Glaucoma can lead to variety of vision and functional issues for patients – not just peripheral vision loss, but also central vision loss, glare sensitivity, and contrast issues.  With this being the case, the key to helping glaucoma patients – and this holds true for all low-vision patients – is determining what functional problems they are facing. 

Below, we will discuss different spectacle options and how they can improve a patient’s daily functioning. 

Peripheral vision loss

If a patient with glaucoma diagnosis presents with peripheral vision loss, their main functional loss is mobility. Here are some of the lenses and visual aids we can use to help the patient:

• Expansion prism lenses. The expansion prism lens is similar to sector prisms in that they displace the image from the blind area into the sighted area. The difference is that the prisms are a thin horizontal band placed above (and sometimes below) the straight ahead position on the frame, but within the sighted field of view. This helps warn the patient when an object is on their blind side. Upon becoming aware, the patient shifts head position to see what is in the periphery. 

• Reverse telescopes. We think of telescopes, or binoculars, as devices to see at a distance. If we reverse the telescope, minification of objects occurs, but the visual field expands in direct proportion to the power of the scope. So, a 2x telescope in normal use magnifies objects 2x but reduces the visual field. When reversed, objects appear 2x smaller (and further away) but the visual field is 2x larger.

Based on their lifestyle, the patient would have the choice of bioptic or full diameter reverse telescopes.

In the bioptic form, the reverse scope is placed above the line of sight in the eyeglass frame. These can be useful for patients who require more visual field when entering a room. When the patient enters the room, they would lower their head to view through the bioptic and see a larger field to identify objects in their pathway.   They would then raise their head to proceed into the room, knowing what to avoid.

In the full diameter position, the reverse system would be centered and the patient would see a wider field consistently. Adjusting to seeing a wider field with objects appearing further away would require considerable learning time. The patient would always require an aide to hold on to until full compensation was completed. The risk of falling would be great since steps and other objects would not be where they appeared. Therefore, one should not prescribe such a device unless the patient understands the risks and has sufficient support in adapting to this new way of seeing.

• Sector prism glasses. Sector prism glasses incorporate high-degree prisms mounted on the lenses just to the side of the vision loss. These 10°, 15°, or 20° prisms are ground into the temporal side of one or both lenses. By scanning to the side, the prisms bring the periphery into sight for the patient to know what obstacles could present a risk. Because the prisms are located in the blind area of the visual field, the patient must learn to regularly look into the prism to see what is there. The prisms can be mounted on any plane, horizontal, vertical or oblique.

Sector prism lenses are useful for patients who do not want a reduction in the size of images. However, patients should be told that what is seen through the prism is a displaced image, so it will not be where it appears to be. Also, because the prism is placed outside of the visual field, there is no warning to the patient that an obstacle is present. Therefore, the patient must be instructed to regularly scan into the prism to detect obstacles.

Central vision loss

Central vision loss does not cause mobility issues but reduces the ability to see detail when driving, reading, or other fine tasks.  There are many spectacle options to help these patients, including the following:

• Microscope spectacles (high plus). High plus lenses, available up to 80 D, have a reduced focal distance and requires the patient to hold material closer which results in magnification. Patients using these spectacles must be willing and able to adapt to the closer reading distance of high-plus lenses.

• Prism readers. Prism readers (plus lenses from 4.00 D to 8.00 D with base in prism) are a good option for patients who have moderate and binocular central vision loss. However, even with these lenses, the patient must be willing and able to hold the material closer.

• Telescopic spectacles. Telescopic spectacles can be custom designed to fit the task requirements of the patient.

Bioptic telescopes are placed above the line of sight for tasks like reading signs and seeing traffic lights when driving. They are also useful for seeing other distance objects. I personally use them at sporting events to “zoom” in on the quarterback, for example. The prescription carrier lens below the telescope allows a full visual field to be seen. Bioptic telescopic spectacles require training and adapting. The patient should be advised that they can cause dizziness the first time they are used, though, fortunately, that symptom does not persist.

Full diameter telescopic spectacles are useful for patients who want to see the television better or better see facial expressions during conversations.

Reading telescopes (tele-microscopes) are focused and converged for magnified reading of small print. Patients must be advised to hold the material at the exact focal distance or blurring of the images will occur.

Glare control

There are two types of glare that are associated with vision loss, be it glaucoma or other vision conditions. These are: discomfort glare and disability glare. Discomfort glare can usually be reduced with a good pair of gray or brown sunglasses. Blue should never be used due to the high amount of UV allowed through the lens that can negatively affect the retina.

Disability glare, which renders the person immobile, usually requires severe reduction of light. Fit-overs (with side shields) that reduce up to 99% of illumination can be very helpful to these patients.

Contrast issues

Glaucoma and other vision loss conditions can cause loss of contrast sensitivity. Occasionally yellow or yellow/orange filters will help. Unfortunately, there aren’t good options for those with severe loss of contrast sensitivity. It is best to have demonstrators available for the patient to try outdoors during your evaluation, as the patient will know immediately what works for them.

Improving vision

Caring for a glaucoma patient (as well as any low vision patient) is ultimately about improving or restoring function to their sight. With the right spectacles, you can improve their mobility and restore some of their independence.  With the right care, you give the patient a new lease on life and make a huge difference to the patient and their family. OM

Dr. Shuldiner is clinical director of Low Vision Optometry of Southern California and president of the International Academy of Low Vision Specialists. He is also the founder of Shuldiner Low Vision Training Institute, more information for which can be found at www.Shuldiner LowVisionTrainingInstitute.com.