Sight difficulties


Updated April 2008 Cataract
Clouding of the lens of the eye, causing loss of vision.

With a cataract, the normally transparent lens of the eye is cloudy as a result of changes in protein fibres in the lens. The clouding affects the transmission and focusing of light entering the eye, reducing clarity of vision. Most people over the age of 75 have some cataract formation, but visual loss is often minimal as only the outer edges of the lens are affected.

Cataracts usually develop in both eyes, but generally one eye is more severely affected. A cataract in the centre part of the lens or one that affects the whole lens can cause total loss of clarity and detail in vision. The affected eye will still be able to detect light and shade.

The structural changes in proteins which cause cataracts are a normal part of ageing, and cause part or all of the lens to become cloudy. If your vision is affected significantly it may be recommended that the cataract is removed surgically and an artificial lens put in the eye. If there is no other reason for visual deterioration, sight should improve greatly after the operation.

Cataracts usually develop over a period of months or years. In most cases, they are painless and usually cause only visual symptoms, such as:
  • blurred or distorted vision
  • star-shaped scattering of light from bright lights, particularly at night
  • altered colour vision: objects appear reddish or yellow
  • in longsighted people, temporary improvement in near vision
  • a severe cataract may make the pupil of the eye appear cloudy.

Macular degeneration (age-related macular degeneration)
Progressive damage to the macula, the area near the centre of the light-sensitive retina that is responsible for detailed vision.

Gradual deterioration of the macula, the most sensitive region of the light-sensitive retina at the back of the eye, is known as macular degeneration. The condition leads to progressive loss of central and detailed vision, and affected people become unable to read or to recognise faces. Macular degeneration is more common in females and sometimes runs in families. The condition usually develops after the age of 70, although there are some rare forms that affect younger people.

There are two main types of macular degeneration, but their causes are not known. Dry macular degeneration is the most common form of the condition. Light-sensitive cells in the macula and cells in the supporting lay underneath fail to take in enough vital nutrients and to clear by-products of cell functioning. This causes tiny abnormal deposits, called drusen, to be left under the retina, making it uneven. Over many years, the retinal cells degenerate and die causing sight loss. In wet macular degeneration fragile new blood vessels grow underneath the macula. If the blood vessels leak fluid or bleed, the light-sensitive cells in the macula are damaged. Wet macular degeneration accounts for 10 to 15 per cent of cases and often develops quickly.

The symptoms of macular degeneration may include:
  • difficulty in reading, watching television, and recognising faces
  • distortion of vision so that objects appear larger or smaller than normal or straight lines appear wavy.
Dry macular degeneration cannot currently be treated; however, the rate of deterioration can be slowed by not smoking and eating a healthy diet. High does of beta-carotene, vitamins C and E, and zinc may also be helpful in slowing the progress of the condition. Residual sight can also be improved through the use of additional lighting and magnifiers.

There are a number of treatments for wet macular degeneration that can prevent further visual loss, and in some cases restore partial sight:
  • photocoagulation uses a hot laser to seal leaking blood vessels (but can only be used in a minority of cases where the leakage is not directly in the centre of the macula)
  • photodynamic therapy (PDT) uses a cold laser to destroy abnormal blood vessels
  • anti-vascular endothelial growth factor (anti-VEGF) treatments have been found to halt sight loss and in some cases restore it. The drugs are injected under the macula where they target a protein involved in the formation of new blood vessels. Two anti-VEGF treatments are currently licensed for the treatment of wet macular degeneration – Ranibizumab and Pegaptanib – although they may not be currently available on the NHS. The use of Ranibizumab and Pegaptanib is being assessed by the National Institute for Health and Clinical Excellence (NICE), who are due to publish guidance in June 2008. Further information can be found on the NICE website.
Presbyopia
Gradual age-associated loss of the eye’s ability to focus on near objects.

After about the age of 40 almost everyone starts to notice increased difficulty in reading small print because of the development of presbyopia. A person with normal vision is able to see close objects clearly because the lens of the eye changes shape, becoming thicker and more curved when focusing on near objects. The thicker lens brings light rays from close objects into sharp focus on the light-sensitive retina at the back of the eye in a process known as accommodation. As we age, the lens becomes less elastic and the power of accommodation is reduced. Eventually, light rays from near objects can no longer be focused on the retina and near objects appear blurred.

Since presbyopia develops very slowly most people are unaware of the initial stages of this condition. However, the symptoms usually become more noticeable between the ages of 40 and 50.

Common symptoms include:
  • the need to hold newspapers and books at arms length to read them
  • increased difficulty in focusing on near objects in poor light
  • if short-sighted (myopia) the need to take off glasses to see near objects clearly.
Presbyopia can be corrected by wearing glasses with convex (outward-curved) lenses, which bring light rays from near objects into focus on the retina. If corrective lenses are already worn, glasses may be prescribed with different power in different parts of the lens.

Presbyopia tends to worsen with age, and lens prescription will probably need to be updated every few years. The condition stabilises at about the age of 60 by which time most of the focusing work is done by glasses instead of the eye.

Further information:

© British Medical Association 2008

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