The Anatomy of the Retina

The retina is a light-sensitive layer that lines the back of the eye. It is only 0.2 mm thick and is about the size of a silver dollar. The retina is made up of 200 million neurons, many of which are photoreceptors. Photoreceptors detect light and transmit those signals through the optic nerve to the brain.

Images come through the eye's lens and are focused on the retina. The retina then converts these images to electric signals and sends them to the brain. There are two main types of photoreceptors in the retina; rods and cones. Cones deliver a better resolution of images and rods are more sensitive.

The fovea in the macula, which is a central space of the retina, has the highest concentration of cones but not one single rod. The periphery of the retina has many rods.

This organization of cones and rods means that a night star will appear dim if you look at it directly, but will be perceived as brighter and more visible if you use your peripheral vision.

Your doctor may dilate your pupils during a comprehensive eye exam to look at the fundus.

The fundus includes the retina as well as the following parts:

• Posterior pole: The posterior pole in the back portion of the retina includes the optic nerve and macula.
• Optic nerve head: The optic nerve head is the face of the optic nerve as it enters the back of the eye. It is made of millions of nerve fibers and transmits visual information to the brain for processing.
• Macula: The macula is a specialized pigmented part of the retina in the very center of the retina that gives us central vision. In the center of the macula is the fovea. The fovea has the region of best visual acuity.
• Equator and mid-peripheral retina: This is the area of the retina as it extends from the posterior pole.
• Ora serrata: The ora serrata is the terminal end of the retina. This junction marks the transition from the non-photosensitive area of the retina to the photosensitive area of the retina.

Common Disorders of the Retina

• A retinal tear or detachment is considered an ocular emergency. This is when the light-sensitive retina is torn or detached away from the back of the eye that feeds it oxygen and nourishment.
• Diabetic retinopathy is a complication of diabetes. It is a condition where blood vessels leak blood and fluid. Sometimes new blood vessels grow and can become destructive, creating vision loss, glaucoma, and retinal detachment if not treated.
• Central serous retinopathy is a relatively common condition in which the central retina develops a cyst and central vision becomes distorted. 
• Macular degeneration is a disease of the macula in which there is a loss in the center of the field of vision. Macular pigmentary changes occur and leaky blood vessels grow beneath the macula. Vision loss can be very mild to very severe with central blindness.

Diagnosis and Treatment

It's important to have your eyes regularly checked, especially if you have eye disease or a condition that increases your risk of eye disease, like diabetes or hypertension (high blood pressure). Conditions that affect the retina may need to be monitored or may require interventions, such as surgery.