Loss of photoreceptor cells is a characteristic of inherited retinal degenerations and other retinopathies, including age-related macular degeneration. The function and metabolism of photoreceptors closely depend on the integrity of the retinal pigment epithelium.
1 In addition to the involvement of photopigment recycling, which is crucial for the maintenance of photoreceptor excitability,
2 the retinal pigment epithelium digests shed photoreceptor outer segments,
3 transports ions, water, and metabolic end products from the subretinal space to the blood,
4 and delivers nutrients such as glucose to the photoreceptors.
5 Dysfunction or degeneration of the retinal pigment epithelium can lead to photoreceptor degeneration and can contribute to the onset of age-related macular degeneration.
1 Mutations in genes that are expressed in the retinal pigment epithelium are the cause of some forms of inherited retinal degenerations.
1 Age-related alterations in retinal pigment epithelial (RPE) pigmentation
6 may result in increased photo-oxidative stress and subsequent loss of RPE and photoreceptor cells.
7 Reduction in the density of RPE cells,
8 accumulation of lipofuscin in the retinal pigment epithelium,
9 and failure of outer segment phagocytosis
10,11 may contribute to inherited retinal degenerations and are suggested to be involved in the pathogenesis of age-related macular degeneration.
1 Breakdown of the blood-retina barrier constituted by the retinal pigment epithelium leads to subretinal edema.
12 Activated RPE cells are also key players in proliferative diseases such as choroidal neovascularization and proliferative vitreoretinopathy, in which migrating and proliferating RPE cells contribute to the formation of periretinal membranous tissues.
13