Teaching case. Two children with moderate amblyopia of 20/80, both with anisometropic hyperopia, both without previous treatment. One is four years old, the other twelve. The twelve-year-old's family has heard that "the train has left". The four-year-old's family is confident that "we still have time, in a year". Both beliefs are costly — for different reasons.
What exactly is known about age as a modifier of response — not from the feeling that "plasticity declines", but from specific samples.
Under seven, moderate amblyopia, start of treatment. ATS1 (PEDIG, Arch Ophthalmol 2002): 419 children under 7 years, amblyopic-eye acuity 20/40–20/100, strabismic or anisometropic amblyopia, randomised to occlusion (minimum 6 hours) or daily atropine 1%. By 6 months the amblyopic-eye acuity had improved on average by 3.16 lines in the occlusion group and 2.84 lines in the atropine group. The criterion "20/30 or better and/or plus ≥3 lines from baseline" was met by 79% and 74% respectively. This is not "everyone recovered". It is "the majority improved substantially" — in a population under seven, with moderate amblyopia, under protocol conditions.
The long tail of the same start. A subgroup of ATS1 was followed up to age 10 and to age 15. In the publication of the 10-year examination (PEDIG, PMC2614351, 2008): mean amblyopic-eye acuity was about 0.14 logMAR (~20/25−2) in those who were under 5 years at randomisation, and 0.20 logMAR (~20/32) in those who were 5 years and older (P<0.001). The proportion with 20/25 or better was 57% vs 38% (P=0.004). Improvement is generally maintained; residual amblyopia is common. The outcome is similar regardless of whether treatment started with atropine or occlusion. Age at the start, not the choice between drop and patch, is what is associated here with how close to normal it was possible to get.
Older children. ATS3: 507 children aged 7–<18 years, unilateral strabismic and/or anisometropic amblyopia of 20/40–20/400. Comparison: optical correction alone versus optics augmented with 2–6 hours of occlusion and an hour of near work; children younger than 13 in the active group also received daily atropine 1%. At 6 months about 25% had already responded to optics alone. In the 7–12-year stratum, 53% responded in the augmented group vs 25% in the control. In the 13–17-year stratum, 25% vs 23% — the added treatment in this stratum showed no advantage in the proportion of responders. The PPP reads this as: treatment can be effective in older children and adolescents, especially those not previously treated; success declines with age.
What age does not explain on its own. The PPP lists prognosis as a function of several variables at once: age at onset, cause, severity, duration of amblyopia, history of and response to previous treatment, adherence, and comorbid conditions. A four-year-old with a dense unilateral cataract that was removed late may have a lower ceiling than a twelve-year-old with moderate anisometropia who was never treated. Age is a strong modifier, not the only one.
The flip side of "let's wait a year". For deprivation in the first months, "let's wait" is a harm in its own right: the PPP describes profound permanent loss. For the refractive and strabismic forms the calendar is gentler, but the natural history is still not in favour of waiting: untreated amblyopia almost always leaves a lifelong deficit. Screening exists precisely because amblyopia, in the formulation of the Pediatric Eye Evaluations PPP, meets the WHO criteria for a disease that benefits from screening: an important problem, an acceptable treatment exists, there is a recognisable early stage, there is a test.
How not to turn the numbers into a false ritual. Do not promise a four-year-old "1.0 in both eyes": even in ATS1 residual amblyopia is common. Do not refuse a twelve-year-old an attempt, especially if there has been no treatment. Do not mix "response to treatment" (lines gained over months) with "the ceiling over a decade" (what acuity remains at 10 and 15 years). These are different questions for different designs.
Boundary. The course does not derive an "age formula" by which the chance can be calculated to a percentage. There is no such formula in the foundations of the PPP. There are RCT strata and an honest sentence for the family: younger — usually more reserve; older — less reserve, but it is not zero as long as the eye is structurally capable.