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M

Macula

MAK-yew-lah

All portions of the retina contribute to sight, but the center area of the retina is responsible for color vision and fine central vision. The macular region contains a very different retinal configuration. In this region, the retina is thinned, especially towards the center of the macula (the fovea). The purpose of this foveal thinning is to permit greater light absorption. An aspect of the fovea is the absence of blood vessels over the photoreceptors which contributes to the high degree of visual acuity found in the macular region because the light path to the photoreceptors is less hindered. Comparatively, the vascularization in the rest of the macula is very dense, creating the potential for many vascular related diseases.

macula

One of the most common macular diseases is macular degeneration, a progressive disease which is primarily a disease of the elderly, but can also be found in younger age groups.

Macula Lutea
The small, avascular region of the retina surrounding the fovea.
Macular Degeneration

MAK-yew-ler dee-jen-ah-RAY-shun

Macular Degeneration is a condition in which the tissue of the macula (a portion of the retina responsible for visual clarity) becomes thin. It is believed to be a natural part of the aging process. Aging, or systemic disease, causes the breakdown of retinal pigment epithelium cells in the macular region. As the disease progresses, central vision diminishes. It is believed that this breakdown may be due to a lack of nutrients being supplied to the region. Additional studies have found a genetic link to this disease.

Symptoms may include a gradual loss of visual clarity, a dark or blank area in your field of vision, a loss of clear color vision, or visual distortion. The following is an example of how you may see with macular degeneration:

macular degeneration

Treatment includes prescribing low-vision aids to help with the loss or deterioration of central vision. Unfortunately, there is presently no way to restore vision lost due to age-related macular degeneration. Diets rich in green leafy vegetables may aid in slowing down the progression of the disease.

Dry Macular Degeneration (Non-neovascular)
Dry macular degeneration is characterized by tiny yellowish deposits under the macular region. These deposits (exudates) may increase in number and size over time. Small clumps of brown pigment from the degenerating RPE layer are also commonly seen. As this form of the disease progresses, retinal layers of RPE are destroyed, and vision in the macular region gradually decreases.

Wet Macular Degeneration (Neovascular)
Wet macular degeneration is associated with more sudden loss of vision. This form of degeneration is characterized by macular hemorrhaging, due to leakage or bleeding from abnormal vessels under the macula. Vision loss can be rapid, due to the disruption of blood flow to the layers of the macula themselves. Eventually, these areas of blood and fluid accumulation may develop into a dense mass of scar tissue beneath the macular region.

Symptoms
The most common symptom of macular degeneration is blurred central vision; noticeably worse when reading. In addition, horizontal lines may appear wavy and/or distorted. The most common method of detecting macular changes is the Amsler Grid test. During an eye examination, you are asked to look at the grid's center dot and asked if you notice any wavy, distorted, missing, or broken lines on the grid. Any one of these irregularities may indicate changes within the macular region of the eye. Your ophthalmologist or optometrist will be able to confirm any suspicions of macular degeneration during a dilated retinal examination.

Treatment For Macular Degeneration
Unfortunately, there is no treatment today for dry macular degeneration. The patient instead must make lifestyle adjustments such as eating a diet rich in green leafy vegetables and learning to use optical devices. For wet ARMD, two treatments are available, but both are limited in their scope. Both of the treatments involve a form of laser surgery that can be performed in an ophthalmologist's office, but only a small number of wet ARMD patients are candidates for these procedures, meaning that only a small minority of macular degeneration patients can be treated at all--and neither procedure restores lost vision or cures the disease.

