This is a place to ask questions about low vision. Together we'll find the answers. I have many questions about my low vision. As I answer our questions I'll post the answers I find.
Monday, February 05, 2007
Nystagmus
'Congenital nystagmus' (CN) and latent/manifest latent nystagmus (LMLN) are the most common types. Those with CN are often partially sighted, legally blind, and unable to drive a car. Most also have problems in everyday life, both practical and social, to the point they have trouble obtaining education and employment.
However, CN or LMLN by themselves do not necessarily cause major vision problems, and many people with these disorders lead normal, active lives. Those with very poor vision usually have sensory deficits that are responsible for most of their vision loss.
Adult onset acquired nystagmus takes many different forms. Some of the symptoms include oscillopsia, meaning the involuntary movement of the eye, poor vision, and loss of balance. Some acquired nystagmus is caused by neurological problems, and can be treated with medication. Visual field problems are caused by strabismus (misalignment of the eyes), which causes problems with depth perception, clumsiness, tripping, and poor eye-hand coordination.
Nyastagmus can be hereditary, have no known cause, or be associated with a sensory problem. The underlying cause is an instability in the motor system controlling the eyes. CN rarely presents later in life, and acquired nyastagmus can be caused by an accident or a range of illnesses.
These observations are from the American Nystagmus Nework:
Glasses or contact lenses do not correct nystagmus.
Vision may vary during the day and is likely to be affected by emotional and physical factors such as stress, tiredness, nervousness or unfamiliar surroundings.
Most people with CN and no other visual problems can see well enough to drive a car.
The angle of vision is important. Most individuals with CN have a null point (a gaze angle where the CN damps); this point can be found and used by looking to one side or the other, where the eye movement is reduced and vision improved. Those with a null point will often adopt a head posture to make best use of their vision. Sitting to one side of a screen, blackboard, etc. does not help because it reduces the angle at which the screen is viewed, causing 'crowding'. A better solution is to sit directly in front and adopt the preferred head turn or have corrective surgery (or use prisms) to eliminate the head turn.
Many can read very small print if it is close enough or with use of a visual aid. However, the option of large print material should be available and all written matter should be clear. It is very hard to share a book with someone because it will probably be too far away or at the wrong angle.
Good lighting is important. If in doubt get the advice of a specialist, particularly as some people are also light sensitive. Computers are used by many people with nystagmus, who benefit from them as they can position screens to suit their own needs and adjust brightness, character size etc. However some find it difficult to read computer screens. Reading speed is not usually reduced by nystagmus itself, but by other associated visual deficits. CN should not be taken as a predictor of poor reading.
Balance can be a problem in acquired nystagmus, which can make it difficult to go up and down stairs.
This is another condition I hadn't heard of before researching the causes of low vision.
Dale L. Edwards
Wednesday, January 10, 2007
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Fuch's Corneal Dystrophy
The cornea is composed of three layers – the outer epithelium (or "skin"), a middle area called stroma and a delicate, single celled inner lining called the endothelium. The corneal endothelium prevents water inside the eyeball from moving into and swelling the other layers of the cornea. The cells of the endothelium actively pump water from the cornea back into the eye. When the endothelium does not function normally, water will seep into the cornea and cause swelling. It is this swelling that causes clouding of the cornea and blurring vision. The more corneal swelling or "edema", the more severe the blurring. Eventually the epithelium also takes on water which results in pain and more severe vision impairment. Epithelial swelling changes the normal corneal curvature and causes a sight-limiting haze to develop. Epithelial swelling may also form small "blisters" on the corneal surface. When these "blisters" burst, it can be extremely painful.
We gradually lose endothelial cells as we age and these cells don't grow back. The remaining cells spread out to cover the empty spaces, trying to pump water from a larger area and become less efficient. Most people have enough endothelial cells throughout life to prevent corneal swelling.
Fuchs’ dystrophy (named after Dr. Fuchs) is an inherited disease that affects the endothelium and hinders its function and causes the cells to die faster than normal. It's a dominant gene and only one parent needs to be a carrier of the disease for an average of 50% of their children to inherit the disease.
Symptoms include:
- Hazy vision that is often most pronounced in the morning
- Fluctuating vision
- Glare when looking at lights
- Light sensitivity
- Sandy, gritty sensation
- Episodes of sharp, sometimes incapacitating pain
Fuch's usually doesn't cause problems until the person is 50-60 years old. There is no cure, but there are some medications that help. Once it gets bad enough a corneal transplant is performed.
This isn't a common condition, but it could become more common as it spreads through the population. Not everyone who carries the gene develops swelling and blurred vision.
Dale L. Edwards
Leber's Hereditary Optic Neuropathy
LHON was first discovered by Theodore Leber in the 19th century, but we didn't really start to understand how it was inherited until the late 1980's. Leber's usually affects one eye first and central vision is lost in that eye over a period of a few weeks. A month or two later, the second eye is affected in the same way. After a few weeks the eyesight stops getting worse.
This is the most common pattern of development, but LHON can affect someone very suddenly, or can affect them more gradually over a period of years. Not everyone in a family affected by Leber's will lose their eyesight, and we can't tell yet know who will get symptoms and who won't. We do know that Leber's is inherited through a gene which is passed on only through the egg cell from the mother. Men can't pass on Leber's Hereditary Optic Neuropathy to their children.
