Mysteries of the eye
It began with a question.
For John Denny, Ph.D., assistant professor of ophthalmology, the
question of how a newly discovered protein in the retina contributes to
eyesight is leading to research that may provide new treatments for people
with low vision.
Originally found to be in various parts of the brain, a
growth-associated protein, known as GAP-43, recently was discovered in
neurons in the retina as well. The mystery was what role this particular
protein played in the eye.
In the brain, GAP-43 allows us to remember things such as phone numbers
of friends and when to pick up the dry cleaning. In the eye, its inner
workings are more mysterious, but Dr. Denny’s research suggests that it
may be an intricate part of the changes the retina undergoes when adapting
to light and darkness.
Along with its partner protein MARCKS, GAP-43 is now known to be found
in certain cells in the eye which release the neurotransmitter dopamine.
Through his investigations, Dr. Denny believes that GAP-43, working in
conjunction with MARCKS, alters the release of dopamine, supporting the
eye’s adaptation processes from light to dark conditions.
The outcome of Dr. Denny’s research may be valuable information on
how these proteins operate and how they can be altered by pharmaceuticals
to enhance eyesight.
“What we would like to understand is the biochemistry of GAP-43,”
said Dr. Denny. “Knowledge of its biochemistry could lead to the
development of a drug that could potentially enhance the function of the
retina. By enhancing GAP-43, we could enhance vision in someone with low
vision.”
To catch a thief
Lisa Ranson, 34, worried that she would inherit glaucoma, the so-called
“sneak thief of sight,” from her grandmother, and that it would indeed
creep into her life without warning and eventually steal her vision.
Glaucoma runs in Ranson’s family. Her grandmother and two of her
great aunts are being treated for the disease. So it was not out of the
realm of possibility that Ranson, an outpatient service representative at
University Hospital, could have it as well.
Glaucoma is a group of diseases that cause the progressive
deterioration of the optic nerve and produce defects in a person’s field
of vision. With nearly 3 million people suffering from glaucoma in the
United States, it is one of the three major causes of blindness. But the
vast majority of those with the disease don’t know they have it until it’s
too late. Symptoms often do not show up until the damage has been done and
cannot be repaired.
Current tests for glaucoma focus almost solely on pressure, alerting
ophthalmologists to patients who have high or low intraocular pressure,
which does contribute to glaucoma. It is now believed that larger numbers
of people suffering from glaucoma have normal pressures and may never be
diagnosed because of testing procedures.
William Sponsel, M.D., chief of glaucoma service and assistant
professor of ophthalmology, is trying to change that by developing new testing tools that target patients with normal intraocular pressure.
One such device is a small, lightweight tabletop unit called the
Frequency Doubling Perimeter (FDP), which is designed to detect the
earliest cases of glaucoma in patients who may normally go untreated.
The visual function test presents 16 squares of light in wave patterns
on the screen that for normal eyes produces a doubling illusion or “ghost
lines” between each of the lines introduced to the patient. People with
glaucoma do not see all the lines. The test targets the large optic
nerves, which is where the disease first begins to do its damage, offering
ophthalmologists an opportunity to catch glaucoma earlier.
The FDP requires an average testing time of five minutes, is small and
portable, and costs less than larger visual field testing equipment while
providing similar results.
“This has proven to be very effective. It is highly specific.
Everyone who failed has a problem,” Dr. Sponsel said. “We had people
who had 20/15 vision—better than 20/20—and normal intraocular
pressure, but failed the FDP. We found they had a problem.”
For Ranson the FDP was quick and easy. In less than 10 minutes, she was
pronounced glaucoma-free for now.
“It is still something I need to keep abreast of, but now I am
breathing a sigh of relief,” Ranson said.
Early detection is just one of the directions Dr. Sponsel’s glaucoma
research is heading. He also
is working on new treatments for the disease, including drugs that may
increase blood vessel capacity and provide better circulation. Such
treatments also may benefit patients suffering from other types of eye
diseases, including macular degeneration.
“What we learn in the eye, in the treatment of the nerves, may help
with age-onset diseases like Parkinson’s and Alzheimer’s. It is
exciting to think of the potential our research could have in other areas
of medicine,” Dr. Sponsel said.
While Health Science Center researchers work to “lift the fog,”
their efforts continue to restore and prevent future loss of one of our
most precious senses—sight.
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