title: Longitudinal evaluation of posterior corneal elevation after laser refractive surgery using swept-source optical coherence tomography.
abstract: OBJECTIVE
  To investigate the change in posterior corneal elevation up to 1 year after myopic femtosecond-assisted LASIK and photorefractive keratectomy (PRK).
  
  
  METHODS
  Prospective, longitudinal, comparative study.
  
  
  METHODS
  Patients undergoing femtosecond-assisted LASIK or PRK.
  
  
  METHODS
  Corneal imaging was performed using swept-source optical coherence tomography at baseline and at each postoperative follow-up. A 2-way analysis of variance model with repeated measures and a linear mixed effect model were used to compare the differences in posterior corneal elevation between LASIK and PRK at different points after adjusting for the preoperative spherical equivalent (SEQ), central corneal thickness (CCT), thinnest corneal thickness (TCT), residual bed thickness (RST), and ablation depth (AD).
  
  
  METHODS
  The changes in posterior corneal elevation 1 month, 3 months, 6 months, and 12 months after surgery.
  
  
  RESULTS
  Ninety-eight eyes of 49 patients (mean age 35.2 ± 8.5 years) (62 LASIK, 36 PRK) were included. The mean change in posterior corneal elevation values after LASIK and PRK were 4.88±0.47 μm versus 3.67±0.48 μm (B-1), 2.42±0.56 μm versus 3.00±0.47 μm (B-3), 3.76±0.46 μm versus 2.76±0.46 μm (B-6), and 2.92±0.46 μm versus 2.72±0.46 μm (B-12), respectively. Significant differences in posterior corneal elevation after LASIK were found from month 1, to month 3, to month 6, to month 12 (P ≤ 0.001), whereas posterior corneal elevation did not change significantly from month 3, to month 6, to month 12 (P ≥ 0.373) after PRK. LASIK and PRK eyes showed significant differences at months 3 and 12 (P ≤ 0.023). A similar pattern was observed for the changes in posterior corneal elevation after LASIK and PRK after adjusting for the effect of SEQ, CCT, TCT, RST, and AD. The adjusted forward displacements of the posterior corneal surface were statistically significant throughout the study period after both refractive surgeries (P < 0.05).
  
  
  CONCLUSIONS
  The findings of our study suggested that there was a mild but significant forward protrusion of the posterior cornea after femtosecond laser-assisted LASIK and PRK. The posterior cornea fluctuated during the first postoperative year after LASIK, whereas it stabilized as early as 3 months after PRK.
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China; Hong Kong Eye Hospital, Hong Kong, China.
authors.forename: Tommy C Y
authors.initials: TC
authors.lastname: Chan
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Dexter
authors.initials: D
authors.lastname: Liu
authors.affiliation: Department of Mathematics and Statistics, Hang Seng Management College, Hong Kong, China.
authors.forename: Marco
authors.initials: M
authors.lastname: Yu
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China; Hong Kong Eye Hospital, Hong Kong, China; Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia. Electronic address: vishaljhanji@gmail.com.
authors.forename: Vishal
authors.initials: V
authors.lastname: Jhanji
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology*; D063171:Corneal Pachymetry; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis; D005500:Follow-Up Studies; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000379:methods*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology; D041623:Tomography, Optical Coherence; D014792:Visual Acuity / Q000502:physiology