Pediatric vision screening is a system of examinations aimed at early detection of children with amblyopia, strabismus, significant refractive errors, and other eye abnormalities.
Amblyopia is a visual impairment caused by abnormal visual input during the visual development period, and is classified into the following four types 1).
The prevalence of amblyopia in Japan is estimated at 0.58% based on a meta-analysis of the referral rate from the 3-year-old health checkup. Internationally, reported prevalence ranges from 0.14% to 4.8%, with epidemiological data from the United States showing 1.5% in African Americans and 2.6% in Hispanics.
Amblyopia can be reversed with appropriate treatment during early childhood, but if left untreated, it can lead to permanent vision loss in one or both eyes and is a leading cause of visual impairment in adults under 40. Even without amblyopia, uncorrected refractive errors can negatively impact learning and school performance.
In Japan, the 3-year-old health checkup is the most important screening opportunity.
Even if missed at the 3-year-old checkup, annual eye exams at nursery schools/kindergartens, school entry health checkups, and annual eye exams at elementary schools can detect problems. However, according to the Japan Ophthalmological Society, approximately 25% of children referred for further evaluation do not visit an ophthalmologist.
In the United States, the U.S. Preventive Services Task Force (USPSTF) recommends at least one amblyopia screening for children aged 3 to 5 years. The American Association for Pediatric Ophthalmology and Strabismus (AAPOS) recommends continued screening every 1 to 2 years after age 5.
In Japan, the 3-year-old health checkup is the primary opportunity, but screening is possible from 6 months of age using devices such as infrared video refractometers. The USPSTF recommends screening at ages 3 to 5, and AAPOS recommends continued screening every 1 to 2 years after age 5.
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 serve as 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 resists covering one side, there may be amblyopia. Also watch for 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
Cause: High refractive error of similar degree in both eyes
Mechanism: Visual acuity does not develop due to impaired image formation on the foveal retina. Includes hyperopic, myopic, and astigmatic types.
Characteristics: Relatively good improvement with spectacle correction.
Anisometropic Amblyopia
Cause: Difference in refractive error between the two eyes
Frequency: Most common type of amblyopia.
Features: Hyperopic anisometropia of about 1 diopter can cause amblyopia. The eye closer to emmetropia becomes the dominant eye.
Strabismic Amblyopia
Cause: Suppression of the non-fixing eye due to misalignment of the eyes
Mechanism: Competition from non-fusible inputs from both eyes leads to dominance of the fixing eye 1).
Features: Fixation testing is important for diagnosis.
Form Deprivation Amblyopia
Cause: Congenital cataract, severe ptosis, corneal opacity, etc.
Mechanism: Blockage of the visual axis results in a degraded retinal image 1).
Features: Rarest but most severe, and highly resistant to treatment.
Children from minority or low-income backgrounds have significantly higher rates of undiagnosed visual impairment. Although 7–20% of school-age children have visual defects, the proportion of undiagnosed and untreated children is even higher among those from socioeconomically disadvantaged environments. The prevalence of vision screening has been declining since 2016, and this trend has continued after the pandemic.
Vision testing in children requires selecting a method appropriate for the child’s age and developmental stage.
| Age | Recommended Examination Method |
|---|---|
| Under 2 years | Blink reflex, fixation and pursuit, aversion reflex, OKN, PL method |
| 2 years | Morizumi dot card, picture optotypes |
| 3–6 years | Single optotype, Landolt C ring |
| 6 years and older | Crowded optotype, Landolt C ring |
This is a test method that requires a response from the child and is most effective for children aged 5 years and older who have language ability.
Covering with the hand is not recommended because children often peek through finger gaps. Use an adhesive eye patch or an opaque occluder. Pediatric occlusion glasses (with one opaque plastic lens) are also useful.
It requires little response from the child and can be applied to younger children.
This is the most basic test that does not require patient cooperation and can be performed from infancy. A light is shone into the pupil using a retinoscope or direct ophthalmoscope, and the color, brightness, and symmetry of the reflex are observed. It is easier to assess in a dark room, but can also be done in a semi-dark or bright room. Abnormalities in the red reflex can lead to early referral for conditions such as congenital cataracts and retinoblastoma.
Used on eyes without dilation, it provides an estimate of refractive error in children. It can be performed on preverbal children and is much faster than visual acuity testing. Main devices include the Grand Seiko binocular autorefractor, Retinomax, and SureSight. However, since most are monocular tests, they do not screen for strabismus.
Because children have strong accommodation, if screening suggests an abnormality, a cycloplegic refraction is essential. Cycloplegic agents include 1% atropine eye drops and 1% cyclopentolate eye drops. For cases of esotropia or amblyopia, it is recommended to test with atropine eye drops at least once.
