The most important part of any eye exam is the health of the eyes!
All children under the age of 16 years are entitled to a sight test on the NHS,
There are different systems that allow us to focus, move and alien our eyes:
- Refractive error (power of the eye) – long-sighted, near-sighted
- Convergence eyes move in toward the nose
- Divergence eyes move out.
- Motilities the eyes move in a slow movement
- Saccadic fast rapid movements
- Accommodation this system focus the light on to the fovea
- Vengeance system move the eyes together to align on a target.
What symptom that can occur if any of the above system are not functioning correctly:
blurred distance vision
Blurred near vision
Avoids reading or near tasks
Loss of place reading
closing one eye
rubbing of eyes
If a person has any of these symptoms then a full sight test is needed.
What treatment is there?
The diagnosis will determine the treatment options. In general, all refractive error so glasses prescription is needed if there is reduced vision. There are many exercises and treatment options that your optometrist can give to improve symptoms.
Once an optometrist has excluded any abnormal findings and treated any weakness that is detected in the vision system, if the symptoms persist investigation is needed to determine if symptoms are related to visual stress.
What is visual stress?
Meares and Irlen observed that some people experience perceptual distortion when reading. Visual stress has a variety of names – Meares-Irlen syndrome, visual discomfort, scotopic sensitivity disorder.
Evans and Wilkins said visual stress is caused by pattern glare. So over –excitement of the visual cortex in the brain due to hyper sensitivity to contrast.
The use of colour could redistribute the cortical hyper excitability therefore reducing the perceptual distortion.
Some symptoms of visual stress are:
Tired eyes, poor concentration, poor comprehension, headache, moving words, patterns on the text, transient colour, halos, blurred text are just a few symptoms.
Visual stress can occur in good readers but is often link to dyslexia (Kriss and Evan 2005)
Treatment for visual stress is not a treatment for dyslexia. Visual stress treatment helps the underlying visual perception problem. The treatment for Visual stress only reduced one of the many factors that contribute to dyslexia. With the reduction in Visual stress this will help a dyslexic person read for longer and reduced the strain on the system allow more concentration on other factors that affect their reading for example memorising, retaining information. A person can have visual stress and not be dyslexic.
Visual stress testing
this test involves comparing different overlay colours and then measuring the speed of reading with and without the overlays. Patients then try the overlay for a few weeks and if there is an improvement in symptoms coloured lenses can be tested for, this however is a different colour to the overlays and a machine is used to determine the correct lens colour.