Three quarters of vision impairment and blindness in Australia is caused by just 4 conditions: cataract, diabetic retinopathy, glaucoma and macular degeneration. There are also many congenital eye conditions (those present at birth) which are either inherited or caused during pregnancy or birth by other means.
Eye conditions leading to vision loss include:
Albinism is a genetic condition in which all or part of the body lacks pigment (colour). In ocular albinism, only the eyes are lacking in pigment, whereas in oculocutaneous albinism, the skin, hair and eyes are all lacking in pigment.
People with oculocutaneous albinism will typically have very blonde/white hair, pale skin and low vision. The irises of the eyes range from pale blue to pink and can’t adequately screen out excessive light, making the child very sensitive to bright light and glare (photophobia).
Amblyopia is also known as lazy eye and is a condition in which an eye that has the potential for full sight has poor vision. It is usually caused by a turned eye or uncorrected refractive error. Because one eye is able to see better than the other, the brain begins to ignore the visual impulses from the weaker eye and if the condition is not treated the weaker eye has permanently low vision. Treatment generally consists of patching the stronger eye to strengthen the weaker one.
Aniridia is when the iris or part of the iris of the eye is missing. This means that the muscles that open and close the pupil are missing. This makes the eye appear as though it has little or no colour and a larger than normal pupil. Other changes in eye structure are often present (e.g. cataracts and glaucoma). The condition can be hereditary or be caused by unknown factors. Aniridia affects visual acuity and can cause other eye disorders such as photophobia (light sensitivity), cataracts, nystagmus and glaucoma.
Cerebral Vision Impairment
Cerebral vision impairment (CVI) occurs when the part of the brain (often the visual cortex) that receives and decodes the message sent from the eye is poorly developed, damaged or missing. This means that messages sent to the brain from the eyes are not properly understood by the brain. Usually the eyes appear to be perfectly normal and function correctly when they are examined.
Sometimes the cerebral blindness is temporary and lasts weeks or months. Sometimes the damage is permanent and messages from the eyes are not decoded.
A cataract is formed when the proteins that make-up the lens are damaged. Vision becomes poor giving the sense of looking through frosted glass. Cataracts typically occur with advancing age, but can occur at birth.
Effects of cataract include:
- Cloudy or blurry vision
- Colours may seem faded or yellowed
- Glare can cause hazy vision particularly on bright sunny days. The person may see a halo or haze around a light source
- A person with cataracts may have to hold reading material closer than usual.
Diabetic Eye Disease
Diabetic Retinopathy is an eye disease that is a complication of diabetes. Elevated blood sugar damages the blood vessels that nourish the retina: the “seeing” part at the back of the eye. If many vessels are damaged, signals are sent to grow new ones, which may be fragile or abnormal. If these new vessels leak, blurred vision and blindness can result.
The damage increases with time, causing either vision impairment or blindness. Vision often becomes patchy and can fluctuate with the blood sugar levels
Effects of diabetic eye disease include:
- In the early stages there may be blurring of both central and peripheral (side) vision.
- As it progresses, there may be cloudiness and blind spots or floaters in the vision.
- In advanced stages, scar tissue forms, causing additional distortion and blurred vision. Retinal detachment may then follow.
Glaucoma is an eye disease caused by high pressures in the eye which lead to damage to the optic nerve. This damage reduces the side or peripheral vision, causing “tunnel vision”. In a normal eye, clear fluid flows from the posterior chamber, around the lens and out of the front chamber of the eye draining out through a spongy mesh area where the cornea and iris meet (called the angle). With glaucoma, this does not happen.
If glaucoma is not treated, it can cause total blindness. Glaucoma has an increased risk with aging, and if there is a family history you have four times the risk. There are different types of glaucoma including open, congenital, closed angle and secondary.
Hemianopia (also known as Hemianopsia) is loss of vision in either the right or left sides of both eyes; a common side effect of stroke or brain injury. This vision loss causes serious problems with mobility, bumping into objects and increased incidence of falls and accidents.
Keratoconus is a degenerative eye condition usually first appearing during adolescence and young adulthood. Keratoconus causes the clear front surface of the eye (the cornea) to thin and a cone-like bulge develops. The bulging cornea affects the way light hits the retina at the back of the eye, causing distorted vision.
Symptoms begin slowly and can be hard to detect and include:
- Distorted, ghosting or blurred vision
- Glare and light sensitivity.
Glasses can correct early stages of Keratoconus, but hard contact lenses may be needed to correct vision as the condition progresses. Collagen ‘crosslinking’ (the combination of ultra violet light and Vitamin B) can help to ‘harden’ the cornea to stop the progression of Keratoconus. Corneal transplants may be required for the most severe cases.
