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Located at the back of the brain, the occipital lobe has both the visual association areas and the primary visual cortex, according to the Merck Manual Professional Edition. When information comes in through the eyes, it crosses the optic chiasm and goes to the primary visual cortex to be processed. Because of the crossover in the optic chiasm, information from the right eye is processed by the left occipital lobe, and vice versa. If the occipital lobe is damaged, a person can have different visual disorders, even if no damage occurs to the eyes.
Visual Object Agnosia
A patient with visual object agnosia can see familiar objects, but when asked to identify the objects, she cannot recognize them. Visual object agnosia occurs when there is damage to the right hemisphere occipital lobe and left hemisphere occipital lobe (bilateral damage). Jenni A. Ogden, PhD, author of Fractured Minds: A Case-Study Approach to Clinical Neuropsychology, states that visual object agnosia is “'modality specific' in that the object can be recognized via the other senses of touch, sound or smell. It is not a disorder of naming, as the subject has no difficulty naming the object if it is recognized via touch or another nonvisual sense.”
There are three different types of visual object agnosia. The first type, apperceptive visual agnosia, affects the patient's ability to copy a picture of an object. The patient cannot tell the difference between shapes. With the second type of visual object agnosia, associative visual agnosia, the patient can copy the picture, but cannot identify what the image is. For example, the patient can copy an image of a bike, but cannot identify that it is a bike. With integrative visual agnosia, the patient can also copy an image, but cannot integrate parts of an image into a whole.
Prosopagnosia
Another condition caused by bilateral damage to the occipital lobe, prosopagnosia affects the patient's ability to recognize faces visually. Prosopagnosia can also occur with visual object agnosia.
Anton's Syndrome
The Merck Manual Professional Edition states that damage to the primary visual cortex causes Anton's syndrome, which is a type of central blindness. The patient cannot visually recognize objects, but denies that she has a blindness problem.
Visual Hallucinations
Seizures may occur in the occipital lobe, which can cause visual hallucinations. The patient may see rapid blinking, colored lights or flickering lights. Occipital lobe seizures, which the NYU Comprehensive Epilepsy Center states account for 5 to 10 percent of epilepsy cases, can be triggered by flashing lights.
Elizabeth Stannard Gromisch received her bachelor’s of science degree in neuroscience from Trinity College in Hartford, CT in May 2009. She is the Hartford Women's Health Examiner and she writes about abuse on Suite 101.
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