Macular degeneration

Macular degeneration is the predominant cause of vision loss in the elderly. However, the word senile macular degeneration is often misinterpreted with respect to age-related macular degeneration (AMD or ARMD). The macula of the eye enables the central vision process. Macular degeneration occurs in dry and wet forms respectively. The dry form is the non-exudative form where as the wet form is the exudative form. In some instances, the advance of AMD is so slow that people may even fail to notice a little change in their vision. Whereas, in others the disease spreads faster and may lead to loss of vision in both the eyes.

Non-exudative Macular degeneration

The extra cellular deposits which are called drusen accumulate under the retinal pigment lead to the dry form. Although they appear pleomorphic, under ophthalmoscopy they generally tend to appear as discrete yellow lesions which are clustered in the macula referred to as pseudo papilledema. The symptoms of macular degeneration include difficulty in reading, recognizing faces etc. The peripheral vision remains but deteriorates gradually.

These lesions gradually become larger leading to multiple conditions such as retinal epithelial atrophy and also loss of photoreceptor function which causes vision loss. The enlargement of these lesions also results in retinal vein occlusion. Treatment with vitamins such as beta carotene, vitamin C and also zinc may slow down the process of dry macular degeneration.

Exudative Macular degeneration

The wet form or the exudative macular degeneration is a rare form of the disease. It occurs when the neovascular vessels arising from the choroid grow through defects in Bruch's membrane into the potential space of the retinal pigment epithelium. When these blood vessels leak, the retina is elevated along with the pigment epithelium leading to distorted or blurred form of vision. The symptoms resulting are generally gradual. However bleeding resulting from the sub retinal choroidal neovascular membranes may lead to acute vision loss. The exudative changes in the eye include hemorrhages, hard exudates, sub retinal / intraretinal fluid. Atrophy caused may be both incipient and geographic in nature. In addition to this, there is also a condition called central scotomas which is generally noticed as the missing areas of vision.

The neovascular membrane is difficult to locate by fundus examination since the locus of the membrane is beneath the retina. Angiography pertaining to the use of fluorescein or indocyanine may yield good diagnostic results. Laser ablation followed by the Angiography may prevent the onset of exudative macular degeneration.

Signs and symptoms of Macular degeneration

In gradual muscular degeneration, vision change is noticed slowly. The symptoms usually developed are:

• Difficulty in adapting to low light levels. This could be exhibited even while entering any dimly lit restaurants.
  
• Need for brighter light while reading or doing any other close work.
  
• Printed words could increasingly blur.
  
• Increase in haziness of central or overall vision.
  
• Difficulty in recognizing faces.
  
• The intensity or brightness of colors could decrease.
  
• Central vision could get crooked.
  
• A blind spot in the center of her field of vision.
  
• Hallucinations of geometric shapes of people can occur in case of advanced macular degeneration.
  

Treatment of Macular degeneration

The wet from of macular degeneration is more likely to cause significant vision loss than the dry from and therefore different treatments for wet forms are available. These could help decrease the amount of vision lost. Laser treatment may stop or lesson vision loss in early stages of the disease. This is performed with specific wavelength designed to cauterize the abnormal blood vessels. A laser beam destroys blood vessels and may stop the growth of new ones. A scar forms after the treatment and this produces a permanent vision loss in that area of retina sacrificed to preserve the rest of the eye layer. Only a small number of people qualify for laser treatment and for many, vision may not improve after laser treatment. Photo dynamic therapy uses a light activated drug called verteportin given intravenously to the patient. A special laser is used to close the abnormal vessels while the retina is left intact. As closed blood vessels can reopen within a treated area, this may be necessary for one or two years. Exposure to light/sunlight should be avoided for five days after treatment. There are a number of drugs that block vascular endothelial growth factor and thus used as a treatment option. These have shown improvement in vision and not just delay or arrest the loss of vision due to macular degeneration.

Although macular degeneration is associated with age, genes related to the degeneration process of the macula have much significance. Factors such as obesity, hypertension, and oxidative stress may cause macular degeneration. Cardiovascular disease may increase the risk of macular degeneration. Among all the risk factors, smoking is considered as the most potent cause of macular degeneration. The risk of this disease in smokers is three times more than the other factors.

Macular Vision

The macula is a vital part of the retina that is responsible for our central vision. It is involved in processing the light rays entering the central vision field. It is rich in cells called cones that convert light rays into impulses that travel through the optic nerve to the brain. Macular vision is about fine details, color and reading. Macular vision is intrinsic to our good vision. Problems in macular vision are usually due to drying out of certain areas of the macula or wet patches. Macular degeneration happens largely due to aging. Dry Macular degeneration or non-exudative macular degeneration is what is mostly noticed. It does not cause as much damage as wet macular degeneration. Symptoms of dry macular degeneration appear gradually and there is no treatment for this. Wet macular degeneration happens rather rapidly due to abnormal blood vessels in the retina. Photo dynamic therapy (laser) and anti-VEGF inhibitors are used to treat wet macular degeneration. Retinal photographs, visual acuity test, Amsler Grid and Fluorescein Angiography are tests that help determine macular vision problems.

Fluorescein Angiography

Fluorescein Angiography is a diagnostic test that aids visualization of the blood circulation in the retina and choroid. Fluorescein is a water-soluble dye that is injected into a vein in the patient's arm. It travels through the blood vessels of the body thereby aiding multiple photographing of the retina. The images obtained help in detecting any swelling or leakage in the blood vessels. The patient's eyes are dilated with mydriatic eye drops so that photographs of the inside of the eye can be taken.

Some patients may notice skin rash, itching or allergic reaction to the dye. Nausea or vomiting may be noticed. But this non-invasive test can usually be safely repeated. Abnormal results of fluorescein angiography test may indicate diabetic retinopathy, macular degeneration, or cancer. Ischaemia or edema in the retina circulation can be detected with the help of fluorescein angiography.