title: The influence of unilateral uncorrected astigmatism on binocular vision and fixation disparity.
abstract: OBJECTIVE
  It is accepted practice to use a spherical equivalent power as an alternative contact lens correction for those patients with lower amounts of astigmatism, allowing for an easier fit, but the blur caused by one diopter of uncorrected astigmatism can reduce acuity of 6/6 to that of about 6/8. This is usually deemed acceptable monocularly, often retaining a good binocular acuity. The purpose of this study is to explore how monocular astigmatic blur may also affect the patient's binocular vision function.
  
  
  METHODS
  A trial frame was outfitted with full correction for 20 healthy subjects (mean age 25.5 years, range 19-36 years) and a baseline horizontal fixation disparity was measured at a distance of 1 m. Thereafter, fixation disparity was measured with induced monocular astigmatic blur in the right eye, creating an astigmatic error in the amounts of -0.75 and -1.25 in axis 90 and axis 45.
  
  
  RESULTS
  It was determined that the differences among full correction and the 4 different types of astigmatic blur were not significant when analyzed as one group (P = 0.5445), nor when separated into groups according to whether the subject had naturally occurring astigmatism or not, (astigmatic group, P = 0.3801; non-astigmatic group, P = 0.5899).
  
  
  CONCLUSIONS
  Monocular astigmatic blur in the amounts of -0.75 and -1.25 did not have a significant effect on tested subjects with regard to the amount of blur or axis orientation. This low amount of blur is likely within the range of compensation for the subjects, proving that spherical equivalent contact lenses are a viable option for low amounts of astigmatic error.
authors: Unit of Optometry, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors: April
authors: A
authors: Nilsson
authors: Maria
authors: M
authors: Nilsson
authors: Scott B
authors: SB
authors: Stevenson
authors: Rune L
authors: RL
authors: Brautaset
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology*; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D012029:Refraction, Ocular / Q000502:physiology; D015357:Vision Disparity / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult