The retina is the innermost layer (also called the neural or sensory layer) of the eyeball wall. The retina contains three different types of nerve cells, each performing distinct functions:
- photoreceptor cells, which are divided into rod cells (responsible for twilight vision) and cone cells (responsible for daylight vision and color recognition),
- bipolar cells – one process of the bipolar cell receives stimulation from a cone or rod cell, while the other process connects with a ganglion cell, forming the third neuron,
- ganglion cells – the processes of ganglion cells form a layer of nerve fibers in the retina that converge to form the optic nerve, which connects the retina to the brain.
The area of the retina where nerve fibers converge is visible on the fundus as the optic disc. Near it lies the macula lutea.
Photoreceptors—rods and cones—contain visual pigments and are adjacent to the pigment epithelium, whose cells are filled with melanin (this pigment absorbs light not captured by the visual pigments, preventing backward reflection of light). It is the photoreceptors that convert light energy into electrical energy: through neural pathways, electrical impulses reach the brain, where the images we see are formed—it is not the eye that sees, but the brain. When any stage of this transmission process is disrupted, visual abnormalities appear.
These abnormalities, which may be the first symptoms of retinal diseases, take the form of:
- scotomas (dark spots),
- floaters (dots, spots, threads) in the visual field,
- flashes of light,
- discontinuity in observed lines,
- eye pain.
