Friday, March 29, 2024

Keratoconus

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 cor

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.

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The fluorescein pattern of a rather flat-fitted ri

The fluorescein pattern of a rather flat-fitted rigid contact lens on an advanced keratoconic cornea.

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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.

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