The World Health Organization estimates that in 2002 there were over 161 million people who had significantly reduced vision (designated "moderate visual impairment"). Of this number, 37 million were blind. Despite the advances in eye surgery that have been made in many countries over the last few decades, cataract remains the leading cause of vision problems in all regions of the world, except in the most developed countries of Western Europe, America and Australasia. Other major causes of visual impairment are, in order of importance: glaucoma, age-related macular degeneration, diabetic retinopathy and trachoma [Resnikoff 2004].

Eye Disease
A third of people aged 65 years and over, has visual impairment (visual acuity less than 6/12) that would prevent them from holding a driving license. The biggest culprits are Age-related Macular Degeneration (AMD) and glaucoma as the leading causes of vision loss, accounting for 57% and 11% respectively of all blindness. The number of people affected has increased since 1990, both as a consequence of greater longevity and increasing proportion of visual impairment.

Macular Degeneration
Macular degeneration is a condition in which part of the light sensitive layer of the eye (the retina) degenerates, causing a reduction in vision. The macula is the part of the retina which provides the most detailed, central vision that we use for reading, driving, watching TV and for recognizing people's faces.

Eye specialists divide AMD into "dry" and "wet" forms of the disease. Most cases are categorized as "dry" macular degeneration where fatty tissue, known as drusen, slowly builds up underneath the retina. Cases of wet AMD result from the growth of abnormal blood vessels under the retina, leading to leakage of blood and other fluid which damages the retina. Wet macular degeneration usually begins as the dry form. If allowed to continue without treatment it may cause very severe damage to the macula, and lead to blindness.

Retinal Detachment
A serious eye disease that requires prompt treatment, retinal detachment occurs when the gel-like substance that fills the eye cavity (vitreous) begins to sag and shrink with age. While this shifting occurs in most peoples' eyes as they age, it becomes dangerous quickly if the retina tears. When fluid from the vitreous begins to leak through the tear under the retina, the retina may begin to peel away from the underlying layer. The patient begins to lose vision in the areas where the retina is detached; if left untreated, this condition can lead to permanent and severe vision loss. Warning signs often appear before retinal detachment occurs, and prompt treatment is almost always successful in preserving vision. Patients should be aware that symptoms such as flashes of light or "cobwebs" floating in the field of vision could signal a serious problem that requires immediate medical attention.

Glaucoma
Glaucoma is a degenerative condition affecting the optic nerve that may cause blindness as a consequence of loss of nerve fibers that lead from the retina to the brain. It is statistically linked with higher eye pressure (intraocular pressure or IOP), although there is no level of IOP that is safe and normal for all people. In cases of glaucoma which are progressive (i.e. getting worse), reduction of IOP is currently the only proven method of preventing further deterioration of established glaucoma. It is important to recognize that when vision is damaged by glaucoma, the lost vision cannot be restored. Hence identifying the disease in its early stages, and preventing deterioration, are the keys to preventing problems.

Diabetes
People whose bodies cannot produce effective or sufficient insulin are said to have diabetes. This chronic disease has several serious long-term effects that are well documented: kidney failure, heart disease, foot disease which may require amputation, neuropathy (sensory loss), and blindness. Vision loss caused by diabetes is known as diabetic retinopathy. Retinopathy is defined as non-inflammatory disorders in the retina. In diabetics, this condition manifests itself in the form of lesions, tears, or scratches on the retina. In the last few years, According to the World Health Organization, an estimated 300 million people will have diabetes by the year 2025. This disease has the potential to reach epidemic proportions, with far-reaching social consequences. Diabetic retinopathy is a serious complication, and the most common cause of blindness in people of working age in the Western world.

Diabetic retinopathy refers to damage to the tiny blood vessels that nourish the retina. These blood vessels are often affected by the high blood sugar levels associated with diabetes. Nearly half of people with diabetes have some degree of diabetic retinopathy. Nonproliferative diabetic retinopathy is most common type. It is the early stage of the disease, and symptoms are often mild or nonexistent. However, blurred vision may occur from swelling of the retina. This swelling occurs because the damaged blood vessels can ooze fluid. In proliferative diabetic retinopathy (PDR), the more advanced form of the disease, abnormal new blood vessels grow on the surface of the retina or into the vitreous cavity. These new vessels may bleed into the vitreous, clouding or blocking vision; in addition, the blood vessels can pull on the retina leading to retinal detachment.

Macular Hole
The macula is the retinal tissue responsible for central vision; firmly attached to the macula is the vitreous gel that fills the center of the eye. With age, the vitreous begins to sag and shrink and separates from the retina. Sometimes this shifting pulls on the macula, causing a hole to form. Macular holes often develop suddenly. Full-thickness macular holes cause distortion or loss of vision in the affected area. It is important to see a physician or ophthalmologist at the first sign of vision change. Early detection gives the best chance for restoring as much vision as possible.