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Cortical visual impairment

The terms "partially sighted" (UK English) and "legally blind" (US English) can refer to many different kinds of severe eyesight problems.  Mine is CVI (cortical visual impairment) which is caused by a brain problem rather than an eye problem.  Eye problems are sometimes called "ocular visual impairment" when discussed in contrast to cortical visual impairment.  Many people with CVI have a form of ocular visual impairment as well. A person with CVI can take longer to learn how to make use of the unusual types of information that their malfunctioning visual system presents to them, and to take into account the context and other clues in a piece of continuous Sherlock Holmes-style detective work.

Symptoms of CVI usually include several (but not necessarily all) of the following:

The presence of CVI does not necessarily mean that the person's brain is damaged in any other way, but it can often be accompanied by other neurological problems, the most common being epilepsy (possibly in a mild form, and it may or may not have an associated increased susceptibility to emotional changes).  Some people with CVI have limited language skills, but this is not necessarily the case.

Diagnosing CVI is difficult.  A diagnosis is usually made when visual performance is poor but it is not possible to explain this from an eye examination.  Before CVI was widely known among professionals, some would conclude that the patient is faking their problems or has for some reason engagaed in self-deception.  However, there are now testing techniques that do not depend on the patient's words and actions, such as FMRI scanning, or the use of electrodes to detect responses to stimuli in both the retina and the brain.  These can be used to verify that the problem is indeed due to a visual cortex malfunction.

Most of the above text was taken from an old version of a Wikipedia article I started.  As the copyright holder I can also use it here. By the way, I do not endorse using Wikipedia without extreme caution as it can temporarily contain highly misleading statements. (Regarding the use of sources in public attacks, see my comments on the ``take it up with them'' fallacy.)
All material © Silas S. Brown unless otherwise stated.