Low Vision and Vision aids

If you have suffered an uncorrectable vision loss-- dwelling in the past other than to learn from it, can be a waste of time and energy. If you have suffered a vision loss-- dwelling on the future except to prepare for it can be counter- productive. The time to do something is NOW.

You have undoubtedly pondered, consciously or subconsciously, upon a miracle cure which would restore your sight. So too, are your doctors and researchers working toward those cures. Millions of dollars are being spent on pharmaceutical and surgical studies. More millions are spent on bio-technologies aimed at producing cures for macular degeneration

, diabetic retinopathy glaucoma, retinitis pigmentosa and other robbers of precious sight. Such miracles as retina transplants, stem cell implants and other exotic cures are in the offing, but realistically they are not around the corner. In truth, most may be several years down the road.

For you, as a partially sighted person, that means that you must use the gift of the present to prepare for future breakthroughs. "Use it or lose it" was never more applicable than in conditions of low vision or partial sightedness. Low Vision Therapy is the art and science of rehabilitating the partially sighted individual. Such therapy embraces the following entities to improve sight: Special illumination, magnification, contrast sensitivity enhancement, eccentric viewing, field enhancers, electronic vision enhancement, computerized vision enhancement and a myriad of non-optical devices which can make life more enjoyable. In many cases Low Vision Aids restore a state of independence for near vision tasks (e.g., reading abilities), distance vision skills (e.g., distinguishing/recognizing faces; ability to drive and see traffic signals, etc.), and mobility and community skills (e.g., ability to go shopping, perform job, etc.).

In this section we provide background information on low vision, blindness, and vision rehabilitation services.

Definitions of Low Vision and Blindness

There is no universal consensus on the definitions for low vision and blindness. In its broadest sense, low vision can be defined as any visual impairment that results in disability and that cannot be corrected medically, surgically, or with conventional eyeglasses. ICD-9-CM defines low vision and blindness using standard measures of visual acuity

and visual field diameter (see Table below) - also see AgingEye in the US

for definitions for low vision and blindness.

The threshold criteria that define an individual as having low vision are an uncorrectable and irreversible visual acuity of less than 20/60 in the better seeing eye. Best vision should be less than 20/60 in both eyes. If one eye has vision less than 20/60 but the other eye can see better than 20/60, then the individual is not considered to have low vision.

Visual acuity 20/60 is the minimum acuity required to read standard newspaper print

In the U.S., the threshold for a diagnosis of low vision is often considered to be a visual acuity of less than 20/40 in the better seeing eye. The use of this higher visual acuity in the definition of low vision is based on the fact that a visual acuity of 20/40 in the better seeing eye is the criterion used by many states for the provision of an unrestricted driver’s license. Many experts contend that this latter threshold (20/40), without other limitations in visual functioning, is an inappropriate threshold with which to define low vision. It is argued that aside from the limitation of being unable to drive, individuals with 20/40 visual acuity rarely suffer significant reductions in their ability to perform other functions and are, therefore, unlikely to be candidates for vision rehabilitation services. This opinion is mirrored by a recent Medicare Program Memorandum (Appendix) that states that, in the absence of visual field disturbance, individuals will not meet Medicare’s suggested medical necessity requirements unless their visual acuity is less than 20/60 in the better seeing eye.

Individuals who meet the ICD-9-CM criteria for severe visual impairment (a visual acuity of 20/200 or less or a visual field of 20 degrees or less in the better seeing eye) meet the minimum requirement for classification as legally blind in the U.S., and are, therefore, entitled to disability benefits. The terms “severe visual impairment” and “profound visual impairment” are preferred by the American Academy of Ophthalmology (AAO) to the term “legal blindness” for the purposes of classifying individuals with low vision and blindness because the former terms more accurately reflect the fact that some residual vision remains in patients with these degrees of vision loss. AAO suggests that, in the context of vision rehabilitation, the term “blindness” be reserved for those individuals with no residual vision at all in the better seeing eye (i.e. complete blindness).

Recognizing that the definitions for low vision and blindness do not encompass all patients with uncorrectable and irreversible visual impairment severe enough to limit an individual’s daily activities and functioning, Medicare has suggested that individuals with the following visual field “disturbances” should also be considered eligible for vision rehabilitation services: a central scotoma in the better seeing eye, generalized contraction or constriction of the visual field in the better seeing eye, homonymous bilateral visual field defects or heteronymous bilateral visual field defects.

Causes of Low Vision and Blindness

Low vision and blindness are not caused by a single disease. Rather, they can result from a plethora of different ophthalmologic and neurological disorders. These disorders include, but are not limited to, age-related macular degeneration (AMD)

, glaucoma

, cataract

, diabetic retinopathy, central retinal vein occlusion (CRVO), retinitis pigemtosa, corneal damage, stroke, atherosclerosis, temporal arteritis, trauma, and tumors. By far the most prominent pathologies underlying low vision and blindness among the elderly Medicare population are age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy. The impact of each of these latter eye diseases on functional vision is summarized in Table 2.

Another common cause of visual impairment among the elderly is cataract. In most cases, however, vision impairment resulting from cataract can usually be successfully corrected through the surgical removal of the cataractous lens. As a consequence individuals with visual impairment resulting from cataract do not meet current definitions for low vision or blindness (irreversible and uncorrectable visual impairment) and will not usually be considered candidates for vision rehabilitation services.

