Prisms

Prisms are an optical aid that redirect where an image is viewed and can be a very beneficial tool in helping people with low vision.

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Prisms are a type of lens prescribed by an optometrist with a special feature that redirects the way the light reaches our eyes. It does not have refractive power like a traditional lens, however it performs a very important function of bringing images to our eyes in specific directions that are otherwise difficult to be seen. With a triangular shape, prisms are available in four directions known as base up, base down, base in and base out. Wherever the base is located indicates that the light is being redirected in the opposite direction. For example, a base down prism helps move the image upwards.

What are prisms used for?

There are many optical uses for prisms in various fields, including vision therapy, and these lenses are also very instrumental in the field of low vision. Prisms are a helpful feature that eye doctors use to customize the prescription glasses to the patients’ individual needs and capabilities. Different applications of the use of prisms are detailed below.

High Magnification

When a person requires strong magnification due to a variety of reasons that are applicable in the low vision world, it could cause difficulty for the eyes to focus. This becomes especially relevant when using strong magnification and trying to look at a target that is close up. For example, when reading and using a high magnification, you need to bring the text very close to your face in order to read. This task requires the eyes to focus extremely inwards which can cause eye strain, and the magnification makes this inward motion challenging. Sometimes it’s too hard to meet these demands and therefore people resort to using magnification in only one eye, like a monocle. This is where prisms come into play because they are an optical tool used to help bring an image to a certain area. Prisms can be incorporated into high magnification glasses to help the eyes focus inwards together, and in a more comfortable way, despite the strong magnification.

Prisms accomplish a number of advantages in high magnification glasses, including:

Preventing eye strain and providing comfortable reading.
Establishing clear vision.
Despite the high magnification and close up vision, prisms enable both eyes to work together properly, known as binocularity.

Visual Field Loss

Visual field loss is a prevalent issue in low vision. For example, up to half the amount of people who suffered from a stroke, have a visual field loss and they may or may not be aware of it. There are many people who suffer from the loss of visual field in certain directions due to a vast range of causes, such as:

Glaucoma
Age related macular degeneration
Diabetic retinopathy
Hypertension
Stroke
Brain tumor
Head injury
Multiple sclerosis

When a person suffers a visual field loss, it is recommended that they are evaluated by a low vision optometrist who can decide the best way to help them maximize their visual abilities and reclaim their independence. Anyone with a visual field loss is at a greater risk of falling or sustaining injuries due to the fact that their vision is obstructed. There is no reason to suffer such risks alone, low vision optometrists can help. Depending on where the location is of the blind spot, otherwise known as a scotoma, the optometrist can add a prism to your glasses in order to help your eyes see images in the area that has suffered a loss of visual field. The eye doctor will help you learn how to adjust to the prisms so that you can enjoy better vision and overall functionality. For example, in the early stages of age related macular degeneration, prisms can be instrumental in enabling the patient to attain vision in the areas that have lost vision.

Double Vision

Many people with low vision suffer from double vision, also known as diplopia, due to a wide variety of reasons, including brain injuries or other neurological conditions. Prisms are used to help people with double vision in a way that can enhance their entire lifestyle by being able to see clearly and to accomplish day to day tasks. When there is double vision, each eye is focusing in a different direction. The eye doctor will prescribe prisms to direct both eyes to focus on the same target which can correct the double vision. Correcting diplopia with prisms can treat the symptoms of double vision including headaches, eye strain and general discomfort, in addition to enabling the person to reclaim clear vision and their independence.

Type of Prisms

There are different kinds of prisms, each with their own benefits, depending on every individual’s needs. There are two main categories of prisms:

Built in Prisms

The traditional way of implementing prisms is when the optical lab makes the lens with a prism built into it. A prism is a triangular feature of the lens in which the base of the triangle is the thick side of the prism and the point of the triangle, known as the apex, is the area that the light is being directed to.

For example, this is a base down prism:

The baseline is the thickest part of the prism and the light is being directed upwards so the base down prism redirects the image upwards.

Base

It is important to consult with a professional when choosing frames for glasses that have prisms, as certain considerations must be taken into account for the thickness of the prism.

Press-On Prisms

These prisms, also known as Fresnel prisms, are temporary and cost-effective as they are placed on the back surface of the lens and are not built into the lens. These prisms are made out of flexible vinyl and do not add any noticeable weight or thickness to the lens. It can be easily cut and placed on the lens in an adjustable way so that it’s easy to alter the prism, as needed.

Summary

Prism lenses can be extremely helpful for patients with low vision, allowing them to regain their clear vision and independence. It is important to see an eye doctor for a low vision eye exam and to receive a prescription customized to your daily needs. You can click here to schedule your low vision consultation Book an Appointment . Patients with low vision visit our clinic from all over Tennessee, and we are proud to be a leading provider of low vision services for patients from Hixson, Chattanooga, Cleveland, and Middle Valley.

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Testimonials

Vision therapy is well worth the response, time and effort. Our Son had a hard time focusing and writing neatly. After vision therapy Seth could complete a task in half the time if previously took. His abilities to focus improved greatly and so did his handwriting.

Also, he was better at listening. As a parent, we wanted learning to be fun for our Son, and vision therapy made this possible.

Amanda T.

Vision Therapy is well worth the expense, time and effort. Our son had a hard time focusing handwriting neatly. After vision therapy Seth could complete a task in half the time it previously took his abilities to focus and improved greatly and so did his handwriting.

Also, he was better at listening. As a parent you wanted learning to be fun for our son and vision therapy made this possible.

Alexa H.

Vision Therapy has given or son the tools he needs to be able to scan and read the written word more effectively and efficiently.

He love working with John and these working sessions give him the motivation to gladly work on his homework assignments.

It amazed us to see the difference in the tracking of his eyes and along a line of it's from the beginning to the end of the treatment.

Dr. McBryar , Kristen and John are all marvelous and we would recommend them to anyone I only wish that we would have found them sooner!

Charlotte M.

Prior to coming to the institute for vision development my son complained of daily headaches. Therapy has eliminated his headaches completely. I love knowing my son is able to learn pain-free for the rest of his life because of the work that has been done over just a few weeks in this office. He he absolutely loved coming that didn't even feel like going to a doctor or therapy. We are grateful for the relief he was able to find by coming here.

Thank you!

Olivia C.

Seems much less frustrated with life

Reads non-stop and fast

Spelling abilities have been hugely improved

Seems much more confident

Thank You!!!

Kelly O.

When we first came to the practice, my son did not have huge issues, but lots of small ones- trouble with reading, sports (hitting the baseball consistently), coordination, etc- that were not easily detectable,but when put together presented issues. The staff here were all very professional and loving towards him. While I was concerned in the reading, my son was concerned with the athletic side. Seeing improvement night off the bat gave him confidence that i have nor seen in him and made him want to not only Come to therapy, but also made him want to work hard. He has surpassed his grade level and above in reading and hit his first home run this year! Thank you!!!