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Adapting Video for VI Learners

Understanding low vision aids and their use with video

Low vision aids

A student with a field defect such as hemianopia (loss of one half of the visual field) or severely reduced peripheral or central field of vision may have been prescribed a distance Low Vision Aid (for instance, a telescope). To use such an LVA requires a very high level of scanning skills. Whatever is viewed through the LVA will only be seen in 'small bits', as it is scanned in a systematic way. The student has to piece these bits together to form a whole. Compare this with a fully sighted person who quickly views the 'whole scene' first without much effort then focuses on the parts that interest them. Teachers can help students anticipate and therefore interpret what they will see by careful use of descriptive language in preparatory information.

Keeping track of moving objects on a video through an LVA will be almost impossible. However, provided that sufficient time is given the student may well be able to scan and process the information on still frames or from OHP transparencies.

Inexperienced or reluctant telescope users may need time to adjust to the different retinal images sent to the visual cortex. They need training to help interpret images, so don't expect miracles for new users. Again, good descriptive language can help them during their training.

LVAs in learning settings

A major disadvantage of all 'high magnification' LVAs such as telescopes is that they have small fields of view which don't collect much light. Therefore the contrast and brightness of monitors may need adjustment. Similarly, the monitor screen needs to be clean - dust particles contribute to problems with glare and interfere with the visual system. As monitors are usually viewed in lower levels of illumination, the amount of light gathered by the lens of the telescope will be reduced compounding any problems.

The size of the monitor is important and needs to be discussed with individual students. Whilst larger screens may be appropriate for non LVA users, a smaller screen cuts down on the amount of scanning needed to follow moving images. Smaller monitors usually give a better resolution than larger ones. Obviously, an ideal solution is for visually impaired students to have their own personal viewing monitor.

Many of the points apply if OHP's are used to provide supplementary information. The high wattage lamp of an OHP generates an intense background illumination to provide contrast, and this can 'dazzle' the visually impaired user, with or without a distance low vision aid.

One way to avoid such problems can usually be solved by giving the student copies of the transparencies.

For viewing both the monitor and the OHP screen, the visually impaired student will need a clear view without the distraction of other student's heads getting in the way whilst trying to locate the screen. Lighting sources must not cause any kind of glare or visual disturbance, eg reflected artificial/sunlight on the screen.

Allow extra time if students are expected to make notes or read additional information during the viewing. A low vision aid user will have the added difficulty of changing focus and possibly LVAs and then using the telescope to find information again on the screen.