education of the siblings, current schooling of the child and the existence of co-morbidities in the child, parents or siblings.
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MATERIALS AND METHODS
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This was a prospective hospital-based cross-sectional study, conducted in the Department of Ophthalmology, Christian Medical College, Vellore. The period of recruitment and data collection was from March 2015 to September 2015.
Institutional review board approval:
The study protocol was approved by the Institutional review Board which included members from outside the institution as per the ICMR guidelines required for any study conducted in the institution. The IRB Reference number was 9302 dated 05.02.2015. (Annexure 1) Inclusion criteria:
All children between the ages of 3 and 6 years coming to the Department of Ophthalmology
Exclusion criteria:
a. Children whose presenting visual acuity was lesser than 6/36 in the better eye when assessed with the Cardiff acuity test at one metre b. Children whose visual acuity could not be assessed uniocularly by the
Cardiff acuity test at one metre
c. Children who were unable to hold their head vertically even with support
d. Children who refused to participate in the study
e. Children whose parents did not consent to let them participate in the study
