The distribution of negative and positive relative accommodation and their relationship with binocular and refractive indices in a young population

Purpose: To determine the distribution of negative relative accommodation (NRA) and positive relative accommodation (PRA) and its relationship with binocular vision indices in a young population. Methods: In this cross-sectional study conducted in a student population, samples were selected through multistage cluster sampling. All the samples underwent the measurement of uncorrected and corrected visual acuity and refraction. Then far and near cover tests were performed. The near point of convergence (NPC) and accommodation, accommodation facility, PRA and NRA were evaluated in all participants. Results: The mean age of the 382 participants was 22.5 ± 4.4 years (18e35 years). Mean NRA and PRA in the total sample was þ2.08 ± 0.33 diopter (D) and 2.92 ± 0.76 D, respectively. Mean NRA was highest in hyperopic (P ¼ 0.002) and mean PRA was highest in myopic (P ¼ 0.003) participants. The multiple model showed that NRA had a direct relationship with accommodation facility and spherical refractive error, while PRA had a direct relationship with amplitude of accommodation (AA). Conclusion: This study provides the normal range of the NRA and PRA and their relationship with accommodation facility, spherical refractive error, and AA in a sample of the Iranian population.