A new screening program for the detection of amblyopia and other early visual disorders in toddlers and preschool children

Drover, James R. (2006) A new screening program for the detection of amblyopia and other early visual disorders in toddlers and preschool children. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Several studies indicate that permanent visual dysfunction can be easily prevented if amblyopia or amblyogenic factors are detected sufficiently early in life. Although this highlights the importance of mass vision screening of young children, the implementation of preschool vision screening programs is lacking in most industrialized countries for at least three reasons. First, the detection of subtle amblyogenic factors is often quite difficult using current techniques of assessment. Second, the screening of young children is often challenging due to the attentional demands of the tests. Third, there is a lack of consensus among researchers/clinicians as to what constitutes an effective vision screening program. -- In order to address these issues, we implemented a population-based screening program to assess toddlers and preschoolers in the St. John's, NL, Canada, metropolitan area. The program was one of the most comprehensive conducted to date, as we attempted to assess 954 children on up to five separate aspects of functional vision (visual acuity, ocular alignment/motility, stereoacuity, refractive error, and contrast sensitivity). The screening battery included commonly used tests to assess toddlers and preschoolers such as the Teller Acuity Cards, Randot E Stereotest, and the cover-uncover test along with promising, new tests such as the Lea symbols, the Randot Preschool Stereoacuity Test, the contrast sensitivity cards, and the Welch-Allyn SureSight autorefractor. Children who failed at least one test were sent to an optometrist for an optometric gold standard exam. To determine which tests should be included in an effective preschool vision screening program, four measures of validity (sensitivity, specificity, positive predictive value, and negative predictive value) were calculated for tests of each visual function and 29 different combinations of tests. -- Results suggested that although all individual tests possessed relatively high positive predictive values, they generally possessed low sensitivity, specificity, and negative predictive value. Combinations of tests tended to yield high sensitivity and positive predictive value, but relatively low specificity and negative predictive value. The most effective combinations were those that included autorefraction and the ocular alignment/motility tests. Also, prevalence estimates of vision disorders based on the present study were in agreement with those from other areas of Canada and other industrialized nations. Finally, completion times and completion rates revealed that of all tests in the screening battery, autorefraction was the easiest for children to complete, whereas contrast sensitivity was the most difficult. -- Based on the data analyses, we have made several important recommendations that may be instrumental in improving the quality of preschool vision screening: (1) vision screening should be conducted with a combination of three to four tests; (2) the program should implement relatively lenient referral criteria; (3) autorefraction should be included as part of the combination in order to assess spatial vision; (4) the combination should include either stereoacuity tests or alignment/motility tests; (5) three-test combinations are preferable to four-test combinations as they are more cost-effective.

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