title: Orthokeratology for slowing myopic progression in a pair of identical twins.
abstract: OBJECTIVE
  To compare the axial length elongation and change in refractive errors in a pair of identical twins wearing orthokeratology (ortho-k) and single vision lenses (SVLs), respectively.
  
  
  METHODS
  Identical Twin A and B, who were 8 years of age, with the same amount of near activities, were assigned to wear ortho-k and SVLs randomly and they were monitored for two years for myopic progression. Twin A and B were assigned to wear ortho-k and SVLs, respectively. Myopic progression was evaluated by the change in axial length and in refractive errors. A faster axial length elongation was observed in each eye of Twin B during the two-year study period. The overall change in axial length was 0.52mm (OD) and 0.70 (OS) in Twin A and 0.77mm (OD) and 0.82mm (OS) in Twin B. In terms of cycloplegic refractive errors (SER), one month after ceasing lens wear (after completion of the two-year study), the increase (from baseline) were 11% (OD) and 48% (OS) in Twin A and 87% (OD) and 67% (OS) in Twin B.
  
  
  CONCLUSIONS
  Ortho-k is more effective in controlling myopic progression in terms of axial elongation than wearing SVLs in this pair of identical twins.
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong. Electronic address: kayin.chan@connect.polyu.hk.
authors.forename: Ka Yin
authors.initials: KY
authors.lastname: Chan
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
authors.forename: Sin Wan
authors.initials: SW
authors.lastname: Cheung
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
mesh_terms: D003261:Contact Lenses; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000175:diagnosis* / Q000628:therapy*; D054158:Orthokeratologic Procedures / Q000295:instrumentation* / Q000379:methods*; D016896:Treatment Outcome; D014430:Twins, Monozygotic
keywords: Axial length; Myopic control; Orthokeratology; Refractive errors; Twins