title: The effect of astigmatism axis on visual acuity.
abstract: OBJECTIVE
  To evaluate the effect of astigmatism axis on uncorrected distance visual acuity (UDVA) in emmetropic eyes that underwent laser refractive surgery.
  
  
  METHODS
  This retrospective study included patients who underwent laser in situ keratomileusis or photorefractive keratectomy between January 2000 and December 2015 at the Care-Vision Laser Centers, Tel Aviv, Israel. Eyes with a 3-month postoperative spherical equivalent between -0.5 D and 0.5 D were included in this study. Eyes with ocular comorbidities and planned ametropia were excluded. Study eyes were divided into 3 groups according to the steep astigmatic axis: with the rule (WTR) (60-120), oblique (31-59 or 121-149), and against the rule (ATR) (0-30 or 150-180). The UDVA of these 3 groups was compared. The oblique group was divided into oblique ATR and oblique WTR, which were compared with each other.
  
  
  RESULTS
  A total of 17,416 consecutive eyes of 8,708 patients were studied. The WTR eyes (n = 10,651) had significantly better UDVA (logMAR 0.01 ± 0.08) than the oblique (n = 3,141, logMAR 0.02 ± 0.09) and ATR eyes (n = 3,624, logMAR 0.02 ± 0.10) (p<0.001). The oblique WTR group had significantly better UDVA than the oblique ATR group (p<0.001). The UDVA of the oblique and ATR groups was similar. Stepwise multiple regression analysis showed that the group accounted for 15% of the UDVA variance (p = 0.04).
  
  
  CONCLUSIONS
  The astigmatic axis has a small but significant effect on UDVA in emmetropic eyes; WTR was better than oblique and ATR astigmatism. Therefore, when correcting astigmatism, it may be preferable to err towards WTR astigmatism.
authors.affiliation: Department of Ophthalmology, Rambam Health Care Campus, Haifa - Israel.
authors.forename: Michael
authors.initials: M
authors.lastname: Mimouni
authors.affiliation: Department of Ophthalmology, Barzilai Medical Center, Ashkelon and the Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheba - Israel.
authors.forename: Achia
authors.initials: A
authors.lastname: Nemet
authors.affiliation: Department of Ophthalmology, Assaf Harofeh Medical Center, Zerifin, affiliated to the Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv - Israel.
authors.forename: Russell
authors.initials: R
authors.lastname: Pokroy
authors.affiliation: Care-Vision Laser Centers, Tel Aviv - Israel.
authors.forename: Tzahi
authors.initials: T
authors.lastname: Sela
authors.affiliation: Care-Vision Laser Centers, Tel Aviv - Israel.
authors.forename: Gur
authors.initials: G
authors.lastname: Munzer
authors.affiliation: Department of Ophthalmology, Barzilai Medical Center, Ashkelon and the Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheba - Israel.|Care-Vision Laser Centers, Tel Aviv - Israel.
authors.forename: Igor
authors.initials: I
authors.lastname: Kaiserman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012029:Refraction, Ocular / Q000502:physiology*; D054140:Refractive Surgical Procedures / Q000379:methods; D012189:Retrospective Studies; D014792:Visual Acuity; D055815:Young Adult