What Does Ocular Chemical Corrosion Mean?
Ocular chemical corrosion refers to tissue destruction of the eye's surface structures—including the corneal epithelium, conjunctiva, limbal stem cells, and potentially deeper anterior segment structures—caused by direct contact with caustic chemical substances, most commonly acids or alkalis. 1, 2, 3
Mechanism of Injury
The pathophysiology differs dramatically based on the chemical class:
Alkali burns (e.g., sodium hydroxide, ammonia, lye) cause tissue damage through saponification of cell membranes and lipid structures, allowing deep penetration into the cornea, anterior chamber, and intraocular structures—these are generally more severe and sight-threatening. 1, 2, 3
Acid burns (e.g., sulfuric acid, hydrochloric acid) cause rapid coagulation necrosis of surface proteins, which paradoxically creates a barrier that limits deeper penetration and typically results in less severe injury compared to alkali exposure. 3
Irritants (e.g., alcohols, solvents) cause superficial epithelial denudation without deep penetration. 3
Structures Affected by Corrosion
Chemical corrosion can damage multiple ocular structures in a hierarchical pattern of severity:
Corneal epithelium: The outermost protective layer undergoes direct destruction, creating epithelial defects visible with fluorescein staining. 1, 3
Limbal stem cells: Located at the junction between cornea and conjunctiva, these cells are critical for corneal epithelial regeneration—their destruction (limbal stem cell deficiency) leads to conjunctival invasion onto the cornea and permanent scarring. 1, 4
Corneal stroma: The structural collagen framework can undergo matrix degradation, ulceration, and perforation in severe cases due to collagenase activity and direct chemical penetration. 3, 4
Conjunctiva and sclera: Ischemia, necrosis, and cicatrizing (scarring) inflammation can occur, particularly with alkali burns. 1, 3
Anterior segment structures: Iris, lens, and trabecular meshwork can be damaged by deep chemical penetration, causing cataracts, glaucoma, and pupillary abnormalities. 3, 4
Clinical Severity Grading
The extent of limbal ischemia (whitening and loss of blood vessels at the corneal-conjunctival junction) is the single most important prognostic indicator for eventual visual outcome. 2, 4
Severe chemical corrosion manifests as:
- Extensive limbal, conjunctival, and scleral ischemia and necrosis 4
- Corneal stromal opacity (clouding) indicating deep penetration 4
- Anterior chamber inflammation or abnormalities 3, 4
- Elevated or depressed intraocular pressure 3
Critical Time-Dependent Nature
The duration of chemical contact with ocular tissues directly determines the extent of tissue destruction and final visual outcome—this is why immediate, copious irrigation at the scene of injury is the single most important intervention. 1, 5, 2, 3
The term "corrosion" emphasizes the progressive, destructive nature of the chemical injury that continues as long as the caustic agent remains in contact with ocular tissues. 1, 2
Long-Term Sequelae of Corrosion
Even after initial management, chemical corrosion can lead to: