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The corneal surface of aquatic vertebrates: microstructures with optical and nutritional function?
1Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria, Australia.
Summary
Corneal surface structures vary across vertebrate species, adapting to different environments to maintain a clear optical surface. These adaptations, including microprojections and cell density changes, support tear film stability and visual function.
Area of Science:
- Comparative anatomy
- Ophthalmology
- Evolutionary biology
Background:
- The mammalian cornea's anterior surface is crucial for sharp vision, supported by a tear film adhering to microprojections.
- Little is known about corneal structural adaptations and tear film support in non-mammalian vertebrates across diverse environments.
Purpose of the Study:
- To examine the density and surface structure of corneal epithelial cells in diverse vertebrate species.
- To understand how corneal adaptations relate to different aquatic environments and tear film support.
Main Methods:
- Field emission scanning electron microscopy (FESEM) was used to analyze corneal surface morphology.
- Species from Cephalaspidomorphi, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia were studied.
Main Results:
- Epithelial cell density decreases progressively from marine to freshwater to terrestrial vertebrates, correlating with reduced osmotic stress.
- Unique microholes in lamprey corneas may release mucus for abrasion protection during burrowing.
- Corneal microridges, common in marine teleosts, stabilize the tear film and enhance epithelial surface area for diffusion.
Conclusions:
- Interspecific variations in corneal surface structure indicate adaptive plasticity in tear film composition and stabilization.
- These findings highlight evolutionary adaptations of the cornea to diverse environmental challenges.