title: Influence of posterior corneal astigmatism on total corneal astigmatism in eyes with moderate to high astigmatism.
abstract: OBJECTIVE
  To evaluate the influence of posterior corneal astigmatism on total corneal astigmatism in patients with 1.00 diopter (D) or more of corneal astigmatism.
  
  
  METHODS
  Private practice, Bologna, Italy.
  
  
  METHODS
  Prospective case series.
  
  
  METHODS
  Corneal astigmatism was measured using a Scheimpflug camera combined with a corneal topographer (Sirius). Keratometric astigmatism, anterior corneal astigmatism, posterior corneal astigmatism, and total corneal astigmatism were evaluated. Vector analysis was performed according to the Næser method.
  
  
  RESULTS
  One hundred fifty-seven eyes were enrolled. Keratometric astigmatism was with the rule (WTR), against the rule (ATR), and oblique in 84.0%, 11.5%, and 4.5% of eyes, respectively. Posterior corneal astigmatism exceeded 0.50 D and 1.00 D in 55.4% of eyes and 5.7% of eyes, respectively. The mean posterior corneal astigmatism was 0.54 D, inclined 91 degrees in relation to the steeper anterior corneal meridian. The steepest meridian was vertically aligned in 93.0% of cases. Compared with total corneal astigmatism, keratometric astigmatism overestimated WTR astigmatism by a mean of 0.22 D ± 0.32 (SD), underestimated ATR astigmatism by 0.21 ± 0.26 D, and overestimated oblique astigmatism by 0.13 ± 0.37 D. In the whole sample, a difference in astigmatism magnitude of 0.50 D or more was detected between keratometric astigmatism and total corneal astigmatism in 16.6% of cases and the difference in the location of the steep meridian was greater than 10 degrees in 3.8% of cases.
  
  
  CONCLUSIONS
  In patients who are candidates for surgical correction of astigmatism, measuring only the anterior corneal curvature can lead to inaccurate evaluation of the total corneal astigmatism.
  
  
  BACKGROUND
  Mr. Versaci and Mr. Vestri are employees of Costruzione Strumenti Oftalmici Srl. No author has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark. Electronic address: giacomo.savini@alice.it.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.affiliation: From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark.
authors.forename: Francesco
authors.initials: F
authors.lastname: Versaci
authors.affiliation: From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Vestri
authors.affiliation: From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark.
authors.forename: Pietro
authors.initials: P
authors.lastname: Ducoli
authors.affiliation: From the Studio Oculistico d'Azeglio (Savini), Bologna, G.B. Bietti Eye Foundation I.R.C.C.S. (Ducoli), Rome, and Costruzione Strumenti Oftalmici Srl (Versaci, Vestri), Florence, Italy; School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University (Savini), Wenzhou, Zhejiang, China; Regions Hospital Randers (Næser), Randers, Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Næser
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000175:diagnosis*; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography; D004728:Endothelium, Corneal / Q000473:pathology; D019573:Epithelium, Corneal / Q000473:pathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010781:Photography / Q000379:methods; D011446:Prospective Studies