Several layers of cells form the retina. These include rod and cone cells. Their function is to receive and turn light into electrical impulses which pass along the optic nerve to the brain, enabling sight to occur.

How does it affect sight?
In some cases people experience tunnel vision. This is because the rod cells at the outer edge of the retina have begun to die. Tunnel vision can be compared to looking through a pipe or tube. Sometimes vision loss is central, leaving side vision intact.

Other major symptoms include poor night vision and difficulty with glare.

Who is susceptible?
Those with RP are born with a genetic condition which results in sight loss later in life. Although it is hereditary, there are types which will skip several generations, so it may be difficult to trace in the family. Recessive RP may appear 'out of the blue' with no family history.

After diagnosis of RP
The rate of rod and cone failure is different in most people, so it is difficult to tell how the condition will progress. For some people vision loss can take place slowly during many years.

Sometimes the loss is quick, following years of no apparent deterioration. It is possible to cope with the limitations and frustrations caused by RP. World wide research aimed at finding a cure for RP is making good progress.

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Macular Degeneration

Macular Degeneration (MD) is damage or breakdown of the macula. The macula is the part of the retina which allows us to see clearly and appreciate color. It is the small spot (approximately 3mm) near the middle of the retina, which is responsible for the central part of what we see. The retina is at the back of the eye. It is made up of cells which are sensitive to light.

How does it affect sight?
In the early stages of MD, central vision is blurred and seeing at a distance or close work is difficult. The eye may still have good side vision, but blank spots appear in the center. This makes reading, sewing or seeing faces difficult.

Other symptoms include: dimming of color vision, difficulty in judging heights and distances, and some difficulty with tasks such as pouring tea. Sometimes only one eye loses vision, while the other eye may see well for years.

MD does not lead to total blindness. People with MD mostly retain good side vision. This means they can cope well with most daily tasks. The latest magnification devices can be very useful.

Who is susceptible?
Apart from some rarer forms, MD is not hereditary. The condition occurs most commonly in older people.

Diagnosis and treatment
An ophthalmologist can detect MD in its early stages. Special magnifying glasses, daily living aids such as needle threaders, large print books, proper lighting or a combination of these can help the person with MD to be independent and lead a normal life. Laser treatment can be useful if the condition is detected early.

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Cataracts

A cataract is a clouding of the normally clear lens of the eye. It may vary in its severity from a small amount of clouding to dense areas of haziness. A cataract is usually an age-related condition, which disturbs the passage of light and prevents the eye from focusing correctly. The lens is situated behind the iris (the colored part of the eye). Its purpose is to bend light rays so that they provide a clear image to the retina at the back of the eye.

A cataract is caused by a disturbance of nutrition to the lens, resulting from a lack of oxygen. It is occasionally caused by injury, radiation, other diseases or exposure to toxic chemicals.

How do cataracts affect sight?
The person with a cataract may have blurred vision, suffer from glare and find bright lights uncomfortable. Colors may not appear to be as bright and objects look dull.

The progression of cataracts varies between each individual and often between each eye in the same person. In some cases, the person affected can see well in the house but find vision is reduced by glare or at night.

Cataracts can cause blindness, but this can be prevented by early diagnosis and treatment.

Treatment
In some cases a change of glasses may be of benefit. In others, cataract surgery may be the best form of treatment. This procedure is usually performed under local anesthetic on a day surgery or inpatient basis. Special lighting and magnifiers are also useful.

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Homonymous Hemianopia

This is a condition sometimes found after a stroke or some injury to the brain. It is not a condition affecting the eye.

Hemianopia relates to the brain's impaired ability to receive the information transmitted to it through both eyes. The person experiencing it has difficulty seeing one side of their surrounding environment, or will report that one side appears different from the other.

Hemianopia may be complete or partial. In the case of complete, the person affected can only see to one side when looking straight ahead. With partial hemianopia, objects appear different in clarity or brightness. Other effects include double vision and difficulty interpreting visual information (especially if the view is complex or involves many moving people). Sometimes, the visual image may completely disappear or distort.

How does it affect daily living?
Hemianopia can cause loss of confidence with doing simple daily tasks. The person may feel unsafe crossing the road or going shopping, for example. Loss of half the visual field will affect many daily tasks including reading, travel and daily living skills.

Diagnosis and treatment
Hemianopia is not progressive but lack of understanding may cause frustration and needless dependence on others. Some hemianopias resolve naturally over time. The majority are permanent. Despite this, there is a great deal which can be done to assist someone with hemianopia.

SEETEC (a service provided by the Guide Dogs Association) uses a portable machine to assess and provide training exercises in effective visual scanning. These scanning techniques help to compensate for vision lost. This assists the person to gain confidence and safety related to walking, personal care, household tasks, leisure and other aspects of daily living. SEETEC helps the person affected to understand their condition and learn how to compensate for it.

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Glaucoma

Glaucoma is a leading cause of blindness. If it is diagnosed early, blindness is nearly always preventable. Glaucoma is usually caused by a build-up of pressure in the eye. This pressure causes damage to the optic nerve. The optic nerve transmits nervous impulses to the part of the brain which is responsible for sight.

The eye is normally filled with 'intra ocular' fluid which constantly drains away and is then replaced. In the case of glaucoma, intra ocular fluid is not drained away properly, or it may be produced in large amounts. If this causes too much pressure in the eye, the optic nerve is damaged, blind areas in the field of vision develop. Glaucoma tends to happen slowly, often with no noticeable changes until after the damage is done.

How does it affect sight?
Side vision is most often affected. The edge of the field of vision starts to fade, causing vision to narrow. Glaucoma can also cause blank areas closer to the center of vision.

Some warning signs include blurred vision, seeing colored rings around lights, loss of side vision, pain and redness of the eye.

Diagnosis and treatment
The good news is that most glaucoma cases can be treated. A painless examination is made to measure the pressure within the eye. The ophthalmologist also views the back of the eye to examine the optic nerve for any damage. Although damage cannot be reversed, treatment can prevent it from becoming worse. The longer high pressure remains in the eye, the more likely damage will occur.

Treatment aims to reduce the pressure by helping fluid to drain out of the eye, or by reducing the amount produced.

Eye drops are most often used to treat glaucoma, although sometimes laser and surgery are necessary. Glaucoma is a lifelong condition which requires continual management to prevent loss of vision.

Who is susceptible?
Most cases of glaucoma occur in the older age group. If there is a family history of glaucoma, there is a higher risk of developing the condition. People over the age of 40 and those with a family history should have a regular glaucoma test.

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Diabetic Retinopathy

This is caused by diabetes, although having diabetes does not necessarily lead to sight loss. Retinopathy affects the retina. The retina is at the back of the eye and is made up of cells which are sensitive to light.

A network of blood vessels feeds the retina. Diabetes can cause blood vessels to break and this can interfere with vision. Blood clots and scars may form on the retina, blocking the light rays from nerve cells and interfering with their nutrition.

Complete loss of vision can occur when scar tissue develops at the back of the eye. This sometimes pulls and detaches the retina.

Prevention and treatment
Preventing diabetic retinopathy or its advancement is helped by correct management of diabetes and regular eye checkups with an ophthalmologist. Laser light beams directed to the affected part of the retina may be used to seal leaking blood vessels.

Who is susceptible?
Diabetics with high blood pressure, pregnancy, nephritis or prolonged poor diabetic management are considered to have a higher risk of developing this condition.

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