Visual development, amblyopia and vision screening in childhood — branching viva

Opening — framing the problem

The examiner begins: a five-year-old is found at school-entry screening to read only the top line with the left eye when the right is covered, an acuity of about 6/60 that does not improve with a pinhole, with structurally normal eyes, symmetric red reflexes and no turn. Talk me through your approach. ^[2]

I would frame this as amblyopia. The unilateral reduction in acuity that does not improve with a pinhole, in a structurally normal eye with a symmetric red reflex, is the signature of a functional cortical deficit rather than an optical or organic one. The key idea is that amblyopia is a brain problem, not an eye problem: during the sensitive period the cortex suppressed or under-developed the input from that eye, so the neural machinery for sharp vision never matured. ^[2]