Children’s vision screening in United Kingdom typically occurs at age 4 to 5 years, with the primary objective to detect and treat amblyopia. Research has established that vision screening reduces the prevalence and severity of amblyopia, reducing the risk of lifelong visual impairment. ^, Children who are 48 months old require less treatment than at age 72 months because their visual pathway is more receptive to early intervention. Amblyopia risk factors (ARFs) that predispose children to amblyopia comprise refractive errors, constant manifest strabismus, and visual axis obstruction. In children aged 4 to 5 years, previously undiagnosed visual defects are most likely to be refractive errors and parents/carers are usually unaware of these.

Appropriate early management of these ARFs is essential for optimizing normal visual development, preventing amblyopia and minimizing potential adverse effects on early literacy and self-reported health and well-being. The criteria for determining whether children pass vision screening vary. There is consensus that all children who fail screening require a comprehensive follow-up eye examination, including cycloplegic refraction. The most widely used ARF criteria are those provided by the American Association for Pediatric Ophthalmology and Strabismus (AAPOS). The AAPOS Vision Screening Committee established guidelines based on expert consensus to define uniform ARF levels which would trigger the management of potential amblyopia. Initially published in 2003 and updated in 2013, these guidelines were revised again in 2021 to minimize over-referrals in young children and ensure a more cost-effective referral process.

Scotland (population ∼5.5 million) has a comprehensive vision screening program (See4School), undertaken by registered orthoptists, for children aged 3.5 to 5.5 years. ^, All children in Scotland registered with a General Medical Practitioner (Family Physician) and not already under the hospital eye service (HES) are invited to participate. The uptake of screening is high (∼85%) and generates approximately 45,000 screening episodes annually. ^, Screening tests include presenting vision, cover test, and other orthoptic evaluations. Fully anonymized data are collated for basic audit purposes by the Scottish Health Boards. Screening failures are referred for an eye examination, performed in the HES or by a community optometrist, which includes a cycloplegic refraction. There is a lack of good data on the prevalence of ARFs in young children in the UK. Analyzing these eye examination data allows us to establish the proportion of children with ARFs in Scotland; information crucial for early intervention to prevent amblyopia, effective resource allocation, policy development, raising awareness, and improving children’s overall well-being. Knowing which ARFs are most prevalent helps clinicians and policy makers determine the best screening tools and referral pathways.

The primary aim of this epidemiological retrospective cohort and trend study was to estimate the overall prevalence of children with any ARF and the proportion of each type of ARF, based on data from children during the 5 years for which full data were available (2013/14, 2014/15, 2015/16, 2020/21, and 2021/22).

The influence of socioeconomic background on the likelihood of children having ARFs is not fully understood. Several studies suggest that individuals from lower income backgrounds are at higher risk of developing amblyopia. ^, Conversely, some studies found no significant associations between amblyopia and socioeconomic status, possibly because children from less affluent communities are more likely to have undiagnosed ocular problems due to lower rates of uptake of eye care. In 2025, using data from the See4School program, we reported an increasing proportion of children with myopia from 2016 to 2022. We also found a strong association between higher rates of myopia and both the proportion of dwellings that were apartments/flats and residences in the most urban areas. Tracking temporal shifts in ARFs can identify whether certain conditions are becoming more or less prevalent; changes which can reflect shifts in environmental or behavioral risk factors and therefore inform policy and resource planning. However, there is a dearth of published data on any possible associations between the prevalence of ARFs and deprivation, types of housing, or location (urban vs rural). Therefore, our secondary aims were to investigate changes in the proportion and prevalence of ARFs over time, and to assess whether the likelihood of young children in Scotland having ARFs is associated with deprivation, urban (c.f., rural) area, or apartment/flat dwellings (c.f., other types of housing).

