title: Corneal power and astigmatism in Down syndrome.
abstract: OBJECTIVE
  Corneal and crystalline lens shape differ in Down syndrome (DS) compared with developmentally normal populations. This study specifically explored the association between corneal curvature and refractive error for the first time in DS.
  
  
  METHODS
  Participants were 29 children with 59 age-matched controls (33 males and 35 females; mean age 12.4 +/- 1.8 years) and DS (9 to 16 years; 19 males and 10 females; mean age 12.8 +/- 1.9 years). Corneal curvature was measured using a hand-held keratometer. Refractive error was assessed by distance static retinoscopy in the control group and Mohindra retinoscopy in the DS group.
  
  
  RESULTS
  The DS group demonstrated a high frequency and magnitude of refractive errors (mean DS + 2.52 +/- 3.00 D; mean controls -0.46 +/- 1.32 D). The majority of controls had little or no significant refractive error. DS cornea were significantly steeper (mean DS 45.62 +/- 2.13 D; mean controls 43.10 +/- 1.37 D). Neither DS nor control data demonstrate significant relations between corneal and total refractive power (M vector). Astigmatic errors in the DS group were more frequently oblique and demonstrated strong right-left specificity. The DS data did not demonstrate a significant association between corneal and total astigmatism along principal meridians (J0), however, a significant relation was found for the control data (linear regression, r = 0.51, p < 0.0001). No significant association between corneal and total oblique astigmatism (J45) was demonstrated by either DS or control data.
  
  
  CONCLUSIONS
  The study is the first to explicitly investigate the association between corneal power and refractive error in children with DS. The majority of the DS group have significant refractive errors including an increased prevalence of oblique astigmatism. Corneal curvature in DS is not related to spherical (M) or astigmatic (J0, J45) refractive error. Further research is required to better understand the association between the ocular structures of the DS eye and their impact on functional vision.
authors.affiliation: School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland. Ja.little@ulster.ac.uk
authors.forename: Julie-Anne
authors.initials: JA
authors.lastname: Little
authors.forename: J Margaret
authors.initials: JM
authors.lastname: Woodhouse
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Saunders
mesh_terms: D000293:Adolescent; D001251:Astigmatism / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology*; D002648:Child; D003315:Cornea / Q000473:pathology / Q000503:physiopathology*; D019781:Corneal Topography; D004314:Down Syndrome / Q000150:complications*; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D012030:Refractive Errors / Q000453:epidemiology / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D042262:Retinoscopy