Myopic Macular Degeneration

What is It?

Myopic macular degeneration (MMD) is also known as degenerative myopia or pathological myopia. It is a condition that usually is present at birth or first develops in children under the age of 13. As patients with MMD get older the condition worsens. By the time patients are 60, 50% are considered legally blind - defined as vision acuity of 20/200 even with glasses, or a visual field of 20 degrees or less (e.g., glaucoma).

The condition is caused by gradual and significant elongation of the eyeball with a resulting high degree of myopia by late teens to early twenties. The eyeball continues to elongate, the walls of the eye stretch, the sclera and retina thin. If there are weak spots already present in the retina or sclera or connective tissue these become increasingly weakened and put the patient at risk for retinal holes, tears and detachment.

If the stretching occurs mostly at the back of the eye the effects are similar to those of macular degeneration and may respond to nutritional support. Scar tissue may develop which damages central vision or new blood vessels (similar to wet macular degeneration) and may cause a distortion of vision and lost vision over time.

If the stretching occurs mostly at the sides of the eye it can give rise to lattice degeneration which increases the risk of retinal tears and detachment.

How is it different from macular degeneration?

Macular degeneration has its roots in genetics, free radical damage, toxins (environmental and drugs), hypertension, lifestyle factors (ie smoking) and nutrient deficiencies. Genetics is the major risk factor for MMD. MMD is similar to AMD in that it causes loss to central vision through damage of the macula portion of the retina, eventually resulting in hemorrhaging of the blood vessel layer of the retina (choroid).

How is it different from myopia?

In 'common' nearsightedness the eyeball is slightly elongated. In myopic macular degeneration the elongation is much greater resulting in thinning of the retina and a higher risk for retinal detachment (along with the other issues mentioned above).

What happens?

• Stretching Most, but not all of the problems seem to occur due to this stretching process as the eyeball elongates. The sclera (the white of the eye), the choroid (the layer of blood vessels supplying nutrients to the eye), the retina and the connective tissue between the retina and the vitreous are all stretched and weakened.
  
  Stretching of the retina increases the risk of retinal detachment, lattice degeneration, retinal holes, thinning and damage to the various layers of the retina: photoreceptors, Bruch's membrane, choroid layer, etc.
• Intraocular pressure To complicate things further, due to the changing shape of the eye, the drainage process through the trabecular meshwork (where the aqueous fluid drains) can also contribute to the elongation of the eyeball shape (the intraocular pressure may remain still within the "normal" range).
• Staphyloma At the macula the stretched choroid layer develops characteristics of macular degeneration with scarring occurring at the macula. The elongation causes a staphyloma behind the macula pushing the macula out of alignment and causing a profound myopic condition.
• Cornea In addition, the cornea becomes thicker and more rigid. This creates multiple additional problems. First, the thicker cornea makes it more difficult for an eye doctor to detect development of glaucoma. Second, the cornea itself plays a role in focusing. In fact the correct alignment of fibers within the cornea contribute 65% to 75% of the focusing ability of the eye.
• Vitreous The vitreous gel may thin and liquefy increasing the risk of vitreous detachment.

Who's at risk

MMD is primarily a genetically based condition. However, those with a number of other conditions are considered 'at risk' for development of myopic macular degeneration. These conditions include Down's (impact on developing eye), ocular albinism (lack of pigment), congenital glaucoma, Marfan's & Ehlers-Danlos Syndromes (weak connective tissue), retinopathy of prematurity (abnormal blood vessel growth), low birth weight, and alcoholism of the mother.

What are the side effects or complications?

Other serious vision conditions may result due to myopic macular degeneration.

• Glaucoma The changing shape of the eyeball also puts strain on the capacity of the trabecular meshwork to function properly to drain fluid from the eye. This causes an increase in intraocular pressure. At the same time due to the thickened cornea it is more difficult to detect glaucoma, partly because the thickened cornea may contribute to an inaccurate interpretation of eye pressure even if the pressure is not elevated. People with thickened cornea may show elevated eye pressure but that higher eye pressure may be "normal" for them. Patients with myopic macular degeneration have to wear very thick eye glass lenses which makes testing of their peripheral vision more difficult.
• Retinal Structural Integrity The stretching and thinning of the retina makes patients more at risk for retinal holes, tears, lattice degeneration and retinal detachment. Symptoms of retinal detachment include sudden appearances of flashing lights and/or a sudden increase in floaters. If both these symptoms appear the risk of retinal detachment is high. Detachment is experienced as though a curtain comes down over part or your vision and should be considered an ophthalmological emergency.