This retrospective cohort and trend study adhered to the principles of the Declaration of Helsinki and was initiated following approval from the UK Health Research Authority (HRA) and following a data-sharing agreement. Vision assessments were conducted by registered orthoptists using age-appropriate, standardized acuity tests. Letter-matching tests (Keeler LogMAR or Sonksen LogMAR) were used when the child was able to complete these reliably; otherwise, the Kay Picture Crowded test was administered. ^, Monocular vision was ensured using either adhesive occlusion patches or occlusive spectacles, depending on local Health Board practice, with close monitoring to prevent peeking. Failures were based on predefined criteria, including reduced vision in one or both eyes and/or the presence of a significant binocular vision anomaly. After failure, a standardized referral pathway was followed across all 15 Scottish Health Boards. This led to comprehensive eye examinations, including cycloplegic refraction, performed by a community optometrist, hospital optometrist, or ophthalmologist.

Anonymized screening outcomes and eye examination outcomes were recorded in a spreadsheet for each Health Board and subsequently compiled into a national database. Author LP, Lead for Child Vision Screening in Tayside, co-ordinates the audit of vision screening data in Scotland, and was responsible for cleaning and consolidating data from Health Boards, providing the research team with deidentified information. The present analyses include data from 8 Health Boards, selected because they provided results for each of the 5 years analyzed: 2013/14, 2014/15, 2015/16, 2020/21, and 2021/22. In total, an estimated 17.2 whole-time-equivalent orthoptists provide vision screening across the 8 included Health Boards, with each orthoptist typically screening between 30 and 40 children during a full preschool day. These 8 Health Boards together cover over 85% of Scotland’s population based on 2021 figures. No vision screening takes place in Scotland before the age of 3.5 years.

Cycloplegic refraction and cover test results were analyzed to determine the proportions of children with any ARF. Autorefractors are not part of the national vision screening service in Scotland. Children were classified as having one or more ARFs according to the AAPOS 2021 criteria, subject to the following adaptations ( Table 1 ). The vision screening did not include an intraocular examination, preventing application of the media opacity AAPOS criterion. The authors regard a constant manifest strabismus to be a stronger ARF than the magnitude of the deviation and adapted this criterion accordingly ( Table 1 ). The AAPOS criterion for anisometropia of >1.25D was interpreted as >1.25 diopters cylinder (DC) for astigmatism and >1.25D spherical equivalent refraction (SER) for hyperopic or mixed anisometropia (where 1 eye is hyperopic and the other myopic). Similarly, although not made explicit in the AAPOS criteria, it was confirmed following communication with the corresponding author of the description of the AAPOS 2021 ARFs that the criterion for hyperopia of SER >+4.00D applied to hyperopia in one or both eyes. For astigmatism, the AAPOS 2021 guidelines suggest an ARF criterion of >3.00DC for children <4 years of age. As most children in our study were 4 years or older at the time of their cycloplegic refraction, a lower threshold of >1.75DC in one or both eyes was adopted.

A linear regression analysis was conducted to evaluate temporal trends in prevalence across the defined population, examining each of the 6 ARFs. This approach was also employed across the various Health Boards to investigate the relationship between the proportion of children diagnosed with each ARF out of those who failed vision screening. The comparison was made between children in the most deprived quintiles (1 and 2) and those in the least deprived quintiles (4 and 5), using data from 2013/2014 and 2021/2022. Additionally, for the same years, linear regression was used to assess the association between the proportion of children with each ARF in each Health Board and the type of dwelling (apartments/flats vs detached houses) based on 2017/18 dwellings data, as well as the proportion of dwellings in large urban areas vs rural areas based on mid-2020 location data. A Bonferroni correction for multiple comparisons was applied for all linear regression analyses. Finally, odds ratios were calculated to assess the likelihood of failing vision screening for children living in each deprivation quintile, relative to those in the third (or middle) quintile of deprivation, for all 5 years. All CIs quoted are 95% intervals.

