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Vision Screening.

All children, regardless of their disability, deserve to have the opportunity to develop to their full potential. Vision is an important part of the developmental process. Children with disabilities, especially those with genetic syndromes, who are at risk for eye problems, should be seen by a qualified eye care professional. Other children should be screened for eye problems just as any child would be.

Children should be screened for problems with visual acuity (clearness of vision), cataracts, tumors, and other problems. Children with autism seem to be at a higher risk for nearsightedness. Children with genetic syndromes are at higher risk for many eye disorders and should be carefully watched by an eye care professional.

Strabismus, or a misalignment of the eyes, and other problems that are correctable with glasses are the most common causes of amblyopia (lazy eye). Because strabismus affects so many children with disabilities, parents should find out whether their children may be at risk for it, and therefore indirectly at risk for developing amblyopia. Risk factors for strabismus include:

* low birth weight,

* prematurity,

* hyperopia (farsightedness),

* anisometropia (a need for a different correction in each eye),

* a family history of strabismus,

* neurological deficits such as cerebral palsy, and

* some genetic syndromes such as Down syndrome.

Screening methods

Screening is a preliminary testing method that identifies children who are at high risk of having visual problems. Screenings may be conducted by primary care providers, school nurses, or organizations like the Lions Club. Unfortunately, many eye problems are not detected until the child reaches school age. There is no reason to wait this long, and there are many reasons not to! Young children learn by exploring their environment. Vision is critical to this process, and children should be screened as early as possible to ensure that they do not miss out on this important and exciting stage of development.

The most frequently used tool to screen for visual acuity is the Allen chart. This is the chart with the large capital E at the top followed by rows of increasingly smaller letters. Younger and pre-literate children are tested with the Snellen chart, which substitutes pictures of common objects, such as a house or apple, for letters. The LEA test, a newly developed test which can be used to screen children as young as 2 years of age, screens for acuity at close range using symbols on a chart or cards. There are also LEA charts and cards for testing distance vision. These screening methods all rely on the child's ability to communicate.

The Bruckner test uses a bright light to test the retinal and corneal reflexes (reaction to light) in both eyes at the same time. This test can detect strabismus, anisometropia, and changes in the eyes that would indicate the presence of tumors, cataracts, or other anatomical abnormalities. There are several devices available that use the Bruckner methodology.

* The MTI PhotoScreener uses black and white Polaroid film. The examiner takes the child's picture from a defined distance, and the images are interpreted on-site or can be mailed or electronically transferred to a centralized location for analysis by an eye care professional.

* The iScreen system uses digital images that are transferred to a centralized location via the Internet.

* The Welch-Allyn system provides information on acuity but no information on strabismus or pupil opacity (tumor or cataract).

* The EyeDx system uses pictures taken with a digital camera and analyzed by a software program. The program generates an instant report, indicating whether or not the child should be referred to an ocular specialist.

These screening methods do not require the child to interpret a vision chart, providing a good screening alternative for children who are non-readers and/or who are non-verbal.

A trained screener may also use a penlight or a colorful toy to test muscle coordination and tracking. They will note whether the child's eyes can move in all directions and whether they can cross the midline. This test, called Fix and Follow, picks up problems that the static tests listed above cannot detect. Primary care physicians, nurses, physical and occupational therapists, and some early childhood education specialists may incorporate this test in their screenings.

The eye care specialist

Once a child has been identified as having the potential to develop visual problems, he or she should be referred to an eye care specialist for a more complete evaluation. The choice of specialist depends on the type of evaluation needed. A child who has visual acuity problems can be seen by an optometrist and fitted for glasses. Optometrists are not MDs, however, and cannot prescribe medication or perform surgery. If the child's needs are more complex than the optometrist is trained to handle, me child should be referred to an ophthalmologist for further evaluation. The ophthalmologist is an MD trained to handle the entire spectrum of eye care.

When choosing an eye care specialist, be proactive. Call in advance and be very candid about your child's disability and special needs. Ask if the specialist will be comfortable treating your child. The specialist you choose should be willing to take the time educating you about your child's vision. They should explain all the treatment options clearly and should not limit the options offered because of your child's disability or cognitive level.

Evaluation methods used by specialists

The specialist has an arsenal of tests that will detect and diagnose the full spectrum of eye problems. Unless indicated, a pediatrician, optometrist, or ophthalmologist can perform these tests.

The optokinetic nystagmus test uses a black-and-white striped cylinder called the optokinetic nystagmus drum (OKN drum). The drum is spun and moved slowly away from the child. The tester watches the movement of the eyes as the child watches the moving, spinning drum. The accuracy of the OKN is highly dependent on the skill of the tester. It may give inaccurate results for children with visual problems that are centered in the brain rather than in the eye (cortical blindness).

The modified cover test is sometimes used to detect strabismus and acuity deficits in infants. The child is asked to look at an object. The examiner watches for any shifting in alignment while he or she covers one eye, then again when it is uncovered. The test is repeated on the other eye. The testing sometimes frightens or distracts the infant. The test does a good job of picking up misalignments and the tendency to turn the eyes, but it is less accurate in determining acuity.

Forced choice preferential looking (FPL) is another visual acuity test that is useful for infants. The infant wears a special pair of polarized glasses and looks at Teller cards (cards with black and white stripes on one side and an amorphous grey tint on the other). The infant will look at the more visually interesting side of the card (the side with the stripes) and ignore the other side. The cards are shown in a series, with the black and white stripes getting smaller and closer together. When the child no longer shows a preference for looking at the striped side, the limit of vision has been reached. This is very accurate.

The Hirschberg test is used to detect strabismus. The child looks at a bright light source while the clinician looks for the corneal reflex. The location of the reflex in one eye is compared to its location in the other. Any asymmetry indicates a misalignment.

The visual evoked potential (VEP) and electroretinograph (ERG) are tests that are performed only by highly trained ophthalmologists. The VEP measures activity in the brain while the child views an object. The ERG measures the electrical activity in the retina in response to light. These tests are effective for evaluating the effectiveness of glasses in non-verbal or mentally impaired subjects, but only if the anatomy of the eye is normal. The results may change and improve over time as a child grows and develops.

Vision is too important to neglect

Children under age 5 are at risk of developing serious visual disorders that can lead to vision loss and developmental delays if not detected early. All children, and especially children with disabilities who are at a higher risk than the general population, should be screened for eye and vision problems as young as possible.

David Ganet is the director of the Abraham Ratner Children's Eye Center, San Diego, CA. He is one of the developers of the EyeDx visual screening system.
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Copyright 1999 Gale, Cengage Learning. All rights reserved.

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Author:Granet, David B.
Publication:The Exceptional Parent
Date:Dec 1, 1999
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