EMMETROPISATION, AXIAL LENGTH, AND CORNEAL TOPOGRAPHY IN TEENAGERS WITH DOWNS-SYNDROME

Aim-To study the refractive status and corneal topography in Down's sy ndrome. Method-A matched cohort subgroup of 50 individuals with Down's syndrome in the Manchester area aged 15-22 years was studied by refra ction, corneal topography, A-scan biometry, slit lamp examination, and orthoptic examination. Results-(l) A Linear relation was found betwee n axial length and spherical equivalent refraction. There was no stati stical relation between keratometry and the axial length. (2) 80% of t he group had a hyperopic refraction (mean +2.46 D, range +0.5 to +7.5 D); 18% were myopic (mean -2.75 D, range -0.5 to -8.0 D); and 2% were emmetropic, (within plus or minus 0.5 D of zero). The overall mean sph erical equivalent refraction was +1.43 (SD 2.86) D. 63% of eyes could see 6/12 or better and 66% of the individuals had a binocular vision o f 6/12 or better. (3) Corneal topography was generally of a regular '' bow tie'' pattern, but there was a high incidence of oblique cylinders . Mean cylinder strength was 1.14 (1.15) D. (4) The prevalence of over t keratoconus was 2%. 6% had corneal topography with inferior steepeni ng which may be a preclinical keratoconic process. Conclusions-In this cohort of late teenagers with Down's syndrome, emmetropisation has fa iled to occur in most individuals. In a similar aged group of non-disa bled individuals one would expect about 83% emmetropic (plus or minus 0.25 D), 13% myopic, and 4% hyperopic. The wide spread of oblique cyli nders and the small proportion of with the rule astigmatism is probabl y related to this failure of emmetropisation. The prevalence of 2% ker atoconus in Down's syndrome compares with that found by other authors of between 5.5 and 15%. The 6% with inferior steepening on topography will be followed up over the next few years to see if there is any dev elopment of clinical keratoconus. Hence we will see if corneal topogra phy is useful as a screening tool for preclinical keratoconus in this high risk group.