The cornea is the external, transparent layer of the eye covering the iris and pupil. The cornea is highly sensitive, and corneal disorders (e.g., abrasions, infection, erosion, ulcers, foreign bodies) are often painful and associated with reduced visual acuity. Diagnosis is most commonly clinical, based on slit lamp examination with fluorescein staining. Treatment includes supportive care (including analgesics) and foreign body removal, if present. Topical antibiotics may be used, e.g., in corneal abrasions and corneal ulcers. Therapeutic contact lenses are used in keratoconus. Keratoplasty (corneal transplantation) is generally a last resort for patients with significant visual impairment or failed treatment for infection.
Anatomy of the cornea
Also see “in “ .”
- Direct injury (e.g., scratch from fingernail or makeup brush)
- Foreign body under the eyelid
- Prolonged contact lens wear or improperly fitted lenses
Clinical features 
- Corneal abrasion is a clinical diagnosis.
- Perform a thorough with , including .
- Characteristic findings on slit lamp examination include:
Exclude corneal abrasion. and in all patients with
- eyelid if present. and/or
- Provide analgesia for corneal pain. 
- Consider prophylactic topical antibiotics for:
- Avoid eye patches and use caution with topical anesthetics. 
Limit use of topical NSAIDs to 2–3 days due to risk of corneal toxicity. 
- Consult ophthalmology urgently for:
- Arrange follow-up in 24 hours if corneal abrasion is > 4 mm, contact lens-related, or accompanied by a decrease in visual acuity.
- Refer to ophthalmology if symptoms have not improved at follow-up.
- Infection (e.g., )
- Corneal ulcer
- Definition: traumatic corneal defect caused by a sharp object
- Diagnostics: slit lamp examination to exclude full-thickness defects and foreign bodies 
Most commonly results from dust or debris blown into the eye during:
- High-risk activities without adequate protective eyewear, e.g., grinding, drilling, sawing, welding, mowing
- Exposure to high winds
Clinical features 
- History of sudden onset and persistent discomfort following trauma
- Signs of ocular inflammation: copious tearing, redness, foreign body sensation, difficulty keeping the eye open, photophobia, and blurred vision
- Perform a thorough eye examination, including , evaluation for , and .
- Characteristic findings on examination include:
- Visible foreign body
- Rust rings
- Corneal defect without visible foreign body
- If no foreign body is seen but suspicion of penetrating injury is high, obtain imaging (e.g., orbital CT scan or ultrasound). 
MRI is contraindicated for the evaluation of suspected metallic foreign bodies.
Corneal foreign body removal
Utilize a stepwise approach from the least to most invasive technique.
- Administer a topical anesthetic (e.g. tetracaine )
- Irrigate the affected eye copiously with saline.
- Sweep a moist cotton swab over the object and cornea.
- Attempt removal with a 25–27 gauge needle, corneal spud, or burr drill.
- Ask the patient to look at a distant object to stabilize the eye.
- Visualize the foreign body using magnification (e.g., loupes, slit lamp).
- Hold the instrument tangential to the cornea.
- If using a needle or corneal spud: Scoop or pick up the foreign body with the instrument.
- If using a burr drill: Hold the burr against the foreign body until removed.
- Residual rust rings may be removed during initial presentation or after 24–48 hours.
Do not attempt to remove the foreign body if an open globe injury is suspected.
Supportive treatment 
- Tetanus prophylaxis
- Analgesia and antibiotic prophylaxis: See “Corneal abrasion” for indications and recommendations.
- Consult ophthalmology urgently for:
- See also “Corneal abrasion.”
Complications from a corneal foreign body are rare but may include:
- Definition 
- Etiology 
- Clinical findings: sudden-onset symptoms similar to those of corneal abrasion, typically upon waking or without obvious signs of ocular trauma.
- Diagnostics: See “Corneal abrasion.”
Acute (within 24 hours of symptom onset)
- As with
- Artificial tears and nightly lubricant eye drops
- Recurrent corneal erosion or symptoms > 24 hours
- Acute (within 24 hours of symptom onset)
- Excellent, provided diagnosis and treatment are initiated promptly
- Complete healing of recurrent corneal erosion may take years.
- Corneal ulcer: (ulcerative keratitis): a defect of the corneal epithelium and underlying stroma that occurs secondary to infection or inflammation
- Infectious keratitis: an infection of the cornea (also called “infectious corneal ulcer”) 
- Peripheral ulcerative keratitis: inflammation at the margin of the corneal stroma caused by autoimmune disease (also called “peripheral corneal ulceration”) 
Corneal ulcers most frequently occur as a complication of . 
