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Adapting Video for VI Learners

Effects of visual impairment

Sensitivity to glare

What is meant by glare?

Glare is light that is not useful; it comes from oblique sources and enters the periphery of the eye thus increasing the background illumination and decreasing contrast. It causes visual fatigue and strain.

What effects does glare produce?

We can distinguish between three interrelated aspects of glare:

disability glare relates to aspects of the visual system so is highly 'personal'. For instance, corneal scarring will cause light to scatter throughout the eye producing a distorted image and extreme discomfort at times.

  • Glare due to corneal scar(D)

    View video (1.8 M)

    discomfort glare is due to poor attention being paid to relative light levels in the workplace: eg poorly designed ceiling lights or windows and the reflections and hot spots they cause. Such stray light, though tiring, usually does not interfere with normal vision but can exacerbate visual impairments causing discomfort and fatigue.

    Discomfort glare(D)

    • environmental glare is due to factors which worsen situations which already produce discomfort glare. It can be caused for example by dust in the air or on a viewing surface or by highly reflective glossy pages in a book or magazine. This type of glare interferes with the resolution of visual information.

    Dust glare(D)

>What general situations make glare worse?

Sunlight coming through ill fitting curtains and venetian blinds or through dirty windows, highly reflective surfaces in a room all contribute to high levels of glare.

It is also important to consider the position of the lecturer when talking to students before, during or after seeing the video. Standing near a window or with their back to the window makes it very difficult to see body language or any demonstration which might take place.

What general situations ease glare problems?

Regular maintenance of blinds etc and the cleaning of windows can help to eliminate glare within a classroom. Similarly, light absorbing instead of light reflecting surfaces obviously help to prevent glare.

How does this affect viewing video screens?

It will depend upon the individual but any glare will reduce visual functioning, cause visual fatigue and in some cases extreme discomfort.

How would you improve screen access?

It is important to pay attention to all the environmental aspects mentioned making sure that light, natural or artificial, is not reflected in the screen. Contrast and brightness controls need to be set at a level which is comfortable for all students.

What names of eye conditions should I watch out for?

All those with a combined central or peripheral field loss of vision for example:

  • central field loss - macula degeneration, Best's disease, Stargardt disease, achromatopsia, cone dystrophies
  • peripheral field loss - retinitis pigmentosa, hemianopia, chorioretinitis, glaucoma, aniridia, Marfan's syndrome, retinal detachment, Leber's amaurosis
  • combined loss - coloboma, optic nerve disorders eg optic atrophy, optic dysplasia and hypoplasia, strokes
  • in addition - albinism, cataracts, high myopia and amblyopia.
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