Corneal disorders

The cornea is the transparent, outermost layer of the eye. Certain corneal conditions, such as infection, injury, abnormal curvature, and opacification, can cause restricted vision. Because the cornea is well innervated by the ophthalmic branch of the trigeminal nerve, it is very sensitive and corneal disorders are often painful. Diagnosis of corneal disorders is made via slit lamp examination and, in some cases (e.g., corneal abrasion or erosion), fluorescein staining. Treatment typically involves local measures, such as antibiotic eye drops, ointments, and therapeutic contact lenses. Corneal transplantation is generally only performed as a last resort in patients with significant visual impairment or failed treatment for infection.

This article covers the following corneal disorders: corneal abrasion, corneal erosion, corneal degeneration (primarily band keratopathy), corneal dystrophy (primarily Fuchs dystrophy), corneal deposits, keratoconus, keratoglobus, astigmatism, and keratoplasty. For other disorders of the cornea, see the Articles on conjunctivitis and keratitis.

Also see cornea in eye and orbit.

Corneal abrasion

• Definition: scrape or scratch injury on the corneal epithelium
• Epidemiology: most common eye injury
• Etiology ^[1]
  • Injury from an object (e.g., tree branch, fingernail, ball, mascara brushes) hitting, flying into, or poking the eye
  • Foreign matter stuck under the eyelid
  • Entropion
  • Prolonged contact lens wear or improperly fitted lenses
  • UV light (i.e., UV keratitis)
  • Thermal burns (e.g., cigarettes, matches)
  • Trachoma
  • Dry eyes (e.g., Sjogren syndrome)
• Clinical findings ^[2]
  • Foreign body sensation in the eye
  • Eye pain
  • Epiphora
  • Blurred vision
  • Photophobia
  • Conjunctival injection
• Diagnostics: examination of the eye using fluorescein staining ^[3]
• Treatment
  • Removal of any retained foreign object
  • Analgesia: oral NSAIDs, topical NSAIDs (e.g., diclofenac, ketorolac), or narcotics, depending on pain severity ^[4]
  • Infection prophylaxis ^[5]
    • In the general population: antibiotic eye drops or ointment (e.g., erythromycin)
    • In contact lens wearers: antibiotic eye drops or ointment with antipseudomonal activity (e.g., ciprofloxacin)
  • Consider eye patching
• Prognosis ^[6]
  • Small, uncomplicated corneal abrasions: rapid healing of the epithelium expected within approx. 24–48 hours; no follow-up necessary
  • Recurrent corneal erosion can occur as a complication of corneal abrasion. Therefore, daily follow-up until healing has been confirmed is recommended in the following cases:
    • Young children
    • Association with decreased vision
    • Abrasions from contact lenses
    • Larger abrasions

Retained foreign bodies in the eye that cannot be removed warrant urgent referral to an ophthalmologist!

Corneal erosion ^[7]

• Definition
  • Detachment of the corneal epithelium from the tissue layers below, including the basement membrane and Bowman membrane
  • Recurrent corneal erosion: chronic relapsing corneal erosion
• Etiology ^[8][9]
  • Spontaneous due to lack of regenerative capacity of the cornea, associated with the following risk factors:
    • Corneal dystrophy
    • Corneal ulcers (e.g., from herpes simplex keratitis)
    • Contact lens use, especially if poorly fitted
    • Diabetes
    • Dry eye disease
  • Secondary to injury of the cornea (e.g., corneal abrasion, entropion)
• Clinical findings: sudden-onset symptoms similar to those of corneal abrasion (see above), typically upon waking or without obvious signs of ocular trauma.
• Diagnostics: See corneal abrasion above.
• Treatment ^[4][10]
  • Acute (within 24 hours of symptom onset)
    • As with corneal abrasion, above
    • Artificial tears and nightly lubricant eye drops
  • Recurrent corneal erosion or symptoms > 24 hours
    • Specialized ophthalmological treatment may include the following ^[11]
      • Therapeutic contact lenses
      • Stromal micropuncture
      • Corneal epithelial debridement and/or phototherapeutic keratectomy
• Prognosis
  • Excellent, provided diagnosis and treatment are initiated promptly
  • Complete healing of recurrent corneal erosion may take years.

Corneal ulcer ^[12]

• Definition: a defect of the corneal epithelium and underlying stroma that most commonly occurs as a complication of keratitis
• Epidemiology: Incidence in the US is estimated at 30,000–75,000 cases per year. ^[12]
• Etiology
  • Bacterial infection (most common; , although viral, fungal, and parasitic infection is also possible) and autoimmune disease (see “Keratitis”)
  • Associated risk factors include:
    • Wearing contact lenses
    • Prolonged use of steroid eye drops
    • Dry eye syndrome
    • Eyelid disorders
    • Bell palsy
    • Herpes simplex/herpes zoster infections
    • Corneal burns/injuries (e.g., due to eye trauma)
• Clinical features: eye pain, conjunctival injection, photophobia, epiphora, blurry vision, foreign body sensation
• Diagnostics: visual acuity examination, intraocular pressure, and slit-lamp examination with fluorescein staining
• Treatment: : For treatment of corneal ulcers, see “Keratitis overview”.
• Complications: corneal scarring and/or perforation, endophthalmitis, vision loss
• Prevention: following hygiene and handling recommendations for contact lenses/lense fluid (e.g., hand-washing before touching lenses/lense fluid, not wearing contact lenses overnight)

Corneal ulcers are an ophthalmological emergency and can result in permanent corneal scarring and vision loss.

