Prism Glasses Expand The View For Patients With Hemianopia

Innovative prism glasses can
significantly improve the vision and the daily lives of patients with
hemianopia, a condition that blinds half the visual field in both eyes. The
peripheral prism glasses, which were invented by Dr. Eli Peli, a Senior
Scientist at Schepens Eye Research Institute, were evaluated in the first
community-based multi- center trial of such a device, which is published in
the May issue of the Archives of Ophthalmology. The study was coordinated
by Dr. Alex Bowers, a Senior Scientific Associate at the Institute.

“This is the first real breakthrough in the rehabilitation of patients
with this condition,” says Peli, a world-renowned low vision expert, the
Moakley Scholar in Aging Eye Research at Schepens and a Professor of
Ophthalmology at Harvard Medical School. Peli had searched for a solution
for his hemianopia patients for many years before designing the peripheral
prism glasses, creating a prototype in his laboratory.

More than a million Americans suffer from hemianopia, which blinds the
vision in one half of the visual field in both eyes, resulting from damage
to the optic pathways in the brain. Most commonly caused by strokes, it can
also be the result of brain damage from tumors or trauma. A patient with
this condition may be unaware of what he or she cannot see and frequently
bumps into walls, trips over objects or walks into people on the side where
the visual field is missing.

Peli’s goal was to find a way to expand the visual field. He did this
by attaching small, specially designed high power prisms on the top and
bottom of one spectacle lens, leaving the center of the lens untouched. The
prisms pull in images missing from the visual field above and below the
line of sight on the side of the vision loss, and alert the patient to the
presence of a potential obstacle or hazard. The patient can then move
his/her head and eyes to examine the prism-captured image directly through
the clear center of the lens.

Prisms by their nature can shift images from one side of the visual
field to the other side (e.g., from the right side of the field to the left
side). Before Peli’s invention, others had tried to develop prism glasses
to bring the missing part of the patient’s visual field into view. However,
these previous techniques placed the prisms in the center of the glasses,
which resulted in double vision, which is disturbing and confusing. Peli’s
solution was to keep the central part prism free and place prisms above and

The Archives of Ophthalmology study evaluated the glasses’ ability to
improve a patient’s walking mobility, which includes obstacle avoidance.
Forty-three patients were fitted with prism glasses in 15 community-based
clinics around the country. The clinicians interviewed them at six weeks
and after 12 months. Success was measured by how many patients continued
wearing the prism glasses and by their ranking of the prisms’ effectiveness
in assisting with obstacle avoidance while walking.

Thirty-two participants (74 percent) continued wearing the glasses at
week six. At 12 months, 20 (47 percent) were still donning the spectacles
eight hours a day and rating them as “very helpful” for obstacle avoidance.
These 12-month-plus patients were reporting significant benefits for a
variety of obstacle avoidance scenarios (e.g. walking in crowded areas,
unfamiliar places, shopping malls). According to Bowers, the first author
of the paper, “These results indicate that the glasses have great promise
for helping patients resume normal daily life.”

Peli partnered with a small optical company in Vermont-Chadwick
Optical, Inc. who funded the study in part through a National Institutes
for Health (NIH) small business grant. Peli and Karen Keeney, the President
of Chadwick Optical, created a permanent version of the prisms with higher
optical quality and better durability than the temporary prisms that were
fitted at the start of the study. These permanent prisms were provided to
15 of the study patients when they became available.

A new, higher power, version of the permanent prism glasses recently
developed by Chadwick Optical should also further expand the visual field
and be even more beneficial for patients’ mobility, according to Peli. The
prototype used in the study expanded the peripheral upper and lower visual
fields by 20 degrees without obstructing central vision. The new glasses
expand the field by 30 degrees.

A larger community-based multi-center study is currently underway to
evaluate the latest model. In addition to the higher power, the new study
is also evaluating a novel design for which Dr. Peli just received a
patient from the US patent office. Details on the new ongoing study are
available at clinicaltrials (clinical trial NCT00494676).

Schepens Eye Research Institute is an affiliate of Harvard Medical
School and the largest independent eye research institute in the nation.

Schepens Eye Research Institute