Supporting people with aniridia and their Families
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| Homepage | Photophobia Also known as Light Sensitivity Definition "An abnormal intolerance of light, in which exposure to light produces intense discomfort of the eyes with tight contraction of the eyelids and other reactions aimed at avoiding the light. " (p.507, "Oxford concise Colour Medical Dictionary", Oxford University press, 1998) Causes The main cause of photophobia is glare, "The undesirable effects of scattered stray light on the retina". (P.273, "Oxford concise Colour Medical Dictionary", Oxford University press, 1998) There are two types of glare; Disability
Glare Symptoms - Contrast
between an object and its background is reduced Causes People with aniridia have differing degrees of imperfection in many different parts of the eye. Because the cornea and the lens may not be perfectly clear, light entering the eye can scatter and does not hit the retina in the correct place. This reduces the contrast and detail of the object being seen. People with Aniridic keratopathy and/or cataracts particularly affected by this type of glare. These causes of disability glare can not be helped, but preventing other factors affecting disability glare you can help maximise vision. Factors Causing Disability Glare - The glare source is relatively intense When a bright light that shines in your eyes it reduces the contrasts of the image and stops you seeing what you are looking at, for example when the headlamps of another car stop you seeing the road. Another example of light intensity is when the sun shines on the TV and the contrast of the picture is lost. - The glare source near the line of sight When the glare source is behind the object being viewed the contrast and detail of the object is reduced. for example if you are reading a book if the light is behind the book it is more difficult to read than if the light is above the book. - The glare source is near the object being viewed If the glare source is close to the object it will both be in the line of sight about have such and intensity on the object that it reduces contrast. Prevention To avoid intense lighting, ensure that rooms are well lit from above and that the light is evenly distributed around the room. Do not watch TV with the lights off. To avoid intense light outside use sunglasses. Avoid placing lights at eye level and that lights point away from the eyes. Ensure that lamps are shielded. When using spot lamps for work the light is not close to the object/book to cause reduced contrast. Discomfort
Glare Symptoms - 'squinting' or close your eyes tight in bright light.
Cause Light sources of excessive brightness or uneven distribution in the field of view can cause glare of varying degrees from a mild sensation of discomfort to an intolerable feeling of pain. People with aniridia mostly experience discomfort glare from natural light, though very strong artificial lights and glare from artificial lights reflected off shiny and reflective surfaces may also cause some discomfort. The reasons why people experience discomfort in these conditions in not fully understood and individuals with aniridia experience discomfort glare in different ways and to different extents difficult can occur in Clear
sunny days.
On bright
overcast days Inside Prevention Try to take the sun and a large proportion of a bright cloudy sky out of the line of sight by wearing a hat with a wide brim such as a baseball cap. Where sunglasses to help reduce the intensity of the light specially from, windows, mirrors, wet surfaces shiny surfaces and white or brightly coloured surfaces. This may not be appropriate on a bright overcast day. Move to a position where glare is not reflected off windows, mirrors, wet surfaces shiny surfaces and white or brightly coloured surfaces. if it is imposible to avoid all of these move to a position where there is the least glare from these sources. Position mirrors so they do not reflect artificial lights into the line of sight. position polished and metalic funiture in such a way it does not reflect a lot of light. If this is not possible or the reflection still bothers the individual place a non reflective dark shaded material (cloth or paper) over the item causing difficulty. Minimise the affect of glare from paper, texts, desk tops and black/whiteboards. References "Oxford concise Colour Medical Dictionary", (Oxford University press, 1998) "Environmental science in Building", 4th ed. Randall McMullan, (Mcmillan 1998) http://www-staff.lboro.ac.uk/~huph/disabg.htm
06/12/02 |