title: Interocular differences in visual latency induced by reduced-aperture monovision.
abstract: OBJECTIVE
  To explore the interocular differences in the temporal responses of the eyes induced by the monocular use of small-aperture optics designed to aid presbyopes by increasing their depth-of-focus.
  
  
  METHODS
  Monocular and binocular pattern-reversal visual evoked potentials (VEPs) were measured at a mean photopic field luminance of 30 cd/m(2) in seven normal subjects with either natural pupils or when the non-dominant eye wore a small-aperture contact lens (aperture diameter 1.5, 2.5 or 3.5 mm, or an annular opaque stop of inner and outer diameters 1.5 and 4.0 mm respectively). Responses were also measured with varying stimulus luminance (5, 13.9, 27.2 and 45 cd/m(2)) and a fixed 3.0 mm artificial pupil.
  
  
  RESULTS
  Mean natural pupil diameters were 4.7 and 4.4 mm under monocular and binocular conditions respectively. The small-aperture contact lenses reduced the amplitude of the P100 component of the VEP and increased its latency. Inter-ocular differences in latency rose to about 20-25 ms when the pupil diameter of the non-dominant eye was reduced to 1.5 mm. The measurements with fixed pupil and varying luminance suggested that the observed effects were explicable in terms of the changes in retinal illuminance produced by the restrictions in pupil area.
  
  
  CONCLUSIONS
  The anisocoria induced by small-aperture approaches to aid presbyopes produces marked interocular differences in visual latency. The literature of the Pulfrich effect suggests that such differences can lead to distortions in the perception of relative movement and, in some cases, to possible hazard.
authors.affiliation: Institute of Vision and Optics, School of Health Sciences, University of Crete, Crete, Greece. plainis@med.uoc.gr
authors.forename: Sotiris
authors.initials: S
authors.lastname: Plainis
authors.forename: Dionysia
authors.initials: D
authors.lastname: Petratou
authors.forename: Trisevgeni
authors.initials: T
authors.lastname: Giannakopoulou
authors.forename: Hema
authors.initials: H
authors.lastname: Radhakrishnan
authors.forename: Ioannis G
authors.initials: IG
authors.lastname: Pallikaris
authors.forename: W Neil
authors.initials: WN
authors.lastname: Charman
mesh_terms: D000328:Adult; D003261:Contact Lenses; D003867:Depth Perception / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D011305:Presbyopia / Q000503:physiopathology*; D011680:Pupil / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology; D015349:Vision, Monocular / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*