The Anatomy of the Macula

The macula is part of the eye's retina. Located in the center of the retina, the macula is responsible for giving us clear vision and the ability to see fine detail. Although it is small, it enables us to see "20/20" and to see our world in color. Learn more about the important role the macula plays inside the eye.

Anatomy

Structure

The macula is an oval-shaped area near the center of the retina. The retina is a light-sensitive layer that lines the back of the eye. It is made up of 200 million neurons, but is only about 0.2 millimeters thick. The retina contains photoreceptors that absorb light and then transmit those light signals through the optic nerve to the brain.

Images that you see 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.

The macula has a diameter of about 5 mm. The macula can be seen with the use of an ophthalmoscope or a retinal camera. It has six clear subdivisions, including the umbo, foveola, foveal avascular zone, fovea, parafovea, and perifovea areas.

Location

The macula is the pigmented part of the retina located in the very center of the retina. In the center of the macula is the fovea. The fovea is the area that allows for the sharpest visual acuity. It contains a large amount of cones—nerve cells that are photoreceptors with high acuity.

Color

The macula is yellow in color. The yellow color is derived from lutein and zeaxanthin in the diet, both yellow xanthophyllcarotenoids contained within the macula.

Function

The main function of the macula is to provide sharp, clear, straight-ahead vision. It is responsible for all of our central vision and most of our color vision. The fine detail we see is made possible by the macula.

Because it is responsible for our central vision, diseases involving the macula, such as macular degeneration, cause loss of central vision.

Clinical Significance

Damage to the macula results in the loss of the ability to see objects clearly in the center of vision. Since peripheral vision is not affected by macular damage, a person with damage to the macula can adapt to life and continue some normal daily activities, such as walking, without assistance.

Several problems can affect the macula. The most common is macular degeneration. Other common conditions that affect the macula are macular edema and macular hole.

Macular Degeneration

Age-related macular degeneration (known as AMD or ARMD) is the leading cause of vision loss in people over 60 in the United States. The condition primarily affects people age 65 and older. AMD causes a deterioration of the macula, the central part of the retina responsible for sharp, central vision. AMD cannot be cured.

There are two types of AMD.

Dry AMD

Dry AMD is the most common type, accounting for about 90% of all AMD cases. In dry AMD, an observable change in the pigmented cells of the eye occurs, leaving areas of depigmentation, pigment clumping, and drusen (yellow deposits under the retina).

Dry AMD progresses very slowly through three stages: early, intermediate, and advanced. The earliest stage is characterized mainly by the presence of drusen and normal vision or mild visual loss. As the condition advances, central vision loss increases, additional drusen may appear or enlarge, and pigmentary changes may develop. Macular tissue atrophy and mild scarring may also develop.

The degree of vision loss varies with dry AMD. Dry AMD can lead to geographic atrophy which can cause significant vision loss.

Wet AMD

Wet AMD accounts for approximately 10% of all AMD cases. With the wet form of this disease, central vision capabilities can be damaged rapidly.

New blood vessel growth (neovascularization) occurs underneath the retina. Although these vessels are new, they are frail in nature. Blood and fluid leak out of the new blood vessels, often lifting the macula and causing visual distortions, potentially resulting in permanent tissue damage.

Scarring may occur, causing significant loss of vision and sometimes legal blindness.

Macular Edema

Macular edema occurs when fluid builds up in the macula. This buildup distorts vision as the macula swells and thickens. Macular edema can develop from any disease that damages blood vessels in the retina.

Macular edema is often caused by diabetic retinopathy, a disease that can happen to people with diabetes. Macular edema sometimes occurs after eye surgery, in association with macular degeneration, or as a consequence of other inflammatory diseases of the eye.

Macular Hole

A macular hole occurs when the nerve cells of the macula become separated from each other and pull away from the back surface of the eye, forming a hole. As the hole forms, central vision can become blurry, wavy, or distorted. As the hole gets bigger, a dark or blind spot appears in the central vision, but peripheral (side) vision is not affected.

Common causes of a macular hole include age-related changes (when the vitreous jelly inside the eye pulls away from the back of the eye and takes a piece of the macula with it), previous eye surgery, ocular trauma, and sungazing.

Symptoms of Macular Damage

If you have damage to the macula, you may notice the following symptoms. It is important to alert your eye care professional if you note any of the following changes.

• Decreased central vision: It may seem as if something is obstructing the central part of the visual field, such as a blurry patch.
• Image distortion: Images may begin to appear distorted, and straight lines, especially, may appear to be curvy. The Amsler grid is a common self-exam for distortion.
• Image size distortion: Objects may appear bigger or smaller than normal. This may develop into diplopia (double vision), as a discrepancy develops between the image perceived in the healthy eye and in the unhealthy eye.