Winning the battle: preventing amblyopia with early detection

Abstract

Aim: Vision disorders in children are a critical public health concern, representing the leading cause of disabling conditions during childhood. Amblyopia, characterized by decreased visual acuity in one or both eyes that cannot be corrected through refractive means, is the most prevalent visual impairment in preschool-aged children. Treatment of amblyopia is effective only during a critical developmental period of the visual cortex, which extends up to approximately seven years of age. Interventions beyond this period are generally ineffective.

The introduction of any screening protocol as part of national health policy transcends medical and scientific concerns, encompassing political, economic, and ethical considerations. In November 2020, during the Seventy-third World Health Assembly, the World Health Organization (WHO) Member States adopted Resolution WHA73.4, which underscored the importance of incorporating evidence-based, cost-effective eye care into universal health coverage. This resolution emphasizes the need to address preventable vision impairments and blindness, particularly through early detection and treatment strategies. Croatia has implemented WHO’s recommendations regarding the prevention of amblyopia. Central to this initiative is the introduction of the National Preventive Program of Early Amblyopia Detection (NPPEAD), and subsequent development of the e-registry: Croatian Registry for Early Amblyopia Detection (CRO-READ).

This paper aims to present Croatia’s amblyopia prevention model – NPPEAD. The model emphasizes visual acuity screening for four-year-olds, ensuring timely detection and treatment of amblyopia to improve vision and public health outcomes.

Methods: A narrative literature review was conducted to examine key sources related to early amblyopia screening and eye care interventions. The literature search was conducted during 2024, December 1-31, using PubMed and official WHO resources. Studies and guidelines were selected based on their relevance and importance to the subject matter. The retrieved references included both national and international recommendations, research on vision screening, and reports on global eye care initiatives.

Results: Between September 2011 and June 2014, the University Eye Department at the University Hospital Sveti Duh conducted amblyopia screenings within kindergartens in the City of Zagreb, encompassing approximately 16,000 four-year-old children. This ZAPS (Zagreb Amblyopia Preschool Screening) study identified an amblyopia prevalence rate of 8.1 %, equating to an estimated 300,000 individuals in Croatia. Based on these findings, the Croatian Ministry of Health implemented mandatory amblyopia screening for all four-year-olds as of June 2015. By 2019, NPPEAD had achieved full nationwide coverage, with all four-year-olds systematically invited to participate in screenings through personalized invitations and informational materials disseminated by the Croatian Public Health Institute.

The NPPEAD employs rigorously standardized protocols for visual acuity testing, modeled on the ZAPS study, which demonstrated a testability rate of 99 %, a sensitivity of 100 %, and a specificity of 97 %. The screenings include binocular and monocular visual acuity assessments conducted at near (40 cm) and distance (3 m) using logMAR inline optotypes. Children who fail to meet the screening criteria are referred for comprehensive ophthalmological evaluations.

Analysis of data from the program’s e-registry yielded significant findings. The cutoff value for normal visual acuity in four-year-old children was confirmed to be ≤0.1 logMAR. Among children who successfully passed the screening, the mean visual acuity was calculated at 0.91 ± 0.1. It was also observed that at the age of four, males were more likely to be nontestable. Furthermore, children referred for follow-up due to binocular causes exhibited a lower mean visual acuity of 0.3, in contrast to a mean of 0.6 for those referred for monocular causes. This disparity reflects a developmental trend toward binocular amblyopia, wherein the visual system adapts to maintain binocular balance.

Conclusions: The NPPEAD operates across all 21 Croatian counties, with 106 ophthalmological teams at 56 locations. Between 2019 and 2023, 95,032 children were screened, achieving a 50 % response rate despite interruptions during the COVID-19 pandemic. Among those screened, 20.1 % were referred for further evaluation.

Croatia’s program addresses a critical gap by initiating screenings at age four, a significant improvement over prior practices that delayed testing until school enrollment. The introduction of the national e-registry, developed in collaboration with Sveti Duh University Hospital and the Croatian Institute of Public Health, simplifies data management and provides real-time monitoring of program outcomes.

Croatia’s amblyopia prevention model combines systematic screenings with advanced technological infrastructure. Its alignment with WHO’s global vision care initiatives and the innovative use of an e-registry sets a benchmark for other nations. Continued investment in public awareness, professional training, and technological advancements will be critical to sustaining the program’s success. As the WHO emphasized in 1968, vision screening programs are hallmarks of national development. Croatia’s efforts position it among the most progressive countries in promoting and safeguarding children’s eye health.