Keratoconus

Updated: Oct 17, 2018
  • Author: Karen K Yeung, OD, FAAO; Chief Editor: Hampton Roy, Sr, MD  more...
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Overview

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.
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.

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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Background

Keratoconus is a progressive, noninflammatory, bilateral (but usually asymmetric) ectatic corneal disease, characterized by paraxial stromal thinning and weakening that leads to corneal distortion. Visual loss occurs primarily from irregular astigmatism and myopia, and secondarily from corneal scarring.

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Pathophysiology

All layers of the cornea are believed to be affected by keratoconus. Characteristic structural changes include epithelial basement membrane fragmentation and scarring, breaks in the anterior limiting lamina (ie, Bowman membrane), and axial stromal thinning and scarring. Deposition of iron in the basal epithelial cells forms the Fleischer rings. Breaks and folds close to the Descemet membrane form commonly seen striae and acute hydrops (although the latter are rare).

The literature on keratoconus is large and contradictory regarding the roles of disruption of collagen fibers, lamellae, and proteoglycans. Keratoconic corneas have been shown to have altered antioxidant enzymes, accumulations of cytotoxic reactive oxygen/nitrogen species, activated caspase pathways, and mitochondrial DNA damage. Abnormal oxidative stress-related properties have been found in keratoconic corneal cells. Oxidative stress elements can induce activation of degradative enzymes and degradation of tissue inhibitors of metal-low proteinases. Genomic deletion in the superoxide dismutase 1 (SOD1) gene has also been associated with the disease. [1, 2, 3, 4, 5]

Although usually believed to be noninflammatory, some data suggest an inflammatory component. [6]

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Frequency

Reported prevalence in the general population varies (50-200 cases per 100,000 population), perhaps with differences in diagnostic criteria. It is commonly an isolated ocular condition but sometimes coexists with other ocular and systemic diseases. [7]

Commonly recognized ocular associations have included vernal keratoconjunctivitis, retinitis pigmentosa, and Leber congenital amaurosis. Systemic putative associations include many of the connective tissue disorders (eg, Ehlers-Danlos and Marfan syndromes), mitral valve prolapse, atopic dermatitis, and Down syndrome, [8] although none of these was found in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) study. [9]

Particular risk factors include atopic history, especially ocular allergies, and perhaps either or both rigid contact lens wear, and vigorous eye rubbing. [10, 11]

Most keratoconus cases appear spontaneously, although approximately 14% of cases present with evidence of genetic transmission. [10]

The prevalence of keratoconus varies by ethnicity. Keratoconus is more common in blacks and Latinos than in whites, with odds ratios of 1.57 and 1.43, respectively. Data are conflicting on whether Asians are at a greater or lower risk for keratoconus. [12] The discrepancy could arise from the large diversity of Asians (eg, subcontinental Indian vs Middle Eastern vs Chinese) given that anecdotal reports suggest an increase in keratoconus prevalence in some parts of the world, Arabia, the Indian subcontinent, and New Zealand. [13]

Personal income, access to health care, and education levels have no known correlation with keratoconus. [12]

Sex

Keratoconus is six times more common in males than it is in females. [12]

Age

Keratoconus typically presents at puberty and progresses until the third and fourth decades of life, although it can occur or progress at any age. Keratoconus progresses at various rates but tends to progress more rapidly in young patients and stabilizes approximately 20 years after initial onset. [14]

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Mortality/Morbidity

Because few elderly patients have been noted with keratoconus, many wonder if keratoconus is associated with a fatal disease. There are mixed results regarding whether keratoconus is associated with an increased mortality risk. [15, 16, 17]

Advanced keratoconus may rarely progress to corneal hydrops. Corneal hydrops are breaks in the Descemet layer that cause aqueous to enter the stroma, leading to central stromal edema and potentially secondary severe corneal scarring. Patients report sudden loss of vision and some ocular discomfort in one eye but usually not much pain or conjunctival injection. Acute treatment of hydrops is palliative; many corneas flatten secondary to hydrops, and both visual acuity and contact lens application may improve following such events. If secondary scarring is severe, corneal transplantation (PKP) may be warranted.

Corneal surgery is indicated when contact lenses are either no longer tolerated or can no longer correct vision to better than 20/40. The rate of patients with keratoconus requiring PKP has been decreasing, from 20% to 2.4%, because of improved contact lens designs and better surgical correction techniques, including CXL. [18] The need for PKP increases when optimal contact lens care is not available. Many patients still require contact lens care for optimum visions following PKP.

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Prognosis

Most patients with keratoconus do well with rigid contact and scleral lens care.

About 10%-20% of patients with keratoconus eventually require corneal transplantation, [18] but this number is believed to increase if good contact lens care is unavailable.

Data suggest that this disease, although progressive, stabilizes after some time in most patients.

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Patient Education

Patients with keratoconus and their family members may benefit from genetic counseling.

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