Foveal cone photoreceptor involvement in primary open-angle glaucoma

BACKGROUND: To test whether foveal cone photoreceptors are impaired in primary open-angle glaucoma (POAG).

METHODS: Nineteen POAG eyes with central glaucomatous visual field defects, and 34 age-matched control eyes were included. Fundus reflectometry, together with a model fit procedure, provided information on a set of parameters: lens optical density, macular pigment optical density, melanin, blood, the directional cone reflectance (Rd), a measure for foveal cone photoreceptor integrity, and RILM, the reflectance at the inner limiting membrane. Optical coherence tomography (OCT) was performed to assess macular thickness. A Kolmogorov-Smirnov Z-test was used to compare parameters between the two groups.

RESULTS: Median age (range) was 55.1 (24.7-73.3) years in the control subjects, and 60.1 (20.7-77.0) years in the POAG patients (P = 0.24). Of all eight model parameters, only Rd and RILM were significantly lower in POAG. Median Rd (range) was 2.21 (0.64-4.93) % in the control subjects and 1.19 (0.08-3.60) % in the POAG patients (P = 0.003). Median RILM (range) was 0.15 (0.00-1.08) % in the control subjects, and 0.08 (0.01-0.29) % in the POAG patients (P < 0.001). Rd showed no linear relationship with central retinal sensitivity on Visual Field test in POAG patients. Retinal thickness of the inner 1-3 mm ring and the outer 3-6 mm ring on OCT, centered on the fovea, was significantly lower in POAG patients than in control subjects.

CONCLUSIONS: The integrity of the foveal cone outer segments, and the reflectance of the central ILM were impaired in POAG with advanced central visual field defects.