Retinoblastoma Health Dictionary

Inability to see. Definitions of blindness and partial sight vary. In the , blindness is defined as a corrected visual acuity of 3/60 or less in the better eye, or a visual field of no more than 20 degrees in the better eye. Blindness may result from injury to, or disease or degeneration of, the eyeball; the optic nerve or nerve pathways connecting the eye to the brain; or the brain itself. Clouding of the cornea may result from Sjögren’s syndrome, vitamin A deficiency, chemical damage, infections, and injury. Corneal ulcers can cause blindness due to scarring of the cornea. Uveitis and cataracts are other common causes of blindness. Diabetes mellitus, hypertension, or injury can all cause bleeding into the cavity of the eyeball and subsequent loss of vision. Bleeding into the fluid in front of the lens (hyphaema) or behind the lens (vitreous haemorrhage) can also result in loss of vision. Other conditions that may cause blindness include glaucoma; retinal artery occlusion or retinal vein occlusion; age-related macular degeneration; retinopathy; retinal detachment; tumours such as retinoblastoma and malignant melanoma of the eye; and retinal haemorrhage.

Loss of vision may be due to nerve conduction problems. These problems may be the result of pressure caused by a tumour; reduced blood supply to the optic nerve; optic neuritis; or toxic or nutritional deficiencies. Blindness can result if there is pressure on the visual cortex from a brain tumour or brain haemorrhage, or if the blood supply to the cortex is reduced following a stroke.

Treatment depends on the underlying cause. If the loss of vision cannot be corrected, the patient may then be registered as legally blind or partially sighted. (See also eye; vision, loss of.)... blindness

Many eye disorders are minor, but some can cause loss of vision unless treated. (See also cornea, disorders of; retinal detachment.)

Squint is sometimes present at birth. Rarely, babies are born with microphthalmos. Other congenital disorders that affect the eye are nystagmus, albinism, and developmental abnormalities of the cornea and retina.

Conjunctivitis is the most common eye infection and rarely affects vision. Trachoma or severe bacterial conjunctivitis can impair vision. Corneal infections can lead to blurred vision or corneal perforation if not treated early. Endophthalmitis (infection within the eye) can occur as a result of eye injury or infection elsewhere in the body.

Narrowing, blockage or inflammation of the blood vessels of the retina may cause partial or total loss of vision.

Malignant melanoma of the choroid is the most common cancerous tumour of the eye. Retinoblastoma is a cancerous tumour of the retina that most commonly affects children.

Various vitamin deficiencies (particularly of vitamin A) can affect the eye. This may lead to xerophthalmia, night blindness, or, ultimately, keratomalacia.

Uveitis may be caused by infection or an autoimmune disorder such as ankylosing spondylitis and sarcoidosis.

Macular degeneration of the retina is common in the elderly, as is cataract.

Glaucoma, in which the pressure inside the eyeball becomes raised, can lead to permanent loss of vision. In retinal detachment, the retina lifts away from the underlying layer of the eye.Ametropia is a general term for any focusing error, such as astigmatism, myopia, or hypermetropia. Presbyopia is the progressive loss with age of the ability to focus at close range. Amblyopia is often due to squint.... eye, disorders of

Tumours of the eye are rare. When eye tumours do occur, they are usually cancerous and painless.

Retinoblastoma is a cancerous tumour of the retina that occurs in one or both eyes and most often affects children. It may be treated by radiotherapy, laser treatment, or cryosurgery, but the eye may have to be removed to prevent spread of the tumour.

Malignant melanoma is a cancer of the choroid. It usually affects older people. There are no symptoms in the early stages, but it eventually causes retinal detachment and distortion of vision. Small tumours can be treated by laser, but the eye may need to be removed to avoid spread of the tumour.

Secondary eye tumours occur when cancer elsewhere in the body spreads to the eye. Symptoms depend on the tumour’s location and growth rate. It may be controlled by radiotherapy.

Basal cell carcinoma is the most common type of tumour affecting the eyelid. It usually has a crusty central crater and a rolled edge. In the early stages, treatment may be possible by surgery, radiotherapy, or cryosurgery.... eye tumours

TThe light-sensitive membrane that lines the back inner surface of the eye, and on which images are cast by the cornea and lens. The retina contains specialized nerve cells (rods and cones) that convert light energy into nerve impulses. The impulses travel from the rods and cones through other cells in the retina and along the optic nerve to the brain. The rods respond to very dim light and cones are responsible for colour vision.

The retina can be affected by congenital and genetic disorders, such as colour vision deficiency and Tay–Sachs disease. It can also be infected, injured (see retinal detachment; retinal tear), or affected by tumours such as retinoblastoma. Other disorders affecting the retina include diabetes mellitus and retinal vein occlusion.... retina