  • Laser Photocoagulation: A technique that uses a laser to seal off leaking vessels that occur in neovascularization, preventing future hemorrhaging from the treated vessels. It doesn't cure the disease since it doesn't address the original cause; New vessels can continue to form, and the treatment almost certainly will need to be repeated. In addition, some of the healthy photoreceptor cells overlying the vessels can be destroyed. If the leaky vessels are too close to the center of the macula, the surgery can't be performed at all because it carries a risk of destroying more central vision than it saves.
  • Photodynamic Therapy: In photodynamic therapy, a drug containing a light-sensitive dye is injected into an arm and allowed to circulate through the vessels growing beneath the retina. When the light of a laser is shown into the eye, the dye absorbs the light and the abnormal vessels are destroyed. The advantage of photodynamic therapy is that the weak vessels are pinpointed with more accuracy and considerably less heat is required from the laser (sometimes called a "cold" laser), which means less damage to nearby healthy cells. Still, photodynamic therapy has the same limitations as laser photocoagulation in the sense that it does not restore vision that has been permanently lost or treat the underlying cause by eliminating neovascularization.
  • Cancer Treatment Therapies: New research is looking into the benefits of cancer treatment therapies for victims of wet macular degeneration. Because the growth of cancerous tumors involves the appearance of new vessels to provide the tumor with a blood supply, some scientists are hopeful that the existing drugs that are beginning to show promise in stopping the formation of new vessels in cancer may be able to halt the the development of wet macular degeneration.
    • Submacular Surgery: An incision is made in the retina and instruments are used to remove abnormal blood vessels beneath the retinal surface.
    • Tissue Plasminogen Activator (TPA): Used to liquefy blood clots so that subretinal blood and fluids can be removed from beneath the retinal surface.
    • Retinal Translocation: In this procedure, the retina is surgically lifted and rotated away from the abnormal blood vessels; the vessels are then exposed to laser treatment without harming the center of the macula.

Additional keywords and misspellings:
maclar mackula mackular degeneraton

Macular Edema

MAK-yew-ler Ah-DEE-mah

The swelling of the macula (the small area of the retina responsible for central vision) caused by fluid leaking from retinal blood vessels.

macular edema

What Causes it?
Because the macula is surrounded by many tiny blood vessels, any condition with vascular effects can cause macular edema. Blood clots or narrowing, eye inflammation, and age-related macular degeneration are associated with macular edema. Macular Edema can also occur following cataract surgery, although it is a temporary condition.

What is the Treatment?
Eyedrops, injections of cortisone around the eye or laser surgery can be used to treat macular edema. Recovery depends on the severity of the condition causing the edema.

Megalocornea
A congenitally enlarged cornea.
Melanoma

mel ah NOH' mah

A tumor that arises from a pigmented area. Melanomas can occur in the conjunctiva, choroid, iris, optic nerve, and other areas of the eye. Melanoma of the choroid is the most common primary malignant eye tumor. Usually, it is symptomless or causes a decrease in vision and is found during routine examinations.

Microphthalmia
An abnormally small eyeball; also called microphthalmos.
Midriatic
A medication causing mydriasis.
Miosis

my-oh'sis

Constriction of the pupil, a reduction in pupil size.

Miotic
A medication causing miosis.
Mirror Coating
A coating applied to the front surface of lenses to reflect light. This coating is used for sunglasses and is a solid, gradient or double mirror finish.
Monovision

Sometimes when people reach the age of 40-45, they become presbyopic and begin to need glasses or bifocals for close vision. Most people will simply get reading glasses.

However, to be free from glasses, some people opt for Monovision. With Monovision, the eye that is used as the dominant eye is focused for distance vision, and the non-dominant eye is focused for near to intermediate vision. This can be done with contact lenses, refractive surgery or intraocular lenses. Since it is a compromise of the two eyes, most people’s vision isn’t perfectly crisp up close or far away.In addition, people who elect Monovision will go through an adjustment period as they learn to see with the eye best suited for the task.

Because Monovision isn't right for everyone, it is important to remember that if you participate in any activities that require crisp, sharp vision either up close or far away, monovision may not be right for you.

Mydriasis

my-dry'a-sis

Dilation of the pupil, enlargement in pupil size.It is the opposite of miosis (constriction of pupil size).

Myopia

my-OH-pee-yah

The medical term for nearsightedness. Myopia occurs when an eye is too long for the cornea's curvature. As a result, light rays entering the eye do not come to a sharp focus on the retina at the back of the eye. Instead, they focus further forward, producing a blurred image.

nearsightedness

myopia

The Eye Encyclopedia is a collection of eye care terminology created by practicing optometrists and ophthalmologists. The information provided is not intended to be a substitute for regular medical care or to diagnose or treat any medical condition, and should be used only as a supplemental source of information. Please consult your doctor if you have any questions or concerns about your eye health.