New visual acuity and crowding tests for better detection of amblyopia
Research type
Research Study
Full title
An examination of new visual acuity and crowding distance tests, for better detection of amblyopia.
IRAS ID
238449
Contact name
Louisa Haine
Contact email
Sponsor organisation
Anglia Ruskin University
Clinicaltrials.gov Identifier
Duration of Study in the UK
2 years, 4 months, 31 days
Research summary
Summary of Research
Amblyopia, or ‘lazy eye’, is the reduction in vision usually in one eye, due to abnormal visual development without organic cause. It is a preventable and leading cause of monocular vision loss (prevalence of around 3%) and increases lifetime risk of bilateral visual impairment from 10% in the general population, to 18% in amblyopes.
In the UK, vision screening in children aims to detect amblyopia and other undiagnosed visual conditions. Laboratory research suggest that amblyopia could be better detected by modifying standard clinical vision tests to enhance and quantify “crowding”. Crowding is the negative effect that surrounding features have on the visibility of a target. Crowding distance and crowding magnitude are considerably greater in amblyopic eyes than in normal healthy eyes. Modifications that should lead to improved amblyopia detection are 1) place letters closer together on a vision chart, 2) define letters by contrast, rather than luminance, and 3) use a new thinner font in the form of numbers, to allow crowding distance in central vision to be measured. In this project, these modifications will be tested in amblyopic children for the first time.
Amblyopic children aged 3 to 11 years (n=32) will be recruited from ACPOS (Addenbrooke’s Community Paediatric Ophthalmology Service) at ARU. They will have their vision measured with the three modified tests as well as an uncrowded test. The child will view letters and numbers on a computer screen and respond (verbally or by indicating their choice on a matching card). Testing is fun and game-like with breaks for rewards. Results will be compared to standard vision measurement (SLT: Sonksen LogMAR Test) from the child’s ACPOS visit. Amblyopic data will be compared to control data from normal healthy children aged 3 to 11 years (n=200), and age-matched children with normal vision (n=16) from ACPOS (false referrals from school screening).
Summary of Results
The researchers would like to thank all study participants without whom, this research would not have been possible.
Study Title: An examination of new visual acuity and crowding distance tests, for better detection of amblyopia.
The research was conducted by researchers at Anglia Ruskin University and sponsored by Anglia Ruskin University. The study was completed at the University Eye Clinic, Anglia Ruskin University, Bradmore street, Cambridge; and examinations took place between February 2019 and June 2021.
Amblyopia is a neurodevelopmental disorder traditionally characterised by deficits of visual acuity, or the ability to resolve small letters and other fine details, usually in one eye. Amblyopes are also more sensitive to the effects of visual crowding, where target identification is harder in the presence of nearby visual clutter, than when seen alone. Some recent research studies have suggested that current vision tests used in clinics could be improved upon by increasing crowding effects and that this could lead to more sensitive detection of amblyopia in children.
We tested 3 new vision tests: 1) surrounding letters are placed close (1/5 letter width) to the target letter, 2) surrounding letters are made from differences in contrast, rather than differences in luminance (this means high-contrast letters are shown on a low-contrast background, rather than black letters shown on a white background), and 3) tall skinny numbers are used to measure crowding distance in central vision. The standard vision test that we compared our results with the new tests to is the Sonksen logMAR Test (SLT). This test consists of four letters in a row, each separated by 1 letter width with a box placed around them.
We asked: 1) Do the new vision tests offer better sensitivity to detection of amblyopia, than the Sonksen logMAR test (SLT)? and 2) Is there a difference in vision test outcomes for two different types of amblyopia. Some amblyopes have straight eyes but a need for glasses to correct for optical differences between the eyes (anisometropic amblyopia) and others have a turned eye so that the two eyes are not perfectly aligned (strabismic amblyopia).
In total, 76 participants were recruited. Fifty-one were amblyopes, of which 26 were anisometropic amblyopes and 25 were amblyopes with strabismus. There were 25 visually healthy controls. All participants were children aged 3-11 years-of-age, with an average age of 6.4 years. Eight participants (1 control and 7 amblyopes) were excluded for compliance or co-existing medical conditions.
