title: Minimum amount of astigmatism that should be corrected.
abstract: OBJECTIVE
  To evaluate how small amounts of astigmatism affect visual acuity and the minimum astigmatism values that should be corrected to achieve maximum visual performance.
  
  
  METHODS
  Optics Laboratory, University of Murcia, Murcia, Spain.
  
  
  METHODS
  Case series.
  
  
  METHODS
  A wavefront sensor was used to measure astigmatism and higher-order aberrations (HOAs) in normal young eyes with astigmatism ranging from 0.0 to 0.5 diopter (D). Astigmatism was corrected for natural pupil diameters using a purpose-designed cross-cylinder device. Visual acuity was measured for high-contrast and low-contrast stimuli at best subjective focus with the natural and corrected astigmatism. From the aberrations, optical image-quality metrics were calculated for 3 conditions: natural astigmatism, corrected astigmatism, and astigmatism only (with all HOAs removed).
  
  
  RESULTS
  The study evaluated 54 eyes. There was no significant correlation between the amount of astigmatism and visual acuity. The correction of astigmatism improved visual acuity for only high-contrast letters from 0.3 D, but with a high variability between subjects. Low-contrast visual acuity changed randomly as astigmatism was corrected. The correction of astigmatism increased the mean image-quality values; however, there was no significant correlation with visual performance. The deterioration in image quality given by astigmatism higher than 0.3 D was limited by HOAs.
  
  
  CONCLUSIONS
  In most subjects, astigmatism less than 0.5 D did not degrade visual acuity. This suggests that under clinical conditions, the visual benefit of precise correction of astigmatism less than 0.5 D would be limited.
authors.affiliation: From Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain.
authors.forename: Eloy A
authors.initials: EA
authors.lastname: Villegas
authors.affiliation: From Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain.
authors.forename: Encarna
authors.initials: E
authors.lastname: Alcón
authors.affiliation: From Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain. Electronic address: pablo@um.es.
authors.forename: Pablo
authors.initials: P
authors.lastname: Artal
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D057108:Corneal Wavefront Aberration / Q000175:diagnosis / Q000503:physiopathology; D005139:Eyeglasses; D006801:Humans; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult