Low-Contrast High-Pass Visual Acuity Might Help to Detect Glaucoma Damage: A Structure-Function Analysis

Abstract

Purpose: The conventional visual acuity (VA) test is not sensitive enough to detect glaucoma macular damage. We aimed to investigate whether VA measurements using low-contrast high-pass optotypes are more sensitive to macular dysfunction in glaucoma and to find the potential structural basis of this difference. Methods: A total of 147 subjects were recruited, including 118 patients with glaucoma (mean age: 46.08 ± 14.64 years) and 29 healthy controls (mean age: 39.83 ± 9.81 years). For each participant, monocular best-corrected VA was measured using a conventional chart and six high-pass charts at 100, 50, 10, 5, 2.5, and 1.25% contrast levels, respectively. The macular retinal thickness and circumpapillary retinal nerve fiber layer (cpRNFL) thickness of all the glaucoma patients were obtained by spectral-domain optical coherence tomography (SD-OCT). Results: Compared with healthy subjects, glaucoma patients with normal vision demonstrated worse VAs in high-pass acuity measurements (0.22-0.93 vs. 0.28-1.08, p < 0.05). Receiver operating characteristic curve (ROC) showed that 1.25% low-contrast high-pass VA was optimal for discriminating between the controls and glaucoma patients (AUC: 0.918, p < 0.001; sensitivity: 77.33%; specificity: 96.55%). Compared with conventional VA, 1.25% high-pass VA correlated better with nasal-side macular retinal ganglion cell (RGC)-related parameters (r = -0.419 to -0.446 vs. r = -0.538 to -0.582; Fisher's Z transformation, p _z < 0.05). There was no difference in the strength of correlations between the VAs measured using different charts and cpRNFL thickness (Fisher's Z transformation; p _z > 0.05). Conclusions: VA measurement taken with low-contrast (1.25%) high-pass acuity chart is more sensitive in detecting central visual loss in glaucoma than that taken with the conventional chart. Macular RGC damage appears to be associated with low-contrast (1.25%) high-pass visual loss in glaucomatous eyes.

Keywords: glaucoma; high-pass optotypes; low-contrast visual acuity; macular damage; optical coherence tomography.

Figure 1

High-pass letter “E” at six different contrast levels, namely, 100, 50, 10, 5, 2.5, and 1.25%. The contrast was defined as Michelson Contrast.

Figure 2

OCT imaging in the current study: (A) the left image shows macular layers that were used for analyzing the structure-function relationships in this study. The right panel shows the overlay of the GCL thickness heat map on a fundus image. The inner and outer annuli were divided into four quadrants (IS, IT, II, IN and OS, OT, OI, ON) according to the ETDRS map. (B) the upper image shows the cpRNFL scan. The lower picture shows the sectoral cpRNFL thicknesses classification, specifically the global average of the circle scan (G) and N, NS, TS, T, TI, and NI quadrants.

Figure 3

Bland-Altman plots for test-retest measurements for the conventional chart (1st test vs. 2nd test) and the high-pass charts (1st test vs. 2nd test) with data for the 20 healthy controls plotted in green (squares) and the 20 glaucoma patients in red (dots). The mean difference of the two tests and 95% Limits of Agreements are also shown in the plots (dotted lines).

Figure 4

Visual acuity measured using the conventional chart and high-pass charts at 100, 50, 10, 5, 2.5, and 1.25% contrast levels among glaucoma patients with normal vision and the healthy controls.

Figure 5

Bland-Altman plots displaying the differences in VAs measured using the conventional chart and high-pass charts in glaucomatous eyes with normal vison (n = 75) and healthy controls (n = 29). The red dots represent data from glaucoma patients, whereas the green squares represent data for healthy controls. The horizontal lines represent the bias of the tests and 95% limits of agreement. The dark red lines represent the best linear fit to the data from glaucoma patients.

Figure 6

Receiver operating characteristic (ROC) curve for each VA test to detect glaucoma damage.

Figure 7

Heat map demonstrates the correlations between each parameter of the macular scan and VA data (Pearson's partial correlation analysis). The red-scale strength range of the correlation coefficients are shown on the right side of the plots. The correlations shown above were all statistically significant at the level of 0.01. The values marked with asterisks are statistically significant at p < 0.05 level (one-tailed) in Fisher's Z transformation and represent stronger structure-function correlations than those between structure parameters and conventional VA. GCL, ganglion cell layer; GCIPL, ganglion cell inner plexiform layer; GCC, ganglion cell complex; IS, inner superior; IN, inner nasal; II, inner inferior; IT, inner temporal; OS, outer superior; ON, outer nasal; OI, outer inferior; OT, outer temporal; InnAnn, inner annulus; OutAnn, outer annulus.