New Visual Acuity and Crowding Tests for Better Detection of Amblyopia

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).