Binocular vision parameters and body mass index

Background: Abnormal body mass Index (BMI) can adversely affect binocular vision. We aimed to assess the presence of possible differences in binocular vision parameters among the four BMI categories. Methods: In this comparative cross-sectional study, we enrolled young adults and categorized them into underweight, normal weight, overweight, and obese groups based on their BMI. A complete orthoptic evaluation was performed to assess the mean values of binocular vision skills. Results: We recruited 120 participants with a mean (standard deviation) age of 21.30 (1.80) years with best-corrected distance and near visual acuities of 6/6 and N6, respectively. The frequency of exophoria > 4 PD was high in the obese group.  The frequency of binocular vision dysfunction was higher in the obese and underweight groups, with vergence dysfunction being the most common. The mean values for near negative fusional vergence (NFV), distance positive fusional vergence (PFV), negative relative accommodation, positive relative accommodation, monocular accommodation facility (AF), and monocular estimation method were comparable among the groups (all P > 0.05). The obese group had significantly receded near point of convergence, and reduced accommodative convergence to accommodation ratio and binocular AF than the normal, overweight, and underweight groups (all P < 0.05). The distance and near vergence facilities were significantly lower in the obese group than in the overweight and normal groups, and the distance vergence facility was significantly lower than in the underweight group (all P < 0.05). The mean values of distance NFV and near PFV in the obese group were significantly lower compared to the normal and overweight groups, and the mean values of distance NFV were significantly lower compared to the underweight group (all P < 0.05). The mean values of near PFV were significantly lower in the underweight group than in the overweight group (both P < 0.05). Both the underweight and obese groups had a significantly lower amplitude of accommodation compared to the normal group (both P < 0.05). Conclusions: The frequency of binocular vision dysfunction was higher in the obese and underweight groups. Most convergence and some accommodation parameters were adversely affected in individuals with obesity. Being underweight adversely affects certain binocular vision skills. Further studies are required to determine the relevance of BMI as a predictor of binocular vision abnormalities.