title: Location of achromatizing pupil position and first Purkinje reflection in a normal population.
abstract: OBJECTIVE
  Quality of vision in patients who have undergone corneal refractive surgery depends upon the optimal centration of the procedures used. The center of the pupil is used as a reference point in some corneal ablation procedures. The achromatic axis would be a more sensible option from an optical point of view, but it is not as readily detectable. As an alternative, other refractive techniques, like the small aperture corneal inlay for presbyopia correction, use the corneal reflex (first Purkinje image). To assess the relative position of these two marks, we developed a new instrument to simultaneously measure both the first Purkinje image (PI) and the intersection of the achromatic axis with the pupil plane.
  
  
  METHODS
  The apparatus records images of the pupil and the PI when illuminated with a circle of infrared light-emitting diodes. A second optical path allows determination of the achromatic axis by using a subjective method. Both the positions of the PI and the achromatic axis intersection are determined simultaneously.
  
  
  RESULTS
  A series of data were obtained in 48 eyes. The mean location of the achromatic point relative to the PI was [x = -0.05 ± 0.15 mm; y = 0.09 ± 0.18 mm]. Considered individually, in 55% of eyes, the distance between locations is less than 0.2 mm, and in 95% of eyes, distances are less than 0.4 mm.
  
  
  CONCLUSIONS
  On average, achromatic axis crossing of the pupil and PI locations coincides within measurement errors. Although there was some intersubject variability, differences in location were less than 0.6 mm in all measured eyes.
authors.affiliation: Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), Murcia, Spain.
authors.forename: Silvestre
authors.initials: S
authors.lastname: Manzanera
authors.affiliation: Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), Murcia, Spain.
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Prieto
authors.affiliation: Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), Murcia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Benito
authors.affiliation: Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), Murcia, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Tabernero
authors.affiliation: Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), Murcia, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Artal
mesh_terms: D057128:Aberrometry / Q000379:methods; D000328:Adult; D001767:Blinking / Q000502:physiology*; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011305:Presbyopia / Q000175:diagnosis* / Q000503:physiopathology; D011680:Pupil / Q000502:physiology*; D012016:Reference Values; D014792:Visual Acuity; D055815:Young Adult
keywords: Purkinje images; achromatic axis; centration; corneal inlay; presbyopia; small aperture