Low Vision Care: An Overview

Low vision patients are the most under-treated, under-referred and generally overlooked patients in many eyecare practices. With the current growth in the elderly population, this may be a perfect time to re-evaluate your approach to this ever-expanding group of patients.

Classically, low vision patients are thought of as patients with an irreversible vision loss, usually beyond the 6/18 level in the better eye. This 6/18 acuity level is a somewhat arbitrary point, chosen because this is the acuity level below which patients begin having increased difficulty reading newspaper print, utility bills, medicine bottle labels, bank statements, food package labels and so many other simple tasks that are required in order to maintain one�s independence.

While it is certainly true that the vast majority of low vision patients suffer from either macular degeneration or diabetic retinopathy, another very important group of patients who should never be overlooked are those with a temporary and often reversible loss of vision. Examples include various keratopathies, severe oedema, etc. Low vision services are also extremely helpful while patients are awaiting surgical procedures such as cataract removal and cornea transplants.

DEMOGRAPHICS

Various experts estimate that the low vision population in the US ranges between 10 and 22 million (7% to 8.5%) when one also includes non-traditional low vision patients, such as those with reversible vision loss or those awaiting surgery. By the age of 65, vision loss beyond the 6/18 level is the third most common ailment, exceeded only by heart disease and arthritis. By the eighth decade, the majority of patients suffer from some level of irreversible vision loss. These patients are at extremely high risk for injury and loss of independence secondary to their vision loss.

It is important to note that the fastest growing segment of the US population today is the 55 and older age group. Finally, this same 55 and older age group has the largest discretionary disposable income of any segment of the population. They represent the patients in a practice whose house is paid for, children are grown, and they have very little overall consumer debt to manage. From this information, we can certainly conclude that the number of low vision patients will continue to increase and, regardless of health service funding issues, they often can afford the devices and services that will assist them in maintaining their independence. You can be certain that as baby boomers enter their later years, they will seek out and demand every possible option available, should they be faced with loss of independence.

LOW VISION REHABILITATION

In the very simplest sense, low vision rehabilitation involves manipulating three basic ingredients: appropriate lighting or glare control, appropriate levels of magnification and, finally, training patients to use their remaining vision more effectively. It is important to have patients set very specific, measurable and realistic visual goals. The more specific the task goal, the more likely that you will be able to help your patients achieve those goals. This is because all low vision aids tend to be somewhat one-dimensional. So a device that helps a patient read a price tag or menu won�t be helpful for reading street signs. Conversely, a spotting telescope will help identify distance objects, but makes a very poor choice for reading and close work. Of course, a patient who has a goal of “just seeing better” is often less satisfied with low vision aids, because they are really asking the practitioner to fix the underlying pathology. In many cases, blaming poor motivation on the part of the patient is the easiest excuse for poor performance by the patient.

LIGHTING AND GLARE CONTROL

Appropriate lighting is often the least expensive, yet most helpful low vision aid for patients with measurable vision loss. Clinical experience indicates that with mild vision loss (6/15 to 6/24), appropriate lighting may be the only low vision aid necessary to help a patient with many of their near-point goals. Studies indicate that low vision patients often require as much as five times more illumination to accomplish various tasks when compared to age-matched normally sighted patients. Unfortunately, glare is also a major problem which most of these patients complain about. This is the reason that most patients don�t normally benefit from just replacing lamp bulbs with a bulb of higher wattage levels.

Several of the low vision product manufacturers have developed very specific task lamps and bulbs for low vision patients. In clinical practice, these lamps have proven to be well worth the relatively low cost to patients. An alternate lighting suggestion which is often very helpful is to have your patient purchase an Anglepoise type task lamp at an office supply store. The lamp should be equipped with a simple 50 watt reflector flood light bulb similar to the type used in track lighting in homes and offices. Adjustable task lamps allow patients to aim the flood light bulb to minimize reflected glare. Above all, be specific in your recommendations. My experience has been, if you simply tell patients they need brighter lighting, very few will take your advice. However, if you tell a patient to get a very specific type of lamp and bulb, they are much more likely to comply with your instructions.

Glare control, both indoors and outdoors, is an issue common for almost all low vision patients, regardless of the underlying pathology.

