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    Drugs & Diseases>Ophthalmology

    Keratoconus

    Updated: Jan 04, 2023
    • 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, assymetrically bilateral etatic corneal disease, characterized by paraxial corneal stromal thinning and steepening. Keratoconus traditionally was thought to be non-inflammatory, though recent studies have found inflammatory cytokines in the tear film. [1, 2, 3, 4, 5, 6]  Decreased visual acuities, occurs primarily from irregular astigmatism and myopia induced from the corneal distortion, and secondarily from corneal scarring. See the image below.

    An optic section of a keratoconic cornea shows corAn 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 riThe 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 [4, 6] :

    • 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 [4, 5, 6] :

    • 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 [4, 6] :

    • 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 [4, 6] :

    • 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 [4, 5, 6] :

    • 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.

    Next: Background

    Background

    Keratoconus derived from the Greek words "keras" (cornea) and "konos" (cone) is a corneal condition characterized by paraxial corneal stromal thinning and steeping which causes the cornea to bulge out in a cone-shape. Keratoconus is a progressive, assymetrically bilateral etatic corneal disease that causes decreased visual acuities, occurs primarily from irregular astigmatism and myopia induced from the corneal distortion, and secondarily from corneal scarring. 

     

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    Next: Background

    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 also has been associated with the disease. [7, 8, 9, 10, 11]

    Although usually believed to be noninflammatory, some data suggest an inflammatory component. [12]

     

     

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    Next: Background

    Frequency

    Keratoconus's rate of prevalence varies from 0.2 and 4,790 per 100,000 persons. [13, 14, 15]  The great variance depends upon the diagnostic criteria, better detection technology, different research protocals, geographic location and ethnicity of the people studied. The middle east has the highest prevalence [16]  whereas areas like Russia and Finland reported very low prevalences. [17, 18]  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.

    It is commonly an isolated ocular condition but sometimes coexists with other ocular and systemic diseases. [19]

    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, [20] although none of these was found in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) study. [21]

    Particular risk factors include atopic history, especially ocular allergies, and perhaps either or both rigid contact lens wear, and vigorous eye rubbing. [22, 23]

    Most keratoconus cases appear spontaneously, although approximately 14% of cases present with evidence of genetic transmission. [11]  A patient with keratoconus has a 15 to 67 times greater risk of developing keratoconus than an individual with no family history of keratoconus

    Personal income, access to health care, and education levels have no known correlation with keratoconus. [24]

    Sex

    Keratoconus affects both males and females though the rate of prevalence is ambiguous given mixed results from various studies. [25, 26]

    Age

    KC typically presents in the early 20's, though it can develop earlier, and then stabilizes by the fourth decades of life. [25] KC progresses at various rates but tends to progress more rapidly in younger patients and stabilizes approximately 20 years after initial onset. [27, 26]

     

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    Next: Background

    Mortality/Morbidity

    Because few patients over the age of 50 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. [28, 29, 30]

    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. [31] 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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    Next: Background

    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, [31] but this number is believed to increase if good contact lens care is unavailable and decrease with early CXL treatment.

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

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    Next: Background

    Patient Education

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

    Previous
    Clinical Presentation
     
     
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