Coloured Overlays and Colorimetry
Investigation into visual stress is carried out only after a full eye examination and when symptoms are still present after any appropriate spectacles or exercises have been implemented. Assessment with coloured overlays usually forms part of this next stage and it is frequently performed as part of our Special Investigation.
Children and adults with visual stress often find that they can read more comfortably when using a carefully selected coloured filter in the form of a coloured overlay or coloured spectacles. Changing the appearance of the page of print in this way helps to reduce perceptual distortions of text, making reading more comfortable. The optimum colour required is specific to each individual and may change over time.
What does the overlay assessment involve?
An overlay is a transparent plastic sheet of a particular colour which is placed on a page of print to change the background colour. Sometimes the overlay assessment will be carried out using specialist computer software. Passages of print are viewed through overlays of different colours and colour combinations to determine whether a specific colour eases the child’s symptoms. The Wilkins Rate of Reading Test is used to help us confirm an improvement in performance when using a chosen colour. (It is important to note that this test is not in any way designed to assess a child’s reading ability; that is not the role of an optometrist.)
If an overlay of a particular colour is found to reduce symptoms and increase comfort it will be issued to be used wherever helpful and appropriate, (e.g., home, school, college.)
Because of the subjective nature of the colour selection process, careful monitoring of the child’s use of an overlay over a period of time, (generally a full school term,) is necessary in order to be sure that colour is of benefit to the child.
Can my child have coloured lenses instead of overlays?
Children will almost always be assessed first with overlays, which is quicker and simpler than colorimetry. Overlays are cheap and portable and well-suited to an unpressurised trial at home and school. It is essential that everyone concerned, (child, parent and teacher, as well as the optometrist) is convinced that colour brings a significant benefit to a particular child before regular coloured spectacle wear is considered. For these reasons children will almost always start with overlays, often progressing to colorimetry once visual stress has been confirmed.
Colorimetry
Some people, particularly younger children, are happy to continue with overlays. Many however find them a little restrictive; you can’t write under an overlay or use it for computer or white-board work. Coloured spectacles are more versatile, and their optimum colour can be determined with much greater precision using the Intuitive Colorimeter.
During a colorimetry assessment, print is illuminated with light which can be continually varied in colour and intensity, enabling us to find the optimum spectacle lens colour necessary to minimise visual symptoms for each individual. Brightness can also be investigated. Thousands of colour combinations are available.
(It is important to note that because of the differing modes of use, the colour required in an overlay is very unlikely to be the same as that required in spectacle lenses. It is never an option to duplicate overlay colour in spectacle lenses.)
Adults
Most of the information above concentrates on assessment for children but it is important to remember that adults too can have visual stress and benefit from coloured filters. It is not uncommon for people to become aware of a problem only when further education or a new job presents greater visual demands. Sometimes when we are assessing a child the parent suddenly understands a problem they have also had, perhaps since childhood. People with photosensitive migraine, photosensitive epilepsy, multiple sclerosis and other neurological conditions can sometimes find that coloured lenses help to ease their visual symptoms.
For adults the investigative process can often take a different path, with a comprehensive extended eye examination often replacing the Special Investigation and a subsequent colorimetry appointment in place of the overlay assessment and trial.
Please see our website information on Visual Stress and Our Special Investigation, and if you are concerned in any way about your child’s vision, (or your own,) please contact the practice for advice. Very often the starting point is a full eye examination.
(Please note that some services are available only at our Houghton Regis practice.)
