title: A comparison of induced astigmatism in 20- vs 25-gauge vitrectomy procedures.
abstract: BACKGROUND
  Surgically induced astigmatism is an unwanted variable that can lead to poorer visual and refractive outcomes in patients undergoing vitrectomy even when a technically precise procedure has been performed. This study assesses the difference in surgically induced astigmatism (SIA) between the traditional 20-gauge vitrectomy and the newer 25-gauge sutureless technique by comparing pre- and post-procedure keratometry readings.
  
  
  METHODS
  The study is a retrospective consecutive case series of vitrectomies performed by a single surgeon. There were a total of 47 patients, eight with bilateral procedures, 24 who underwent the 20 gauge, and 31 who had the 25-gauge procedure. Patients were excluded for corneal altering pathology or scleral buckling procedures. Vector analysis of pre- and post-vitrectomy readings was performed using Alpin's method, facilitated by the ASSORT program version 4.1.
  
  
  RESULTS
  Mean time at which post-operative keratometry readings were taken was 3.9 months (1-36). Mean astigmatism at presentation was 0.63 D and 0.92 D and at post-surgically follow-up 1.14 D and 0.91 D (20 and 25 gauge, respectively). Mean SIA was 0.66 D (SD=0.8 D) for the 20-gauge group and 0.27 D (SD=0.23 D) for the 25 gauge (P=0.037). The calculated figure of SIA variability representing the 95% CI for the maximum amount of SIA for each procedure was 2.26 D and 0.73 D for the 20- and 25-gauge procedure, respectively.
  
  
  CONCLUSIONS
  The study shows that the 25-gauge technique involves a statistically significant reduction in the amount of SIA. This can ultimately lead to a better visual and refractive outcome for the patient.
authors.affiliation: Department of Vitreoretinal Surgery, Vision Retinal Institute, Queensland, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Galway
authors.forename: B
authors.initials: B
authors.lastname: Drury
authors.forename: B G
authors.initials: BG
authors.lastname: Cronin
authors.forename: R D
authors.initials: RD
authors.lastname: Bourke
mesh_terms: D001251:Astigmatism / Q000209:etiology* / Q000517:prevention & control; D003315:Cornea / Q000033:anatomy & histology; D006801:Humans; D012189:Retrospective Studies; D014792:Visual Acuity; D014821:Vitrectomy / Q000009:adverse effects* / Q000379:methods*