The 3-year-old health checkup is an infant and toddler health examination conducted by municipalities under the Maternal and Child Health Act, and includes visual screening. Its main purpose is early detection of amblyopia, strabismus, and significant refractive errors.
There are three main opportunities for screening visual function in children.
The School Health and Safety Act was revised and enacted from the former School Health Act in 2009, expanding the scope of school health.
Amblyopia is a visual impairment caused by abnormal visual input during the visual development period, and is classified into the following four types1).
The prevalence of amblyopia in Japan is estimated at 0.58% from a meta-analysis of 3-year-old health checkups. Overseas, reports range from 0.14% to 4.8%, with epidemiological data in the US showing 1.5% in African Americans and 2.6% in Hispanics.
Amblyopia can be reversed with appropriate treatment in early childhood, but if left untreated, vision may permanently decrease. Even without amblyopia, uncorrected refractive errors can negatively affect learning and school performance.
Even if missed at the 3-year-old health checkup, annual eye exams at nursery schools/kindergartens, pre-school checkups, and annual eye exams at elementary schools can lead to detection. According to the Japan Ophthalmologists Association, about 25% of children requiring further examination do not visit an ophthalmologist2).
The 3-year-old health checkup is the most important screening opportunity. Photoscreeners and infrared video refractometers can be used from 6 months of age. The US Preventive Services Task Force (USPSTF) recommends screening at ages 3 to 53). Even if missed at age 3, there are opportunities for detection at pre-school checkups and annual elementary school checkups.
Amblyopia and strabismus often have few subjective symptoms, and the affected person may not notice them. The following items included in the health checkup questionnaire for 3-year-olds can provide clues for early detection at home.
When a child is concentrating on playing with a toy, gently cover one eye at a time and observe any difference in reaction between the eyes. If the child strongly dislikes having one eye covered, it may indicate amblyopia in that eye. Also pay attention to abnormal head posture while watching TV, squinting one eye, or getting extremely close to objects.
The following are known factors that increase the risk of developing amblyopia:
Refractive Amblyopia
Mechanism: Occurs when both eyes have a similar degree of high hyperopia, and even using accommodation, a clear image cannot be formed.
Features: Bilateral. Main causes are high hyperopia (+5D or more) and high astigmatism. Since it is not accompanied by strabismus, it is often detected late.
Anisometropic Amblyopia
Mechanism: Occurs when the refractive difference between the two eyes causes the retinal image in one eye to be constantly unclear.
Characteristics: The most common type of amblyopia. Hyperopia can cause it even with a difference of 1D between eyes. It is not easily noticeable externally, so detection during health checkups is important.
Strabismic Amblyopia
Mechanism: Occurs when one eye is consistently used for fixation in strabismus, leading to persistent suppression of the non-fixating eye.
Characteristics: Unilateral. It is easily detected when strabismus is obvious, but mild cases may be overlooked 1).
Form Deprivation Amblyopia
Mechanism: Caused by congenital cataracts, severe ptosis, corneal opacities, etc., which block the visual axis and prevent visual stimulation of the fovea.
Characteristics: The rarest but most severe type. It worsens rapidly after onset, so early surgery is essential 1).
When reduced visual acuity is identified during school health checkups, refractive error is the most common cause, but amblyopia and psychogenic visual disturbance should also be considered in the differential diagnosis. School doctors should also pay attention to whether the child has been examined.
Psychogenic Visual Disturbance: Temporary visual impairment caused by psychological stress. Visual acuity is often moderately reduced, and daily life is not significantly affected, but the child complains of “not being able to see the blackboard in class” or “not being able to read textbooks.” Goldmann kinetic perimetry typically shows spiral or tubular visual fields. Collaboration with school and family is key to treatment.
Visual acuity testing in children requires selecting a method appropriate for age and developmental stage.
| Age | Recommended test method |
|---|---|
| Under 2 years | Blink reflex, fixation and pursuit, aversion reflex, OKN, PL method |
| 2 years | Morizane dot card, picture optotypes |
| 3 to 6 years old | Single-character target, Landolt C |
| 6 years and older | Crowded target, Landolt C |
Visual acuity in infants and young children varies depending on developmental factors, stranger anxiety, unfamiliarity with the environment, health status, and daily mood. Note that results may also differ depending on the testing method.
