Most of our sensory information is provided by our vision. Human vision is complex and sometimes our eyes don’t work the way they should because of common eye conditions. The eye should take in the physical stimuli of light rays. These focus onto the retina, a thin membrane that lines the inside of the eyeball that converts light into signals transmitted along the optic nerve to the brain.
Structure of the eye
Our eyes may be relatively small, but they are incredibly powerful allowing us to see the world around us.
- Cornea – clear tissue at the front of the eye
- Iris – the coloured part of the eye surrounding the pupil that regulates light
- Pupil – hole in the iris that allows light into the eye
- Lens – a small clear disc that focuses light rays onto the retina
- Vitreous – clear, jelly like substance that fills the middle of the eye and maintain’s the eye’s shape
- Retina – a layer of tissue that that lines the back of the inside of the eye , senses light, and creates electrical impulses that travel through the optic nerve to the brain
- Macula – small central area in the retina that is responsible for sharp, direct vision
- Optic nerve – connects the eye to the brain and carries the electrical impulses formed by the retina to the visual cortex of the brain
There are many conditions that cause vision impairment and blindness in Australia. the causes and onset of these vary. They can be present at birth, inherited through genetics or develop later in life due to ageing and systematic diseases.
Eye conditions leading to vision loss can include:
Albinism is a genetic condition that reduces the amount of melanin pigment (colour) in the skin, hair and eyes. In ocular albinism, only the eyes are lacking in pigment. 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. It means a child is very sensitive to bright light and glare (photophobia).
Amblyopia is also known as lazy eye. It occurs in just one eye, when it turns or there is a large difference in vision between the eyes. As one eye is able to see better than the other, the brain begins to ignore the visual impulses from the weaker eye, so favouring the other eye. If it’s left as it is, the weaker eye will continue to have 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. It makes the eye appear as though it has little or no colour and is larger than a normal pupil. The eye is, however, unable to control the amount of light entering and this leads to blurred vision and light sensitivity (photophobia). It can be a hereditary condition or develop through other factors. Aniridia can be present with other eye disorders such as 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 damaged or poorly developed. Often the eyes appear to be perfectly normal and function correctly under examination.
Sometimes the cerebral blindness is temporary and lasts weeks or months, but the damage can be more permanent.
A cataract is a clouding of the normally clear lens of your eye. For someone who has a cataract it is like looking through a foggy window. It is formed when the proteins that make up the lens are damaged; signals are sent to grow new ones which may be fragile or abnormal. Vision becomes poor giving the sense of looking through frosted glass. Cataracts typically occur with advancing age, but can occur at birth.
Diabetic Eye Disease
Diabetic Retinopathy is an eye disease associated with diabetes (link opens in new window). Elevated blood sugar damages the blood vessels that nourish the retina: the “seeing” part at the back of the eye. If 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
Glaucoma is an eye disease caused by high pressures in the eye which leads 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 drainage is impacted due to insufficient drainage channels or overproduction of fluid.
If it is not treated, it can cause blindness. Risk factors for glaucoma include family history and being aged over fifty, although there is also a congenital form.
Hemianopia is loss of half vision in either the right or left sides of both eyes. It is a common side effect of an acquired brain injury such as a stroke or brain tumour. People with a hemianopia can experience difficulty with mobility and everyday tasks due to missing visual information about half their world.
Keratoconus is a degenerative eye condition usually first appearing during adolescence and young adulthood. It causes the clear front surface of the eye (the cornea) to thin and develop a cone-like bulge. 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.
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. This degenerative disease which progresses over time, is caused by the abnormal development of light-sensitive cells in the retina. It 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 an involuntary oscillation or movement of the eyes. The eyes most often 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, strabismus or albinism. Nystagmus causes blurred vision and reduces depth perception.
Optic Nerve Atrophy
Optic nerve atrophy is when damage occurs to part or all of the optic nerve fibres. This results 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. 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 and may affect one or both eyes.
Optic Neuropathy is a disease, generally non-inflammatory, of the eye, where there has been 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 one of the more common genetic eye conditions 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 in dark places or at night. There then follows a loss of peripheral (side) vision, which means that the field of vision gets narrow. People with RP may also become sensitive to light and glare. The symptoms of RP usually increase with time. The condition develops between the ages of ten and 30 years as this is typically when symptoms begin to show.
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) appears soon after birth, generally in premature infants exposed to high oxygen levels. The combination of high oxygen and immature blood vessels gives 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 which remains, to 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.
Symptoms are usually first noticed between the ages of six and 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.
If you have concerns about your own or someone else’s vision, please see your ophthalmologist in the first instance. If necessary, they can refer you for a low vision vision assessment by our Orthoptics Team.