Medical amblyopia is a reversible decrease in visual acuity that occurs when there is no organic lesion in the visual organ and appropriate visual stimulation is prevented during the sensitive period of visual development. Its greatest feature is that early detection and treatment can improve visual acuity.
The prevalence is reported to be 0.7–2.6% 1), and the detection rate at three-year-old health checkups is approximately 1.4%.
Occlusion therapy (patching therapy) is a treatment that involves placing a patch over the healthy eye to forcibly use the amblyopic eye, thereby improving visual acuity. Occlusion time varies from partial occlusion of 2–3 hours per day to full occlusion except during sleep. It is important to expose the eye to fine shapes (form vision), as light alone is not sufficient stimulation.
This article focuses specifically on occlusion therapy, distinguishing it from general discussions of amblyopia, with emphasis on treatment protocols, dosage settings, and evidence.
A brief classification of the causes of amblyopia.
Anisometropic amblyopia
anisometropic amblyopia: Unilateral amblyopia due to a difference in refractive error between the two eyes. It is the most common cause of amblyopia.
Indication: Occlusion therapy is added when visual acuity does not improve sufficiently after refractive correction.
Strabismic Amblyopia
Refractive Amblyopia
Form deprivation amblyopia
Microtropic amblyopia is unilateral amblyopia associated with a small-angle strabismus of 10 prism diopters or less, and is sometimes classified as a fifth type.
Treatment within the visual sensitive period (up to about 8 years of age) is most effective. Recent PEDIG studies have shown significant visual improvement in 53% of children aged 7–12 years and 47% of untreated adolescents aged 13–17 years, so treatment should not be abandoned due to age.
In unilateral amblyopia, there are often no symptoms, and it is mostly discovered incidentally through vision screening.
The following shows the standard normal visual acuity by age.
| Age | Normal visual acuity (average) |
|---|---|
| 3 years 0 months | 0.55 |
| 3 years 6 months | 0.82 |
| 4 years 0 months | 0.88 |
| 4 years 8 months | 1.00 |
The diagnostic criteria for amblyopia (AAO PPP) are shown below1).
Severity classification: mild (visual acuity 0.2 or better), moderate (visual acuity 0.1 or better but less than 0.2), severe (visual acuity less than 0.1)
During occlusion therapy, watch for the development of reverse amblyopia (decreased visual acuity in the healthy eye). If the visual acuity in the healthy eye drops by 2 steps or more, temporarily discontinue occlusion 1).
Vision screening at the 3-year-old health checkup is often the first opportunity. At home, you can check for an aversion reflex (observe if the child resists when the good eye is covered). A formal diagnosis requires an eye exam with cycloplegic refraction and visual acuity testing.
Visual sensitivity is low immediately after birth, increases from around 3 months of age, and peaks at around 1 year and 6 months. It then gradually declines and persists until age 8. In recent years, sensitivity has been found to exist even after age 8, and visual improvement through treatment has been reported.
The threshold for developing anisometropic amblyopia (AAO age-specific spectacle prescription criteria) is shown below.
| Type of anisometropia | 0–1 year | 1–2 years | 2–3 years |
|---|---|---|---|
| Myopic anisometropia | ≥-2.50D | ≥-2.50D | ≥-2.00D |
| Hyperopic anisometropia | ≥+2.50D | ≥+2.00D | ≥+1.50D |
| Anisometropic astigmatism | ≥2.50D | ≥2.00D | ≥2.00D |
Other risk factors include preterm birth, low birth weight, developmental delay, and a history of amblyopia in first-degree relatives 1).
For anisometropic astigmatism with a difference of 1.5D or more, early occlusion of the healthy eye is recommended.
Amblyopia is a diagnosis of exclusion after ruling out organic diseases.
At the initial visit, the following examinations are performed1).
In children, objective refraction under cycloplegia is mandatory. The characteristics of each agent are shown below.
| Cycloplegic agent | Paralytic effect | Peak effect | Duration of effect | Side effects |
|---|---|---|---|---|
| 1% atropine (twice daily in both eyes for 7 days) | Complete | 7 days | 2–3 weeks | Fever, facial flushing |
| Cybregin® (Cyclopentolate 1.0%) | Incomplete (difference of 0 to +1.5D compared to atropine) | 60–120 minutes | 2–3 days | Hallucinations, transient ataxia |
For infants under 6 months, 1% atropine diluted to 0.5% may be used.
If visual acuity improvement is poor despite appropriate spectacle wear and occlusion of the healthy eye, exclude achromatopsia, retinitis pigmentosa, retinoschisis, autosomal dominant optic atrophy, macular hypoplasia, brain tumor, and retinoblastoma.
Children have very strong accommodative ability, and refraction testing without cycloplegia underestimates the true refractive error. In particular, hyperopia is compensated by accommodation, so accurate spectacle power cannot be determined without objective refraction under cycloplegia. Complete paralysis with atropine eye drops is the most accurate and is often used for the initial spectacle prescription.
