[Classification of light-evoked distribution of interphotoreceptor matrix]

Distributional patterns of the interphotoreceptor matrix (IPM) under several different light conditions were examined in adult rats using colloidal iron staining. In the dark, the IPM distributed uniformly throughout photoreceptor outer segments including apical halves of inner segments. After exposure to light for 1 min, the colloidal iron-bound IPM concentrated in bands at apical and basal regions of outer segments and at apical inner segments. After exposure to light for 5-30 min, the IPM distributed throughout inner segments, in addition to the distribution at apical and basal outer segments. In excessive light, diffuse IPM staining was observed throughout the photoreceptor layer. These findings suggest that the light response of the IPM around outer segments precedes that around basal inner segments. It is also remarkable that the excessive light-induced distributional pattern of the IPM is similar to patterns in inherited retinal dystrophy and light-induced retinal degenerations.