Scientists believe that the particdular gene changes linked to Leber's Hereditary Optic Neuropathy lower the amount of energy available to the cells of the optic nerve and retina. These cells are damaged and can even die because of this lack of energy. The damage to the optic nerve and retina is what causes the symptoms of Leber's.
Doreid Berro has written an informative paper about LHON and it's published on the internet with documentation.
Genetics Home Reference also has quite a bit of information about Leber's on their site.
Carver Laboratory has information about Leber's and other hereditary eye conditions. They also have some interesting pictures on their website.
I never knew there were so many different causes of low vision.
Dale L. Edwards
Saturday, January 06, 2007
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Blind Mice Regain Sight
"We think this is a major breakthrough because it shows what can be achieved," said study lead researcher Dr. Robert MacLaren, a consultant vitreoretinal surgeon at Moorfields Eye Hospital and a clinician scientist at the University of London, in England.
Scientists have tried to use stem cells before to restore sight, but their efforts failed. Dr. MacLaren believes that timing is crucial to success. He transplanted the photreceptors from newborn mice into the blind mice's retinas (they are looking for a way to use adult stem cells) and the retinas accepted these photoreceptors and made connections to the mice's brains. The mice are receptive to light.
"These cells were transplanted extremely quickly (i.e., 30 minutes out of their normal environment)," MacLaren said. This rapid transfer, plus their positioning in a conducive retinal environment, means that the cells "were able to form quick connections with host cells," he said.
This certainly sounds hopeful. If they can learn how to use adult stem cells they won't need embryonic stem cells.
Dale L. Edwards
New Treatment for Diabetics
An increase in VEGF, a growth factor, appears to play a role in macular edema. Ranibizumab, a VEGF blocker, given as ocular injections shows promise in the treatment of macular edema and macular degeneration. An earlier study showed an improvement in patients with macular degeneration.
"The results are impressive," lead author Dr. Quan Dong Nguyen, from Johns Hopkins Wilmer Eye Institute in Baltimore, said in a statement. However, "we will not know until we begin a larger clinical trial what the long-term benefits of the drug might be."
Nguyen's team investigated the effects of ranibizumab in 10 patients with diabetic macular edema. The subjects were given intraocular injections of ranibizumab at the start of the study and at 1, 2, 4, and 6 months.
At the 7-month checkup, researchers noted a significant drop in macular thickness and improvement in visual acuity in study subjects.
There appear to be no side effects from this injection. More studies are planned.
Dale L. Edwards
Friday, January 05, 2007
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Coping with Low Vision
Safety Tips For Solo Travelers
Women are especially smart to take precautions when traveling alone, especially when they are visually impaired. Here are some strategies to help ensure a safe trip:
Ask about security when making hotel reservations. For instance, check if the doors have dead-bolt locks, chain locks, or peepholes, if you have enough vision to use them.- Request a room that is not secluded - for instance, one near an elevator.
- Register using your last name and first initial only.
- Leave valuable or expensive-looking jewelry or unnecessary credit cards at home.
- Leave extra cash, passport, and other valuables in a hotel safe, or carry them in a pouch or money belt under your clothes.
- Carry a cell phone with you at all times.
At Home
- Contrasts in wall, floor, and furniture coverings should be carefully considered. Dark furniture against light walls, for example, is much easier and more comfortably identified.
- Placing items on tables (particularly low ones, such as coffee tables) or covering them with varied colored cloths, call attention to their corners and will avoid many "shin scrapes."
- Light switches should be of contrasting color to the wall around them or a piece of tape can be placed around them. A night light near the switch allows for better visual discrimination.
- Lamps for specific tasks are helpful as well as having good ceiling lighting. A rheostat-type switch to allow for dimming can add to the ambiance of the room and give comfort as well.
- Persons who have impaired vision find that accommodating to light or darkness takes longer. A night light left on can shorten the adjustment period.
- Putting most-used items, such as glasses, house-shoes, canes, etc., in the same place each time makes finding them easier.
- Organization is essential. A box on the night stand, for example, to hold small items is a good idea.
Some tips from Gladys Loeb on organizing the kitchen for the visually impaired.
- Keep all cleaning supplies well separated from the edibles.
- In storing canned goods such as fruits, vegetables and soups, I reserve a shelf or section of it for each general line. Cardboard dividers can be used. The line of food most used (soups in my case) is placed in the most convenient-to-reach location and the remaining cans arranged in alphabetical order according to their contents. As dividing sections and for filling empty spots, position easily recognized items such as ketchup, mayonnaise, etc.
- A must in every kitchen is an electric clock and a timer. These are available in Braille. However I have found very satisfactory ones in our local department stores. I selected an open-faced decorator clock with large raised numbers and a timer with minute and second markings clearly distinguishable by touch.
- Rubber bands represent an old standby marking method. They are Practical but have their limitations in that their meaning becomes confusing after three or four bands. I put them to good use in this way. I place one band on my favorite can of soup for example, two bands on the next favorite and so on. You can do the same with your canned vegetables and canned fruits as long as you store the food lines in separate shelves. After three rubber bands I resort to other labeling techniques.
For more tips follow the links. I hope these help. I'm going to use the rubberband idea because I've opened the wrong can more than once.
Dale L. Edwards