Teaching case. A five-year-old, no strabismus, clear media. Cycloplegia: OU +6.50 D sph. Distance acuity with correction 0.4 in each eye; reads better at near than you would expect from the distance chart. The family is sure that "the eyes are healthy, he just doesn't want to look into the distance". This is not laziness. It is bilateral defocus that the cortex never learned to resolve.
Refractive amblyopia develops because of untreated unilateral or bilateral refractive errors. The PPP separates two mechanisms that must not be glued together.
Isoametropic (high bilateral, bilateral refractive) — the less common form: a bilateral reduction in acuity due to similar significant defocus. There may be no "who is in charge" competition. What spoils things is the very fact that both retinal images have been blurred for a long time. PPP: this is thought to be a direct effect of bilateral blurred images.
Anisometropic — the subject of the next lesson: here it is enough to know that it is unilateral and adds competition to the blur.
What magnitude of refractive error "counts". The PPP does not set hard thresholds of the "from here on it is always amblyopia" kind in its definition chapter; it refers to the correction table of the Pediatric Eye Evaluations PPP (journal publication 2022/2023; highlighted Table 2 corrected in February 2026). This table is not a diagnostic criterion for amblyopia but the minimum values at which glasses are already prescribed for an infant or preschool child in the absence of other abnormalities. "Indication for glasses" and "diagnosis of amblyopia" must not be confused. But without these numbers a resident does not know which refractive error must never be left to "see in a year".
Thresholds for isoametropia (similar refractive error in both eyes) — current Table 2 of the Pediatric Eye Evaluations PPP (official AAO PDF; the highlighted block of the same table was brought into line with the full table in February 2026):
| Condition | <1 year | 1–<2 years | 2–<3 years | 3–<4 years |
|---|---|---|---|---|
| Myopia | ≥5.00 D | ≥4.00 D | ≥3.00 D | ≥2.50 D |
| Hyperopia without manifest deviation | ≥5.00 D | ≥5.00 D | ≥4.50 D | ≥3.50 D |
| Hyperopia with esotropia | ≥1.50 D | ≥1.00 D | ≥1.00 D | ≥1.00 D |
| Astigmatism | ≥3.00 D | ≥2.50 D | ≥2.00 D | ≥1.50 D |
These are consensus minimums, "based solely on professional experience and clinical impressions", not a diagnostic threshold for amblyopia. A class of error worth naming aloud here. The 2022/2023 journal highlighted copy gave 6.00 D for hyperopia without deviation at <1 year. The full Table 2 and the February 2026 correction give 5.00 D. The course teaches 5.00 D, because that is what the current PDF holds. Confusing the highlighted block with the table means prescribing glasses to an infant one dioptre later than the panel considers indicated.
For older children the table deliberately does not give equally hard numbers: the decision rests on the magnitude of the error, acuity and symptoms.
A separate trap is hyperopia with esotropia. Here glasses are needed already at 1.00–1.50 D, because the task is not only amblyopia but also the accommodative component of the deviation. Leaving a "small" hyperopia uncorrected in a child with esotropia means feeding both the strabismus and the strabismic amblyopia.
What the isoametropic form does clinically. The child may not complain: the world has always been slightly foggy for them; there is nothing to compare it with. Screening catches both eyes. Treatment starts with optics; the PPP specifically stresses that acuity in bilateral refractive amblyopia improves substantially with correction alone. Occlusion is often not needed here — both eyes already "work"; what they lack is sharpness, not access to the cortex. Prescribing patching to an isoametropic child "just in case" is a typical error of transferring the strabismic template.
Boundary. The course does not cover myopia progression, orthokeratology or lens protocols. Refractive error is of interest here only as an amblyogenic input. And the course does not claim that every uncorrected +4.0 hyperopia in a three-year-old is already amblyopia: the diagnosis requires a BCVA deficit plus a factor. Glasses at the table threshold are prevention and treatment of defocus; amblyopia is when acuity has already failed to catch up with the age norm.