title: Agreement Between Autorefraction and Subjective Refraction in Keraring-Implanted Keratoconic Eyes.
abstract: OBJECTIVE
  To assess the agreement between subjective refraction and autorefraction and to explore the relationship between the magnitude of higher order aberration, and visual acuity and refraction, before and after keraring implantation.
  
  
  METHODS
  This prospective, randomized, interventional study enrolled 27 subjects (mean age 28.1±6.5 years) with keratoconus. Noncycloplegic refraction was performed subjectively by one clinician and with an autorefractor by another clinician, before and 6 months after surgery. The limit of agreement (LoA) between methods was assessed, and the relationships between the corrected distance visual acuity, logMAR on the one hand and refraction measurements and higher-order aberrations on the other, were examined.
  
  
  RESULTS
  The agreement in mean spherical equivalent refraction (MSER) between methods was good postoperatively but poor preoperatively. The autorefractor gave a more myopic refraction than subjective refraction preoperatively (-3.28±3.06 D; LoA -9.27 to +2.71 D, P<0.0001) and postoperatively (-0.63±1.64 D; LoA -3.85 to +2.58 D, P=0.055), and returned higher negative cylinders preoperatively (-1.10±1.17 D; LoA -3.40 to +1.19 D, P<0.0001) and postoperatively (-1.08±1.27 D; LoA -3.60 to +1.41 D, P<0.0001) in keratoconic eyes. The difference in MSER between methods was significantly related to the refractive error at both visits (P<0.05) and to the magnitude of higher-order aberrations in keratoconic eyes preoperatively (P<0.05). The logMAR visual acuity achieved subjectively worsened as the magnitude of higher-order aberrations increased preoperatively (P<0.001).
  
  
  CONCLUSIONS
  The autorefractor returns values that are significantly more myopic in MSER and higher negative cylinders than subjective refraction, preoperatively, but the MSER was similar between devices postoperatively. The autorefactor seems a valid starting point for subjective refraction in keratoconic eyes treated with keraring, but the cylinder should be corrected by about +1 D. The instruments agree more in less myopic than high myopic eyes.
authors.affiliation: Refractive Surgery Unit (W.S.A.-T., H.R.), Elite Medical & Surgical Center, Riyadh, Saudi Arabia; Department of Medicine (K.C.O.), Dunedin School of Medicine, University of Otago, Dunedin, New Zealand; Department of Optometry and Vision Sciences (M.A.A.), College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia; and Institute of Health and Biomedical Innovation (U.L.O.), Chronic Disease and Ageing, Department of Optometry and Vision Sciences, Queensland University of Technology, Brisbane, Queensland, Australia.
authors.forename: Waleed S
authors.initials: WS
authors.lastname: Al-Tuwairqi
authors.forename: Kelechi C
authors.initials: KC
authors.lastname: Ogbuehi
authors.forename: Haya
authors.initials: H
authors.lastname: Razzouk
authors.forename: Mana A
authors.initials: MA
authors.lastname: Alanazi
authors.forename: Uchechukwu L
authors.initials: UL
authors.lastname: Osuagwu
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology; D011446:Prospective Studies; D019736:Prostheses and Implants; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis*; D014787:Vision Tests / Q000379:methods* / Q000592:standards; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult