This can occur more frequently when a person has CVI. Hence, a person with CVI can look at an optical illusion or abstract picture and perceive something that is significantly different from what a person without CVI will perceive.The presence of CVI does not necessarily mean that the persons brain is damaged in any other way, but it can often be accompanied by other neurological problems, the most common being epilepsy. Diagnosis
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 was faking their problems or had for some reason engaged in self-deception. However, there are now testing techniques that do not depend on the patients 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 malfunction of the visual cortex and/or the posterior visual pathway. See also
Cortical blindness

References
Further reading
Tallent, Aubri & Tallent, Andrei (2012). Little Bear Sees: How Children with Cortical Visual Impairment Can Learn to See. Little Bear Sees Publishing, of Wyatt-MacKenzie. p. 156. ISBN 978-1936214822. OCLC 1936214822. Roman-Lantzy, Christine (2019). Cortical Visual Impairment: Advanced Principles. New York: AFB Press. ISBN 978-1616480073. OCLC 1055566701. Roman-Lantzy, Christine (2017). Cortical Visual Impairment: An Approach to Assessment and Intervention 2nd Ed. New York: AFB Press. ISBN 978-0891286882.
Sometimes it is possible for a person with CVI to see things while moving their gaze around that they didnt detect when stationary. However, movement that is too fast can be hard to track; some people find that fast-moving objects "disappear." Materials with reflective properties, which can simulate movement, may be easier for a person with CVI to see. However, too many reflections can be confusing (see cognitive overload). Some objects may be easier to see than others. For example, the person may have difficulty recognising faces or facial expressions but have fewer problems with written materials. This is presumably due to the different way that the brain processes different things. Colour and contrast are important. The brains colour processing is distributed in such a way that it is more difficult to damage, so people with CVI usually retain full perception of colour. This can be used to advantage by colour-coding objects that might be hard to identify otherwise. Sometimes yellow and red objects are easier to see, as long as this does not result in poor contrast between the object and the background. People with CVI strongly prefer a simplified view. When dealing with text, for example, the person might prefer to see only a small amount of it at once. People with CVI frequently hold text close to their eyes, both to make the text appear larger and to minimise the amount they must look at.