Most often, changing a person's glasses will not improve their distance vision. This is because glasses are in focus on the retina, and in the case of a low vision patient, that part of the retina is not working and a more peripheral retina must be used to see properly.
To improve distance vision, patients can use hand-held telescopes that are demonstrated in (fig. A). These can be used for short-term viewing tasks such as traveling and needing to see signs.
These same telescopes can be miniaturized and mounted into a pair of glasses for more continued use such as when sitting in a classroom lecture hall and viewing chalkboards.(fig. B) In very limited cases, the bioptic or spectacle mounted telescope can be used for driving.
These are reading lenses or lens systems that allow a patient to read small print but require the reading material to be held very close to the eyes.
Often the simplest of devices such as standard hand held and stand magnifiers are the best solution for improving an individual's ability to use their remaining vision. Shown in the picture to the right is an array of common magnifiers that are used in the clinical setting. Most of these will have better optics and lighting than those purchased over-the-counter and more importantly will be correctly prescribed to the patient's acuity and demands of the task or activity being performed.
There are a number of electronic magnification systems, self-focusing telescopes and video displays with virtual reality mountings that can be very beneficial in helping individuals improve vision function. These prescribed devices are especially helpful in letting individuals maintain employment. A big asset to those who are visually impaired are the new and constantly improving video magnification systems.
They range from the standard closed-circuit television which allows someone to read printed material and do a variety of near tasks under high magnification, yet with comfort and proficiency (fig. A). Newer systems are designed so that someone views a magnified world through a video display mounted as glasses (like virtual reality glasses) as shown in fig. B. Our clinic is constantly updating the technology available for the visually impaired.
There are filters or sunglasses designed for the special needs of the visually impaired. These will allow individuals to function in brightly lit areas or dim areas where they are unable to use their vision at present. Special lamps and lighting is very important to the successful use of most prescribed devices.
Lighting is very important for all patients, no matter what the cause of vision loss. It is important to note that there can be too much light as well as too little light when it comes to maximizing visual performance. The appropriate amount of lighting and type of lighting (fig. A) will be evaluated in the clinical assessment as well as the need for filters and special sunglasses (fig. B).
In addition to the prescribing of optical systems for improving vision, the clinic has very special programs in working with individuals with severe peripheral field loss. Shown here is a new ophthalmic prism system which is incorporated into the patients prescription. This prism is placed so as to allow the patient to view peripheral objects much like using a side-view mirror in a car.
Our contact lens service works in conjunction with the low vision service to provide a variety of unique contact lens prescriptions. Special contacts are used with central occluders to prevent diplopia or double vision. Other contacts are used to create an artificial pupil to reduced sensitivity to light (photophobia).
In almost all cases it is important that the individual being prescribed an optical (or even non-optical) device be given some instruction in its use and care. More importantly, the instructional sessions make sure that the intended prescription, which is based on clinical data, actually works for the intended tasks. The instructional sessions with our low vision instructor will give the patient an opportunity to use the device to read the materials or perform activities they will be using at home instead of just reading some small print on a clinical chart.(fig. A) It will give the individual an opportunity to bring in the cross stitch project discontinued months back and work with the new optical prescription to see how practical it is before having to purchase the prescription. As with all new devices, the more one uses the device, the more proficient they will become. Our training sessions allow for this time to be spent with the device (or a simulated Rx) in more normal settings such as home and outdoors (fig. B). It is not until the doctor, instructor and patient are happy with the actual performance with the device, that it will be prescribed.
We cannot replace the eye or its normal functioning. Prescription devices allow an individual to perform specific tasks or activities. Patients will need to learn to use these systems properly and that is why training is provided in our clinic. The success of the rehabilitation program is totally dependent on the patient's participation and willingness to modify their lifestyle and accept performance limitations of their prescribed devices. While this may sound very negative, the positive side is that low vision prescription devices will allow the patient the opportunity to do things they would otherwise be unable to do.