title: Surgically induced astigmatism in phacoemulsification, pars plana vitrectomy, and combined phacoemulsification and vitrectomy: a comparative study.
abstract: OBJECTIVE
  To study the surgically induced astigmatism (SIA) in combined phacoemulsification and vitrectomy, and compare with that when either procedure is performed alone.
  
  
  METHODS
  This is a prospective comparative interventional trial comprising of 60 eyes of 60 consecutive patients with cataract and/or vitreo-retinal pathology. They were divided equally into three groups based on the type of procedure: Group A, phacoemulsification alone group, using a 3.0-3.2 mm wide unsutured sclero-corneal tunnel incision at 1.0 mm post-limbus at 10 o'clock; Group B, par plana vitrectomy alone group, using three sclerotomies at 3.5 mm post-limbus at 2, 8, and 10 o'clock (right eye) or at 2, 4, and 10 o'clock (left eye) positions; and Group C, combined phacoemulsification and pars plana vitrectomy group. Main outcome measures were the amplitude (K-induced) and the axis of SIA calculated by rectangular coordinate method using the Holladay-Cravy-Koch formula.
  
  
  RESULTS
  The mean K-induced amplitudes were 0.19+/-0.14 D, 0.17+/-0.11 D, and 0.23+/-0.19 D for groups A, B, and C, respectively. The range of K-induced amplitudes for the entire cohort was 0.00-0.77 D. No overall statistically significant differences in the pre- and postoperative topographic astigmatism amplitudes and the K-induced between groups A, B, and C were found (all P>0.05). Minor shifts, of doubtful clinical significance, in the axes of SIA were present.
  
  
  CONCLUSIONS
  Combined phacoemulsification and pars plana vitrectomy does not induce significant astigmatic change per se, and its amount is similar to that when either procedure is performed alone.
authors.affiliation: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, The People's Republic of China. can_yuen@yahoo.com.hk
authors.forename: C Y F
authors.initials: CY
authors.lastname: Yuen
authors.forename: B T O
authors.initials: BT
authors.lastname: Cheung
authors.forename: C-W
authors.initials: CW
authors.lastname: Tsang
authors.forename: R F
authors.initials: RF
authors.lastname: Lam
authors.forename: N B
authors.initials: NB
authors.lastname: Baig
authors.forename: D S C
authors.initials: DS
authors.lastname: Lam
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000209:etiology*; D019781:Corneal Topography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018918:Phacoemulsification / Q000009:adverse effects* / Q000379:methods; D011446:Prospective Studies; D016896:Treatment Outcome; D014821:Vitrectomy / Q000009:adverse effects* / Q000379:methods; D055815:Young Adult