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Unique morphology of the human eye


Human eyes have a widely exposed white sclera surrounding the darker coloured iris, making it easy to discern the direction in which they are looking1. We compared the external morphology of primate eyes in nearly half of all primate species, and show that this feature is uniquely human. Humans have the largest ratio of exposed sclera in the eye outline, which itself is elongated horizontally. We suggest that these are adaptations to extend the visual field by allowing greater eye movement, especially in the horizontal direction, and to enhance the ease of detecting the gaze direction of another individual.

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Figure 1: Variation of WHR and SSI (mean±s. d.).
Figure 2: Relationship between SSI and walking height.


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We thank our colleagues for discussion and for communicating unpublished results; P. Freemont, N. Jones and A. Parker for their suggestions and for critically reading the manuscript; P. Chambon for pBL1, pASV3 and the anti-ER monoclonal antibody; B. Katzenellenbogen for 2EREppS2-CAT; N. Jones for the yeast strain; K. Hobbs for oligonucleotides; N. O'Reilly for peptides; W. Bessant for photography; and G. Clark for automated sequencing. D.M.H. and E.K. were supported by grants from the European Community TMR program and the Netherlands Organisation of Scientific Research (NWO), respectively.

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Kobayashi, H., Kohshima, S. Unique morphology of the human eye. Nature 387, 767–768 (1997).

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