Is contrast sensitivity suitable for early detection of primary open-angle glaucoma?

Abstract

Introduction Primary open-angle glaucoma (POAG) is an optic neuropathy characterized by progressive damage of the optic nerve and retinal ganglion cells, leading to irreversible visual loss. An early diagnosis, with adequate treatment, can minimize the loss of vision. Patients are generally asymptomatic early in the disease, therefore diagnosing POAG at first stages is still a challenge. Since POAG is a leading worldwide cause of blindness, it is essential to explore potential tools for identifying the changes produced in the very early stage, before a permanent visual loss occurs. Contrast sensitivity (CS) is a robust tool for evaluating functional vision. It is the inverse of the minimum contrast detected at a stimulus size (spatial frequency). Although there is broad evidence that CS is affected in moderate to advanced POAG, there is not enough information about the first stages which are critical for early diagnosis. Therefore, to investigate if functional changes measured by CS could provide evidence of early deficits caused by POAG is especially important.ObjectiveThe main objective was to assess CS for detecting visual changes at early stages of POAG. Methods CS was measured using sinusoidal gratings of 4 cycles/degree. First, foveal and peripheral CS were assessed in suspected POAG patients (n=34) age-matched with healthy control subjects (n=99). Second, foveal CS was assessed in early POAG patients age-matched with the suspected POAG group. Analyses were carried out considering two age ranges: Under and Over 50 years of age. Results Peripheral CS was decreased in older POAG suspect patients compared to the control group. Foveal CS was reduced in POAG suspect participants and in early POAG patients, both compared to the control group and for the two age ranges. For the older patients, foveal CS in early POAG was lower than for POAG suspects. Foveal CS was correlated with age in suspect POAG, early POAG, and healthy control groups. Also, it was correlated with cup-disc ratio only in early POAG patients. Finally, foveal CS differentiated suspect (under 50) and early POAG (under and over 50) patients from control individuals with fair diagnostic accuracy. Conclusions CS is affected in both groups, patients with a high risk of developing POAG and with early POAG diagnosis. We argue that early visual damage may occur before structural changes can be detected. Foveal CS could be a fair discrimination tool for early POAG and young suspect patients.