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 absorb light and then convert and transmit those signals through the optic nerve to the brain.

There are two main types of photoreceptors, rods and cones, in the retina. The fovea in the macula, which is a central space of the retina, has the highest concentration of cones but not one single rod. Cones deliver a better resolution of images. The periphery of the retina on the other hand, has many rods, and these types of photoreceptors are better detectors. This organization of cones and rods means that a night star looked at directly will appear very dim, but if seen using peripheral vision, will be perceived as brighter and more visible.

Much like film in a camera, 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.

When a doctor dilates your eyes during a comprehensive eye exam, it is said that he or she is looking 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 and 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 serrated area between the retina and the ciliary body. 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

• Retinal Tear or Detachment: A retinal tear or detachment is considered an ocular emergency where the light-sensitive retina is torn or detached away from the back of the eye that feeds in oxygen and nourishment.
• Diabetic Retinopathy: Diabetic retinopathy occurs in people who have diabetes and it is a condition where blood vessels leak blood and fluid. Sometimes new blood vessels grow that become destructive and can create vision loss, glaucoma, and retinal detachment if not treated.
• Central Serous Retinopathy: Central serous retinopathy is a relatively common condition in which the central retina develops a cyst and central vision becomes distorted. 
• Macular Degeneration: 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.