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.