Estimating the Prevalence and Severity of Isolated Small-Angle Strabismic Amblyopia.

Background: Isolated small-angle (< 20PD) strabismic amblyopia (is-asa) is not obvious to parents and pediatricians and can be missed by current photoscreeners. To improve early screening methods, the previously unknown prevalence and severity of is-asa is estimated from a twenty-year prospective observation. Methods: Published population data from the Multi-Ethnic and Baltimore Pediatric Eye Disease Studies (MEPEDS and BPEDS) were combined to estimate the cumulative prevalence. Then prospective, consecutive digital images of Brückner Test from 2003 to 2025 by one pediatric ophthalmologist were obtained with confirmatory exams. These were then compared to Alaska population and vision screening data. Results: From MEPEDS and BPEDS community screening data, patients with all strabismus, constant strabismus and strabismic amblyopia were stratified by strabismus angle suggesting that isolated small-angle strabismus (is-as) may occur in 1/200 children while is-asa may be 1/400 children. Over 22 years, 34 Alaska Brückner patients had isolated, constant strabismus less than 20 prism diopters of which 9 presented with amblyopia of which 4 had post-treatment residual amblyopia worse than 20/40. Considering population, doctors and referral rates, the Alaska prevalence of is-as is about 1 in 700 (0.03-0.24%) children while is-asa is about 1 in 7000 (0.006-0.024%) children. Conclusion: From two imperfect sources; review of large community screening studies and from prospective Brückner Test analysis, the prevalence of isolated small-angle strabismic amblyopia is so rare that future screening methods would require very high specificity. The Rebion blinq and 2WIN CR-function can identify is-asa in older children. Current photorefraction methods with early specific instrument referral criteria followed by sensitive acuity screening are still effective since is-asa is so rare.