Advertisement

Journal of Comparative Physiology A

, Volume 190, Issue 2, pp 131–137 | Cite as

Variations in the off-axis refractive state in the eye of the Vietnamese leaf turtle (Geoemyda spengleri)

  • M. J. Henze
  • F. Schaeffel
  • M. OttEmail author
Original Paper

Abstract

Lower-field myopia has been described for various vertebrates as an adaptation that permits the animal to keep the ground in focus during foraging, and, at the same time, to look out for distant objects, such as predators, in the upper visual field. Off-axis measurements with infrared photoretinoscopy in the eye of Geoemyda spengleri revealed a constant refractive state in the horizontal plane of the visual field but variable refraction in the vertical plane. In the three turtles investigated, the refractions increased continuously from the ventral to the dorsal visual field over a range of 35, 40 and 56 D, respectively. While this finding confirms the presence of an adaptive change of the refractive state equivalent to lower field myopia, subsequent measurements with a rotated retinoscope showed that at least part of the variation in the ventral field was attributed to astigmatism. The reason for this astigmatism is unknown. Anatomical investigation of the retina revealed that the constant refractive values in the horizontal plane corresponded to a stripe of increased ganglion cell density. A maximum density of 4,200 ganglion cells mm−2 was counted in the centre of this visual streak.

Keywords

Astigmatism Infrared photoretinoscopy Lower-field myopia Ramp retina Visual streak 

Notes

Acknowledgements

We thank M. and W. Matzanke for putting their Vietnamese leaf turtles at our disposal to take some preliminary measures. The experiments reported in this paper comply with the Principles of Animal care, publication No. 86-23, revised 1985, of the National Institutes of Health and were carried out in accordance with the German “Tierschutzgesetz”.

References

  1. Bellintani-Guardia B, Ott M (2002). Displaced retinal ganglion cells project to the accessory optic system in the chameleon (Chamaeleo calyptratus). Exp Brain Res 145:56–63CrossRefPubMedGoogle Scholar
  2. Brown KT (1969) A linear area centralis extending across the turtle retina and stabilised to the horizon by non-visual cues. Vision Res 9:1053–1062CrossRefPubMedGoogle Scholar
  3. Catania AC (1964) On the visual acuity of the homing pigeon. J Exp Anal Behav 7:361–366Google Scholar
  4. DeCarlo L, Salmon M, Wyneken J (1998) Comparative studies of retinal design among sea turtles: histological and behavioral correlates of the visual streak. Proceedings of the 18th International Symposium on Sea Turtle Biology and ConservationGoogle Scholar
  5. Diether S, Schaeffel F (1997) Local changes in the eye growth induced by imposed local refractive error despite active accommodation. Vision Res 37:659–668CrossRefPubMedGoogle Scholar
  6. Fitzke FW, Hayes BP, Hodos W, Holden AL, Low JC (1985) Refractive sectors in the visual field of the pigeon eye. J Physiol (Lond) 369:17–31Google Scholar
  7. Glickstein M, Millodot M (1970) Retinoscopy and eye size. Science 168:605–606PubMedGoogle Scholar
  8. Henze M, Schaeffel F, Wagner HJ, Ott M (2004) Accommodation behavior during prey capture in the vietnamese leaf turtle (Geoemyda spengleri). J Comp Physiol A (in press)Google Scholar
  9. Hodos W, Erichsen T (1990) Lower-field myopia in birds: an adaptation that keeps the ground in focus. Vision Res 30:653–657CrossRefPubMedGoogle Scholar
  10. Land MF, Nilsson DE (2002) Animal eyes. Oxford University Press, New YorkGoogle Scholar
  11. Miles FA, Wallman J (1990) Local ocular compensation for imposed local refractive error. Vision Res 30:339–349CrossRefPubMedGoogle Scholar
  12. Millodot M, Blough P (1971) The refractive state of the pigeon eye. Vision Res 11:1019–1022CrossRefPubMedGoogle Scholar
  13. Nye PW (1973) On the functional differences between the frontal and lateral visual fields of the pigeon. Vision Res 13:559–574CrossRefPubMedGoogle Scholar
  14. Ott M, Schaeffel F, Kirmse W (1998) Binocular vision and accommodation in prey-catching chameleons. J Comp Physiol A 182:319–330CrossRefGoogle Scholar
  15. Peterson EH, Ulinski PS (1979) Quantitative studies of retinal ganglion cells in a turtle, Pseudemys scripta elegans. I. Number and distribution of ganglion cells. J Comp Neurol 186:17–42PubMedGoogle Scholar
  16. Schaeffel F, Farkas L, Howland HC (1987) Infrared photoretinoscope. Appl Opt 26:1505–1509Google Scholar
  17. Schaeffel F, Hagel G, Eikermann J, Collett T (1994) Lower-field myopia and astigmatism in amphibians and chickens. J Opt Soc Am A 11:487–495PubMedGoogle Scholar
  18. Sivak JG (1976) The accommodative significance of the ramp retina in the eye of the stingray. Vision Res 16:945–950CrossRefPubMedGoogle Scholar
  19. Walls GL (1942) The vertebrate eye and its adaptive radiation. Hafner, New YorkGoogle Scholar

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  1. 1.Institute for AnatomyUniversity of TübingenTübingenGermany
  2. 2.Section of Neurobiology of the Eye, Department IIUniversity Eye HospitalTübingenGermany

Personalised recommendations