Visual impairment takes a number of forms, each posing a different mix of problems for field study. According to the RNIB, there are about 80 different eye conditions which can affect sight in various ways (SSC, 2000a, provides definitions of over 60). These conditions include short- and long-sightedness, colour blindness, cataracts (responsible for almost half of all cases of blindness worldwide (Sight Savers International, 2000)) and glaucoma (often referred to as the world's leading preventable cause of blindness).
It is worth noting that some eye conditions are selective (e.g. colour blindness is most common in males; glaucoma and cataracts are more frequent in older people), while others are more randomly distributed in the population. Another important thing to recognise is that people who are registered as blind or visually impaired often have significant residual abilities — e.g. 70% can use text if it is clear and large enough (SSC, 2000c).
In most cases, students will know on entry to a course whether they have a specific eye condition and, if so, what effect it might have on their study. However, this is not always the case, because some eye conditions develop slowly, and may only become apparent under specific study conditions. Colour blindness, for example, may become more noticeable when a student is asked to interpret multi-coloured maps or analyse graphical images on screen in preparation for a field course, or when asked to distinguish soil horizons or vegetation patterns in the field. There are several common forms of colour blindness — or colour deficiency — each of which poses different problems. Tests for several forms of colour blindness are available on the Web, including:
Ishihara test — www.toledo-bend.com/colorblind/Ishihara.html
Waggoner test — members.aol.com/protanope/colorblindtest.html
(N.B. These tests should not be used as substitutes for visiting a trained ophthalmologist.)
Another condition, which does not reside in the eye, is the inability to accommodate properly when using a stereoscope, with the result that the student is unable to form a three-dimensional image from pairs of overlapping aerial photographs — a commonly used field study resource.
In the case of colour blindness, steps can be taken to replace confusing colours in printed or computer displays. It is more difficult to overcome the problem of stereoscope accommodation.
A useful distinction can be made between the congenitally blind (those who are blind from birth) and the adventitiously blind (those who developed blindness later in life, perhaps as a result of accident, trauma, disease, or medication). Most visually impaired people lose their sight rather than being born sightless — some 85% suffer progressive sight loss (SSC, 2000c).
The difference between these two visual impairment groups can be substantial, because a student who has been blind from birth is more likely to have developed mature adaptive mechanisms, whereas someone who has recently become blind may still be learning to cope, and therefore require considerably more support and assistance while undertaking fieldwork. Another difference lies in the development of spatial concepts. Congenitally blind children, for example, may find it more difficult making sense of tactile maps than adventitiously blind children, because they have not previously acquired spatial awareness through visual interaction with their environment.
Other differences among in the experience of visual impairment can also be educationally significant. For example, visual impairment may be congenital or adventitious, it may be the result of numerous causes (e.g. age related, triggered by disease or subsequent to an accident), and while many visual impairments occur gradually, others happen very suddenly.
Some forms of visual impairment are permanent, while others are reversible. Although some rare forms of blindness (e.g. those caused by trauma) may reverse themselves, most blind people never regain their sight, particularly if they have been blind from birth. By contrast, some conditions (e.g. conjunctivitis) are usually temporary, and others (e.g. glaucoma or diabetic retinopathy) may be reversed by an operation. Where the eye condition is age-related, such medical procedures are especially important for senior citizens wishing to return to formal study. The difference between temporary and permanent condition is significant, both in terms of student expectations and staff/departmental support. Where an eye condition is temporary, a field visit may possibly be deferred, whereas a permanent condition may require a different strategy.
It is also worth noting that in some cases the severity of the condition can fluctuate through time, which means that its impact on a student attending a fieldcourse may be partly down to chance.
The severity of most eye conditions, and therefore the degree of impairment, can vary considerably. In broad terms, the range of impact can run the entire gamut from total blindness through low vision to minor impairment. A broad distinction often made in UK disability legislation is between people who are registered as blind and those who are registered as partially sighted. These two groups may exhibit rather different study patterns and difficulties, and may require different kinds of support, especially during fieldwork. The following table summarises some of the main differences between the two kinds of visual impairment:
(List adapted from University of Edinburgh handout on student disability.)
In the US, a distinction is made between three degrees of vision loss: visual acuity of 20/200, low vision, and partial sight (UMNDS, 2000).
See the accompanying document on the potential impacts of various eye conditions on fieldwork.
Page updated 14 December 2001
GDN pages maintained by Phil Gravestock
© Geography Discipline Network/authors, 2001
ISBN: 1 86174 115 4