This method captures corneal reflex images from the pupils to detect strabismus, refractive errors, and anisometropia. Since it tests both eyes simultaneously, unlike autorefraction screening, it can directly screen for manifest strabismus. Changes in the red reflex can also detect anatomical abnormalities such as cataracts, coloboma, and ptosis.
Main devices include iScreen, MTI, plusoptiX, Spot, and Visiscreen. MTI, iScreen, and Visiscreen use visible light flash, while plusoptiX and Spot use infrared light.
In recent years, binocular open-field infrared videorefractometers have been developed, some usable from 6 months of age. They are increasingly used in pediatrics, and the age at which amblyopia is detected tends to be lower.
This records brain waves generated when flash or pattern stimuli (checkerboard or grating) are presented, estimating visual acuity. It reflects the function of the visual pathway from the retina to the occipital visual cortex. VEP acuity tends to be higher than acuity measured by PL or OKN methods, because VEP directly assesses occipital cortical responses. The child must be calm during the test, and it is preferable to perform it at a facility experienced with the procedure.
In the primary screening, a visual acuity test using a 0.5 optotype and a questionnaire are completed at home. The secondary screening is a group checkup at a health center, where all children undergo refraction testing, and if necessary, a repeat visual acuity test, followed by a pediatrician’s examination. If amblyopia or eye disease is suspected (e.g., abnormal refraction test, poor visual acuity, or positive questionnaire items), the child is referred for a detailed examination (complete pediatric eye exam including cycloplegic refraction) at an ophthalmology clinic.
| Age | Visual Acuity |
|---|---|
| 3 months | 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 varies depending on the testing method and individual differences, so these values are only guidelines.
Most autorefractors are monocular and specialized for estimating refractive errors. In contrast, photoscreeners test both eyes 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 colobomas.
Pediatric vision screening is a testing system; there is no “treatment” for the screening itself. Here, we outline the treatment of major diseases detected by screening.
This is the foundation of amblyopia and strabismus treatment. In Japan, glasses for treating esotropia and amblyopia are covered by insurance up to age 8. Refraction tests must always be performed under cycloplegia. Refractive values in children, especially infants, change significantly, and re-evaluation with cycloplegic agents is necessary during follow-up.
This is the central method of 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.
Visual sensitivity is highest from 1 to 18 months of age, then gradually declines, but considerable sensitivity remains until around age 8. Generally, the earlier risk factors for amblyopia are identified and treatment is started, the higher the likelihood of developing normal vision.
However, there are reports of cases where treatment started after age 12 improved vision, and adult cases where vision in the amblyopic eye improved due to impairment of the fellow eye, making it difficult to define a clear critical period.
To prevent form deprivation amblyopia, surgery must restore light stimulation by 6–8 weeks of age for unilateral cases and by 10–12 weeks for bilateral cases.
Visual sensitivity is thought to remain considerable until around age 8, but it declines with age. There are reports of vision improvement even after age 12 with treatment, so an absolute upper age limit has not been established. It is well established that earlier treatment is more effective.
Human visual acuity develops through visual experience after birth.
The developmental process of normal visual acuity in children is shown below.
| Age (months/years) | Visual Development Milestones |
|---|---|
| 1 month | Appearance of visual tracking |
| 2 months | Binocular fixation, tracking across midline |
| 3 months after birth | Complete pursuit in all directions. Confirmed at 3-month checkup. |
| 1 year old | Visual acuity 0.1–0.2 |
| 2 years old | Visual acuity 0.3–0.5 |
| 3 years old | Visual acuity 0.5–0.8 (may reach 1.0) |
| 6–8 years old | Visual development nearly complete |
If visual input is blocked during the visual development period, irreversible visual impairment occurs, especially when the blockage occurs earlier, lasts longer, and is 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 pathways.
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.
Amblyopia is a functional disorder of the central nervous system resulting from abnormal processing of visual information. It involves not only reduced visual acuity but also impaired contrast sensitivity and accommodation. Subtle functional abnormalities may also be observed in the fellow eye 1).
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.
In a study using the early model Pediatric Vision Scanner, sensitivity of 100% (95% CI, 54%-100%) and specificity of 85% (95% CI, 80%-89%) were reported, with a median measurement time of 28 seconds. The latest model blinq™ has received FDA approval and is funded by the National Eye Institute (NEI). A prospective cross-sectional study of 200 individuals aged 1–20 years showed 100% sensitivity and 91% specificity for detecting amblyopia and strabismus requiring referral.
Smartphone-based deep learning systems have been shown to identify visual impairment in infants due to various causes including anisometropia, strabismus, cataract, and congenital anomalies. In the future, this may greatly improve the efficiency and reach of 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 decision.
