This cross-sectional study was designed in order to demonstrate the differences in anterior segment parameters in children with trisomy 21. This is important as it may impact on surgical planning when undertaking procedures in the anterior segment such as corneal grafting, or cataract surgery. The study looked at 38 children with trisomy 21, and 42 children with no known genetic polyploidy. All patients underwent ophthalmological assessment including; slit-lamp examination, cycloplegic refraction, intraocular pressure measurement (IOP), and Scheimpflug imaging measurement. Scheimflug imaging system (SI) acquires 3-dimensional images by illuminating the anterior segment in different meridians. A weakness of this study is that all of the cycloplegic refractions were undertaken with an autorefractor, and all intraocular pressure measurements were taken with a tonopen. Additionally, children with corneal scar or degeneration were excluded from the study, which is clearly relevant in anterior segment procedures. Comparative groups were in more or less the same age range, being 5-13 in the trisomy 21 group, and 5-12 in the control group. In the group of children with trisomy 21, 44.7% were emmetropic, 31.6% hyperopic, and 23.7% myopic. There was no significant difference in intraocular pressure measurement between the two groups. Central corneal thickness (CCT) was found to be less in the trisomy 21 group, however, and the mean pupil diameter was also significanty less when compared to the control group (but all trisomy 21 patients achieved good dilatation for cycloplegic refraction). The rationale for the finding of thinner corneas in the trisomy 21 is that this may represent the beginnings of ectatic disease. Reassuringly anterior chamber depth, angle and volume were comparable for both children with trisomy 21, and the control group. Overall this study demonstrates largely what is known already, in that significant anterior segment abnormalities lie within the cornea in individuals with trisomy 21.