Leber’s Congenital Amaurosis (LCA)
Leber’s Congenital Amaurosis (LCA) is an inherited eye condition, which appears at birth or in the first few months of life. It is a degenerative disease (progresses over time) that is thought to be caused by abnormal development of the light-sensitive cells in the retina, which usually results in very reduced vision or blindness.
Macular Degeneration is a condition affecting the central area of the retina called the macula. The macular is responsible for detailed vision, for uses such as reading.
Macular Degeneration damages the central vision, but side or peripheral vision remains intact. For example, sufferers may be able to see the outline of a clock, but not the numbers or hands. People with Macular Degeneration may experience difficulty reading, writing, seeing colours, watching television and recognising faces. There are both ‘wet’ and ‘dry’ forms of macular degeneration.
Nystagmus is a fluttering movement of the eyes which a person has no control over. The eyes can move from side to side, but they may also move up and down, around in circles or a combination of these movements. It is usually present in both eyes and can occur alone or together with another vision problem such as congenital cataracts or albinism. Nystagmus causes blurred vision and reduces depth perception.
Optic Nerve Atrophy
Optic nerve atrophy occurs when part or all of the optic nerve fibres are damaged resulting in permanent loss of part or all of the nerve function. The optic nerve carries electrical impulses from the retina to the brain, which translates the message into what we see. Affect on vision ranges from almost normal visual acuity to complete blindness. People with optic nerve atrophy may also develop nystagmus.
Optic Nerve Hypoplasia
Optic nerve hypoplasia occurs when the optic nerve is underdeveloped or even missing and it may occur in combination with other brain and endocrine (system of glands that secrete hormones) abnormalities. Affect on vision ranges from almost normal visual acuity to complete blindness. ONH may affect one or both eyes.
Optic Neuropathy is a disease, generally noninflammatory, of the eye, characterized by dysfunction or destruction of the optic nerve tissues. Causes include an interruption in the blood supply, compression by a tumor or aneurysm, a nutritional deficiency, and toxic effects of chemical. The disorder, which can lead to blindness, usually affects only one eye.
Retinitis Pigmentosa (RP) is a genetic eye condition which causes the retina to slowly and progressively deteriorate. This causes vision to slowly and progressively decrease. One of the first symptoms of RP is difficulty seeing at night or in places that are dimly lit. This is usually followed by a loss of peripheral (side) vision, which means that the field of vision is narrowed. People with RP may also become sensitive to light and glare. The symptoms of RP usually increase with time. The condition is usually diagnosed between the ages of 10 and 30 years as this is typically when symptoms begin to develop.
Retinoblastoma is a fast growing childhood cancer of the eye, which develops in the cells of the retina. If it is left untreated it can spread through the optic nerve to the brain and may be fatal. However the tumour itself is very treatable and recovery rates are good. Treatment can require complete removal of the eye (enucleation) and may need radiation therapy to prevent spread of the tumour.
Retinopathy of Prematurity
Retinopathy of Prematurity (ROP) is a condition that appears soon after birth, generally in premature infants exposed to high oxygen levels. The combination of high oxygen and immature blood vessels is thought to give rise to the abnormal development of blood vessels in the retina and can lead to retinal detachment and blindness. Sometimes there is a small area of healthy retina left and this may give the person some useful vision.
Stargardt’s Macular Dystrophy
Stargardt’s Macular Dystrophy (SMD) is a hereditary condition, which affects the macular of the retina. Central vision is usually affected first with progressive vision loss over a period of years.
The condition is generally identified after 6 years of age and before 20 years of age. However in some people it may not cause problems with sight until they are 30 or 40 years old. SMD is an inherited disease, which affects males and females equally.
The movement of each eye is controlled by six eye muscles that work in pairs. When one eye muscle contracts (tightens), its partner relaxes and the eye moves in the desired direction. If one eyes muscle is out of balance (that is, under-acting or overacting) the affected eye will not move with the unaffected eye. This is known as strabismus.
When the eyes do not co-ordinate, each eye is seeing a different image to the other. This is confusing to the brain and it shuts out the image received from the ‘turned’ eye. This is called suppression. A person with strabismus effectively uses only one eye. If the eye is not straightened early in life, before a child’s visual system has stopped developing, the eye will never develop ‘normal’ vision.
Australia is the only western country in the world to still have trachoma. It is present in many aboriginal communities, particularly in remote areas. Trachoma is a bacterium that infects the eyes and initially causes watery eyes and an aversion to light. It is easily treated, but if not treated the cornea can become severely scarred.