The numbers presented at the “eligible” and “screened in all Health Boards” levels for the PRISMA flow diagram ( Figure 1 ), represent data for all 15 Scottish Health Boards (HBs). The number of children eligible for screening excludes children already under the Hospital Eye Service or whose guardians opted out of screening. The figures shown under “screened in 8 Health Boards“ refer specifically to children from the 8 HBs that consistently submitted data across all 5 years (Ayrshire and Arran; Forth Valley; Greater Glasgow and Clyde; Grampian; Highland; Lanarkshire; Lothian; Tayside). Cover tests were conducted by orthoptists at the screening stage, whereas cycloplegic refraction was performed at follow-up eye examinations. To calculate the prevalence of at least 1 ARF and of each individual ARF, the denominator used was the number of children screened in these 8 HBs. Inclusion criteria for “attended eye exam” data in Figure 1 required complete clinician reports to be submitted following eye examination. The “≥1 ARF detected” counts include children with a constant manifest strabismus identified during screening stage and/or those with refractive ARFs based solely on complete returns post eye exam.

PRISMA flow diagram summarizing the identification of vision screening data used for the final analysis and presenting, for each year analyzed, the prevalences of the presence of one or more ARF. See below for more details on samples at each stage. ARF, amblyopia risk factor.

Across the 5-year period analyzed, only 2% to 3% of children wore spectacles to their vision screening appointments. Between 57.06% and 66.24% of those who failed screening subsequently attended their follow-up eye examination and had valid data returned following their appointments. The proportion of those who actually attended for their follow-up examination would be higher than these figures but, because anonymized data were not always returned by clinicians, we are unable to more precisely determine the overall follow-up attendance rate.

The prevalence of children in the defined population having at least 1 ARF ranged between 4.41% (4.21-4.60) in 2013/14 and 5.15% (4.92-5.38) in 2021 to 22 ( Table 2 ). Regression analysis found no statistically significant relationship between the prevalence of individuals with any of the 6 ARFs over the years investigated ( P -values ranged from.03 to 1.00, all of which failed to meet the Bonferroni-corrected P -value for statistical significance of.008). Similarly, no significant relationship was found between the proportion of individuals within a Health Board exhibiting each of the 6 ARFs and the proportion of children who failed vision screening living in deprivation quintiles 1 and 2 vs quintiles 4 and 5 ( P -values ranging from.06 to.97) for either the 2013/14 or 2021/22 data. Additionally, across both years, there was no significant relationship between the proportion of individuals within a Health Board diagnosed with each ARF and the proportion of dwellings classified as apartments/flats vs detached houses ( P -values ranging from.14 to 1.00) or the proportion of dwellings in large urban areas vs rural areas (based on mid-2020 location data, P -values ranging from.09 to.92).

TABLE 2

The Prevalence and 95% CIs of Amblyopia Risk Factors (ARFs) Among Children Who Failed Vision Screening for All 5 Screening Years analyzed

	Prevalence of Children (%)
	2013-14	2014-15	2015-16	2020-21	2021-22
Any ARF (≥1 ARF)	4.41 (4.21-4.60)	5.04 (4.83-5.25)	5.13 (4.92-5.34)	4.62 (4.41-4.84)	5.15 (4.92-5.38)
Constant manifest strabismus	0.60 (0.53-0.68)	0.75 (0.67-0.83)	0.59 (0.52-0.66)	0.61 (0.53-0.69)	0.71 (0.62-0.79)
Hyperopia >+4.00D (in one or both eyes, SER)	1.71 (1.59-1.83)	2.04 (1.91-2.18)	2.23 (2.09-2.37)	1.72 (1.59-1.85)	1.81 (1.67-1.95)
Astigmatism >1.75DC (in one or both eyes)	1.78 (1.66-1.91)	2.21 (2.07-2.35)	2.18 (2.04-2.32)	2.09 (1.95-2.24)	2.48 (2.32-2.64)
Hyperopic Anisometropia >1.25D (SER)	1.35 (1.24-1.46)	1.34 (1.23-1.45)	1.47 (1.35-1.59)	1.40 (1.28-1.52)	1.37 (1.25-1.49)
Astigmatic Anisometropia >1.25DC	0.60 (0.53-0.68)	0.66 (0.58-0.73)	0.61 (0.54-0.69)	0.58 (0.51-0.66)	0.65 (0.57-0.73)
Mixed Anisometropia >1.25D (SER)	0.08 (0.05-0.11)	0.07 (0.05-0.10)	0.08 (0.05-0.11)	0.10 (0.06-0.13)	0.10 (0.07-0.13)

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