The Medical Post
VOLUME 36, NO. 02, January 11, 2000
Parkinson's hinders patients' ability to distinguish contrast
By Derek Cassels
Condition often goes undiagnosed, doctors don't pass on helpful tips
LUBBOCK, TEX. - An Americanneurologist with a long-term interest in
Parkinsonism says it is not widely known visual acuity, particularly the
ability to perceive contrast, appears to diminish as the disease
progresses.
As a result, patients unaware of the gradual deterioration of sight do
little to protect themselves again such injuries as falls and unexpected
collisions.
He says many physicians are unaware of the faltering sight associated
with Parkinsonism and do not pass on simple tips that could avert
injuries from the annoying to the catastrophic.
Dr. Thomas Hutton, director of the neurology, research and education
centre at Covenant Health System, Lubbock, Tex., said these visual
symptoms are frequently overlooked and go undiagnosed.
He gives the example of a patient whose wife put a new off-white bath
mat on the white bathroom floor. This was totally invisible to the
patient. When a green mat was substituted the problem was solved.
Similarly a white safety handle in the shower went unused because it
could not be seen.
In an interview, Dr. Hutton said as Parkinson's progresses so does the
ability to differentiate shades of grey.
Some medicines, like L-dopa generally give "significant improvement" and
this may persist for months or even years.
So Dr. Hutton said this observation supports the theory reduced contrast
sensitivity is related to dopamine deficiency. However, others drugs,
like some dopamine agonists, may make things worse.
This is potentially clinically significant in light of the association
between dopamine agonists and visual hallucinations and confusion.
Whether some visual problems are also associated or exacerbated by the
use of dopamine agonists is now being studied.
"Contrast sensitivity seems to be somewhat phasic and depends on the
state of the Parkinsonism. We are trying to relate this to visual
misperceptions which are quite common and think this also may be related
to the hallucinations you can find in Parkinson's.
"Visual contrast problems are not seen in phase one (of the disease) but
are there at grades two through five. In the more advanced grades ...
four and five, these are extremely severe.
"I think in terms of becoming clinically very significant this is a
concern only in the advanced stages ... four and five. I don't think we
could push it to say that phase two patients have visual problems but
there are changes nevertheless."
Clinically, he said, this means doctors should listen when Parkinson's
patients bring complaints such as not being able to see well at night.
"Typically these patients are found to have normal acuity and no eye
disease that would explain their visual complaints. Many undergo
repeated visual exams and needless changes in eyeglasses in the effort
to see better. This can be very frustrating for these patients.
"So we think an analogy to what we are doing in the lab is what a
Parkinson's patient sees at night when the light is fading at dusk ...
or not seeing at night when the ambient lighting is low."
He said the take-away message is that patients with this problem should
not be driving. He said they also need to increase the lighting in their
hallways, stairwells and bathrooms.
"Often they can't see the steps and they tend to fall down them. Make
sure steps are clearly contrasted in the home and places like garages.
This can be done simply by the use of tape to edge stairs, for example."
Dr. Hutton said colour perception is also affected by progression with
the whole colour range diminishing in time.
"It is quite surprising what these people cannot see on our research
testing screen. We have worked with coloured lenses a bit but there are
no major conclusions other than we did not see any dramatic
improvements."
© Copyright 1999 The Medical Post. All rights reserved.
~~~~
Judith Richards, London, Ontario, Canada
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