Visual field width above the head is significantly correlated (rs = 0.92, n = 11, p < 0.001) with eye size in a sample of terrestrial birds that differ in their phylogeny and ecology. These species can be divided into two groups. Smaller-eyed sun-observers (axial length <18 mm) have comprehensive or near comprehensive visual coverage of the celestial hemisphere and are thus unable to avoid viewing the sun. Larger-eyed sun-avoiders (axial length >18 mm) have restricted visual fields and various types of optical adnexa (enlarged brows, hair like feathers on the eye lids and around the eye) which can prevent solar illumination of the cornea. We suggest that these differences relate to visual rather than pathological problems and argue that the reduction of disability glare, produced by sunlight falling directly upon the eye, becomes increasingly significant as eye size increases. We propose that the reduced visual fields and optical adnexa of the larger-eyed birds are primarily concerned with the maintenance of high spatial resolution.

Keywords:
Birds, Vision, Visual fields, Sunshades, Optical adnexa, Eye size, Spatial resolution
1.
Brooke, M.d.L., S. Hanley, and S.B. Laughlin (1999) The scaling of eye size with body mass in birds. Proc. R. Soc. Lond. B Biol. Sci., 266: 405–412.
2.
Charman, W.N. (1983) The retinal image in the human eye. In Progress in Retinal Research, Vol. 2 (ed. by N. Osborne and G. Chader), Pergamon Press, Oxford, pp. 1–50.
3.
Charman, W.N. (1989) Light on the peripheral retina. Ophthal. Physiol., 9: 91–92.
4.
Charman, W.N. (1991) Optics of the human eye. In Vision and Visual Dysfunction, Vol. 1 (ed. by W.N. Charman), Macmillan, London, pp. 1–26.
5.
del Hoyo, J., A. Elliott, and J. Sargatal (1992) Handbook of the Birds of the World, Vol. 1, Lynx Edicions, Barcelona.
6.
Dickinson, C.M. (1991) Optical aids for low vision. In Vision and Visual Dysfunction, Vol. 1 (ed. by W.N. Charman), Macmillan, London, pp. 183– 228.
7.
Ho A., and S.M. Bilton (1986) Low contrast charts effectively differentiate between types of blur. Am. J. Ophthal. Physiol. Opt., 63: 202–208.
8.
Hughes, A. (1977) The topography of vision in mammals of contrasting life style: comparative optics and retinal organization. In Handbook of Sensory Physiology, Vol. VII/5 (ed. by F. Crescitelli), Springer-Verlag, Berlin, pp. 613–756.
9.
Katzir, G., and G.R. Martin (1998) Visual fields in the Black-crowned Night Heron Nycticorax nycticorax: nocturnality does not result in owl-like features. Ibis, 140: 157–162.
10.
Land, M.F. (1981) Optics and vision in invertebrates. In Handbook of Sensory Physiology, Vol. VII/6B (ed. by H. Autrum), Springer, Berlin, pp. 471–592.
11.
Le Claire, J., M.P. Nadler, S. Weiss, and D. Miller (1982) A new glare tester for clinical testing: results comparing normal subjects and variously corrected aphakic patients. Arch. Ophthal., 100: 153–158.
12.
Marshall, J. (1991) The effect of ultraviolet radiation and blue light on the eye. In Vision and Visual Dysfunction, Vol. 16 (ed. by J. Marshall), Macmillan, London, pp. 54–66.
13.
Martin, G.R. (1984) The visual fields of the tawny owl, Strix aluco L. Vision Res., 24: 1739–1751.
14.
Martin, G.R. (1986a) The eye of a passeriform bird, the European starling (Sturnus vulgaris): eye movement amplitude, visual fields and schematic optics. J. Comp. Physiol. A, 159: 545–557.
15.
Martin, G.R. (1986b) Total panoramic vision in the mallard duck, Anas platyrhynchos. Vision Res., 26: 1303–1306.
16.
Martin, G.R. (1994) Visual fields in woodcocks Scolopax rusticola (Scolopacidae; Charadriiformes). J. Comp. Physiol. A, 174: 787–793.
17.
Martin, G.R. (1998b) Eye structure and amphibious foraging in albatrosses. Proc. R. Soc. Lond. B Biol. Sci., 265: 1–7.
18.
Martin, G.R. (1998a) Optical structure and visual field in birds: their relationship with foraging behaviour and ecology. In Adaptive Mechanisms in the Ecology of Vision (ed. by J. Archer, M.B.A. Djamgoz, E.R. Loew, J.C. Partridge, and S. Vallerga), Chapman and Hall, London, pp. 485–508.
19.
Martin, G.R., and G. Katzir (1994a) Visual fields and eye movements in herons (Ardeidae). Brain Behav. Evol., 44: 74–85.
20.
Martin, G.R., and G. Katzir (1994b) Visual fields in the stone curlew Burhinus oedicnemus. Ibis, 136: 448–453.
21.
Martin, G.R., and G. Katzir (1995) Visual fields in ostriches. Nature, 374: 19–20.
22.
Martin, G.R., and G. Katzir (1999) Visual field in Short-toed eagles Circaetus gallicus and the function of binocularity in birds. Brain Behav. Evol., 53: 55–66.
23.
Martin, G.R., and S.R. Young (1983) The retinal binocular field of the pigeon (Columba livia): English racing homer. Vision Res., 23: 911– 915.
24.
Reymond, L. (1985) Spatial visual acuity of the eagle Aquila audax: a behavioural, optical and anatomical investigation. Vision Res., 25: 1477–1491.
25.
Shlaer, R. (1972) An eagle’s eye: quality of retinal image. Science, 176: 920–922.
26.
Sliney, D.H. (1985) Looking at light. Res. Clin. Forums, 7: 9–16.
27.
Sliney, D. H. (1991) Measurement of light exposure and the geometry of exposure of the human eye. In Vision and Visual Dysfunction, Vol. 16 (ed. by J. Marshall), Macmillan, London, pp. 23– 29.
28.
Westheimer, G. (1972) Visual acuity and spatial modulation thresholds. In Handbook of Sensory Physiology, Vol. VII/4 (ed. by D. Jameson and L.M. Hurvich), Springer-Verlag, Berlin, pp. 170–187.
29.
Whiten, A. (1978) Operant studies on pigeon orientation and navigation. Anim. Behav., 26: 571– 610.
30.
Wiltschko, R., and W. Wiltschko (1999) The orientation system of birds – 1. Compass mechanisms. J. Ornithol., 140: 1–40.
© 2001 S. Karger AG, Basel
2001
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.