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. The retina contains photoreceptors that absorb light and then transmits those signals through the optic nerve to the brain. 

The photoreceptors in the retina are called rods and cones. Our retina contains 120 million rods and about 1 million code photoreceptors. The fovea in the macula has the highest concentration of cones and rods are completely absent. The cones deliver a better resolution of images but the rods are better detectors. This is why when you look right at a star at night, it appears very dim, but if you look right off to the side of the star, it becomes 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 is described with 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.

• 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 when 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.