Visual rehabilitation with low vision magnifiers has been the mainstay of treatment for patients with advanced dry macular degeneration, diabetic retinopathy, and retinal vein occlusions.13
Patients with these diseases have a decreased ability to carry out activities of daily living including reading, writing, and grooming which in turn causes a deterioration in their QOL.
Currently there are many nonsurgical options for visual rehabilitation, some examples are: hand/stand magnifiers, spectacles, hand held telescopes, closed circuit televisions, and high plus spectacles in conjunction with high minus contact lenses to create a telescopic effect. Although these tools maybe effective for correcting overall visual functioning, there are several limitations especially when correcting distance and near acuity.
In order to obtain effective magnification, patients have to bring objects closer to the eye to increase the angle of resolution. In addition to moving objects closer, these devices are cumbersome to use, they are cosmetically burdensome, and most of all, these external devices restrict effective field of view. The majority of these magnifying devices have a restricted field-of-view and have to be manually scanned across the text, magnifying only a small portion at a time. In all cases, the scanning is slow and limits the usefulness of the device. Patients are also required to use head movements or hand movements more often than using natural eye movements to scan which results in vestibular-ocular conflict and motion sickness. Furthermore, patients afflicted with arthritis, Parkinson’s disease or other neuromuscular disorders, or dementia, among others, will have difficulty maneuvering these devices in a useful way. Despite all this, patients are willing to try anything for a chance of better vision, no matter how difficult and burdensome these devices may be.
In addition to the hand-held and stand magnifiers, spectacle- mounted telescopes are a great alternative. They not only provide good magnification but also allow using eye movements to a limited field of fixation. The drawback of these devices is that they are very dependent on vertex distance. For example, Nguyen et al reported fields from 5° to 11° for varying telescopes set at 10 mm from the cornea.14
Bailey reported for a 3.0× spectacle-mounted telescope a field-of-view of 11° for the Galilean design and 14° for the Keplerian design.15
With such a narrow field, navigation in the visual environment is difficult and may be dangerous. Patients are forced to use head scanning to cover a wider angle through the telescope.
The limitations on the field-of-fixation are even more severe with the combined IOL/spectacle telescopic (or contact lens/spectacle) system. With this device, the field-of-fixation was computed to be only between 1° and 5° depending on lens design and vertex distance.14
For distance vision, the choice is limited to telescopes, headset devices, and closed circuit televisions, all of which have a high cost/benefit ratio and generally lead to patient frustration and abandoning of the device.15
However, for many years, low-vision magnifiers have provided patients with an opportunity to enhance their existing vision with the goal to improving their QOL. Furthermore, this was an attractive option as a noninvasive way for patients to avoid surgery and have the opportunity to gain vision and until recently, this was the only option available. Current research and development are aiming at ways to utilize the natural eye and visual system to augment the parts of the patient’s architecture with normal function. The future of low magnifiers now includes devices that can be implanted in the eye, improving the field of magnification and ease of use.