Low Vision Spectacles
Low vision spectacles are high plus aids used in conjunction with the patients’ distance prescription. They include bifocals, prismatic spectacles, aspheric lenticulars, microscopic doublets, and clip-on loupes. Patients typically request spectacles as their first form of correction because they’re socially acceptable and allow your hands to be free to hold reading material. They come in a wide range of power, are easy to use and have a wide field of view. Unfortunately in higher powers, they do require a closer working distance, and as reading material becomes closer, the field of view will decrease.
Because of this, they may not be helpful for patients who reject a closer working distance or patients with hand tremors who cannot hold the reading material steady.
Low vision spectacles are typically prescribed for patients who have difficulty reading standard print. Their acuity can range from 20/40 to 20/800, but ideally, they should be used for patients with 20/400 or better. Patients who are able to hold reading material closer and are not rejecting a closer working distance. Lower powered glasses are helpful for reading, writing and using the computer, but higher powered lenses are better for less visually demanding tasks such as reading the mail, reading price tags, menus or identifying money.
Prismatic spectacles range in power from plus 4 to plus 12 diopters and include base in prism in both eyes to help the patients converge easily. The prism power is typically two more than the dioptric power of the spectacle so a plus 10 prismatic spectacle will have 12 diopters base in both eyes for a total of 24 prism diopters. For powers higher than a 12 we would use a monocular aspheric lenticular, microscopic doublet, or clip-on loupe as patients cant typically fuse binocularly at the higher powers. Most first-time low vision patients will come to the examination expecting a strong pair of glasses that will meet all of their visual needs. This is almost never the case. While low vision glasses can address some of their visual needs, patients will need to learn to use them differently than standard glasses.
Spectacles Tips and Tricks
- Most patients are initially resistant to the changes needed to read and function using low vision spectacles but with patience, practice, and instruction, they will come to realize they can improve their functional vision using the low vision devices as long as they’re willing to make the changes necessary to use the devices.
Low vision spectacles are high plus lenses used for reading, writing and hobbies. Because they are stronger lenses, they require a much closer working distance than standard spectacles. Most patients will initially resist this closer working distance. One trick is to encourage your patient to touch their nose with the reading material and slowly bring it away until the words become focused. Once they maintain the correct focal point, you can instruct them on how to properly use the glasses. Have them move the reading material from side to side instead of moving their eyes or head to help them maintain the working distance and avoid visual distortions. By moving your head, your eyes shift position and your changing the working distance. Even slight changes with strong lenses can cause blur and distortion. Another challenge a patient may experience is moving line to line without losing their place. One trick is to have them read the sentence to the end, trace it backward and then move down to continue to read on the next line. Patients can also use a typoscope to help them keep their place. Place the typoscope over the reading material to isolate a single line. Move the typoscope to the end of the line to continue reading. Trace the line backwards and move down to avoid losing your place. This can help also with glare and visual distortions that may be caused by too much information on a page. Another trick to learn to read with high powered spectacles is to hold your thumb at the beginning of the sentence. Have the patient read to the end of the sentence, then trace that sentence backward until you see your thumb and then move down to the following line. When reading columns it can be helpful to draw a dark line down the center of the page to isolate the column. Have the patient read across, when they get to the dark line they know to trace the sentence backwards and move down. You can also fold the page to reveal one column at a time so the patient knows where the text will end. Trace the sentence backwards, get to your thumb and then drop down to continue reading.
Using a clipboard or lap desk can help to maintain posture and keep reading material at the proper distance. Remember lighting is also critical. Most glasses will not come with a built-in light source although some do. Using a gooseneck lamp with the light angled over the patients’ left shoulder and directly on the page will help avoid glare. Writing with spectacles is generally easier than reading and does not require the same amount of magnification. Have your patient try writing using a lower-powered spectacle which will offer a further working distance. Using a lap desk, bold lined paper, and a felt-tipped pen can also make writing easier. “Remember the working distance is still critical when writing so stress for the patient to get closer to the page until the image becomes clear while writing.