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Individuals with Down's syndrome have been reported to have a higher incidence of refractive errors 1-3 and keratoconus. 4-6 All these studies have been on random groups, presenting to normal clinical practice or found in various institutions. We present some findings from a study on a representative sample of the Greater Manchester Down's Syndrome Cohort, all of whom resided in the family home.
Method
A cohort consisting of 90% of the total known Down's syndrome births in Greater Manchester over the 7 year period between August 1973 and August 1980 had been studied since birth by the Hester Adrian Research Centre of the University of Manchester and comprised 181 individuals. Their medical, social, and psychological histories were well known because of this study. 7 By September 1995, 118 of these were still living locally, the rest having been lost to the study because of movement out of the area or death. All 118 were contacted by post and in the period allocated for the study, 57 had been studied, of which 50 were selected and agreed by the original researchers of the cohort to be representative of the total cohort for age, mental ability, general health, and social class. This subgroup (29 male, 21 female) of ages 15-22 years (mean 17.4 years) was studied by refraction, orthoptic examination, corneal topography, A-scan biometry, and slit lamp examination. Refraction was done in the normal way, without cycloplegia. Corneal topography was done using a TMS-1 machine. Biometry was done using a Storz A-scan ultrasound machine. Slit lamp examination and fundal examination through the undilated pupil using an indirect 78 D lens was also done.
Results
A linear relation was found between axial length and spherical equivalent refraction (Fig 1 ).
Forty (80%) of the group had a hypermetropic refraction ( mean +2.46 D, range +0.5 to +7.5 D); nine (18%) were myopic (mean -2.75 D, range -0.5 to -8.0 D); one (2%) was emmetropic (within plus or minus 0.5 D of zero). The overall mean spherical equivalent refraction was +1.43 (SD 2.86) D (Fig 2 ). In terms of visual acuity, 63% of eyes could see 0.5 (6/12) or better and 66% of the individuals had a binocular vision of 6/12 or better (Fig 3 ). Visual...