Refractive Index of the Mammalian Cornea and Its Influence During Pachometry

Patei, S.

doi:10.1111/j.1475-1313.1987.tb00787.x

Cited by 10 publications

(1 citation statement)

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“…The refractive properties of the cornea are governed by Snell's law, also known as the law of refraction, which dictates that when light travels between two isotropic media, such as water, glass or air, the angle of refraction is proportional to the difference in refractive indices between the two media. Since the evolution of the vertebrate eye initially occurred in water, the cornea with a refractive index (1.376) almost identical to that of water (1.333) played little role in the refraction of light to the retina regardless of corneal shape, serving primarily as a transparent protective cover, while the crystalline lens with a higher refractive index (1.4-1.5) performed the refractive function (Collin and Collin, 2000;Leonard and Meek, 1997;Patel, 1987;Patel, Marshall and Fitzke, 1995;Sivak et al, 1989). The vertebrate cornea has a greater potential refractive power in air given the difference in the refractive index between air (1.000) and the cornea.…”

Section: Introductionmentioning

confidence: 99%

Evolution of the vertebrate corneal stroma

Koudouna

Winkler

Mikula

et al. 2018

Progress in Retinal and Eye Research

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Although the cornea is the major refractive element of the eye, the mechanisms controlling corneal shape and hence visual acuity remain unknown. To begin to address this question we have used multiphoton, non-linear optical microscopy to image second harmonic generated signals (SHG) from collagen to characterize the evolutionary and structural changes that occur in the collagen architecture of the corneal stroma. Our studies show that there is a progression in complexity of the stromal collagen organization from lower (fish and amphibians) to higher (birds and mammals) vertebrates, leading to increasing tissue stiffness that may control shape. In boney and cartilaginous fish, the cornea is composed of orthogonally arranged, rotating collagen sheets that extend from limbus to limbus with little or no interaction between adjacent sheets, a structural paradigm analogous to 'plywood'. In amphibians and reptiles, these sheets are broken down into broader lamellae that begin to show branching and anastomosing with adjacent lamellae, albeit maintaining their orthogonal, rotational organization. This paradigm is most complex in birds, which show the highest degree of lamellar branching and anastomosing, forming a 'chicken wire' like pattern most prominent in the midstroma. Mammals, on the other hand, diverged from the orthogonal, rotational organization and developed a random lamellar pattern with branching and anastomosing appearing highest in the anterior stroma, associated with higher mechanical stiffness compared to the posterior stroma.

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Section: Introductionmentioning

confidence: 99%