Normal values of distance heterophoria and fusional vergence ranges and effects of age

Abstract

Although it is well known that age affects visual function, we still have much to learn about the impact of aging on binocular vision. Our aim was to establish distance heterophoria and distance fusional vergence ranges in a large non-clinical population of wide age range, to provide normal values for comparisons. A cross-sectional study was performed on 271 non-clinical subjects stratified into six age groups. Distance heterophoria measurements were obtained using the von Graefe technique and distance horizontal fusional vergence ranges using Risley rotary prisms in each subject, with best spectacle correction. The mean heterophoria value for distance fixation was exophoric except for the 71-80 year age group, which was esophoric. No effects of age were observed on distance heterophoria and distance base-in and base-out break means. However, a significant effect of age was noted on base-in recovery and base-out recovery. Between the youngest and oldest age groups, mean base-in recovery decreased by 2.5 Delta and mean base-out recovery by 3.3 Delta. Distance base-in and base-out recovery means diminished significantly with age such that recovery values fell outside the norm in subjects in the 61-70 year age group and older. This study establishes statistical normal values for distance heterophoria and fusional vergence in a non-clinical population. Mean values such as these are valuable tools for identifying subjects with far binocular anomalies.