- : most common in agricultural workers and patients using corticosteroids
- Noninfectious keratitis 
Clinical features 
- Eye pain and/or foreign body sensation
- Conjunctival injection
- Blurry/decreased vision
- Discharge from eye
- Characteristic findings on slit lamp examination
- Findings indicating viral corneal ulcer
- Consult ophthalmology urgently.
- Provide .
- Corneal ulcer secondary to bacterial keratitis 
- Corneal ulcer secondary to herpes simplex keratitis 
Corneal ulcer secondary to herpes zoster keratitis
- Initiate .
- See also “Herpes zoster ophthalmicus.”
- All patients should be seen by ophthalmology within 24 hours.
- Admit patients with:
Corneal denegeration, dystrophy, and deposits
- Definition: changes of the cornea that cause corneal deterioration and, potentially, dysfunction
Band keratopathy 
- Definition: a type of corneal degeneration that involves the appearance of a band-shaped area of calcification across the central cornea 
- Pathophysiology: increased serum calcium, serum phosphate, and/or corneal surface pH (caused by chronically inflamed eyes) → change in solubility of calcium and phosphate → calcium phosphate precipitation out of tears, aqueous humor, and corneal tissue → calcium phosphate deposition as salts in the Bowman layer and superficial stroma of the cornea
- Clinical findings
- Prognosis: Visual deficits caused by band keratopathy can typically be treated successfully but will recur if the underlying condition is not addressed.
Corneal dystrophy 
- Definition: A group of inherited noninflammatory disorders that cause the buildup of various substances in the cornea and result in morphological changes.
- Classification: There are many different types of corneal dystrophy. The most common are:
- Etiology: inherited condition
Clinical findings: Because corneal dystrophies are a heterogeneous group of diseases, they can affect the eye in different ways. Symptoms may include:
- Progressive visual impairment
- Corneal erosion (see “Symptoms” in , above)
- Diagnostics: visible structural changes and/or deposits on slit lamp examination.
Fuchs dystrophy 
- Definition: inherited disease that predisposes to progressive loss of corneal endothelial cells
- Pathophysiology: corneal endothelial cells are responsible for maintaining the transparency of the cornea by balancing water and electrolyte flow into and out of the corneal layers; deterioration of corneal endothelial cells → decreased outflow of water from the corneal stroma → corneal edema, opacification, and bullous epithelial detachment 
- Clinical findings
- Early Fuchs dystrophy is asymptomatic, but cornea guttata (droplet-shaped structures in the Descemet membrane consisting of collagen and thought to have been secreted by stressed corneal endothelial cells) can be seen on slit lamp examination. 
- Advanced disease: Slit lamp examination shows corneal thickening, edema, bullae, and fibrotic scarring.
- Asymptomatic patients do not require treatment.
- Symptomatic treatment
- Keratoplasty: indicated in advanced disease with marked loss of vision that does not improve over the course of the day and if pain cannot be alleviated by symptomatic treatment
A variety of substances can accumulate in the cornea to create deposits. Two of the more well-known causes of corneal deposits are presented below.
Arcus senilis (corneal arcus)
- Definition: a condition associated with normal aging, in which annular deposits of lipids appear around the corneal margin 
Epidemiology: Incidence increases with age. 
- 60% in those 50–60 years
- Almost 100% in those > 80 years
- Clinical findings: asymptomatic
- Diagnostics: slit lamp examination
- In older patients: no treatment necessary
- Occurrence before 50 years of age: rule out
- Definition: green-brown, copper deposits are a diagnostic sign of (See “Clinical features” in Wilson disease.)
Curvature anomalies of the cornea
- Definition: a noninflammatory corneal condition in which the cornea becomes thinner than normal and develops a conic shape, bulging outward at the center 
- Etiology: unknown; frequently associated with other conditions
- Clinical findings: symptoms are often initially unilateral; however, they always become bilateral in the further course of disease 
- Treatment 
- Definition: noninflammatory corneal condition, in which the cornea becomes thinner than normal and develops a more globular shape, bulging outward at the center
- Etiology: unknown; associated with disorders of collagen synthesis (Marfan syndrome, Ehlers-Danlos syndrome)
- Clinical findings, diagnostics, and treatment: similar to those of keratoconus
Keratoplasty (corneal transplantation)
Keratoplasty (corneal transplantation) 
- Procedure: replacement of diseased cornea with cornea harvested from a recently deceased donor
- Follow-up care