What is low vision?
"Low vision" covers a variety of different kinds of vision problems caused by diseases such as age-related macular degeneration (AMD). Low vision means that your vision is still useful, but is worse than can be readily helped by glasses - and specifically that you have trouble reading without some form of external magnification.
HumanWare makes a wide variety of products for low vision - from portable magnifiers, desktop units and transportable products for sustained reading. We are innovators in this field, offering products widely recognized as among the best available anywhere.
Low vision means having a level of vision where you need more than just glasses or contact lenses to see well enough to read or do everyday tasks. Your central or side vision, or both, may be reduced. Your vision may not be able to be corrected with surgery, but you can still see something. And with the help of vision aids you can still stay independent. A person may have low vision as the result of an injury to the eye or one of a number of eye related conditions such as macular degeneration, glaucoma, and diabetic retinopathy. Some people are also born with low vision.
What are the symptoms?
The symptoms of low vision depend on the cause of vision loss and where the problem is in the eye.
Symptoms can include:
- Blank spots, dark spots or wavy lines in the centre of your vision
- Blurred, hazy or cloudy vision or double vision
- Loss of side (peripheral) vision
Follow these links to find out more about four very common low vision conditions.
Normal Vision Macular Degeneration
Age-related macular degeneration affects 25 to 30 million people worldwide.
The macula is located in the centre of the retina, at the back of the eye. It processes the images our brain translates into central vision. The size of a pea, the macula helps to see sharp detail, such as a freckle on a nose.
As our eyes get older, the membrane separating the macula from retinal blood vessels can weaken, depriving the macula of nourishment. When the macula degenerates, so too does central vision.
AMD can seriously affect one's central vision in just a few months or over the course of several years. In severe cases, scar tissue from leaky blood vessels can cause irreversible blind spots. Note that AMD will never cause total blindness since peripheral vision remains unaffected. People with AMD may see the color of someone's shirt, but not his face. They might spot a small coin on the floor as they walk through a room but cannot read the clock on the wall.
While no two individuals with AMD experience exactly the same degree of vision loss, brighter light and sharp contrast in color can make objects more visible to anyone with the condition.
There are two forms of AMD:
The dry form, which is the most common, and the wet form, which is less common but causes more severe and sudden sight loss.
With dry AMD, varying degrees of sight loss are caused by deposits of drusen (age spots) that form in the macula. Wet AMD results from abnormal blood vessels forming and leaking into the macula.
The cause and cure for AMD are unknown. However, treatments are available in a small percentage of cases. Possible risk factors for the condition include smoking, genetics, hypertension, sun exposure, far-sightedness, light skin or eye color, and poor diet.
What are the symptoms?
In the early stages your central vision may be blurred or distorted with things looking an unusual size or shape. This may happen quickly or develop over several months. You may be very sensitive to light or actually see lights that are not there. This may cause some discomfort occasionally but otherwise macular degeneration is not painful.
Normal Vision Cataracts
A cataract is a clouding of the normally clear and transparent lens of the eye.
When a cataract develops, the lens becomes as cloudy as a frosted window, and light cannot be properly focused on the retina, resulting in an unclear image. Often, only a small part of the lens is affected and, if sight is not greatly impaired, there is no need to remove the cataract. If a large portion of the lens becomes cloudy, sight may be partially or completely lost until the cataract is removed.
Depending on the size and location of the cloudy areas in the lens, a person may or may not be aware that a cataract is developing. If the cataract is located on the outer edge of the lens, no change in vision may be noticed, but if it is located near the centre of the lens, it usually interferes with clear sight.
Cataracts related to ageing are the most common type, but cataracts can also result from hereditary factors, diseases, medications or injury. Although it's rare, cataracts also can affect children and young adults.
What are the signs or symptoms?
- Blurred or double vision, ghost images, or the impression of a "film" over the eyes
- Problems with light (too much or too little), sensitivity to bright light and glare
- The need for frequent changes of eye glass prescriptions - none of which seem to help
Normal Vision Glaucoma
Glaucoma causes the gradual loss of peripheral, or side, vision. Although linked to older age, glaucoma may develop at any age - even infancy.
The cause of glaucoma is unknown, but a number of risk factors have been identified. These include age, heredity, myopia (near-sightedness), increased intraocular pressure (IOP), or pressure inside the eye, and systemic disease such as diabetes and hypertension. Vision loss from glaucoma may be caused by increased IOP and other influences on the optic nerve, located at the back of the eye. The diminishing nerve function causes loss of peripheral, or side, vision painlessly and without notice.
It is important to be aware of the possibility of glaucoma, particularly if you have any of the risk factors. Some drugs, such as cortisone (steroid) drops, can cause glaucoma. As well, some visual disturbances that cannot be corrected by glasses may be a sign of glaucoma. This is also true for AMD and diabetic retinopathy.
What are the signs and symptoms?
In the vast majority of cases, especially in the early stages, there are few signs or symptoms. In the later stages of the disease, symptoms can occur and include loss of side vision, an inability to adjust the eyes to darkened rooms, difficulty in focusing on close work, rainbow colored rings around lights and frequent changes of prescription glasses.
Normal Vision Diabetic Retinopathy
In the early stages of diabetic retinopathy, small blood vessels weaken and leak fluid or tiny amounts of blood, which distort the retina. At this stage, the person may have normal vision or may experience blurred or changing vision. Although 25 per cent of people with diabetes have some degree of retinopathy, most cases do not progress to more severe problems.
In a more advanced stage, blood vessels in the retina are blocked or closed completely, and areas of the retina die. Proliferative diabetic retinopathy affects about five per cent of people with diabetes and occurs when new, abnormal blood vessels grow to replace the old ones. These new vessels are fragile and often rupture and bleed into the eye, blocking vision. Scar tissue forms, shrinks, and tears the retina, causing bleeding or detachment from the back of the eye. This can result in severe visual loss or blindness. Fortunately, this occurs only in a small minority of people with diabetes.
The chances of having some form of diabetic retinopathy increase the longer a person has had diabetes. Diabetic retinopathy is present in 90 per cent of those who have had diabetes for more than 20 years.