Covering with the hand is not recommended because children often peek through finger gaps. Use adhesive eye patches or opaque occluders.
This is the most basic test that does not require patient cooperation and can be performed from infancy. Shine light into the pupil using a retinoscope or direct ophthalmoscope and observe the color, brightness, and symmetry of the reflex. Abnormal red reflex may indicate congenital cataract or retinoblastoma, prompting early referral 1).
Used without cycloplegia, it provides estimated refractive error values. Common devices include Grand Seiko binocular autorefractor, Retinomax, and SureSight. Note that most are monocular tests and do not screen for strabismus.
Captures corneal light reflex images from the pupils to detect strabismus, refractive errors, and anisometropia. Because it tests both eyes simultaneously, it allows direct screening for manifest strabismus. It can also detect cataracts, colobomas, and ptosis 4).
Main devices and features:
| Device | Method | Features |
|---|---|---|
| iScreen | Visible light flash | Remote expert analysis available |
| plusoptiX | Infrared video | Auto-refraction value calculation. Referral criteria adjustable. |
| Spot Vision Screener | Infrared video | Equipped with eye tracking. Measurement completed in seconds. |
| GoCheck KIDS | iPhone app | Low cost, compatible with electronic medical records. |
This is an essential definitive test for cases suspected of abnormalities on screening.
Electroencephalography is recorded in response to flash or pattern stimuli to estimate visual acuity. VEP acuity tends to be higher than that measured by PL or OKN methods.
| Age | Normal Visual Acuity (Approximate) |
|---|---|
| 3 months | About 0.05 |
| 1 year | 0.1–0.2 |
| 2 years | 0.3–0.5 |
| 3 years | 0.5–0.8 |
| 6 years | 1.0 |
Visual acuity in infants develops rapidly from birth to 3 years of age and is nearly complete by 6–8 years. These values are only guidelines, and individual differences are large.
| Examination Item | Details |
|---|---|
| Visual Acuity Test | Measure uncorrected visual acuity in each eye using an internationally standardized vision chart. For spectacle users, also measure corrected visual acuity. |
| Eye Diseases/Abnormalities | Infectious eye diseases, external eye abnormalities, eye position abnormalities, etc. |
| Examination Item | Details |
|---|---|
| Visual Acuity Test | Measure uncorrected visual acuity in each eye. Evaluate on a 4-level scale: A (1.0 or higher) to D (less than 0.3). |
| Eye Diseases/Abnormalities | Infectious eye diseases, other external eye diseases, eye position/eye movement tests, etc. |
| Color Vision Test | Not a mandatory item, but can be performed with the consent of the student and guardian (removed from mandatory items in 2002). |
Autorefractors are mostly monocular and specialized in estimating refractive errors. In contrast, photoscreeners perform binocular testing simultaneously, allowing direct screening for manifest strabismus in addition to refractive errors. They also differ in being able to detect anatomical abnormalities such as cataracts and coloboma4).
A screening result indicating need for further examination is not a definitive diagnosis. It is important to promptly visit a pediatric ophthalmologist and undergo a detailed examination including cycloplegic refraction. Reports indicate that about 25% of children requiring further examination do not see an ophthalmologist, and failure to do so means losing the opportunity for amblyopia treatment2).
The 3-year-old health checkup and vision screening are examination systems; there is no “treatment” for the screening itself. Here, we outline the treatment for major diseases detected by screening.
Glasses for treating esotropia and amblyopia are covered for children under 9 years old, with insurance covering 70% of the purchase price up to a maximum of 36,700 yen × 104.8/100 for glasses (frame type). Renewal conditions require an interval of at least 1 year for children under 5 years old and at least 2 years for those 5 years and older. Refraction must always be evaluated under cycloplegia.
This is the central method for amblyopia treatment. The healthy eye is covered with an eye patch to encourage active use of the amblyopic eye, promoting visual development. There is a risk of occlusion amblyopia (impaired visual development in the healthy eye) due to patching, so regular visual acuity assessment is essential. If the visual acuity of the healthy eye drops by 2 lines or more, patching should be temporarily stopped and an ophthalmologist consulted.
