Abstract
The growth and maintenance of nearly every tissue in the body is influenced by systemic hormones during embryonic development through puberty and into adulthood. Of the ~130 different hormones expressed in the human body, steroid hormones and peptide hormones are highly abundant in circulation and are known to regulate anabolic processes and wound healing in a tissue-dependent manner. Of interest, differential levels of sex hormones have been associated with ocular pathologies, including dry eye disease and keratoconus. In this review, we discuss key studies that have revealed a role for androgens and estrogens in the cornea with focus on ocular surface homeostasis, wound healing, and stromal thickness. We also review studies of human growth hormone and insulin growth factor-1 in influencing ocular growth and epithelial regeneration. While it is unclear if endogenous hormones contribute to differential corneal wound healing in common animal models, the abundance of evidence suggests that systemic hormone levels, as a function of age, should be considered as an experimental variable in studies of corneal health and disease.
Highlights
The cornea is an avascular, immune-privileged, transparent tissue located at the front of the eye that protects the posterior segments from infection and injury
The cornea is avascular, it is evident that certain factors found in circulation may reach the cornea via diffusion from the tear film and/or aqueous humor
The endogenous expression of certain hormones by resident cells found within the cornea has been posited as a local source of these factors in the anterior segment
Summary
The cornea is an avascular, immune-privileged, transparent tissue located at the front of the eye that protects the posterior segments from infection and injury. An overlaying tear film on the surface of the cornea is essential for providing dissolved oxygen and nutrients to the corneal epithelium and lubrication of the ocular surface, while maintaining an anti-microbial environment with the presence of lysozyme and other proteins that inhibit bacterial and fungal growth The tear film functions as a conduit for systemic factors, including metabolites and hormones, to reach the corneal surface. The effects of androgens and estrogens (both cholesterol-derived) and growth hormone (GH, peptide) on tissue growth and regeneration have been most-well characterized due to their high systemic abundance and targeted effects associated with aging, and we focus our review of the literature on these select hormones. We focus on the broad function of hormones in corneal physiology with a review of the sex hormones (androgens and estrogens) and growth-associated hormones, GH and IGF-1, and their reported roles in ocular surface maintenance, wound healing, and tissue growth
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