Lack of concordance between fixation preference and HOTV optotype visual acuity in preschool children - The Baltimore Pediatric Eye Disease Study

Objective: To compare the results of fixation preference testing and standardized visual acuity testing in white and black children aged 30 through 71 months. Design: Cross-sectional study. Participants: The Baltimore Pediatric Eye Disease Study is a population-based evaluation of the prevalence of vision disorders in children aged 6 through 71 months in Baltimore, Maryland, United States. A total 1714 children 30 through 71 months of age were eligible for inclusion in this report, with 1435 (83.7%) testable by both fixation preference and Amblyopia Treatment Study (ATS) visual acuity testing protocol. Methods: The vision of all children 30 through 71 months of age was tested using both the ATS visual acuity testing protocol (using single HOTV symbols with surround bars) and fixation preference testing (FPT). Main Outcome Measures: The ability of fixation preference testing to identify children with clinically important interocular differences (IOD) in visual acuity (i.e., two or more logarithm of minimum angle of resolution units of difference or more). Results: Fifty-three children had 2 or more lines of IOD in visual acuity. Seven of them were graded as having momentary or no fixation (sensitivity = 13.2%; 95% confidence interval [CI], 5.3-27.2]), whereas 45 were graded as normal by FPT. In all 7 of the cases of poor FPT, the better-seeing eye was preferred. Low sensitivity and high specificity for detecting an IOD of 2 lines or more with FPT were seen for both white (33.3% sensitivity; 95% CI, 9.5-57.2; 99.6% specificity; 95% CI, 98.7-100) and black (6.5% sensitivity; 95% CI, 0.6, 23.2; 99.3% specificity; 95% CI, 98.3-99.8) children. When assessing FPT performance for 3 or more lines of IOD, only 5 of the 20 children (sensitivity, 25%; 95% CI, 6.0-44.0) had FPT grades of momentary or no fixation. Conclusions: Fixation preference testing, when used as part of a population-based research project, does not identify accurately preschool children with 2 lines or more of IOD in presenting visual acuity. The clinical value of this test is poor and its use for diagnosis and monitoring interventions should be reconsidered.