Contrast sensitivity assessment using the Mars letter contrast sensitivity test

Abstract

Background: Contrast sensitivity (CS) represents an individual’s ability to detect differences in luminance between two areas and is an essential component of vision. Various studies have evaluated the relevance of different charts to assess CS in ophthalmology practice. We evaluated the CS of healthy individuals using the Mars letter CS chart. Methods: In this hospital-based cross-sectional study, we consecutively recruited healthy individuals older than 18 years with unremarkable ocular examinations who attended the general outpatient clinic at Benue State University Teaching Hospital, Makurdi, Nigeria, between March 2021 and July 2022. Each participant was allocated to one of five groups with 10-year age intervals and 1:1 male-to-female ratios. All participants underwent a detailed ophthalmic examination. We tested visual fields using the 24-2 program on a Humphrey visual field analyzer with appropriate refractive correction. Monocular testing of CS with appropriate spectacle correction was performed using a Mars letter CS chart. The tribe, age, and sex of each individual, along with the best-corrected visual acuity (BCVA), intraocular pressure, mesopic pupil size, cup-to-disc ratio (C/D ratio), and mean deviation (MD) of the visual field for each eye were recorded. Results: A total of 100 eyes of 50 patients with a mean (standard deviation [SD]) age of 44.6 (12.8) years and a 1:1 male-to-female ratio were enrolled. The mean (SD) CS score for the 100 included eyes was 1.67 (0.09) log units. The mean (SD) CS score was comparable between sex groups and tribes (both P > 0.05) yet differed significantly between age groups (P < 0.001). We found a significant good inverse correlation between CS score and age (r = - 0.60; P = 0.001), a low inverse correlation with BCVA (r = - 0.29; P < 0.003), and a low direct correlation with C/D ratio (r = + 0.23; P = 0.023); however, we observed no significant correlation with tribe (r = + 0.07; P = 0.053), sex (r = + 0.16; P = 0.123), IOP (r = + 0.07; P = 0.481), mesopic pupil size (r = - 0.02; P = 0.861), and mean deviation of visual field (r = + 0.02; P = 0.873). Conclusions: We observed a progressive decline in the mean CS score in healthy eyes with each decade of increase in age. Our findings are similar to those of previous studies and could be used as reference values for the healthy population among various age groups. However, further studies with larger sample sizes are necessary to encourage clinicians to incorporate CS into routine examinations. Further studies must compare these normative values with those of disease conditions to further understand the clinical application of the CS test.