title: Pre-operative visual evaluation for implantable collamer lenses in highly myopic eyes.
abstract: OBJECTIVE
  The aim of this study was to evaluate a clinical procedure based on trial rigid gas-permeable (RGP) contact lenses fitting to assess the real pre-operative visual acuity (VA) of highly myopic eyes undergoing surgery with an implantable collamer lens.
  
  
  METHODS
  Highly myopic eyes with a spectacle visual acuity (SVA) of 0.2 logMAR (6/9.6 Snellen) or worse were enrolled. A trial RGP contact lens with high dioptric power was fitted before collamer lens implantation. The trial contact lens residual refractive error was corrected by spectacle over-refraction to estimate contact lens VA (CLVA). The three-month post-operative uncorrected vision and visual acuities were also measured. The safety and efficacy indices of collamer lens implantation were calculated based on pre-operative SVA and CLVA, respectively.
  
  
  RESULTS
  The study enrolled 42 patients with 68 highly myopic eyes with a mean pre-operative spherical equivalent of -16.40 ± 4.43 D. The mean pre-operative SVA was 0.38 ± 0.19 logMAR. Pre-operative trial RGP contact lens fitting resulted in a significant improvement of VA (2.02 ± 1.05 lines), which was statistically insignificantly different from the VA with the implantable collamer lens (2.07 ± 0.8 lines). The safety index of collamer lens implantation was 1.70 ± 0.38 in reference to the pre-operative SVA but significantly decreased to 1.02 ± 0.17 in reference to CLVA. Similarly, the efficacy index of 1.17 ± 0.48 on SVA decreased to 0.71 ± 0.28 on CLVA.
  
  
  CONCLUSIONS
  Trial RGP contact lens fitting was found to indicate the potential implantable collamer lens VA more accurately than spectacle refraction. Consideration should be given to the use a trial RGP contact lens as part of the pre-operative work-up prior to collamer lens implantation in order to provide an assessment of the patient's potential post-operative VA.
authors.affiliation: Department of Ophthalmology, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, China. idrshen@zju.edu.cn.
authors.forename: Yangshun
authors.initials: Y
authors.lastname: Gu
authors.forename: Chen
authors.initials: C
authors.lastname: Xie
authors.forename: Jianping
authors.initials: J
authors.lastname: Tong
authors.forename: Nan
authors.initials: N
authors.lastname: Hong
authors.forename: Ye
authors.initials: Y
authors.lastname: Shen
mesh_terms: D000328:Adult; D005500:Follow-Up Studies; D006801:Humans; D007910:Lenses, Intraocular; D008875:Middle Aged; D009216:Myopia / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D011300:Preoperative Care / Q000379:methods*; D011446:Prospective Studies; D011474:Prosthesis Design; D012029:Refraction, Ocular; D054140:Refractive Surgical Procedures / Q000379:methods*; D014792:Visual Acuity; D055815:Young Adult
keywords: contact lenses; high myopia; implantable contact lens; rigid gas-permeable contact lens; visual acuity