What is the retina?
The retina is a thin layer of tissue in the back wall of the eye, made up of different cells (retinal pigment epithelium, nerve cells and photoreceptor cells). The photoreceptor cells (cones and rods) react to light and send electrical signals to the brain, which interprets these signals as vision. The retina is, therefore, what allows us to see.
The retina, along with the optic nerve, develops in the embryo as part of the brain tissue, making it part of the central nervous system. Being a nervous tissue, the retina does not have the ability to regenerate.
Function of the retina
The retina is responsible for our vision. The photoreceptor cells react to light entering the eye, releasing chemicals, which in turn trigger a nerve impulse, which is sent to the cerebral cortex via the optic nerve. The pattern of light hitting the photoreceptor cells triggers a unique set of electrical signals, which the brain interprets as an image.
Rod cells work well in low light, giving us our night vision. They contribute little to color vision, making it difficult for us to distinguish colors in the dark. They tend to concentrate around the edge of the retina and are also used for peripheral vision.
Cone cells, on the other hand, are less sensitive to light, but are responsible for our color vision. Most people have three types of cone cells. Each type is sensitive to different visible wavelengths of light, giving us trichromatic vision. The mixture of signals sent by the different cone cells that are stimulated to different degrees creates the mix of colors we can perceive. Some people are born with only two types of cone cells, which limits the range of colors they can perceive, making them easily confuse colors that appear different to someone with all three types of cone cells.
Pathologies that can affect the retina
Retinal pathologies can affect vision with different degrees of severity, and can be acquired or inherited:
- Diabetic retinopathy: diabetes causes the capillaries that irrigate the retina to leak fluid into or under the retina, resulting in swelling and distorted vision.
- Retinal tear: when the jelly-like vitreous inside the eye contracts, it can pull on the retina and sometimes this can cause a tear.
- Retinal detachment: a condition in which the retina becomes loose and detaches from the tissue underneath. It usually occurs when fluid passes through a retinal tear.
- Retinitis pigmentosa: a group of degenerative and hereditary ocular pathologies characterized by a slow and progressive loss of vision.
- Macular degeneration (AMD): age-related deterioration of the macula, quite common after the age of 60. The macula is the part of the eye responsible for providing clear vision. As we grow older, its function loses its powers, leading to macular degeneration.
- Macular hole: a break in the macula, perhaps caused by trauma or traction between the retina and the vitreous.
- Retinal cancer.
Treatments for retinal pathology
Treatment will vary depending on the specific pathology. Some pathologies can be treated with intravitreal injections; but for other pathologies, surgery is the only option. The most typical surgeries are:
- Laser thermal photocoagulation surgery for the treatment of wet macular degeneration.
- Vitrectomy for the treatment of macular hole, retinal detachment or diabetic retinopathy, among others.
Specialist who treats retinal pathologies
The pathologies of the retina are treated and diagnosed by specialists in Ophthalmology.