A comparative study of vertebrate corneal structure: The evolution of a refractive lens

Moritz Winkler, Golroxan Shoa, Stephanie T. Tran, Yilu Xie, Sara M Thomasy, Vijay K. Raghunathan, Christopher J Murphy, Donald J. Brown, James V. Jester

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

PURPOSE. Although corneal curvature plays an important role in determining the refractive power of the vertebrate eye, the mechanisms controlling corneal shape remain largely unknown. To address this question, we performed a comparative study of vertebrate corneal structure to identify potential evolutionarily based changes that correlate with the development of a corneal refractive lens. METHODS. Nonlinear optical (NLO) imaging of second-harmonic-generated (SHG) signals was used to image collagen and three-dimensionally reconstruct the lamellar organization in corneas from different vertebrate clades. RESULTS. Second-harmonic-generated images taken normal to the corneal surface showed that corneal collagen in all nonmammalian vertebrates was organized into sheets (fish and amphibians) or ribbons (reptiles and birds) extending from limbus to limbus that were oriented nearly orthogonal (ranging from 77.7°-88.2°) to their neighbors. The slight angular offset (2°-13°) created a rotational pattern that continued throughout the full thickness in fish and amphibians and to the very posterior layers in reptiles and birds. Interactions between lamellae were limited to “sutural” fibers in cartilaginous fish, and occasional lamellar branching in fish and amphibians. There was a marked increase in lamellar branching in higher vertebrates, such that birds ≫ reptiles > amphibians > fish. By contrast, mammalian corneas showed a nearly random collagen fiber organization with no orthogonal, chiral pattern. CONCLUSIONS. Our data indicate that nonmammalian vertebrate corneas share a common orthogonal collagen structural organization that shows increased lamellar branching in higher vertebrate species. Importantly, mammalian corneas showed a different structural organization, suggesting a divergent evolutionary background.

Original languageEnglish (US)
Pages (from-to)2764-2772
Number of pages9
JournalInvestigative Ophthalmology and Visual Science
Volume56
Issue number4
DOIs
StatePublished - 2015

Keywords

  • Collagen
  • Cornea
  • Nonlinear optical
  • Second-harmonic generation
  • Stroma

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems
  • Cellular and Molecular Neuroscience

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