Teaching case A. An eight-week-old infant, unilateral white reflex. This is not a scenario for "elective at six months". PPP: deprivation amblyopia is the least common form, often the most severe and difficult to treat; acuity is often 20/200 or worse.
Visual deprivation is a complete or partial obstruction of the visual axis that destroys the retinal image. A common cause is congenital or early-onset cataract. Also: corneal opacities, intraocular inflammation, vitreous haemorrhage, ptosis. Unilateral obstruction is more severe than bilateral obstruction of similar density because of competition. Untreated significant deprivation in the first 3 months produces a profound permanent loss of high-contrast acuity, typically 20/200 or worse; after 3 months the loss may be less profound, but "less profound" is not a synonym for "safe".
Not every cataract is equally amblyogenic. The PPP distinguishes: dense central ones — high risk; polar ones around which retinoscopy is possible, and lamellar ones through which the fundus can be seen — mild or moderate amblyopia or no effect on development at all. Many partial cataracts have an associated refractive error that must be corrected anyway. This is not a reason to "wait, in case it resolves". It is a reason to look at whether the opacity covers the axis and what input the cortex is receiving.
The timing for a visually threatening unilateral cataract in a newborn that the PPP associates with a better prognosis: removal and optics by 2 months. The Infant Aphakia Treatment Study (IATS): 114 infants aged 1–6 months, unilateral cataract, randomised to primary IOL versus aphakia with a contact lens. At 4.5 years the median acuity was 0.90 logMAR in both groups (P = 0.54). About 50% of operated eyes in both groups had acuity of 20/200 or worse. Acuity of 20/32 or better — 13 children (23%) in the contact lens group versus 6 (11%) in the IOL group (body of JAMA Ophthalmol 2014;132:676–682). Primary IOL produced more complications (81% vs 56%) and more repeat intraocular operations (72% vs 21%). The investigators' conclusion, which the course does not expand into a surgical protocol: for most children operated on before 7 months, leaving them aphakic with a contact lens is reasonable in terms of outcome versus repeat interventions. Amblyopia after even ideal surgery remains a separate, often severe, task: the PPP calls deprivation amblyopia difficult to treat successfully.
Ptosis. Not every drooping lid is amblyogenic. The risk rises when the lid margin covers the visual axis or induces significant astigmatism. The decision about the timing of ptosis surgery is not set out in this course; the principle is the same: if the axis is covered within the sensitive window, it is deprivation, not "cosmetics that can wait until school".
Reverse (occlusion) amblyopia is deprivation created by treatment: patching or cycloplegia of the fellow eye. In ATS1, after 6 months fellow-eye acuity had decreased by 2 or more lines in 1% of children on occlusion ≥6 hours a day and in 9% of children on daily atropine; the PPP notes that in many atropine cases fellow-eye acuity was not measured with optimal correction, so not all episodes were true reverse amblyopia. In almost all cases fellow-eye acuity returned to baseline without active treatment — by stopping therapy and continuing optics. In subsequent studies of lower doses of occlusion and atropine, cases of reverse amblyopia are few. This is not permission to forget the fellow eye. It is a proportion to face squarely: the risk is real, usually reversible with monitoring, and it is higher when penalisation is stronger.
How not to confuse the forms at the end of the module.
| Form | Main spoiled input | First step | Typical severity |
|---|---|---|---|
| Isoametropic | bilateral defocus | glasses | more often moderate, both eyes |
| Anisometropic | unilateral defocus + competition | glasses, then occlusion/atropine if needed | mild to severe, often detected late |
| Strabismic | non-fusable inputs, suppression | glasses (if there is refractive error) + activation of the worse eye; surgery for the angle is separate | depends on constancy and alternation |
| Deprivation | destroyed image ± competition | remove the obstruction in time, then optics and activation | least common, often the most severe |
| Reverse | iatrogenic deprivation of the fellow eye | reduce/stop treatment, monitor | usually reversible with timely monitoring |
The module's boundary. The course does not replace the IOL protocol in infants, does not teach MRD measurement and does not cover laser treatment of congenital glaucoma. It teaches you not to call deprivation "ordinary amblyopia" and not to prescribe a patch as the first step where the axis is still covered.