Participants had their visual acuity measured for each eye with the Sonksen logMAR test (SLT). Then the new vision tests were conducted in varying orders, to ensure that average measurements were not influenced by practice, attention, or fatigue. The eye tested first was also randomised.
In the first two new tests, target letters that are laterally reversible (H, O, T or V) were surrounded by four other letters (U, A, L, C). The child identified the central letter. A computer varied letter size systematically and the experiment stopped automatically when the measure was reliable. After a short break, the second eye was tested. The second vision test used letters defined by contrast instead of luminance but these were presented in the same way.
In the third test, crowding distance was measured with tall skinny “Pelli” numbers. Being tall and skinny gives them an advantage over normal letters because they can get closer together and smaller crowding distances can be measured. We measured crowding distance for each eye using 2 arrangements. In the trigram arrangement, a trio of numbers was presented and the child identified the middle number. For the repeated arrangement, two numbers were repeated in a line across the screen and the child identified 2 numbers. The repeated arrangement is thought to be helpful when horizontal eye movements are unstable, because the eye finds numbers regardless of where on the line it looks.
No patients experienced any adverse side effects other than the task seeming tedious at times.
Results
Visual acuity with black and white letters in the first new test revealed significantly larger differences between eyes of strabismic amblyopes than when measured with the SLT. No difference was seen between old and new tests for children in the control group.Visual acuity using the letters defined by contrast revealed similar differences between the eyes to those found for the SLT for control and amblyopic groups of children. So this new test, did not improve sensitivity to detecting amblyopia.
Crowding distances with ‘Pelli’ numbers showed differences between eyes in strabismic amblyopes that were larger those found for visual acuity. In anisometropic amblyopes, acuity and crowding distance differences between eyes were similar. Thus, measurement of crowding distance could improve sensitivity of detecting strabismic amblyopia in children.
Summary of findings
This study has established that new crowding tests can enhance sensitivity to detecting strabismic amblyopia, compared to results with the SLT. This finding may be helpful particularly for detecting small misalignments of eyes. Use of letters defined by contrast to measure acuity did not enhance sensitivity for detecting amblyopia. Further analysis is needed to examine specific ability of these new arrangements to classify between amblyopia subtypes. In addition, the question of whether separate acuity and crowding tests are needed in screening could be further addressed.Results from this study have been published in abstract form and presented at the Vision Sciences Society Annual General Meetings 2021 and 2022. Further publication of the results of this study are in progress.
Haine, L., Waugh, S.J., Formankiewicz, M.A. & Pelli, D.G. Simplifying the repeated crowding-distance test for normal and amblyopic children. Journal of Vision 2021;21(9):1982. doi: https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fu2790089.ct.sendgrid.net%2Fls%2Fclick%3Fupn%3DXv3JSvJ-2B3M71ppf7N9agbZ-2BvCANJgIA8xNXXhp7QQugdXNl1Hxi0SeusKWxto6YK1BBw_E1aO2-2BZlVOSJJV-2FajQqskegTd6IRomHYTi-2Fbt8SH3YKJOpd4QWtbQPaY51JnajZE3nXxNId2N4wn6ZzAVzB71iNk-2B7FLQom24OvuGW2dnK9zQM-2BK5B0-2FjdssaNLmL-2BaBHZntVOeV0dFzocPTTBsDI3CWcZRFLCgdU2fNtywj3NiYLA9hGoR0I3-2Br3Ck-2BXCUPPf2UFczPun-2FX-2BrPLtDuGnw-3D-3D&data=05%7C01%7Capprovals%40hra.nhs.uk%7Cdd818d03a3bc444f33ac08da59216d76%7C8e1f0acad87d4f20939e36243d574267%7C0%7C0%7C637920297341731256%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=UrkqP%2FXcDCn0XSW6TgFbF7Tl%2FjUo%2F%2FUZg1jt%2BRhhDjw%3D&reserved=0
Waugh, S.J., Haine, L., Formankiewicz, M.A. & Pelli, D.G. Crowding distance beats acuity and crowded acuity in detecting strabismic amblyopia. Journal of Vision 2022; in press
REC name
East of England - Cambridge South Research Ethics Committee
REC reference
18/EE/0167
Date of REC Opinion
8 Aug 2018
REC opinion
Further Information Favourable Opinion