Corneal degeneration

• Definition: changes of the cornea that cause corneal deterioration and, potentially, dysfunction
• Etiology
  • Normal aging
  • Secondary to various pathological processes (e.g., calcium salt deposits in band keratopathy associated with hypercalcemia in the setting of sarcoidosis)

Band keratopathy ^[13]

• Definition: a type of corneal degeneration that involves the appearance of a band-shaped area of calcification across the central cornea ^[7]
• Etiology
  • Idiopathic
  • Risk factors
    • Hypercalcemia (e.g., hyperparathyroidism, sarcoidosis), hyperphosphatemia (e.g., chronic renal failure)
    • Chronic, inflammatory eye disease (e.g., uveitis, keratitis)
    • Exposure to harmful chemicals (e.g., mercury vapors)
    • Family history of band keratopathy
• 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
  • Decreased visual acuity
  • Foreign body sensation
  • Photophobia
• Diagnostics
  • Slit lamp examination showing band-like, horizontal, opaque white areas on the cornea
  • Followup includes investigation of underlying causes and may include:
    • Serum calcium and phosphate measurement
    • Parathyroid hormone level measurement
    • Renal function tests
    • Sarcoidosis workup (e.g., serum ACE, chest x-ray)
• Treatment
  • Treatment of the underlying cause (e.g., uveitis, hypercalcemia)
  • Superficial debridement and lamellar keratectomy
• Prognosis: Visual deficits caused by band keratopathy can typically be treated successfully but will recur if the underlying condition is not addressed.

Corneal dystrophy ^[14]

• 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:
  • Fuchs corneal dystrophy (see below for details)
  • Lattice corneal dystrophy
  • Map-dot-fingerprint corneal dystrophy
• 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 corneal erosion, above)
• Diagnostics: visible structural changes and/or deposits on slit lamp examination.
• Treatment
  • See “Treatment” in corneal erosion, above.
  • Keratoplasty in severe cases or when other treatment modalities have not been successful

Fuchs dystrophy ^[15]

• 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 ^[16]
• Clinical findings
  • Reduced visual acuity
  • Blurred vision, glare, and halos, often improving over the course of the day ^[17]
  • Eye pain or foreign body sensation in the eye
• Diagnostics
  • 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. ^[18]
  • Advanced disease: Slit lamp examination shows corneal thickening, edema, bullae, and fibrotic scarring.
• Treatment ^[19]
  • Asymptomatic patients do not require treatment.
  • Symptomatic treatment
    • Medical treatment to dehydrate the cornea: hyperosmolar eye drops, warm dry air (e.g., hair dryer held at arm's length)
    • For pain or foreign body sensation in the eye: NSAIDs, bandage contact lenses
  • 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

Corneal deposits

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 ^[20]
• Epidemiology: Incidence increases with age. ^[21]
  • 60% in those 50–60 years
  • Almost 100% in those > 80 years
• Clinical findings: asymptomatic
• Diagnostics: slit lamp examination
• Treatment
  • In older patients: no treatment necessary
  • Occurrence before 50 years of age: rule out lipid disorders

Kayser-Fleischer ring

• Definition: green-brown, copper deposits are a diagnostic sign of Wilson disease (See “Clinical features” in Wilson disease.)

Keratoconus

• Definition: a noninflammatory corneal condition in which the cornea becomes thinner than normal and develops a conic shape, bulging outward at the center ^[22]
• Etiology: unknown; frequently associated with other conditions
  • Neurodermatitis
  • Allergic asthma
  • Hay fever
  • Marfan syndrome
  • Ehlers-Danlos syndrome
  • Down syndrome
  • A positive family history of keratoconus has been found in a minority of cases (10%)
• Clinical findings: symptoms are often initially unilateral; however, they always become bilateral in the further course of disease ^[14]
  • Progressive decrease in visual acuity
  • Myopia
  • Astigmatism
  • Photophobia
• Diagnostics
  • Slit lamp examination showing protrusion and thinning of the cornea
  • Ultrasound pachymetry (measurement of corneal thickness via ultrasound)
  • Computerized corneal topography
• Treatment ^[23]
  • Correcting astigmatism and myopia: glasses or rigid gas permeable contact lenses ^[23]
  • In progressive keratoconus: crosslinking with UV-A light (corneal crosslinking)
  • If conservative treatment options fail: keratoplasty
• Complications
  • Corneal hydrops (corneal rupture): tearing of the Descemet membrane and endothelium → penetration of intraocular fluid into the stromal tissue of the cornea → acute pain and deterioration in vision caused by corneal opacification

Keratoglobus ^[23]

• 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

Astigmatism

• See astigmatism

• See the following articles:
  • Keratitis
  • Conjunctivitis

Keratoplasty (corneal transplantation) ^[24]

• Indications
  • Significant visual impairment as a result of pathological changes in the cornea, e.g., opacification, irregular curvature
  • Keratitis that cannot be controlled by conservative treatment
• Procedure: replacement of diseased cornea with cornea harvested from a recently deceased donor
  • Perforating keratoplasty (replacement of the complete cornea): indicated when both anterior and posterior corneal layers are damaged
  • Lamellar keratoplasty (replacement of only the anterior or posterior corneal layers): indicated when only anterior or posterior corneal layers are damaged
• Follow-up care
  • Graft rejection prevention: corticosteroid eye drops
  • Monitoring and treatment for graft rejection