Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

Vision in context

Low vision: assessment, aids, and support 678

Visual impairment registration 680

Driving standards 681

Professional standards 683

678 CHAPTER 20 Vision in context

Low vision: assessment, aids, and support

In the United States, around 15–20% of elderly people over the age of 65 suffer from some visual disability. This represents 7.3 million individuals and will rapidly increase with the aging of the baby-boomer generation.

There is concern that there is a wide-scale lack of access to support and services for patients with visual disorders. It is probable that many of these people may never seek help. However, even those who get to an ophthalmologist may only be rewarded with a delayed diagnosis of an incurable eye disease for which “nothing can be done.”

In these circumstances, those involved in eye care must be aware of what can be done to optimize the patient’s remaining vision and how best to advise and assist the patient. This is often best coordinated in a low-vision aid (LVA) clinic, ideally with access to specialists, optometrists, rehabilitation workers, counselors, and social services.

Assessment

General—what are their concerns?

People are extremely variable in their needs. For some, the priority will be to continue to be able to read or solve the crossword puzzle, whereas others will be afraid of social isolation and lack of independence. Sometimes assessment will also reveal misunderstandings about their condition.

Specific—consider the following:

Reading

Is reading an issue for them? If so, what do they want to read—what size print and in what context (i.e., at home or out-and-about)? The answers to these questions will affect the type of optical devices used.

Television

If this is an issue for patients, consider size of the television, viewing distance, and whether it is standard color or HDTV (higher contrast).

Activities of daily living and recreation

Are patients managing to look after themselves (± dependents)? What about shopping, cooking, and hygiene? Can they still do their hobbies?

Mobility

Do they manage to get around? Do they have access to public transport or rides from family or friends?

Work and financial support

Do patients have the help they need to continue working if they wish to? What resources are available to them for equipment or personal assistance? Do they know how to access any benefits they are entitled to?

Psychosocial

Are they coping emotionally with their visual impairment? Do they have access to local support groups? Would they benefit from talking to a counselor?

LOW VISION: ASSESSMENT, AIDS, AND SUPPORT 679

Management

General

Optimize lighting conditions (e.g., brighter bulbs, more lights around the house, good reading light). Improve contrast whenever possible.

Registration

If patients are eligible but not yet registered, ensure that the purpose of registration is explained and that it is offered to them.

Support

Ensure that they have access to support from social services and local support groups and that they know how to get help when they need it.

Equipment

Refraction (near and distance) should be optimized. In addition, consider the following issues.

Optical devices (near)

•Reading glasses should be optimized, although they are often not sufficient on their own. Up to +4.00D is usually well tolerated but beyond this, the reading distance is uncomfortably short. Higher reading additions may require a prism to assist convergence.

•Hand magnifiers are usually practical and inexpensive but are limited by a small field of view (especially for the higher powers).

•Stand magnifiers have the advantage of keeping both hands free and keeping the working distance constant but are less transportable.

•Illuminated magnifiers improve contrast (provided that the batteries are charged), but are generally bulkier.

•Reading telescopes may be useful for specific near work because they have a greater working distance than that of reading glasses of an equivalent magnification. However, they are expensive and are unattractive.

•Closed-circuit television: excellent magnification with high contrast can be achieved with a television camera directed down onto reading material(s) and viewed on the adjacent screen. However, it is expensive, not portable, and generally superceded by computeror scanner-based technology.

Optical devices (distance)

•Distance telescopes can be useful for specific tasks, although generally they are limited by the small field of view. They may be spectacle mounted (useful for static tasks, e.g., watching television, theater, music, sports) or hand-held (used as required, e.g., bus number, direction signs).

Computers and other nonoptical devices

Personal computers (with enlarged text or speech facility) have made a spectacular difference in the lives of many visually impaired people. They provide an easy method of writing, reading (with scanner and optical character recognition) and instant letter communication by e-mail. Web-based facilities also increase access to shopping, entertainment, and support.

Other devices include talking watches and clocks, writing guides, liquidlevel indicators (to prevent overfilling cups), tactile controls on domestic appliances, talking scales, and modified games (e.g., large playing cards).

680 CHAPTER 20 Vision in context

Visual impairment registration

Registration of visual impairment has traditionally had three roles: to formally recognize an individual’s vision loss; to identify those patients eligible for assistance due to their disability; and to help eye services, social services, and governmental organizations know the extent and distribution of visual impairment in the community.

However, a recent review showed that for many people the registration process actually excluded or delayed access to services. More than half of those eligible choose not to be registered, and many are unhappy about being registered blind when they have (and are expected to continue to have) residual vision.

