title: Influence of different types of astigmatism on visual acuity.
abstract: OBJECTIVE
  To investigate the change in visual acuity (VA) produced by different types of astigmatism (on the basis of the refractive power and position of the principal meridians) on normal accommodating eyes.
  
  
  METHODS
  The lens induced method was employed to simulate a set of 28 astigmatic blur conditions on different healthy emmetropic eyes. Additionally, 24 values of spherical defocus were also simulated on the same eyes for comparison. VA was measured in each case and the results, expressed in logMAR units, were represented against of the modulus of the dioptric power vector (blur strength).
  
  
  RESULTS
  LogMAR VA varies in a linear fashion with increasing astigmatic blur, being the slope of the line dependent on the accommodative demand in each type of astigmatism. However, in each case, we found no statistically significant differences between the three axes investigated (0°, 45°, 90°). Non-statistically significant differences were found either for the VA achieved with spherical myopic defocus (MD) and mixed astigmatism (MA). VA with simple hyperopic astigmatism (SHA) was higher than with simple myopic astigmatism (SMA), however, in this case non conclusive results were obtained in terms of statistical significance. The VA achieved with imposed compound hyperopic astigmatism (CHA) was highly influenced by the eye's accommodative response.
  
  
  CONCLUSIONS
  VA is correlated with the blur strength in a different way for each type of astigmatism, depending on the accommodative demand. VA is better when one of the focal lines lie on the retina irrespective of the axis orientation; accommodation favors this situation.
authors.affiliation: Centro de Tecnologías Físicas, Universitat Politècnica de València, 46022 Valencia, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Remón
authors.affiliation: Centro de Tecnologías Físicas, Universitat Politècnica de València, 46022 Valencia, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Monsoriu
authors.affiliation: Departamento de Óptica y Optometría y Ciencias de la Visión, Universitat de València, 46100 Burjassot, Spain. Electronic address: walter.furlan@uv.es.
authors.forename: Walter D
authors.initials: WD
authors.lastname: Furlan
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D001251:Astigmatism / Q000503:physiopathology* / Q000628:therapy; D005139:Eyeglasses; D005260:Female; D006801:Humans; D008297:Male; D011932:Reading; D014792:Visual Acuity
keywords: Accommodation state; Agudeza visual; Astigmatism; Astigmatismo; Axis; Defecto esférico; Eje; Estado de acomodación; Spherical defocus; Visual acuity