The basic principles of amblyopia treatment are three steps: (1) removal of cause → (2) refractive correction → (3) vision training (occlusion therapy or penalization). Light does not provide stimulation; it is important to present fine shapes (form vision).
Occlusion Therapy (Eye Patch)
The most standard treatment for amblyopia. The healthy eye is occluded to force visual input to the amblyopic eye.
Dosage: 2–6 hours/day for moderate amblyopia, 6 hours/day to full-time for severe amblyopia.
Activities during occlusion: Performing fine motor tasks (e.g., drawing, coloring, bead threading) is effective.
Atropine Penalization
1% atropine eye drops paralyze accommodation in the healthy eye, encouraging use of the amblyopic eye.
Daily and weekend-only instillation have been shown to be equally effective1).
Indicated for mild to moderate amblyopia. Useful in cases where occlusion is difficult.
Bangerter filter
A penalization method that uses a semi-transparent filter to reduce vision in the healthy eye.
It offers vision improvement equivalent to occlusion with less burden and stress on caregivers2).
Digital therapy (research stage)
A new approach using dichoptic images and games.
At present, no clear superiority over conventional occlusion or atropine has been demonstrated2).
Treatment begins with prescribing refractive correction glasses. The following data show visual acuity improvement with spectacle wear alone2).
After the child has become accustomed to wearing glasses (1–2 months), visual acuity is assessed. If improvement is insufficient, patching of the sound eye is initiated.
For anisometropic amblyopia and strabismic amblyopia, the usual occlusion time is 2 to 6 hours per day (partial occlusion). Full-day occlusion may also be performed. If sufficient occlusion time cannot be achieved, short periods several times a day or performing fine tasks during occlusion are recommended.
The main PEDIG RCT results are summarized 1).
| Trial (Study Name) | Subjects (N, Age, Duration) | Intervention | Outcome |
|---|---|---|---|
| ATS 2B (Repka 2003)5) | Moderate amblyopia, ages 3–7, 189 patients, 4 months | 2 hours/day vs 6 hours/day | Equivalent effect |
| ATS 2A (PEDIG 2003)6) | Severe amblyopia, ages 3–7, 175 participants, 4 months | 6 hours/day vs. full-time | Equivalent effect |
| ATS 1 (PEDIG 2002)4) | Moderate amblyopia, ages 3–7, 419 patients | Occlusion vs atropine, 6 months | Equivalent (occlusion slightly faster) |
| ATS 15 | 3–8 years, 169 patients, 10 weeks | Stagnation at 2 hours → increase to 6 hours | Additional improvement observed |
| ATS 3 (Scheiman 2005)8) | 507 participants aged 7–17 years | Glasses + patching vs glasses alone | 53% improvement in ages 7–12 (25% with glasses alone) |
Summary of occlusion dosage:
In the electronic occlusion time monitoring study (MOTAS), refractive correction alone resulted in an average improvement of 0.24 logMAR (18 weeks), and amblyopia resolved in 22% of cases 2).
It shows the dose-response relationship between occlusion amount and visual acuity improvement 2).
Actual compliance: With prescriptions of 6 hours/day or more, the average adherence rate is less than 50%. This is one reason why 2-hour and 6-hour prescriptions achieve similar effects2).
1% atropine eye drops paralyze accommodation in the sound eye, reducing distance visual acuity. Daily instillation and weekend-only (Saturday and Sunday) instillation have shown equivalent efficacy (ATS 4: 168 patients, 3–7 years, Repka 20047)). Combination of atropine and patching in severe amblyopia provided an additional 0.14 logMAR improvement compared to monotherapy1).
This method involves attaching a translucent filter to the spectacle lens of the healthy eye. In a PEDIG RCT (186 children aged 3–7 years with moderate amblyopia), there was no significant difference in visual acuity improvement between the Bangerter group and the patching group, and the Bangerter group had less burden and stress for parents 2). It is useful as an alternative when compliance with occlusion therapy is difficult to achieve.
Indication for treatment termination: After achieving sufficient Landolt C visual acuity with no significant interocular difference, confirm stability for an additional 3–6 months with the same occlusion time. Then gradually reduce occlusion time.
Recurrence data:
For at least 2 years after completion, regular follow-up with visual acuity testing is necessary1).
Even amblyopic children first seen after age 10 often respond to treatment. It is important to initiate treatment first.
Therapeutic eyeglasses for children under 9 years of age are eligible for medical expense benefits.
Depends on the severity of amblyopia. For moderate amblyopia, 2 hours/day is considered sufficient and has equivalent effect to 6 hours/day 1). For severe amblyopia, 6 hours/day is recommended, and has been reported to be as effective as full-time occlusion 1). If improvement stalls, increasing the duration is considered.
Alternatives include atropine eye drops (effective even on weekends only 1)), Bangerter filters (translucent filters), and liquid crystal shutter glasses (Amblyz, intermittent occlusion for 30 seconds per minute). All have been shown to be as effective as occlusion 2). If patching is difficult, consult an ophthalmologist to select the best alternative.
