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What is Low Vision? |
What is Low Vision?
To consider low vision in relation to uveitis it is always worth making the point that uveitis is a diverse collection of conditions. Just as there is a wide variety of type of uveitis, the vision may be affected in distinctly different ways. The vision may always remain normal, or in the minority of cases be permanently and severely impaired. There are also different types of vision loss.But first, it is a good idea to define what is meant by low vision:
Low vision is visual loss that cannot be corrected by glasses or contact lenses and interferes with daily living activities.
Why read up about vision loss?
Vision loss in uveitis can take several different forms. It is a good idea to be aware of these so that early signs can be recognised and passed onto your doctors. It is also important to know about the differences so that the right type of visual aids can be selected to overcome any problems.
Types of vision loss.
-see table below (These may be due to the direct effects of uveitis or the indirect ‘complications’ of uveitis such as cataract:
Types of Vision loss
Caused by
Effect
Central vision loss
-Macula oedema
-Central scotoma (blind spot)
-Difficulty in recognising faces,
-reading things close up and in the distance
-carrying out detailed type of work like sewing.
-Sometimes straight lines appear distorted.
- Sensitivity to bright light is generally not a problem and detecting movement in the field of view and ‘getting around’ may be good.
Loss of peripheral vision (’tunnel vision’)
Glaucoma a result of raised pressure in the eye, a possible complication of uveitis.
In the later stages of the glaucoma, those affected will see the central part of their vision through a ‘tunnel’ with the periphery missing. This will lead to difficulty in mobility.
General Haziness or blurring of vision
-Cataract formation
-Vitreous opacification
-Active anterior uveitis (the blurring may be due to the inflammation but also caused by the dilating drops).
A more variable group.
-There is a general blurring or haziness.
-The field of vision may be affected.
-Often glaring or bright light may be uncomfortable.
Floaters (Black wisps or dots)
Cells and debris, as a result of the uveitis, affecting the vitreous gel.
Seen by the patient as small black objects, "floating" across the front of the eye, usually as dots or wispy lines which are sometimes described as “beasties” or “spiders”.
The table above briefly describes some or the common types of vision loss associated with uveitis. It is difficult to define completely because the vision loss that we experience varies a good deal and it will be very ‘subjective’, two patients describing the same thing quite differently.
However being aware that there are differences may well help our doctors if there has been a change in our vision. For example; a good description may help the doctors to determine whether it is a cataract progressing or a ’flare up’ of the uveitis. It is also useful to know that not all changes in vision are due to flare ups in the uveitis. (We should, of course let our doctors know of any change in our vision).
How is Vision loss measured?
There are different ways in which the degree of visual loss can be measured. They have their limitations but it is important for our doctors to know what the vision is like in order to know, for example, how vigorously to treat, and to detect any changes. It is also important for us to know what these measurements are, and mean, because we will often come across references to them when reading about visual aids or about other peoples experiences.
The level of vision is measured with the help of any glasses we already use:
Distance vision
This is measured using the familiar Snellan chart, shown below, our vision being that of the smallest line we can read.
NB This chart is just a diagram and can not be used to assess vision.
This chart has some limitations as there are so few letters at the top. You may well come across other charts that are more complicated.
Without worrying too much what the measurements literally mean, we can link the figures given for our sight to the number of lines we can manage to see on the chart.
The range of eyesight may go from 6/5 to 6/60 to 3/60 to terms like CF.
6/5 describes very good eyesight, slightly better than most people can manage. It means that at a distance of 6 metres you can read the bottom line of the eye chart.
6/60 would mean that you can only make out the top, largest, letter.
3/60 would mean that you would have to move closer to the chart (3m, instead of 6m away) in order to see the top most letter.
If the topmost letter can not be made out from a metre away then an assessment is carried out as follows:
- ability to count fingers (CF)
- hand movements (HM)
- perception of light (POL)
- no perception of light (NPOL)
The level of eye sight required for driving is approx. 6/10 (it is actually tested by the ability to read a number plate at 25 metres.
It may be worth pointing out here that this is a rather limited way of testing eye sight. Deciding whether you are able to drive is obviously a sensitive subject., and depends on other factors such as how much you see around you, your field of vision. However I can only recommend that if in any doubt, then it would always be best to talk it over with your eye specialist or Optometrist.
Near Vision
This is an important measurement to regularly have monitored. The test is carried out using any reading glasses already used. The smallest print size which is able to be read is noted. Each ‘font’ size is given a number. N5 is a measure of normal close vision. As a guide, newspaper print is usually N8 and this newsletter is printed in N16.
Visual Fields
Any defects in visual fields as in glaucoma or with scotoma (blind areas) may be measured by apparatus kept in the eye clinics. The test involves looking into a hollow sphere whilst staring straight ahead at a dot in front of you. You are then asked to push a button every time you see a light on the curved screen in front of you. The extent of your field if vision is thus measured and appears mapped out on a chart.
Registration as Blind or Partially sighted.
Many people who are eligible for registration do not take it up. The level of vision loss to become eligible is not clear cut because it can depend on, for example, a combination of visual acuity and field of view.
The best thing to do is to ask your Optometrist (Optician) or Eye Specialist if you think you may be eligible.
There are some official guidelines as follows which show why this is not a straightforward issue:
For Blind registration:
1) Best VA 3/60 (corrected)
2) 3/60-6/60 if associated with considerable field loss. (But National assistance act says that not blind if longstanding defect and unaccompanied by any material contraction of the field!)
3) better than 6/60 Only if marked contraction of the visual field (especially if involving inferior field.)
For Partial registration:
1) 3/60 - 6/60 with full field.
2) less than 6/24 with moderate field constriction or media opacities or aphakia (lens in the eye has been removed) .
3) less than 6/18 With a gross field defect of marked contraction of the visual field.
The benefits of registration are:
- Uveitis will be more accurately recognised as a cause of vision loss and this can only help in attracting research funding and clinical resources.
- There are benefits, e.g. free train and bus travel in Scotland.
What to do if you have low vision
There are many, many things that can be done to overcome low vision.
Some involve visual aids of varying complexity and some involve the most simple of things like lighting and altering the size of things we use.
Although there is much that can be done just by trying to work out different ways of doing things, when it comes to using optical aids like magnifiers, telescopes etc. then the most important thing to do is to get a good assessment and good advice as to what low vision aids you may require.
This service is provided by specially trained Optometrists who are usually based at Eye Outpatient Depts. They are able to assess the need and usually provide any low vision aids such as magnifiers on free loan. Certain Optometrist practices also provide this service.
To find out where the nearest low vision service is to you (in the UK) then you can access the RNIB website and go to ‘Low Vision’ see low vision links below, or you are very welcome to contact the UIG and we can do this for you.
Useful Low vision links
RNIB - Low vision services -find the nearest to you. From there you can browse the RNIB site for all sorts on low vision.
Magnifiers: Good Hope Hospital NHS Trust A good site containing information on magnifiers which will be covered in the next UIG newsletter.
There is so much to cover on low vision aids that this will be the subject of an article in the next newsletter.
Please ask or tell us about how you manage with low vision
It would be great to get some help for that article by hearing from anyone who has any questions about overcoming low vision or any suggestions, or useful tips, etc.
Any experiences of using different low vision aids, hi or low-tech, would be helpful as well.
It would be useful to hear about the different kinds of problems that people have with their vision with all the different kinds of uveitis.
