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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 73, Iss. 12 — Dec. 1, 1983
  • pp: 1701–1708

Optics of photorefraction: orthogonal and isotropic methods

Howard C. Howland, Oliver Braddick, Janette Atkinson, and Bradford Howland  »View Author Affiliations


JOSA, Vol. 73, Issue 12, pp. 1701-1708 (1983)
http://dx.doi.org/10.1364/JOSA.73.001701


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Abstract

Analysis of the optics of photorefractively computed ray tracing shows that, for short camera-to-subject distances, the function relating image size to defocus of the eye is not symmetrical for errors of focus in front of and behind the camera. This asymmetry is exploited in the new method of isotropic photorefraction, in which the supplementary cylinder lenses of the original orthogonal photorefractors are replaced by defocusing of the camera lens itself. By comparing photographs taken with the camera focused in front of and behind the subject, the sign of the eyes' defocus (myopic or hyperopic relative to the camera) can be determined. The axis of any astigmatism is readily apparent as the direction in which the photorefractive images are elongated. The method is well adapted for the refractive screening of infants and young children.

© 1983 Optical Society of America

Citation
Howard C. Howland, Oliver Braddick, Janette Atkinson, and Bradford Howland, "Optics of photorefraction: orthogonal and isotropic methods," J. Opt. Soc. Am. 73, 1701-1708 (1983)
http://www.opticsinfobase.org/josa/abstract.cfm?URI=josa-73-12-1701


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References

  1. H. C. Howland and B. Howland, "Photorefraction: a technique for study of refractive state at a distance," J. Opt. Soc. Am. 64, 240–249 (1974).
  2. O. Braddick, J. Atkinson, J. French, and H. C. Howland, "A photorefractive study of infant accommodation," Vision Res. 19, 1319–1330 (1979).
  3. We refer to instances when the subject focused at a closer distance than that of the photorefractor as myopic errors and to instances of focusing further than the photorefractor as hyperopic errors. These do not necessarily imply that with relaxed accommodation the subject would be myopic or hyperopic, respectively.
  4. This theoretical treatment ignores the influence of aberrations of the eye. Of these, longitudinal chromatic aberration results in the formation of red and blue color fringes around the photorefractive images (see Fig. 10). Spherical aberration and coma may cause some increase in the size of the photorefractive images, but it may be estimated that in most eyes this represents less than 0.1-D equivalent defocus.
  5. J. Atkinson, O. Braddick, L. Ayling, E. Pimm-Smith, H. C. Howland, and R. M. Ingram, "Isotropic photorefraction: a new method for photorefractive testing of infants," Doc. Ophthalmol. 30, 217–223 (1981).
  6. J. Atkinson and O. J. Braddick, "The use of isotropic photorefraction for vision screening in infants," Acta Ophthalmol. Suppl. 157, 36–46 (1983).
  7. J. Atkinson, O. J. Braddick, K. Durden, P. G. Watson, and S. Atkinson, "Screening of 6–9 month old infants for refractive errors using photorefraction," Br. J. Ophthalmol. (to be published).
  8. J. Atkinson and O. Braddick, "Vision screening: the relation of refractive error to strabismus and amblyopia," Behav. Brain Ryes. (to be published).
  9. V. Dobson, H. C. Howland, C. Moss, and M. S. Banks, "Photorefraction of normal and astigmatic infants during viewing of patterned stimuli," Vision Res. (to be published).
  10. H. Howland and N. Sayles, "Photorefractive measurements of astigmatism in infants and young children," Invest. Ophthalmol. (to be published).
  11. H. C. Howland, "Infant eyes: optics and accommodation," Curr. Eye Res. 2, 217–224 (1983).
  12. H. C. Howland and N. Sayles, Photorefractive studies of normal and handicapped infants and children," Behav. Brain Res. (to be published).
  13. J. Atkinson, "Assessment of vision in infants and young children," in Proceedings of the Second International Workshop on the "At Risk" Infant (Brooks, Bakersfield, Calif., to be published).
  14. K. Kaakinen, "A simple method for screening of children with strabismus, anisometropia or ametropia by simultaneous photography of the corneal and fundus reflexes," Acta Ophthalmol. 57, 161–171 (1979).
  15. K. Kaakinen, "Simultaneous two flash static photoskiascopy," Acta Ophthalmol. 59, 378–386, 1981.
  16. H. C. Howland, "The optics of photographic skiascopy," Acta Ophthalmol. 58, 221–227 (1980).

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