Aetiology
Corneal abrasions are caused by a variety of mechanisms, including direct trauma, foreign bodies, contact lenses, or recurrent erosions. Trauma can be self-induced (e.g., by fingernails) or from external objects striking the eye (e.g., branches, tools, or chemical splashes). Motor vehicle collisions with frontal airbag deployment may increase the proportion of minor eye injuries, including corneal abrasions, but decrease the overall incidence of severe eye injury.[6]
Occupations that involve grinding, cutting, and construction are likely to have a higher incidence of eye trauma due to an increased potential for foreign bodies to enter the eye. Among US automobile workers, an annual incidence of 15 work-related eye injuries per 1000 employees has been reported.[7] Corneal abrasions and superficial foreign bodies accounted for 87% of all ocular injuries. The risk of corneal abrasion is increased if protective eyewear is not worn.[7]
Foreign body-related injuries are typically caused by objects that lodge under the lid. Pieces of rust, glass, or dust are often responsible and may have spontaneously dislodged by the time of presentation.
Contact lens-related abrasions can occur during insertion but most commonly occur during removal owing to excessive adherence to the corneal epithelium, which is also removed. This can occur with relative dehydration of the lens and eye or an improper fit.
Patients are at risk of recurrent corneal erosions if they report previous injuries to the cornea, epithelial basement membrane degeneration, corneal dystrophies, or prior refractive surgery. However, they can also occur spontaneously.[4][5]
Pathophysiology
The corneal epithelium is richly innervated with pain fibres from the trigeminal nerve. Irritation of the epithelium causes severe eye pain and a foreign body sensation. Defects to the cornea typically involve the epithelial layers and do not penetrate the basement membrane (Bowman's membrane). Severe injuries, due to direct trauma, may involve deeper structures, ultimately resulting in scar formation or globe rupture.
Once injured, the cornea heals rapidly. Adjacent epithelial cells expand rapidly to fill superficial defects, typically within 1-2 days. Corneal epithelialisation may take 4-5 days for lesions covering more than 50% of the cornea.[8]
Classification
Classification by aetiology
External trauma
Injuries resulting from mechanical trauma to the eye when external objects strike the corneal epithelium.
Foreign body
Injuries from foreign bodies that may be lodged under the eyelid or on the corneal surface.
Contact lens use
Injuries caused by poorly fitting, overly worn, dehydrated, or inadequately cleaned contact lenses.
Recurrent erosions
Injuries that occur spontaneously with no immediate trauma or foreign body presence, but with structural damage to the epithelium from prior injury.
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