Fine structure of the retinal pigment epithelium, Bruch’s membrane and choriocapillaris in the horse.

The research article investigates the detailed structure of the retinal pigment epithelium (RPE), Bruch’s membrane, and choriocapillaris in the horse eye using both light and transmission electron microscopy.

Retinal Pigment Epithelium (RPE)

• The study found that the RPE in the horse eye, regardless of its location, was composed of a single layer of low cuboidal cells.
• The epithelial cells were joined laterally by apically located tight junctions, which are imperative for maintaining the selective permeability of the RPE and protecting the outer retinal layers.
• The researchers noted significant basal infoldings and thin apical processes in these cells, which surrounded the rod outer segments. Rods are a type of photoreceptor cell in the retina that help in low-light vision.
• The nuclei of the epithelial cells were observed to be large and positioned at the base of the cells.

Cellular Organelles within the RPE

• The smooth endoplasmic reticulum within the cells was in abundance, while its rough counterpart was scarce. The smooth endoplic reticulum is involved in lipid metabolism and detoxification processes, while the rough endoplasmic reticulum is instrumental in protein synthesis.
• The researchers also noted abundant polysomes and mitochondria, which are critical for protein synthesis and energy production respectively, within the epithelial cells. Some mitochondria were found to exhibit a ring-like structure.
• Melanosomes, which are special organelles for synthesis and storage of melanin, were found to be abundant in the non-tapetal region of the eye but were entirely absent in the tapetal region.

Bruch’s Membrane and Choriocapillaris

• The researchers found that Bruch’s membrane, a pentalaminated tissue separating the RPE from choroid, was consistent throughout the retina.
• The endothelium of the choriocapillaris, a vascular layer containing the capillaries that supply oxygen and nutrients to the outer retina, displayed hefty fenestrations. Fenestrations are pores that allow the passage of molecules, indicating a high metabolic activity and exchange of materials in this area.