Practice Essentials
Keratoconus (KC) is a progressive, noninflammatory, bilateral (but usually asymmetric) ectatic corneal disease, characterized by paraxial stromal thinning and weakening that leads to corneal surface distortion. Visual loss occurs primarily from irregular astigmatism and myopia, and secondarily from corneal scarring. See the image below.
An optic section of a keratoconic cornea shows corneal thinning. Vogt striae and some scarring can also be seen centrally; superiorly, a small (brown) section of the Fleischer ring is noted.
The fluorescein pattern of a rather flat-fitted rigid contact lens on an advanced keratoconic cornea.
Signs and symptoms
Patients with keratoconus may report the following:
Distortion
Glare/flare
Monocular diplopia or ghost images
Multiple unsatisfactory attempts to obtain optimum spectacle correction
Itchy eyes
Keratoconus is differentiated into mild, moderate, and advanced cases.
Characteristics of mild keratoconus may include the following:
Absent or minimal external and corneal signs
Moderate-to-high myopia with oblique astigmatism on refraction
Irregular astigmatic keratometry values
Corneal inferior steepening, central corneal astigmatic steepening, or bilateral temporal steepening on corneal topography or tomography
Characteristics of moderate keratoconus may include the following:
Presence of one or more corneal signs of keratoconus (eg, enhanced appearance of corneal nerves, Vogt striae, Fleischer ring, corneal scarring)
Superficial corneal scarring (fibular, nebular, or nodular)
Deep stromal scarring
Scarring at the level of the Descemet membrane resembling posterior polymorphous corneal dystrophy
Paraxial stromal thinning
Keratometry values of 45-52 diopters (D)
“Scissoring” or the oil drop sign
Munson sign
Characteristics of advanced keratoconus may include the following:
Keratometry values greater than 52 D
Enhancement of all corneal signs, symptoms, and visual loss/distortion
Vogt striae; Fleischer ring and/or scarring
Acute corneal hydrops
See Presentation for more detail.
Diagnosis
No laboratory workup is necessary.
Diagnostic measures that may yield evidence of keratoconus include the following:
Refraction (including retinoscopy)
Slit-lamp biomicroscopy
Corneal topography
Corneal tomography
See Workup for more detail.
Management
Nonsurgical treatment measures include the following:
Rigid contact lenses or scleral lenses (mainstay of vision therapy): Patients with early keratoconus may successfully use spectacles or spherical/toric soft contact lenses. Those with moderate-to-advanced keratoconus almost always require rigid contact lenses or scleral contact lenses.
Corneal collagen cross-linking
Although no direct pharmacologic management is available, the following agents may be useful as adjunctive therapy for complications that occur concurrently with contact lens wear and atopy, which is common with keratoconus:
Combination topical antihistamine/mast cell stabilizer
Antihistamines
Mast cell–stabilizing topical medications
Ophthalmic cyclosporine
Steroid drops
Nonsteroidal anti-inflammatory drugs (NSAIDs)
Hyperosmotic agents
Topical antibiotics
Surgical options include the following:
Collagen cross-linking (CXL)
Superficial keratectomy
Excimer laser phototherapeutic keratectomy
Implantation of intrastromal corneal rings (ICRS)
Bowman layer transplantation
Deep anterior lamellar keratoplasty (DALK)
Penetrating keratoplasty (PKP)
See Treatment and Medication for more detail.