The Moving Dynamic Random Dot Stereosize Test: Development, Age Norms, and Comparison With the Frisby, Randot, and Stereo Smile Tests Susan J Leat, BSc, PbD; Jessica St Pierre, OD; Saloumeb Hasan-Abadi, OD; and Jocebn Faubert, PbD Purpose: To determine the response of infants and children to the Moving Dynamic Random Dot Stereosize (MDRS) test and to collect cross-sec- tional age-related data. Methods: Sixty visually normal individuals were divided into four age groups: 0.5-<2, 2-<5, 5- <8, and 8420 years. Stereopsis was measured with the MDRS test on two occasions, plus the Frisby, Randot, or Stereo Smile tests, as was age appropriate. Results: All children aged >2 years and 80% of the children between ages 6 months and 2 years were able to perform the MDRS test on at least one occasion. Sixty percent of the 6-month to 2-year- old children were able to perform the Stereo Smile test on both occasions. Performance on the MDRS test improved with age up to 9 years. Improvement on the Frisby and Randot tests was seen in children aged up to 7 years. Mean and 95% confidence interval ranges for each test are given. Conclusion: This study gives evidence that aspects of the visual system are not fully mature until age 7-9 years. The MDRS test is a visually demanding but cognitively simple test that shows potential for detecting visual anomalies in young children. Journal of Pediatric Ophthalmology and Strabismus 2001 ;38:284-294. From the School of Optomety (Dr Leat), University of Waterloo, Waterloo, Ontario; and the Ecole d'optometrie (Dr Faubert), Université de Montreal, Montreal, Québec, Canada. This study was supported by Kid Action Research formely Easter Seal Research Institute) Grant Nos. 9 629 and 9733 and by the Canadian Optometric Education Trust Fund. This study was conducted at the School of Optometry,University of Waterloo, Waterloo, Ontario, Canada. This material was presented at the annual meeting of the American Academy of Optometry; December 10-14, 1998; San Francisco, Calif: The authors thank all of the participants who took part and Ken Robertson for comments on the text. Originally submitted ]uly 27,2000. Accepted for publication October 26 2000. Reprint requests: Susan J. Leat, BSc, PhD, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. INTRODUCTION The measurement of stereopsis is an important component of an ocular assessment or a vision screening procedure, It can assist in ruling out stra- bismus, anisometropia, and amblyopia.' The demonstration of typical stereopsis for age indicates normal development of sensory and motor func- tions.2 However, not all stereotests provide equally valuable information. In general, random dot stereograms that are believed to measure global stereopsis are more valid than contour stereograms that measure local stereopsis. Contour stereograms 284 SEPTEMBERIOCTOBER 2001No~ 38 No 5