title: The Boston keratoprosthesis provides a wide depth of focus.
abstract: OBJECTIVE
  To measure the through-focus curve for eyes implanted with a type 1 Boston keratoprosthesis (KPro) and compare it to that of pseudophakic controls with fixed pupil sizes. The results should assist in evaluating postoperative visual quality after surgery. They should also help to determine the necessary KPro inventories in terms of refractive power steps.
  
  
  METHODS
  Autorefraction and manifest refraction were performed on all eyes. The monocular through-focus acuity curve was plotted in reference to the best-corrected visual acuity by spectacle plane defocus ranging from +5.00 to -5.00 dioptres in 0.50 dioptre increments. These measurements were obtained on KPro-implanted eyes, pseudophakic eyes as controls, and on the same control eyes after fixing the pupil diameter to 3 and 2 mm using black painted iris contact lenses.
  
  
  RESULTS
  Ten KPro eyes and five control eyes were included. Good agreement was noted between the subjective refractions and autorefraction in KPro eyes. The average through-focus curve for the control eyes was significantly steeper than that of the KPro curve, but became comparable after fixing the control pupil to 2 and 3 mm.
  
  
  CONCLUSIONS
  The KPro's wide depth-of-focus makes the visual acuity less dependent on an exact refractive correction at distance and explains the 'pseudoaccomodation' experienced by these patients. This is primarily due to the small pupil diameter of the KPro. The current manufacturing steps in 0.50 dioptre increments appears to be sufficient.
authors.affiliation: University Hospitals Eye Institute, University Hospitals Case Medical Center, Case Western Reserve University School of Medicine, Cleveland, USA; Schepens Eye Research Institute, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, USA.
authors.forename: Rony R
authors.initials: RR
authors.lastname: Sayegh
authors.forename: Claes H
authors.initials: CH
authors.lastname: Dohlman
authors.forename: Scott H
authors.initials: SH
authors.lastname: Greenstein
authors.forename: Eli
authors.initials: E
authors.lastname: Peli
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001187:Artificial Organs; D016022:Case-Control Studies; D003315:Cornea; D003316:Corneal Diseases / Q000503:physiopathology / Q000601:surgery*; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D008297:Male; D008875:Middle Aged; D019736:Prostheses and Implants; D012030:Refractive Errors; D014792:Visual Acuity / Q000502:physiology*
keywords: depth of focus; keratoprosthesis; optics; refraction; through-focus