Evaluation of corneal biomechanical properties in mustard gas keratopathy

Role of aquaporins in corneal healing post chemical injury

Aquaporins (AQPs) are transmembrane water channel proteins that regulate the movement of water through the plasma membrane in various tissues including cornea. The cornea is avascular and has specialized microcirculatory mechanisms for homeostasis. AQPs regulate corneal hydration and transparency for normal vision. Currently, there are 13 known isoforms of AQPs that can be subclassified as orthodox AQPs, aquaglyceroporins (AQGPs), or supraquaporins (SAQPs)/unorthodox AQPs. AQPs are implicated in keratocyte function, inflammation, edema, angiogenesis, microvessel proliferation, and the wound-healing process in the cornea. AQPs play an important role in wound healing by facilitating the movement of corneal stromal keratocytes by squeezing through tight stromal matrix and narrow extracellular spaces to the wound site. Deficiency of AQPs can cause reduced concentration of hepatocyte growth factor (HGF) leading to reduced epithelial proliferation, reduced/impaired keratocyte migration, reduced number of keratocytes in the injury site, delayed and abnormal wound healing process. Dysregulated AQPs cause dysfunction in osmolar homeostasis as well as wound healing mechanisms. The cornea is a transparent avascular tissue that constitutes the anterior aspect of the outer covering of the eye and aids in two-thirds of visual light refraction. Being the outermost layer of the eye, the cornea is prone to injury. Of the 13 AQP isoforms, AQP1 is expressed in the stromal keratocytes and endothelial cells, and AQP3 and AQP5 are expressed in epithelial cells in the human cornea. AQPs can facilitate wound healing through aid in cellular migration, proliferation, migration, extracellular matrix (ECM) remodeling and autophagy mechanism. Corneal wound healing post-chemical injury requires an integrative and coordinated activity of the epithelium, stromal keratocytes, endothelium, ECM, and a battery of cytokines and growth factors to restore corneal transparency. If the chemical injury is mild, the cornea will heal with normal clarity, but severe injuries can lead to partial and/or permanent loss of corneal functions. Currently, the role of AQPs in corneal wound healing is poorly understood in the context of chemical injury. This review discusses the current literature and the role of AQPs in corneal homeostasis, wound repair, and potential therapeutic target for acute and chronic corneal injuries.

Ocular toxicity of mustard gas: A concise review

Sulfur mustard (SM) is a chemical warfare agent that has been used throughout recent history and remains a threat today. Exposed soldiers and civilians experience a variety of symptoms primarily in the respiratory system, skin, and eyes. The ocular tissues are highly sensitive to damage by SM and undergo unique manifestations of acute, chronic, and delayed complications that can persist for months and years after exposure. The mechanisms of this unique mustard gas keratopathy are still not fully understood and animal models for the study of this disease are discussed. Recent advances in mechanisms of injury are included in this review. Ophthalmic manifestations of SM injury including persistent epithelial defects, limbal stem cell deficiency, corneal neovascularization, dry eye, and corneal opacification have been reported. A wide variety of medical and surgical therapies have been studied and are reviewed here along with potential future therapies.