Vision screening standardization recommended

April 15, 2006

Portland, OR?Mass vision screening of school-age children was first recommended in 1983. At that time there was not a large population of children of preschool age, a situation that has changed markedly since then because today many more 3- and 4-year-olds are in a preschool setting. However, there is still no standardization in vision screening.

Portland, OR-Mass vision screening of school-age children was first recommended in 1983. At that time there was not a large population of children of preschool age, a situation that has changed markedly since then because today many more 3- and 4-year-olds are in a preschool setting. However, there is still no standardization in vision screening.

"There is no consensus on what test to use, the appropriate age of the children to be tested, or who should perform screening for amblyopia in children," said Pamela Hutt Berg, CO, COMT, Casey Eye Institute, Oregon Health and Science University, Portland.

In 1980, the National Academy of Science recommended standard procedures for the clinical measurement of visual acuity. The committee members recommended that all optotypes should be equally detectable, evenly spaced, have left/right symmetry, and adhere to the Snellen gold standard. Despite these recommendations, in clinical practice no such standardization exists, she explained.

She recommended ways to maximize the screening process. A key contact at the schools should be identified in each institution who can coordinate the screening effort by setting up the time and place of the examination and obtaining parental consent forms. Special attention should be paid to the illumination of the space in which the screening will be carried out.

"It is important that children are taught [what to expect] before the actual screening takes place," she emphasized. "Most importantly, a follow-up mechanism should be in place so that children who fail screening can be appropriately and promptly referred for follow-up."

The characteristics of a good screening test are that it must be inexpensive, portable, simple to learn for both the screener and the child, and age-appropriate for the child. The most frequently used tests are the Lea symbols, the HOTV test, and the tumbling E. For children in grade 2 and older, the most commonly used tests are the HOTV test and letters or numbers. The Titmus screener is still in use in the Midwest for screening older children, Berg explained.

The chart can be presented as a light box either on an adjustable pole or tabletop, flip chart, a chart attached to a wall, or less commonly a flash card, she pointed out.

"The format of the eye chart can be presented as a linear or a proportionally spaced chart or a single line with either crowded or uncrowded optotypes," Berg explained. "Use of a single optotype is not recommended unless it is within crowding bars."

Ideally, testing should be carried out by two volunteers (one at the chart and the other pointing at the line to be read) in a quiet location, preferably at 10 feet. No more than two or three children should be in the room at once. In many cases, however, the testing is done with numerous children in a gymnasium, which tends to be distracting for the children.

Eyes can be occluded best, she pointed out, with 3-M tape cut in 3-inch squares or animal glasses with one side blocked. In reality, because of time restraints, many school volunteers cut index cards in half to use for occlusion, and children are sometimes allowed to cover their own eyes. This is a recipe for disaster, she said. The most common reason amblyopia is missed during screening is due to failure to ensure that each eye is tested separately.

"In acuity testing, the tester must go to the critical acuity line as quickly as possible," Berg said. "That line is 20/40 in children under 4 years and 20/30 in children older than 4."

Passing is defined as the correct identification of four of five optotypes on the critical line, she explained.

Some programs, Berg noted, do not record the actual visual acuity and specify only that the child has passed or failed the testing.