The role of photoreceptor cells and the macula
The retina lines the back of the eye; it is composed of several cellular layers. Light enters and strikes the bottom layer, the retinal pigment epithelium, and is then collected by light-receptive cells called photoreceptors that convert light signals into electrical signal.
The Retinal Pigment Epithelium
The retinal pigmented epithelium (RPE) is a layer of cells placed between the photoreceptors and the choroid (part where the eye vessels are situated). Its role is to feed the photoreceptors.
The retina is composed of 125 million photoreceptor cells that exist under two forms:
- Rods (95-97% of photoreceptors) involved in night-vision, enabling black-and-white vision
- Cones (3-5% of photoreceptors) involved in daytime vision, enabling colour vision and the vision of small detail
The cell layers, photoreceptors and RPE and interdependent: if one dies, so do the others.
The macula (macula lutea) is located at the back of the eye, in the centre of the retina. It is the area where light rays concentrate. In the centre of the macula, a depression called the fovea, composed only of cones (light detecting cells) constitutes the area of visual acuity (ability and quality of vision). Rods are more numerous around the fovea.
The macula enables central vision of elements situated in the line of sight, vision of details (writing, reading, details of faces …) and the determination of colour.