Amblyopia, commonly known as "lazy eye," is one of the most widespread vision issues in children, marked by reduced vision in one eye without a clear physical cause. The condition, if left untreated, can impact a child’s school performance, confidence, and overall quality of life. With estimates suggesting that amblyopia affects between 0.2% to 6.2%of children globally, early detection and treatment are essential.

A 2022 study we conducted in Madrid highlights the role of school-based vision screening programs for detecting amblyopia and other refractive errors early on, especially through the use of photorefraction technology. In this article, we will explore the study’s methodology, its findings on amblyopia prevalence, and the benefits of early school-based vision screenings, and what they mean for parents, educators, and eye care professionals.

Amblyopia occurs when one or both eyes don’t develop properly, often because of uncorrected vision issues like nearsightedness, farsightedness, or astigmatism. If left untreated, amblyopia can lead to permanent vision loss. Unlike other eye diseases, amblyopia does not stem from structural eye abnormalities. Instead, it is caused by conditions that impair or distort vision, such as anisometropia (significant difference in prescription strength between the two eyes), high astigmatism, myopia, or hyperopia. If these refractive errors are not corrected early, the brain begins to ignore input from the affected eye, which can lead to long-term impairment.

The American Association for Pediatric Ophthalmology and Strabismus (AAPOS) outlines several risk factors for amblyopia:

• Uneven vision strength (Anisometropia greater than 1.5 diopters (D)): Differences in refractive power between the two eyes can prevent one eye from achieving clear vision.
• Significant farsightedness (Hyperopia greater than 3.5 D): High degrees of farsightedness hinder the eye’s ability to focus, especially on nearby objects.
• Severe nearsightedness (Myopia greater than -3.0 D): Significant nearsightedness leads to blurred vision at greater distances, causing strain and underuse of the affected eye.
• High astigmatism (greater than 1.5 D at major axes): High astigmatism creates blurred vision due to an irregularly shaped cornea or lens.
• Oblique astigmatism (greater than 1.0 D): Misalignment in astigmatic angles further reduces clarity, especially in peripheral vision.

Identifying these risk factors early and providing corrective measures can help prevent the onset of amblyopia. However, without routine screening, these refractive errors often go undetected, especially in young children who may not communicate visual difficulties effectively.

School is a crucial place for detecting vision problems in kids. Many children may not know they have vision issues, and without routine screenings, problems like amblyopia often go unnoticed. To address this, researchers in Madrid collaborated with AMIRES (Association of Magna Myopia with Retinopathies) and contacted ten schools in the city, inviting students within this age range to participate in a school-based screening program to assess the vision of children ages 4 to 12 using a tool called the PlusOptix A12R photorefractor. This non-invasive device measures refractive errors from a comfortable distance, making it ideal for screening young children in a school setting.

In the study, 1,347 children in Madrid, Spain, participated in school-based screenings. Researchers found the program highly effective in identifying kids with undetected vision issues. To enhance accuracy, two measurements were taken for each child, and any differences greater than 0.5 D between the readings warranted additional testing.

The screening program adhered to the AAPOS criteria to identify potential amblyopia risk factors in children. The ultimate aim was to assess the prevalence of amblyopia and refractive errors, and to determine how many children had undiagnosed vision issues that warranted further intervention.

Fig. 1: Distribution of spherical (a) and cylindrical (b) power as a function of age. The red lines establish
the limits for the presence of amblyopia in children according to the AAOPS.

The study yielded several significant findings regarding amblyopia risk and refractive errors among the children:

• Prevalence of Refractive Errors and Amblyopia Risk:
  • Approximately 20% of children under the age of 7 showed signs of potential amblyopia, predominantly due to uncorrected refractive errors.
  • In children older than 7, the prevalence of amblyopia risk factors remained between 10% and 20%, indicating a persistent need for screening as children grow older.
• Distribution of Amblyopia Risk Factors:
  • Anisometropia greater than 1.5 D was present in 3.9% of the children, a significant factor in unilateral amblyopia risk.
  • High degrees of astigmatism (over 1.5 D) affected 10.3% of the sample, particularly in younger children, contributing to poor visual acuity.
  • Oblique astigmatism greater than 1.0 D was noted in 8.5% of children, a risk factor less commonly recognized but impactful in the development of amblyopia.
  • Hyperopia above 3.5 D was found in 0.4% of participants, and myopia below -3.0 D in 1.9%, both of which contributed to the overall risk profile.
• Undiagnosed Cases and Age-Related Trends:
  • A concerning 68% of children identified as being at risk for amblyopia had no previous diagnosis or corrective measures. Among the youngest group (4 to 6 years), 77% of children with amblyopia risk factors were undiagnosed.
  • The percentage of undiagnosed amblyopia cases decreased slightly in older children, from 77% in ages 4-6, to 67% in ages 7-9, and to 56% in ages 10-12. This age-related decline in undetected cases suggests that screenings are happening but could benefit from being implemented earlier in a child’s development.

These findings underscore the importance of early screening programs in schools, especially for younger children who are more likely to have undiagnosed vision issues. Early intervention is crucial in preventing the progression of amblyopia, as the condition becomes increasingly difficult to treat as children grow older.

Fig. 2: Percentage of subjects with refractive errors (dark blue), potentially amblyopic (light
blue) and uncorrected subjects (gray).

One of the standout elements of this study is the use of photorefraction technology, which streamlines the process of detecting refractive errors in children. Unlike traditional acuity-based assessments, photorefraction provides an objective and accurate measure of a child’s refractive status. Devices like the PlusOptix A12R offer several advantages:

• Infrared Light Usage: By utilizing infrared light, photorefraction avoids causing glare, allowing the pupil to remain naturally dilated without the need for pharmacological dilation.
• Non-Contact Procedure: Unlike traditional autorefractometers that require the child to rest their head on a chin rest, photorefraction is a non-contact method. This feature is especially advantageous when working with small or uncooperative children.
• Comfortable Working Distance: Measurements can be taken from approximately one meter away, reducing discomfort and making the process less intimidating for children.

In a school environment, these benefits are invaluable. The ability to screen for amblyopia and refractive errors rapidly and objectively makes photorefraction an ideal solution for integrating vision screenings into routine school health programs. The technology’s efficiency also ensures that even large student populations can be screened, significantly increasing the number of children who receive timely referrals for further eye care.

The findings of this study provide compelling evidence for the need to integrate vision screenings as a standard practice in school health programs. Amblyopia and refractive errors, if undetected and untreated, can lead to long-term visual impairments that affect academic performance and overall quality of life. By adopting technologies like photorefraction, schools can become frontline advocates for childhood eye health, identifying and addressing vision issues before they become more complex to treat.

For parents, educators, and health practitioners, the message is clear: early detection is crucial. Children’s eyes are constantly developing, and issues like amblyopia can be corrected most effectively if treated early. A simple, non-invasive screening in a school setting can make all the difference, enabling children to reach their full potential both academically and personally.

As more studies highlight the benefits of school-based vision screenings, there’s a strong case for making these programs a standard part of school health services. Uncorrected vision issues can hold children back in school and in life, but simple, non-invasive screenings can change that.

For anyone involved in children’s health or education, supporting school-based screenings is an important step toward improving kids’ vision and overall well-being. Let’s ensure that every child has the opportunity to see clearly and succeed fully.