Ultrastructure of the human cornea

Abstract

The transparent nature of the cornea and its importance in the visual pathway as the major refracting lens of the eye have intrigued workers in many different disciplines and their studies have added immeasurably to the understanding of the cornea in health and disease. Reviews of the structure of the cornea date back to the earliest days of electron microscopy (Hogan et al., 1971; Klyce and Beuerman, 1988; Kuwabara, 1978; Rouiller et al., 1954), yet, due to changing insights into corneal structure provided by cell biology, as well as new clinical developments, current ultrastructural reviews of the cornea have new relevance in both basic science and clinical ophthalmic research. Evolving as an avascular tissue with the need for increasingly better optical properties, the cornea has acquired many unique structural adaptations. In addition to its optical properties, the cornea also serves a major protective function for the visual organ. The position at the front of the globe subjects the cornea to the greatest number of interactions with the environment of any ocular structure. It is subject to insult from both airborne and solid objects, as well as disease organisms, and has developed an elaborate array of sensory nerves to signal impending danger. At birth, the cornea is relatively large compared with the rest of the globe. The growth of the cornea occurs mainly between the ages of six months and one year, although the adult size of approximately 1.3 cm2 is not attained until some time between the first and second years. The optical properties of the anterior surface, or tear surface, of the cornea have become increasingly refined in mammals to allow more precise image projection at the retina (Walls, 1942). Specialized skin covering the eye in lower vertebrates, for example in the lamprey, has given way to a refracting surface in amphibians and, ultimately, to the cornea and lids in mammals. However, the more primitive structures are not as clear as the mammalian and human cornea, and a layer similar to Bowman's in human corneas begins to be seen in reptiles and birds (Thomas, 1955). © 1996 Wiley‐Liss, Inc.

Histological evaluation of mechanical epithelial separation in epithelial laser in situ keratomileusis

“…The lamina fibroreticularis lies beneath the lamina densa, contains anchoring fibrils comprising type VII collagen, and forms a complex network with type I and type V collagens to attach the epithelium and its basement membrane to the underlying Bowman layer (Figure 1). [15][16][17] Although the clinical outcomes of epi-LASIK have been evaluated, [18][19][20] the exact site of epithelial separation during epi-LASIK remains unclear. Pallikaris et al 12 found that the epithelial separation was beneath the basement membrane with intact basal cells.…”

A comparative study of the corneal endothelium in vertebrates

“…In some mammals, there is a mitotic turnover of endothelial cells and a mitotic response to endothelial injury. 2 However, in both human and non-human primates, although mitosis occurs in the young, 32 the endothelial cell population does not regenerate in any significant fashion in the adult. 2,32 This gives rise to a decreasing cell density with age.…”

Characterization of immortalized rabbit lacrimal gland epithelial cells

“…Warm fixative consisting of 2% glutaraldehyde and 1% paraformaldehyde in 0.1 M sodimn cacodylate (NaC) buffer (pH 7.4) containing 0.02% picric acid was slowly introduced into the plate and left for 2 h (Beuerman and Pedroza, 1996). The plates were washed with 0.1 M NaC buffer and the cells were scraped off the plate, pelleted, briefly resuspended, and transferred to a 1.5-ml nficrocentrifuge tube.…”