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Sight difficulties

Updated July 2006

• Cataract
• Macular Degeneration
• Presbyopia

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.

All cataracts occur as a result of structural changes to protein fibres within the lens, which 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
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. In dry macular degeneration, light-sensitive cells in the macula and cells in the supporting lay underneath die. 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.

Macular degeneration causes progressive visual loss over several months and symptoms 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 be treated. The early stages of wet macular degeneration can sometimes be treated by laser surgery, which seals off any abnormal blood vessels and can prevent further loss of vision. If abnormal blood vessels continue to develop, the process may need to be repeated.

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 arm’s 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:
- Institute of Ophthalmology - Age-related macular degeneration
- MEDLINEplus Health topics – Cataract
- MEDLINEplus Health topics – Macular degeneration
- MEDLINEplus Medical Encyclopaedia – Cataract
- MEDLINEplus Medical Encyclopaedia – Macular degeneration
- MEDLINEplus Medical Encyclopaedia – Presbyopia
- NHS Direct Online - Visual impairment
- Royal College of Ophthalmologists
- Royal College of Ophthalmologists booklets
- Royal National Institute of the Blind
- Royal National Institute of the Blind – Understanding age-related macular degeneration
- The Macular Disease Society