DRIVING STANDARDS 681

Driving standards

Evidence that visual impairment alone causes automobile accidents is surprisingly scarce. The strictness of driving standards varies internationally; this is in part affected by the density of traffic and driving conditions. In some parts of the United States, partially sighted people may drive during daylight hours within a specified radius of their home.

Visual acuity

For Class C vehicle drivers

•20/40 when both eyes are tested together.

•20/40 in one eye.

•20/70, at least in the other eye.

•Uninterrupted visual field of at least 100 degrees in the horizontal meridian.

Commercial vehicle drivers

•At least 20/30 in the better eye AND

•At least 20/40 in the worse eye AND

•Uncorrected acuity in each eye must be at least 20/400

Some drivers who fail these requirements may be permitted to drive under “grandfather rights,” which take into account the initial date of the driver’s license. The license holder needs to contact the Department of Motor Vehicles (DMV), which will require a certificate of recent driving experience and confirmation of no eyesight-related road accidents in the previous 10 years.

Visual fields

The preferred method of testing is the Humphrey visual field. For those patients who cannot use an automated perimeter, Goldmann testing is acceptable in exceptional circumstances. A maximum of 20% false positives and of three attempts for each test is allowed.

Class C license drivers

•At least 120 feet on the horizontal (Goldmann III4e setting or equivalent) AND

•No significant defect in the binocular field encroaching within 20 feet of fixation above or below the horizontal meridian. “Insignificant” central defects (equivalent to the normal blind spot in a monocular field) comprise

•Scattered single missed points.

•A single cluster of 2 or 3 missed points.

When a patient has fully adapted to a static, longstanding defect, the DMV may consider them an “exceptional case” and perform a practical driving assessment.

Commercial drivers

•Full binocular field of vision.

•No missed points in the central 20 feet.

682 CHAPTER 20 Vision in context

Other

These patients should inform the DMV of their condition.

Monocularity

Patients may drive (Class C vehicles only) when clinically advised that they have adapted to the disability and they satisfy the usual visual acuity requirements and have a normal monocular visual field.

Diplopia

Patients with uncorrected diplopia must not drive. Driving may be resumed if it is controlled; patching is acceptable subject to the above constraints on monocularity. Very rarely, the DMV may permit someone to drive despite uncorrected diplopia if it is stable (>6 months).

Blepharospasm

Patients with severe blepharospasm must not drive. Patients with mild, successfully treated blepharospasm may drive subject to physician approval.

All drivers

If patients fail to reach these standards, they must not drive, and they have a legal requirement to notify the DMV. Failure to comply is a criminal offense and can result in a fine or loss of license.

PROFESSIONAL STANDARDS 683

Professional standards

Pilots (civil aviation authority)

Class 1 pilots (commercial: airplane and helicopter)

Visual acuity

•Distance: at least 20/30 in each eye and 20/20 with both eyes together (best corrected).

•Near: at least N5 at 30–50 cm and N14 at 100 cm (best corrected).

Refractive error and correction

•Refractive error less than +5.0D or –5.0D and anisometropia <2.0D.

•Contact lenses may be used if they can be reliably used for >8 hours/day.

•Refractive surgery: stability of refraction must be demonstrated; usually pilots are unable to fly for 3 months post-LASIK and 1 year after

other procedures. Preoperative refractive error may still be a bar to qualification (see above).

Color

•Satisfactory Ishihara testing is required; if patients fail this then they must pass the Lantern test.

Other

•Normal visual fields.

•No diplopia.

Class 2 pilots (private: airplane and helicopter)

Visual acuity

•Distance: at least 20/40 in each eye and 20/20 with both eyes together (best corrected); amblyopes with 20/60 in one eye may be permitted to fly, provided the other eye is at least 20/20 uncorrected.

•Near: at least N5 at 30–50 cm and N14 at 100 cm (best corrected).

Refractive error and correction

•Refractive error less than +5.0D or –8.0D (in the most ametropic meridian) and anisometropia <3.0D.

•Contact lenses may be used if they can be reliably used for >8 hours/day.

•Refractive surgery: stability of refraction must be demonstrated; usually the pilot is unable to fly for 3 months post-LASIK and 1 year after other procedures; preoperative refractive error may still be a bar to qualification (see above).

Perioperative care

Preoperative assessment (1) 686

Preoperative assessment (2) 688

Ocular anesthesia (1) 690

Ocular anesthesia (2) 692

Treatment of anaphylaxis 693