Interocular agreement in melanin and macular pigment optical density

Macular pigment (MP) and melanin possibly protect the macular area by absorbing blue light and acting as antioxidants. Because little is known about the interocular correlation of melanin, we determined its optical density (MOD) in both eyes of healthy subjects using fundus reflectometry. The measuring method also provided optical densities of MP (MPOD). In addition to evaluating its interocular correspondence we checked its dependency on central retinal thickness as measured with optical coherence tomography (OCT). Spectral fundus reflectance was measured in 69 eyes of 37 healthy participants. Both eyes of 32 subjects (15 males and 17 females, aged 57.9+/-14.6 years) were used to evaluate interocular correspondences. MPOD data from 35 right eyes of 18 males and 17 females, aged 55.7+/-15.7 years, was used to evaluate the relation between central retinal thickness and MPOD. MOD was 0.99+/-0.30 (range: 0.57-2.07) for the left eyes and 1.02+/-0.28 (range: 0.62-2.07) for the right eyes. The intraclass correlation coefficient (ICC) was 0.89 (P<0.001). MPOD was 0.49+/-0.19 for the left eyes (range: 0.12-0.81) and 0.47+/-0.17 (range: 0.14-0.73) for the right eyes. The ICC was 0.91 (P<0.001). Macular retinal thickness (MRT), representing the average macular thickness in the central 1000 microm zone, was 210+/-28 microm. Foveal retinal thickness (FRT), representing the retinal thickness at the crossing of the 6 radial scan lines on OCT, was 175+/-34 microm. Pearson's correlation coefficient showed no significant linear association between MRT and MPOD (r=-0.04, P=0.82), and between FRT and MPOD (r=0.05, P=0.78). The optical density of melanin showed a high interocular correspondence in healthy white participants. Similar results were found for MPOD. Relative interocular differences of more than 32% in MOD, or more than 34% in MPOD, may point to pathology. No relation between central retinal thickness and MPOD was found.