title: Cone location-dependent outcomes after combined topography-guided photorefractive keratectomy and collagen cross-linking.
abstract: OBJECTIVE
  To evaluate the effect of keratoconus cone location on the change in refractive outcomes, corneal aberrations, and biomechanics after combined topography-guided photorefractive keratectomy (PRK) and collagen cross-linking (CXL).
  
  
  METHODS
  Prospective, comparative case series.
  
  
  METHODS
  Topography-guided PRK was performed followed by accelerated CXL using riboflavin A and enhanced-intensity (30 mW/cm(2)) ultraviolet light. Outcome parameters including uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (BDVA), corneal tomography and biomechanics (corneal hysteresis [CH] and corneal resistance factor [CRF]), and corneal wavefront aberrations were assessed before and a year after the procedure. Eyes were subdivided into 2 groups preoperatively for statistical analysis: Group 1, cone located within the central 2-mm zone; and Group 2, cone located outside the central 2-mm zone.
  
  
  RESULTS
  UDVA, BDVA, sphere, cylinder, and simulated keratometry improved after treatment in both groups (P < .05). However, BDVA improved more in Group 1 than in Group 2 (P = .04) and the other variables were not affected by cone location. A few corneal wavefront Zernike aberrations changed after treatment (P < .05) but none were affected by cone location (P > .05). CH and CRF increased after treatment in both groups (P > .05). Interestingly, the increases in CH and CRF were greater in Group 2 than in Group 1 (P > .05).
  
  
  CONCLUSIONS
  Cone location appeared to impact only visual acuity and biomechanics after the combined procedure. The greater increase in CH and CRF in Group 2 may indicate differences in the ablation profile and variability in CXL outcomes and requires further study.
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Rohit
authors.initials: R
authors.lastname: Shetty
authors.affiliation: Cornea Clinic, Department of Ophthalmology, Maastricht University Medical Center, Maastricht, Netherlands.
authors.forename: Rudy M M A
authors.initials: RM
authors.lastname: Nuijts
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Maneck
authors.initials: M
authors.lastname: Nicholson
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Koushik
authors.initials: K
authors.lastname: Sargod
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Chaitra
authors.initials: C
authors.lastname: Jayadev
authors.affiliation: Cornea and Refractive Surgery Division, Narayana Nethralaya, Bangalore, India.
authors.forename: Himabindu
authors.initials: H
authors.lastname: Veluri
authors.affiliation: Imaging, Biomechanics and Mathematical Modeling Solutions, Narayana Nethralaya, Bangalore, India. Electronic address: asroy27@yahoo.com.
authors.forename: Abhijit
authors.initials: A
authors.lastname: Sinha Roy
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism*; D003131:Combined Modality Therapy; D003315:Cornea / Q000503:physiopathology; D003319:Corneal Stroma / Q000378:metabolism; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000503:physiopathology; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000378:metabolism / Q000473:pathology* / Q000628:therapy*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D010778:Photochemotherapy; D018903:Photorefractive Keratectomy; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011446:Prospective Studies; D012256:Riboflavin / Q000627:therapeutic use; D014466:Ultraviolet Rays; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen; D012256:Riboflavin