Prisms are a popular, specialized device for low vision patients that helps those with visual field defects and other vision problems too great for regular corrective lenses to fix.
Many people who suffer from low vision experience a decrease in their peripheral vision and visual field. In conditions such as scotoma, patients can develop non-seeing areas in their visual field which make many tasks more difficult. Prism lenses can also help patients who have central vision loss, double vision, and symptoms associated with that such as headaches and balance issues.
While for most low vision patients the vision loss cannot be reversed, there are devices, such as prisms, designed to help improve their vision and allow them to regain some measure of their independence.
Prisms also help reduce the eye strain that can be caused by using close vision with glasses for extended periods of time. For patients who need high levels of magnification, prisms allow them to keep working for extended periods in comfort.
These prisms, also known as fresnel prisms, are made of optical polyvinyl chloride, which increases the chromatic dispersion and produces a loss of contrast. These effects have been found to be helpful for patients with blurry and diplopic vision with distance viewing.
For visual field issues, the prisms can focus the image into a part of the retina unaffected by vision loss. Additionally, if the eyes have different visual capabilities, prism lenses can help equalize things and help avoid eye strain.
These are very thin lenses designed to fit onto ophthalmic lenses to provide additional lens power without making the lenses overly thick (which is an issue with standard high power prism lenses.) This makes the glasses both more comfortable to wear, and better looking. It will be less obvious that the wearer requires significant vision assistance.
Another option are custom made prism glasses. These are great for patients with a regular need of prism visual assistance, though they are thicker, and have a different look from regular glasses.
Low vision readers are prism lenses specifically designed to help patients with central scotomas have an easier time reading. Through significant magnification, they reduce the impact of the scotoma and make reading less of a struggle. Low vision readers can be both handheld and hands-free.
Prism lenses are prescription products, so you will need to see a low vision optometrist for a low vision eye exam, so they can determine what type and strength of prisms will be best for you to maximize your vision to suit your needs. The wrong prisms can lead to discomfort and eye strain, so properly prescribed prism lenses are vital.