title: Effect of anterior chamber depth on the choice of intraocular lens calculation formula in patients with normal axial length.
abstract: OBJECTIVE
  To compare the accuracy of  Sanders-Retzlaff-Kraff II (SRK II) and 3(rd) and 4(th) generation intraocular lens (IOL) formulas and to compare the effect of different anterior chamber depths among the IOL formulas in cataract patients with normal axial length (AL; 22.0-24.5 millimeters, mm).
  
  
  METHODS
  A retrospective chart review was performed of patients with normal AL who underwent cataract surgery. The SRK II and 3(rd) generation IOL formulas (Hoffer Q, SRK T, Holladay 1) were compared to the 4(th) generation Haigis formula. For analysis, preoperative anterior chamber depth (ACD) was divided into three subgroups: ≤3, 3-3.5, and ≥ 3.5 mm. The mean error (ME) and mean absolute error (MAE) of each formula was compared for each subgroup against the total. The difference between the ME and MAE of the formulas were compared for each ACD subgroup. P < 0.05 was considered statistically significant.
  
  
  RESULTS
  The study sample was comprised of 309 eyes. The MAE were 0.56 D, 0.52 D, 0.51 D, 0.50 D, and 0.50 D with Haigis, Hoffer Q, SRK T, Holladay 1, and SRK II formulas, respectively. The Haigis formula was a significantly weaker predictor than the SRK T (P < 0.001) and Holladay 1 (P = 0.035) formulas. The ME with Haigis formula was -0.23 D which changed to -0.06 D with ACD ≥ 3.5 mm (P = 0.002). The ME was -0.24 D with SRK II and changed to -0.09D with ACD ≤ 3 mm (P = 0.004). There was no statistically significant difference between Hoffer Q, SRK T, and Holladay formulas 1 in ACD subgroups (P > 0.05, all comparisons).
  
  
  CONCLUSIONS
  The SRK II formula can predict refraction in patients with normal AL and ACD less than 3 mm with less error and is preferred over other formulas. The Haigis formula is the preferred choice in patients with a normal AL and ACD longer than 3.5 mm. The prediction accuracy of Hoffer Q, SRK T, and Holladay 1 is comparable in normal AL.
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Miraftab
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Hassan
authors.initials: H
authors.lastname: Hashemi
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Akbar
authors.initials: A
authors.lastname: Fotouhi
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran ; Dezful University of Medical Sciences, Dezful, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Khabazkhoob
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran.
authors.forename: Farhad
authors.initials: F
authors.lastname: Rezvan
authors.affiliation: Noor Ophthalmology Research Center, Noor Eye Hospital, Tehran, Iran ; Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran ; International Campus (TUMS IC), Tehran, Iran.
authors.forename: Soheila
authors.initials: S
authors.lastname: Asgari
mesh_terms: D000368:Aged; D000867:Anterior Chamber / Q000033:anatomy & histology*; D058452:Axial Length, Eye / Q000033:anatomy & histology*; D001699:Biometry / Q000379:methods*; D002387:Cataract Extraction; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D055095:Optics and Photonics; D012029:Refraction, Ocular / Q000502:physiology; D012189:Retrospective Studies
keywords: Anterior Chamber Depth; Intraocular Lens Formula; Normal Axial Length