A guide for parents and non specialist VI professionals

Characteristics – seeing may be hard work

Nystagmus is a complex and little understood eye condition. It cannot be cured and there is no known treatment for it. Glasses do not correct Nystagmus, but should be worn to correct reduced visual acuity.

The condition can be highly variable and change throughout the day. Its effect can become more prominent and pervading at times of stress so for example when a learner is having to meet deadlines, perform during exams or is generally under pressure seeing can become harder. Nystagmus for many can get worse when the learner is tired so may impact at the end of the school day. Conversely, mornings may be best for visual tasks or very demanding work.

These characteristic should be born in mind during eye tests too. Consequently the visual acuity score obtained during a stressful eye test may not be accurate for all situations. That is, the score should not be relied upon to set expectations in learning. The eye test might cause the eyes to flicker more than at other times and thereby affect the learner’s visual acuity score.  

Null point

A null point represents the position a learner holds her/his eyes to minimise the eyes flickering. This can mean a learner holding her/his head in an unusual position. S/he does this to maximise vision and it should not be prevented.

Consequently, one of the hardest aspects of Nystagmus to understand is that vision will vary during the day and may be made worse by such things as tiredness, stress and unfamiliar surrounds. Nystagmus impacts on the individual’s life during, education, leisure, employment and relationships of all kinds. Below, are a few effects,

• Very poor vision, especially distance
• Slow to see
• Clumsiness and poor depth perception
• Vision varying and worsening when tired, under pressure, in unfamiliar surrounds.
• The world jumps around (oscillopsia) when the Nystagmus movement is more pronounced.
• Light sensitive

Enlargments

If the individual has poor visual acuity enlarging things will make them bigger but not necessarily make things clearer. No amount of enlargement can make things look the same as they do to someone with normal sight. Enlargement helps to carry out a task, but it does not fully compensate for the impairment or give normal vision.

Wearing glasses

If the learner wears glasses it is extremely important that a highly skilled and experienced optometrist assess the learner’s sight and fits the glasses. The learner may for example adopt a null point which means s/he is not using the correct part of the lens. The situation therefore needs to be correctly assessed and balanced to include for example positioning the lenses’ centre to the side or build in a prism to compensate for the null point

Specialist assessments

The learner requires regular specialist assessments. These should be written partly or wholly in functional terms. That is, how do the findings impact on the learner’s life? Regarding vision the assessment should include what the learner sees and how s/he users sight. The learner should be assessed in different conditions outside the sometimes ideal environment of a clinic to include for example the classroom, a place without natural light and outside in bright sun light. Many believe that the correct lighting is the most important low vision aid and inappropriate lighting can seriously impact upon the learner accessing visual information.

Print size

Sometimes we hear that the minimum print size a learner can access is used to argue or imply that a print size which the learner requests is in fact unnecessary. Research however has told us that we need a reserve of acuity to be able to read fluently and quickly. Studies have shown that we need an acuity reserve of 3:1. This means that in order to read print size 12 fluently we need to be able to read print size 4 or to read print size 36 we need to be able to read print size 12 fluently.

Magnification and reading fluency

Reading speed and fluency will be affected by the number of letters or words we can see at one time. When we read a sentence we are looking directly at words but we are also taking in the next few words ready to read them. If the learner uses a magnifier the visual field is restricted and the stronger the magnifier the narrower the field. Research has shown us that in order to read fluently we need to see 4 to 6 letters in one go. Consequently when the learner uses medium powered magnifiers reading can be restricted and this is why it is hard to read with anything but the weakest magnifier.

Some learners do not like using low vision aids. This can of course be to do with personal image and not wanting to appear different. It can however also result through the trade off between magnification and visual field size not working to the learner’s satisfaction and is hampering reading fluency. This can be addressed in part through the learner holding the magnifier closer to the eye and thereby allowing for a wider field of view. There is always a trade off however between ease of use and the best theoretical magnification.  

Contrast sensitivity

Another, and sometimes under estimated effect on the learner accessing visual information is contrast sensitivity. Contrast sensitivity or contrast acuity means for example the greater the difference between the darkness of letters and the whiteness of background. This contrast is measured and called the contrast acuity. In functional and everyday terms this results in different sized objects stand out visually in differing degrees from their background. Also, when we access print it is not all very black or all very white and sometimes dark print is overlaid on top of pictures. All of this may result in a poor contrast and thereby be visually confusing to the learner. Moreover when photocopying the more we enlarge and the more we re-copy an image clarity and contrast will be affected.

Consequently the contrast between print, objects and the background impacts upon reading speed and accurately accessing information. As a result we need a reserve of acuity to read fluently and quickly. This means that in order to read print fluently, which has a 70% contrast we need to be able to see a much fainter 7% contrast. A contrast test allows us to measure the contrast threshold and hence predict reading fluency. For example, if a child has reduced contrast sensitivity then we know that simply increasing the power of magnification will not help. High contrast and suitable lighting also have an impact.

This also impacts on mobility. When the learner accesses steps or changes in threshold reduced contrast acuity, where different parts of the environment represent different shades of grey may cause confusion and thereby be dangerous.

Therefore a low vision assessment should offer a balance between magnification, lighting and contrast with the assessment written in functional terms and be applicable to the learning environment.

Next time

Following on I will next consider the content of specialist reports and appropriate support. There is also a great deal more about curriculum access in my book, WHAT IS RED, A POPPY’S RED. Available from Kindle via my web site.