In 42% of children who abruptly stopped occlusion with good vision, a decrease in visual acuity was observed. Relapse has been reported in about 25% of children who completed treatment before age 8. Regular visual acuity examinations are necessary for at least 2 years after treatment ends. Response to resuming treatment after relapse is good, and vision can be quickly recovered and maintained.
Therapeutic glasses for children under 9 years old are eligible for medical expense benefits, with 70% of the purchase price covered by insurance (up to 36,700 yen × 104.8/100 for glasses). However, eye patches themselves are not covered. Renewal conditions require an interval of at least 1 year for children under 5, and at least 2 years for those 5 and older.
The essence of amblyopia is functional changes in the visual cortex and lateral geniculate body, not organic lesions.
In Wiesel’s monkey experiments, it was reported that in layer 4C of the visual cortex of monkeys with one eye closed, neural input from the closed eye was reduced and associated with the other eye. This forms the neurophysiological basis for occlusion therapy of the healthy eye.
Cortical plasticity is most active from birth to 8 years of age, but persists even after age 8. Age dependence is also reflected in the dose-response relationship: the occlusion time required for a 2-line improvement increases with age, being 170 hours at 4 years, 236 hours at 6 years, and 490 hours at 8 years 2).
Nonlinearity of dose-response: The rapid improvement in the early phase of treatment, followed by a gradually diminishing response pattern that reaches a plateau, reflects changes in cortical synaptic plasticity during the sensitive period 2).
A new approach that presents different images to each eye to encourage use of the amblyopic eye and binocular coordination 2).
Luminopia (viewing dichoptic images via VR headset, fellow eye contrast set to 15%) RCT in 4–7-year-olds (Xiao 202210)): 72-hour prescription improved amblyopic eye visual acuity by 0.18 logMAR vs. 0.08 logMAR with glasses alone. First FDA-approved digital therapeutic device for pediatric amblyopia in 2021.
PEDIG Dig Rush RCT (138 children aged 7–12, 20 hours of gameplay): dichoptic game group improved by 0.025 logMAR vs. refractive correction alone group improved by 0.036 logMAR, no significant difference 2).
PEDIG RCT (dichoptic game vs. patching, 385 participants, ages 5–12, 16 weeks, Holmes 20169)): Patching group improved by 0.135 logMAR vs. dichoptic game group improved by 0.105 logMAR. Patching was superior.
Currently, dichoptic therapy has not demonstrated clear superiority over conventional occlusion or atropine2). It offers advantages in compliance and is being studied as an option for cases where occlusion is difficult.
Liquid crystal shutter glasses that provide intermittent occlusion (30 seconds per minute) have shown effectiveness comparable to conventional patching2). They are less conspicuous and have higher acceptance among children.
Drews-Botsch et al. (2025) followed 105 children with unilateral congenital cataract (UCC) and showed that visual acuity at age 4 strongly predicts visual acuity at age 10.5 (Spearman r=0.83) 3). There was no correlation between the amount of occlusion after age 4 and changes in visual acuity; cases with 20/200 or worse did not reach 20/100 or better even with additional patching. The importance of treatment within the sensitive period was reaffirmed.
Cruz OA, Repka MX, Hercinovic A, et al. Amblyopia Preferred Practice Pattern®. Ophthalmology. 2023;130(3):P136-P180.
Meier K, Tarczy-Hornoch K. Recent treatment advances in amblyopia. Annu Rev Vis Sci. 2024.
Drews-Botsch CD, Cotsonis G, Celano M, et al. Is patching after age 4 beneficial for children born with a unilateral congenital cataract? Ophthalmology. 2025;132:389-396.
Pediatric Eye Disease Investigator Group. A randomized trial of atropine vs. patching for treatment of moderate amblyopia in children. Arch Ophthalmol. 2002;120:268-278.
Repka MX, Beck RW, Holmes JM, et al. A randomized trial of patching regimens for treatment of moderate amblyopia in children. Arch Ophthalmol. 2003;121:603-611.
Pediatric Eye Disease Investigator Group. A randomized trial of prescribed patching regimens for treatment of severe amblyopia in children. Ophthalmology. 2003;110:2075-2087.
Repka MX, Cotter SA, Beck RW, et al. A randomized trial of atropine regimens for treatment of moderate amblyopia in children. Ophthalmology. 2004;111:2076-2085.
Scheiman MM, Hertle RW, Beck RW, et al. Randomized trial of treatment of amblyopia in children aged 7 to 17 years. Arch Ophthalmol. 2005;123:437-447.
Holmes JM, Manh VM, Lazar EL, et al. Effect of a binocular iPad game versus part-time patching in children aged 5 to 12 years with amblyopia: a randomized clinical trial. JAMA Ophthalmol. 2016;134:1391-1400.
Xiao S, Angjeli E, Wu HC, et al. Randomized controlled trial of a dichoptic digital therapeutic for amblyopia. Ophthalmology. 2022;129(1):77-85.
