Restoring Peripheral Vision to Glaucoma Patients with Prism Glasses

We often talk about the latest and greatest technological developments in the fight against glaucoma, but today we’re going to look at something a little more down to earth than gene therapy or optic nerve regeneration. Today, we’re going to talk about glasses.

Researchers looking into ways to reduce pedestrian collisions for individuals with partial blindness have managed to determine the direction that collisions are most likely to originate. Now they are taking it a step further, developing a new type of glasses that contain a prism that will redirect the sight of a person with limited peripheral vision. This could be an amazing aid to people with glaucoma suffering from peripheral blindness.

The Question

According to Dr. Eli Peli of the Schepens Eye Research Institute, patients with retinitis pigmentosa (RP) and similar diseases like advanced glaucoma, typically maintain good central visual acuity for a while, but lose peripheral vision early. Peripheral field loss (PFL) creates problems with orientation and mobility. These patients tend to trip over things and collide with other people when in crowded places such as bus terminals or airports.

The study found out why this is: PFL patients do not compensate for their lost peripheral vision by scanning (looking from side to side) across a wider area in front of them, preferring to spend most of the time looking straight ahead. This is how our visual system naturally works. Additionally, there were no reliable studies showing that training patients to use wider scans changes that. Therefore, the research team decided that identifying the direction of highest risk, and providing what they called “islands of vision” in that direction when the patient is gazing straight ahead would be the optimal strategy.

“We found that the risk of collision is highest from pedestrians at an angle of 45 degrees from the patient’s walking path,” said Peli. “This means that any visual-field expanding device will be most effective if it can cover that angle.”

The Solution

The answer to this puzzle resulted in eyeglasses with prisms in the lenses that widen the field of vision. The researchers had been experimenting with a number of designs, trying to keep central vision clear while increasing peripheral vision. These designs included inserting the peripheral prisms into lenses that also had a combination of two Fresnel segments.

Fresnel lenses are a type of lens that is divided into a set of concentric, step-like sections. In certain lenses, like those used in this experiment, the curved surfaces are replaced with flat surfaces, each with a different angle, which turns the lens into a circular array of prisms. To create the glasses, these Fresnel segments were attached at the base and angled to each other (bi-part prisms), and creating Fresnel prism-like segments from non-parallel reflective prisms.

The research team found that glasses equipped with high-power, bi-part and reflective prisms increased the wearer’s effective eye scanning range and increasing the wearer’s peripheral vision by more than 15 degrees into the area of blindness.

The Future

With these prism-containing lenses directing light to those areas of the retina that still function, these new glasses enlarge the visual field of the wearer and compensate for the wearer’s decreased field of vision. The researchers expect the prisms to be effective for patients with residual central field diameters between 108 and 308. Assuming a typical residual field area loss of a few percent per year, patients might benefit for decades.

This is great news for glaucoma patients as well as any other person dealing with peripheral vision loss. Hopefully, this form of treatment will go a long way toward improving quality of life for patients by making it easier for them to get around on their own and retain their independence and dignity for a longer period of time.