Vision Rehabilitation Services

Vision rehabilitation services aim to maximize the use of any residual vision that an individual might have and provide practical adaptations that reduce the disabilities associated with low vision or blindness. The desired outcome for those who enter a vision rehabilitation program is that they will attain the maximum function of any residual vision that they may have, increase their level of functional ability, increase their degree of independence, and, as a consequence, experience an improvement in their quality of life. Comprehensive vision rehabilitation services are interdisciplinary. Most vision rehabilitation programs provide access to a number of different vision rehabilitation personnel. These personnel include both licensed (ophthalmologists, optometrists, occupational therapists, psychologists and counselors, and social workers) and unlicensed personnel (low-vision therapists, vision rehabilitation teachers, and orientation and mobility specialists).

Two Examples of Comprehensive Vision Rehabilitation Services in the US

• Department of Veterans Affairs Blind Rehabilitation Centers (VA BRC) program. (VA Website

)

The VA BRC program provides rehabilitation services to veterans who are legally blind (visual acuity worse than 20/200 or a visual field worse than 20 degrees). The VA BRC system is an intensive, highly structured, rehabilitation service. Enrolled veterans are admitted as inpatients. Length of stay in the center depends on individual circumstances but can be several months. During their stay at the center, each patient participates in rehabilitation activities consisting of seven 50 minute sessions, five days per week. Rehabilitation services include: orientation and mobility instruction, communication skills instruction, activities of daily living training, manual skills training, vision skills training, computer access training, physical conditioning and recreation, and counseling.

All rehabilitation departments and clinical providers within the VA BRC program contribute to an individualized interdisciplinary plan of care that is cosigned by the team coordinator (usually an orientation and mobility specialist, a rehabilitation teacher or a low-vision therapist), an optometrist, a psychologist, a geriatric physician/nurse practitioner, and a social worker. The interdisciplinary plan of care is updated throughout each veteran’s program. Orientation and mobility specialists, vision rehabiltation teachers, and low-vision therapists are not directly supervised by a Medicare-defined physician in this program. However, clinical direction is provided by an optometrist (a Medicare-defined physician) through the rehabilitation plan that prescribes any low-vision devices that are to be integrated in the veteran’s rehabilitation program and the general approach to training that should be provided by low-vision therapists.

• Department of Veterans Affairs (VA) Visual Impairment Centers to Optimize Remaining Sight (VICTORS) program. (VA Website

)

The VA VICTORS program differs from the VA BRC program in that it provides rehabilitation services to veterans who are not legally blind but who have a disabling visual impairment (defined by the VA as an uncorrectable visual acuity of worse than 20/50, near VA worse than 20/50, or significant loss of visual field). VA VICTORS services, though comprehensive in that they are staffed by a multidisciplinary team, differ from the services provided by the VA BRC program in that they are geared toward individuals with low vision who are not legally blind. As such, they are less intensive than VA BRC services. Also, orientation and mobility services and rehabilitation teaching are not provided by the VA VICTORS program.

Patients with low vision are typically admitted to a VICTORS unit for a period of three to five days. Services available to the veteran enrolled in the VICTORS program are similar to those offered to those enrolled in the BRC program. However, an emphasis is placed on learning how to use assistive devices in order to maximize residual vision. Consequently, in this program, clinical management is closely supervised by on optometrist who prescribes low-vision aids and instructs low-vision trainers on the types of training that the veteran with low vision requires.

Near Vision Tasks (reading)

Although reading is the activity most often mentioned by low vision patients, one should not forget that some patients never read much and that over-emphasis on reading will only frustrate them. Reading is often thought of as a substitute for all near-activities, but not all of these activities have the same visual requirements. Writing can be done with a felt-tipped pen and in letters that are much larger than newsprint. Thus, for writing tasks patients may be happier with a less extreme reading add then is needed for reading. A pair of +6 half-eye glasses with base-in prism often is satisfactory and leaves enough room (about 6 in, 16 cm) to manipulate a pen.

For reading of newsprint (1 M) more magnification may be needed. Kestenbaum's rule states that the reciprocal of the visual acuity indicates the minimum number of diopters needed. Thus, a patient with 20/100 (1/5) needs at least 5 diopters; a patient with 20/200 (1/10) needs at least 10 diopters. Some extra power often results in a higher reading speed, but also requires a closer reading distance, to which many patients will object, at least initially.

Placing the required lens power in reading glasses will result in the widest field of view and the most effective use of that power. However, the short reading distance also requires attention to an adjustable light source. When the lens is moved away from the eye, it is called a magnifier. Usually magnifiers require some additional dioptric power. Handheld magnifiers are small and easily carried around. Stand magnifiers are bulkier, but often can have built-in illumination, which is an advantage, unless the batteries run out. Newer LED light sources provide more light for less battery power.

Electronic video-magnifiers are usually not portable, but offer the advantages of binocular viewing, more postural freedom and enhanced contrast, while the magnification can be varied to suit the requirements of a particular type of print. Some newer models can also be semi-portable.

(REFERENCE: Colenbrander A et al. Vision rehabilitation and AMD. Int Ophthalmol Clin. 2007 Winter;47(1):139-48)

Distance Vision Tasks (Driving)

For most people, their ability to drive is an essential symbol of their independence. Because most North American cities have developed around the use of the automobile, it also is a necessity for shopping and to maintain social contacts.

Some patients will require the use of bi-optic telescopes to drive. The telescopes are mounted in the top of the carrier lens, usually over the better eye. Bi-optic telescopes can be brought into the line of sight to read a road sign.

Drivers with vision impairement can increase their safety margin by restricting their driving to familiar surroundings, where orientation is by landmarks, rather than by reading street signs, and where they know which intersections have traffic lights, so that they can search until they have detected the light. Another strategy to increase their safety margin is to avoid driving after dark, at times of peak traffic, and under adverse conditions.

(REFERENCE: Colenbrander A et al. Vision rehabilitation and AMD. Int Ophthalmol Clin. 2007 Winter;47(1):139-48)

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