Dr. Grossman’s Blog

Hemianopia is a blindness in one half of the visual field due to damage of the optic pathways in the brain. This damage can result from brain injuries caused by stroke, tumor or trauma.  A patient with hemianopia may be unaware of what he or she cannot see and may frequently bump into walls, trip over objects or walk into people on the side in which the visual field is missing.

Prism eyeglasses were invented by Dr. Eli Peli of the Schepens Eye Research Institute, an affiliate of Harvard Medical School, to assist patients with hemianopia.  Dr. Peli attached small 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.  The prisms alert the patient to the presence of a potential obstacle, so that the patient can then move his/her head and eyes to examine the prism-captured image directly through the clear center of the lens.

In the trial, 32 of 43 participants (74%) who were fitted with prism glasses continued wearing the glasses at week six; at 12 months, 20 (47%) were still wearing the spectacles eight hours daily and rating them as “very helpful” for obstacle avoidance.

A larger study is currently underway to evaluate a newer model of the eyeglasses. 

SOURCE: “Community-Based Trial of a Peripheral Prism Visual Field Expansion Device for Hemianopia”, Bowers, et al, Archives of Ophthalmology, 2008, vol. 126, no5, pp. 657-664.

Study could lead to new therapies to help improve sight following trauma or stroke

Neuroscientists studying the mind’s ability to process images have completed the first empirical study to demonstrate how nerve cells in the visual cortex adapt to changing images. 

In the study, researchers at the University of Texas Health Science Center measured the effects of visual stimulation on the responses of multiple neurons whose electrical activity was measured simultaneously in animals. They examined the responses of a population of cells in visual cortex to dynamic stimuli (movie sequences displayed on a video monitor).

Results showed that brief exposure or adaptation to a fixed stimulus caused changes in the degree of cooperation between individual neurons and improved the efficiency with which the population of cells encoded information.

“Our perception of the environment relies on the capacity of neural networks to adapt rapidly to changes in incoming stimuli,” wrote senior author Valentin Dragoi.  “It is increasingly being realized that the neural code is adaptive, that is, sensory neurons change their responses and selectivity in a dynamic manner to match the changes in input stimuli.” The neural code is the set of rules that converts electrical impulses in the brain into thoughts, memories and decisions.

“Right now, we don’t know the causes of brain illnesses such as Alzheimer’s disease or disorders caused by trauma,” Dragoi said. “However, it is our belief that understanding not only how individual neurons work, but how they cooperate with their neighbors to impact the functions of the brain involved in diseases may help develop better diagnostic tools and therapies to improve visual function following trauma, stroke or disease, or even prevent brain disorder.”

SOURCE:  “Populations Of Brain Cells Adapt To Changing Images,” Dragoi, et al., Nature 452, 220-224 (13 March 2008).