MIST (Melbourne Initial Screening Test) evaluation studies

The aim of these three studies was to assess the test-retest reliability of the MIST (Melbourne Initial Screening Test), a new vision screening tool designed for use by vision screeners of preschool children and to determine the positive and negative predictive value. In the first study, 471 children participated in two sessions, either with the Sheridan Gardiner Singles (SGS) or the MIST. The children were allocated to four groups Group A, test-retest with SGS, one orthoptist; Group B, test-retest with MIST, one orthoptist; Group C, test-retest with MIST, two different orthoptists; or Group D, test-retest with MIST, an orthoptist and a nurse. The test-retest reliability of the MIST demonstrated correlations of 0.79 and 0.78 for the right and left eyes respectively, in comparison to the SGS score of 0.71 and 0.79. The inter-rater reliability of the MIST demonstrated correlations of 0.60 and 0.74 for orthoptists, and 0.63 and 0.60 with orthoptists in comparison to nurses. These results confirm that the MIST is a reliable screening tool for pre-school vision screeners. In the second study, 201 children participated in a gold standard orthoptic and ophthalmic examination after passing their MIST screening. The negative predictive value of the MIST vision screening program was found to be 97.5%. Five children were found to have failed the gold standard examination. Four of the children had an astigmatic error of 1.50 dioptres in one eye, one of whom also failed the visual acuity criterion. One other child had an intermittent esotropia. This result means that 2.5% of the children who pass the MIST vision screening test may actually have strabismus, amblyopia or a refractive error, something to be noted in any screening program. Both nurses and parents must be aware of this information when vision screening is performed. In the third study, forms were returned for 3,854 children referred from the MIST vision screening program over a three-year period. Visual assessment results of 2,623 of these children were obtained from examining clinicians. The positive predictive value of the MIST was found to be 44.4%. Given the less than 5% prevalence of amblyopia in children of this age group, this over-referral rate would be considered acceptable. A balance must be reached between the positive and the negative predictive values. The follow-up examination of each child is a cost to the health care system to be considered in balance with the early detection of a visual problem and any long-term costs associated with visual disorders.