The Mind's Eye
Stuart Kieran, MD
1019 West Main Street
Hamilton, MT 59840
Vision is a complicated sensory ability that starts at the eye but ends
in the brain. Disturbances anywhere along the line can cause visual disturbances.
Ophthalmologist and optometrists treat the vast majority of these conditions,
many we have heard of including refractive problems (the need for eyeglasses),
cataracts, glaucoma, macular degeneration, as well as a host of other
conditions. There is however a number of less common conditions that affect
vision but where the problem lies in the brain. These have some unusual
and sometimes bizarre symptoms and often cannot be well treated per se
but the discovery of the cause can lead to prevention for further visual
First, a short anatomy lesson. Light enters the eye through the opening
called the pupil, is focused by the lens and then hits the retina. The
retina is the back of the eye where the light sensing cells are. The retina
is actually a very complicated 10 layered structure but one layer called
ganglion cells send out their fibers and merge together to form the optic
nerve which then passes into the brain itself. Although the front of the
optic nerve can be seen by looking through the eye with a simple device,
it is actually a nerve tract of the brain. This optic nerve then passes
backward, makes some detours, crosses and uncrosses and finally ends up
in the very back portion of the brain called the occipital lobes. As these
nerve fibers pass through the brain they receive and give off branches
from other structures and damage to these, although not directly in the
visual pathway, can produce a number of unusual symptoms. A lesion however
in the occipital lobe can cause a visual defect as profound as damage
to any structure in the eyeball itself. Some of these conditions also
have loss of other abilities such as reading, writing or recognizing objects.
Alexia is the inability to read and usually means the loss of the previous
ability to read. Sometimes this is called pure word blindness. While inability
to read can be caused by many things, if these have been ruled out (such
as macular degeneration or cataracts) then a brain lesion is possible
and this is usually in the left occipital lobe. The lesion in or near
the comparable right occipital lobe can produce a condition called prosopagnosia.
Here a person cannot recognize faces unless clear given clues such as
a prominent facial feature or voice. They can, however, see and recognize
Achromatopsia is the impairment of color vision. This of course can be
a hereditary condition; more common in men and starts out therefore in
childhood but it can be an acquired condition. If this is the case it
is caused by lesions, often strokes, involving nerve pathways to (i.e.
before) the back of the brain. People will often see the world on a grayscale
which can be quite unpleasant. Thankfully this rare situation occurs when
damage occurs to both occipital lobes. This can be seen in stroke disease
or severe head injury. A person in this case is legally blind but strangely
denies that they have a problem. This is in spite of injuries to themselves
as well as severe compromised abilities.
At the other end of the spectrum of visual deficits are visual hallucinations.
As a point of definition, hallucinations are when one sees images that
are not there at all; illusions are when one perceives real objects as
something else, and delusions that are psychiatric symptoms of incorrect
perceptions of one's own abilities or traits. Hallucinations and illusions
can be seen from many conditions, one of the most common would be drugs,
alcohol or drug withdrawal and degenerative disease. Alzheimer's or
another form of brain degeneration called Lewy body disease, which is
a form of Parkinson's disease associated with dementia and hallucinations
can cause this. The most important thing when one has hallucinations,
or typically when one observes it in a family member, is to try to find
the cause, and if possible, to decrease or minimize the dose. There are
some medications, such as one's that are used for Parkinson's
disease that are known to cause or aggravate hallucinations but many other
medications can do this and the first step would be to review these medications
with one's physician and/or pharmacist.
This health column was provided by Stuart Kieran, MD at Bitterroot Neurology,
Hamilton, MT 59840. To schedule an appointment please contact your primary
care physician for a referral. Working together to build a healthier community!