Test characteristics of orthoptic screening examination in 3 year old kindergarten children

Abstract

Aim: To analyse the test characteristics of orthoptic screening for amblyopia or amblyogenic risk factors (target conditions) in kindergarten.

Methods: 1180 three year old children were screened by orthoptists in 121 German kindergartens. Orthoptic screening consisted of cover tests, examination of eye motility and head posture, and monocular visual acuity testing with the Lea single optotype test. Children were re-examined in kindergarten by different orthoptists after 3-6 months using a more demanding pass threshold for visual acuity. All children with at least one positive orthoptic test result or an inconclusive re-examination were referred to an ophthalmologist for diagnosis. The gold standard was set positive if a target condition was diagnosed on ophthalmological examination. It was set negative if no target condition was found upon ophthalmological examination, or if a child who screened negative or inconclusive passed the orthoptic re-examination without any positive test result.

Results: The gold standard was ascertained in 1114 children. 26 (2.3%) children had a "positive" gold standard. In 10.8% of the children the initial screening was "inconclusive," mostly due to lack of collaboration. Screening test sensitivity (based on conclusive results only) was 90.9% and specificity was 93.8%.

Conclusions: Orthoptic vision screening of 3 year olds in kindergarten is sensitive and specific. However, owing to a substantial proportion of inconclusive screening results, rescreening of non-cooperative 3 year old children should be considered.

Figure 1

Flow diagram of gold standard determination. A child could be classified gold standard “negative” in several ways: the result was “negative” or “inconclusive” in the orthoptic screening and “negative” in the orthoptic examination: children who had a visual acuity of >0.63 (10/17) in either eye or better and no anomalies in the orthoptic examination were classified gold standard “negative” without further examination; children with “positive” or “inconclusive” or “borderline” results in the orthoptic examination were referred. Children with a “positive” screening were all referred. To be classified gold standard “positive,” a child had to be referred and had to have target conditions upon ophthalmological examination.

Figure 2

From the number of orthoptic screenings (phase I), orthoptic examinations (phase II), and ophthalmological examinations the overall test characteristics (sensitivity or specificity) of the gold standard may be assessed using conditional probability calculation. For example, assuming a 90% sensitivity of orthoptic screening, a 90% sensitivity of the orthoptic examination, and a 100% sensitivity of ophthalmological examination, the overall sensitivity of the gold standard would be 98.4%. Likewise, for those 993 children with conclusive results of phase I, the sensitivity of the gold standard would be 99.0% × 867/993 + 100% × 126/993 = 99.1%. (Only those ophthalmological examinations were included which were conducted because of inconclusive or missing orthoptic examinations in phase II; 42 additional ophthalmological examinations, which were conducted although the gold standard was already “negative” based on the orthoptic examinations, were not included. Those 132 ophthalmological examinations conducted as a consequence of “positive” orthoptic screening or orthoptic examinations were not included either.)