title: Posterior corneal astigmatism in refractive lens exchange surgery.
abstract: OBJECTIVE
  To assess the anterior, posterior and total corneal spherical and astigmatic powers in patients undergoing refractive lens exchange (RLE) surgery.
  
  
  METHODS
  In 402 consecutive patients planned for RLE at Koskelas Eye Clinic, Luleå, Sweden, right eye data from pre- and postoperative subjective refraction, preoperative IOLMaster(®) biometry and Pentacam HR(®) measurements were collected. Postoperative Pentacam HR(®) data were collected for 54 of the patients. The spherical and astigmatic powers of the anterior and posterior corneal surfaces and for the total cornea were assessed and compared, and surgically, induced astigmatism was calculated using vector analysis.
  
  
  RESULTS
  The spherical power of the anterior corneal surface was 48.18 ± 1.69D with an astigmatic power of 0.83 ± 0.54D. The corresponding values for the posterior surface were -6.05 ± 2,52D and 0.26 ± 0.15D, respectively. The total corneal spherical power calculated with ray tracing was 42.47 ± 2.89D with a 0.72 ± 0.48D astigmatic power, and the corresponding figures obtained by estimating the posterior corneal surface were 43.25 ± 1.51D (p < 0.001) with a 0.75 ± 0.49D astigmatic power (p = 0.003). In eyes with anterior astigmatism with-the-rule, the total corneal astigmatism is overestimated if the posterior corneal surface is estimated; in eyes, with against-the-rule astigmatism it is underestimated. Had the posterior corneal surface been measured in this material, 14.7% of the patients would have received a spheric instead of a toric IOL, or vice versa.
  
  
  CONCLUSIONS
  Estimating the posterior corneal surface in RLE patients leads to systematic measurement errors that can be reduced by measuring the posterior surface. Such an approach can potentially increase the refractive outcome accuracy in RLE surgery.
authors.affiliation: Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Rydström
authors.affiliation: Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden.
authors.forename: Oscar
authors.initials: O
authors.lastname: Westin
authors.affiliation: Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden.
authors.forename: Timo
authors.initials: T
authors.lastname: Koskela
authors.affiliation: Department of Clinical Sciences/Ophthalmology, Umeå University Hospital, Umeå, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Behndig
mesh_terms: D000328:Adult; D000368:Aged; D000867:Anterior Chamber / Q000473:pathology; D001251:Astigmatism / Q000503:physiopathology*; D058452:Axial Length, Eye / Q000473:pathology; D001699:Biometry; D003315:Cornea / Q000503:physiopathology*; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D008297:Male; D008875:Middle Aged; D055095:Optics and Photonics; D018918:Phacoemulsification; D011305:Presbyopia / Q000601:surgery; D012029:Refraction, Ocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology
keywords: astigmatism; posterior corneal astigmatism; refractive lens exchange; refractive outcomes