What is corneal injury?

Corneal injury refers to damage or trauma to the cornea, which is the transparent, dome-shaped outer layer of the eye that covers the iris and pupil. The cornea plays a crucial role in focusing light onto the retina and protecting the inner structures of the eye.


Corneal injuries can occur due to various causes, including:


  • Mechanical Trauma: Mechanical injuries to the cornea can result from foreign objects entering the eye, such as dust, sand, metal fragments, or contact lenses. Scratches, abrasions, or cuts on the corneal surface can cause pain, redness, tearing, and blurred vision.


  • Chemical Exposure: Exposure to chemicals, such as acids, alkalis, solvents, or household cleaners, can cause chemical burns or irritation to the cornea. Chemical injuries can lead to severe pain, inflammation, corneal ulceration, and potentially permanent damage to the eye if not promptly treated.


  • Thermal Injury: Thermal injuries to the cornea can occur due to exposure to extreme heat or cold. For example, exposure to hot steam, flames, or welding arcs can cause thermal burns to the cornea, resulting in pain, redness, and vision changes.


  • Ultraviolet (UV) Radiation: Prolonged exposure to ultraviolet (UV) radiation from sunlight or artificial sources, such as tanning beds or welding arcs, can damage the cornea and surrounding eye structures. UV-related corneal injuries can lead to photokeratitis (sunburn of the cornea), inflammation, and temporary vision loss.


  • Infection: Bacterial, viral, or fungal infections of the cornea, such as bacterial keratitis or viral keratitis (e.g., herpes simplex keratitis), can cause inflammation, ulceration, and scarring of the corneal tissue. Infections can result from contact lens wear, eye trauma, or compromised immune function.


  • Foreign Bodies: Foreign bodies trapped under the eyelid or embedded in the cornea can cause corneal abrasions, irritation, and discomfort. Prompt removal of the foreign body is necessary to prevent further damage to the cornea and reduce the risk of infection.


What is the relationship between corneal injury and oxidative stress?

Oxidative stress plays a crucial role in mediating the cellular damage and inflammation associated with corneal injuries. When the cornea is injured or exposed to various harmful stimuli, such as mechanical trauma, chemical exposure, or infection, oxidative stress can occur due to the imbalance between the production of reactive oxygen species (ROS) and the ability of antioxidant defense mechanisms to neutralize them. Here’s how corneal injury and oxidative stress are interrelated:


  • Inflammation: Corneal injury triggers an inflammatory response characterized by the release of pro-inflammatory cytokines, chemokines, and inflammatory mediators. Activation of immune cells, such as neutrophils, macrophages, and dendritic cells, leads to the production of ROS and reactive nitrogen species (RNS) as part of the host defense mechanism. ROS serve as signaling molecules that amplify the inflammatory cascade and recruit additional immune cells to the site of injury. However, excessive ROS production can overwhelm antioxidant defenses and exacerbate inflammation, leading to tissue damage and delayed wound healing.


  • Epithelial Dysfunction: The corneal epithelium, the outermost layer of the cornea, serves as a protective barrier against environmental insults and microbial invasion. Corneal injury disrupts the integrity of the epithelial barrier and exposes underlying stromal tissue to oxidative stress. ROS generated during corneal injury induce oxidative damage to epithelial cells, leading to cell death, loss of cell junctions, and impaired epithelial regeneration. Oxidative stress-mediated epithelial dysfunction compromises the cornea’s ability to repair and regenerate, prolonging the healing process and increasing susceptibility to infection.


  • Stromal Remodeling: The corneal stroma, the middle layer of the cornea, provides structural support and transparency to the tissue. Corneal injury can induce stromal remodeling characterized by collagen degradation, fibroblast activation, and extracellular matrix remodeling. ROS generated by activated fibroblasts and infiltrating immune cells contribute to oxidative modifications of collagen fibers and matrix proteins, leading to impaired stromal architecture and corneal opacity. Oxidative stress-mediated stromal remodeling can compromise corneal transparency and visual acuity, resulting in long-term vision impairment.


  • Neovascularization: Corneal injury and inflammation can stimulate the growth of new blood vessels (neovascularization) into the cornea, which compromises its optical clarity and visual function. ROS generated during corneal injury promote angiogenesis by inducing the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). Excessive angiogenesis in the cornea exacerbates inflammation, impairs wound healing, and increases the risk of corneal scarring and vision loss.


  • Endothelial Dysfunction: The corneal endothelium, the innermost layer of the cornea, maintains corneal transparency by regulating corneal hydration and deterring stromal swelling. Corneal injury and oxidative stress can impair endothelial function, leading to endothelial cell loss, corneal edema, and endothelial dysfunction. ROS-induced endothelial damage compromises pump function and barrier integrity, resulting in corneal decompensation and visual disturbances.


Overall, oxidative stress plays a critical role in mediating cellular damage, inflammation, and tissue remodeling in response to corneal injury.