Information on Common Eye Disorders
 
Retina And Vitreous

Macular Hole
 
The macula is the part of the retina responsible for acute central vision, the vision one uses for reading, watching television, and recognizing faces. A macular hole is a small round opening in the macula. The hole causes a blind spot or blurred area directly in the center of your vision.

Most macular holes occur in the elderly. When the vitreous (the gel-like substance inside the eye) ages and shrinks, it can pull on the thin tissue of the macula, causing a tear that can eventually form a small hole. Sometimes injury or long-term swelling can cause a macular hole. No specific medical problem is known to cause macular holes.

Vitrectomy surgery, the only treatment for a macular hole, removes the vitreous gel and scar tissue pulling on the macula and keeping the hole open. The eye is then filled with a special air bubble to push against the macula and close the hole. The air bubble will gradually dissolve, but the patient must maintain a face down position for one to two weeks to keep the gas bubble in contact with the macula. Success of the surgery often depends on how well the position is maintained.

With treatment, most macular holes shrink and some of the lost central vision slowly returns. The amount of visual improvement typically depends on the length of time the hole was present. Some people with normal vision in the other eye may not want surgery, since vitrectomy surgery cannot completely restore vision.
Ocular Histoplasmosis Syndrome (OHS)
OHS is a major cause of visual impairment in the eastern and central United States where 90 percent of adults have been exposed to histoplasma capsulatum. This common fungus is found in molds from soil enriched with bat, chicken or starling droppings and yeasts from animals.

Although the fungus is not found directly in the eye, people with OHS usually test positive for previous exposure to histoplasma capsulatum.

Histoplasmosis is usually mistaken for a cold. The symptoms are very similar. The body's immune system normally overcomes the infection in a few days. The only evidence of histoplasmosis is histo spots, tiny scars on the retina. Generally histo spots do not affect vision, but for unknown reasons, some people can have ocular complications years or decades later.

Doctors believe that the histoplasmosis spores travel from the lungs to the eye where they settle in the choroid, the layer of tiny blood vessels that provides blood and nutrients to the retina, the light-sensing layer of cells lining the back of the eye.

Ocular histoplasmosis develops when fragile, abnormal blood vessels grow under the retina. The abnormal blood vessels form a lesion known as choroidal neovascularization (CNV). If left untreated, the CNV lesion can turn into scar tissue and replace the normal retinal tissue in the macula.

The only proven treatment for OHS is a form of laser surgery called photocoagulation. The laser's small, powerful beam of light destroys the abnormal blood vessels, as well as a small amount of the retinal tissue. Treatment is not necessary unless the new vessels are in the macula, the part of the retina responsible for acute central vision.

Although only a tiny fraction of people infected with the histoplasmosis virus develop OHS, if you have been exposed to histoplasmosis you should be sensitive to any changes in your eyesight.
Proliferative Diabetic Retinopathy (PDR)

Proliferative diabetic retinopathy is a complication of diabetes caused by changes in the blood vessels of the eye. If you have diabetes, your body does not use and store sugar properly. High blood sugar levels create changes in the veins, arteries and capillaries that carry blood throughout the body. This includes the tiny blood vessels in the retina, the light-sensitive nerve layer that lines the back of the eye.

In PDR, the retinal blood vessels are so damaged they close off. In response, the retina grows new, fragile blood vessels. Unfortunately, these new blood vessels are abnormal and grow on the surface of the retina, so they do not resupply the retina with blood.

Occasionally, these new blood vessels leak and cause a vitreous hemorrhage. Blood in the vitreous, the clear gel-like substance that fills the inside of the eye, blocks light rays from reaching the retina. A small amount of blood will cause dark floaters, while a large hemorrhage might block all vision, leaving only light and dark perception.

The new blood vessels can also cause scar tissue to grow. The scar tissue shrinks, wrinkling and pulling on the retina and distorting vision. If the pulling is severe, the macula may detach from its normal position and cause vision loss.

Laser surgery may be used to shrink the abnormal blood vessels and reduce the risk of bleeding. The body will usually absorb blood from a vitreous hemorrhage, but that can take days, months or even years. If the vitreous hemorrhage does not clear within a reasonable time, or if a retinal detachment is detected, an operation called a vitrectomy can be performed. During a vitrectomy, the eye surgeon removes the hemorrhage and the abnormal blood vessels that caused the bleeding.

People with PDR sometimes have no symptoms until it is too late to treat them. The retina may be badly injured before there is any change in vision. There is considerable evidence to suggest that rigorous control of blood sugar decreases the chance of developing serious proliferative diabetic retinopathy.

Because PDR often has no symptoms, if you have any form of diabetes you should have your eyes examined regularly by an ophthalmologist.