Visual sensitivity is highest from 1 to 18 months of age and persists until around 8 years of age. Earlier treatment offers a higher chance of normal visual development 1). However, cases of visual improvement after starting treatment at age 12 or older have been reported, making it difficult to set a clear critical period. If treatment response is poor, consider organic diseases such as achromatopsia, retinitis pigmentosa, retinoschisis, autosomal dominant optic atrophy, macular hypoplasia, brain tumor, or retinoblastoma.
Treatment is most effective until around 8 years of age, when visual sensitivity remains 1). Recent evidence shows significant response to occlusion therapy even at ages 7–12, with effectiveness decreasing as age increases, but no absolute upper age limit has been established. It is well established that earlier treatment yields better results.
Screening opportunities are available at school entry health checkups and regular school health checkups. Annual eye exams at daycare or kindergarten can also serve as alternative screening. If concerned, an eye examination is recommended regardless of age. Since treatment during the sensitive period is most effective, it is important to seek care early even if detection is delayed.
Human visual acuity develops through visual experience from birth.
The normal visual development process in children is shown below.
| Age (months/years) | Visual Development Indicators |
|---|---|
| 1 month after birth | Appearance of visual tracking |
| 2 months after birth | Binocular fixation, tracking beyond midline |
| 3 months after birth | Complete pursuit in all directions. Confirmed at 3-month checkup. |
| 1 year | Visual acuity 0.1–0.2 |
| 2 years | Visual acuity 0.3–0.5 |
| 3 years | Visual acuity 0.5–0.8 (may reach 1.0) |
| 6–8 years | Visual development nearly complete |
If visual input is blocked during the visual development period, irreversible visual impairment occurs when the blockage is earlier, longer, and more severe. Animal experiments have shown that this involves degeneration and atrophy not only functionally but also organically, extending from the retina to the optic tract and visual pathway.
According to Awaya’s theory, human visual sensitivity is low immediately after birth, becomes very high from 1 month to 18 months of age, then gradually declines, but considerable sensitivity remains until around 8 years of age.
The essence of amblyopia is a functional change in the visual centers (visual cortex and lateral geniculate nucleus), not an organic lesion. Amblyopia is a functional disorder of the central nervous system resulting from abnormal processing of visual information, and is accompanied not only by reduced visual acuity but also by impaired contrast sensitivity and accommodation1).
Proportion of uncorrected visual acuity less than 1.0 according to the Ministry of Education, Culture, Sports, Science and Technology School Health Statistics Survey (FY2014):
| School type | Uncorrected visual acuity < 1.0 | Uncorrected visual acuity < 0.3 |
|---|---|---|
| Kindergarten | 26.53% | 0.97% |
| Elementary school | 30.16% | 8.14% |
| Junior high school | 53.04% | 24.97% |
| High School | 62.89% | 35.84% |
The proportion of individuals with uncorrected visual acuity below 1.0 is on the rise. Compared to fiscal year 1979 (kindergarten 16.47%, elementary school 17.91%), the current rates have increased significantly. In kindergartens and elementary schools, this is the second most common health issue after dental caries, while in junior high and high schools, it is the most prevalent health problem.
School ophthalmologists play the following six roles in school health checkups:
Severe eye injuries from sports are most common in ball games, especially baseball, softball, and soccer. For predictable injuries such as sports injuries or chemical experiment accidents, guidance on wearing protective eyewear should be provided.
The blinq™ pediatric vision scanner developed by Rebion uses polarized laser scanning to examine retinal nerve fibers and detect small-angle strabismus and slight foveal misalignment. It is held about 35 cm from the child’s eye and scans both retinas simultaneously in 2.5 seconds.
A study using the early model Pediatric Vision Scanner reported sensitivity of 100% (95% CI, 54%-100%) and specificity of 85% (95% CI, 80%-89%). The latest model blinq™ has received FDA approval, and a prospective cross-sectional study of 200 individuals aged 1-20 years showed sensitivity of 100% and specificity of 91%1).
Smartphone-based deep learning systems have been shown to identify visual impairment in infants due to various causes including anisometropia, strabismus, cataracts, and congenital anomalies1). GoCheck KIDS is based on an iPhone app, offers low cost and electronic medical record integration, and may contribute to the widespread adoption of large-scale screening.
The sweep VEP device provided by Diopsys uses sweep VEP to estimate visual acuity or interocular acuity difference and automatically outputs a pass/refer decision1).