In addition to the glare sensitivity that patients often complain of, we can almost always document a loss of contrast sensitivity. Contrast sensitivity loss is an area that can best be addressed by prescribing one of the contrast enhancing tints. This family of tints has the unique ability to reduce glare while enhancing contrast appreciation. Various low vision aid manufacturers such as Corning, Eschenbach, and NoIR carry such tints and can supply your practice with supporting guidelines and recommendations for prescribing.

MAGNIFICATION LEVEL

In low vision rehabilitation, we are rarely able to make images sharper or clearer for the patient. I often communicate this somewhat foreign concept to our clinic patients by using an analogy of a camera with a damaged roll of film. No matter how carefully we focus our “camera”, the clarity of the photograph is ultimately controlled by the condition of our film and not the strength or focus of the lens. Instead of sharpening an image, our job is to make the image large enough to identify, despite the blur. Determining the level of magnification needed to accomplish a patient’s visual goal is based on the level of best corrected vision versus the acuity demand of the visual goal. For instance, if the best corrected vision is about 6/60 and the task goal is newsprint (about 6/15), we will need a minimum of 4x enlargement. Various continuing education courses can give the practitioner additional, more sophisticated methods of determining appropriate levels of magnification for prescribing low vision aids based on a patient’s specific visual goals.

Once the level of magnification is determined and verified through clinical testing, the type of low vision aid which may be appropriate becomes much less mysterious. As a general philosophy, simple hand-held magnifiers are most helpful for very short-term tasks such as reading a price tag, medicine bottle label, or a menu. Tasks which require reading for longer periods of time are better achieved with stand-type magnifiers or specially prescribed reading glasses. Another treatment strategy which is very effective is to combine magnification. This requires using spectacles for a portion of the magnification and a secondary device to augment the visual performance for even more demanding tasks. An example of this would be helping patients to write checks and pay bills. Clinical studies indicate that it takes about half the level of magnification for a patient to write as it does to read printed materials. This makes good common sense as few of us write as small as the size of type used in most of the mail we receive everyday. Therefore, we can adjust the level of magnification such that a patient can write adequately under good lighting. Then we can provide an additional magnifier to combine with the reading glasses to provide the total magnification necessary to read the bills. The reason that combining magnification is a good strategy is that it allows a patient to hold things slightly further away from the face as compared to prescribing eyeglasses with 100% of the indicated magnification for the more demanding task. If a visual goal requires identifying details at a greater distance, such as reading addresses or bus destination signs, a hand-held spotting telescope will often provide a workable solution to your patient’s needs.

Don’t overlook the probability that you will be recommending multiple low vision aids if the patient has multiple visual goals. Even in a case where the vision loss is reversible, it is not uncommon to have patients require special lighting, glare control glasses and various types of magnification if they are to continue to maintain a reasonable level of independence.

PATIENT TRAINING

Unfortunately, simply counseling a patient about lighting and providing appropriate optical devices based on the visual demand is rarely enough to help many low vision patients achieve functional success at work, or in their homes. This is due to a host of factors including metamorphopsia, the size, location and density of scotomas, as well as the length of time since the patient was able to read continuous text. Another important, but often overlooked factor, is the eye that was dominant prior to the vision loss. If the non-dominant eye becomes the better seeing eye, patients often need to be trained to use this eye more effectively. Additional factors that cannot be overlooked are the patient�s level of motivation, cognitive skills, and additional physical problems. As challenging as the training aspects can be, training is without doubt the ingredient that converts optical success into functional success for most of your patients.

SUMMARY

We all know of the ethical and moral obligations we have to our patients. Low vision rehabilitation represents another option you need to consider when formulating a comprehensive treatment plan. Whether a patient suffers from an irreversible vision loss from AMD or diabetes, or a temporary and reversible loss, we have an obligation to include everything possible to help our patients maintain their maximum visual potential throughout their lives. Until the day comes when we can immediately fix all of our patient’s visual problems, don’t fail to ask yourself the big three questions – “Can it be bigger?”, “Can it be brighter?” and, finally, “How can I teach the patient to use the vision they have now better?” Rather than telling your patients, “Nothing more can be done”, you have an obligation to offer them low vision services or refer them to someone who does. For some patients, low vision care is a lifeline.

Thomas Porter is the Director of the Low Vision Service at St Louis University, Department of Ophthalmology, St Louis, Missouri, USA.

One Comment

  1. hi i will like to ask
    - all yellow lemon lens was suitable to all low vision patient ??
    or must be polarize ???

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