Keratoconus Clinical Presentation

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

History

Patients with keratoconus often report decreasing vision (distortions, glare/flare, and monocular diplopia or ghost images), with multiple unsatisfactory attempts in obtaining optimum spectacle correction.

Soft contact lenses and spectacles may initially give satisfactory vision, but vision tends to decline over time and requires rigid gas-permeable contact lenses for correction. Other contact lens options include piggyback lens systems (usually a gas-permeable lens over a soft, perhaps silicone hydrogel, lens), hybrid lenses (eg, Synergeyes TM) and, increasingly over the past decade, gas-permeable scleral lenses. [9, 19]

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Physical

Keratoconus is differentiated into mild, moderate, and advanced disease, as well as by shape.

Mild keratoconus

External and corneal signs are often absent or minimal.

A history of multiple inadequate spectacle corrections of one or both eyes may be noted and may include oblique astigmatism on refraction as well as moderate-to-high myopia.

Irregularly astigmatic keratometry values (egg-shaped), not necessarily on the steep side of normal (approximately 45 D), are consistent with diagnosis.

Diagnosis can be confirmed with corneal topography or tomography, which may reveal inferior corneal steepening (approximately 80% of keratoconus cases), central corneal astigmatic steepening (approximately 15% of keratoconus cases), or even bilateral temporal steepening (extremely rare).

Corneal tomography shows paraxial corneal thinning.

Corneal sensitivity and tear secretion are decreased. [20]

Moderate keratoconus   [10]

One or more corneal signs of keratoconus are often present, as follows:

  • Enhanced appearance of the corneal nerves is noted.
  • Approximately 40% of eyes in patients with moderate keratoconus develop Vogt striae (fine-stress lines) in the deep stroma.
  • Approximately 50% develop Fleischer ring, a deposition of iron in the basal epithelial cells in a (often partial) ring shape at the base of the conical protrusion.
  • Approximately 20% develop corneal scarring.

Superficial corneal scarring can be fibular, nebular or nodular.

Deep stromal scarring may occur, perhaps representing resolved mini-hydrops events.

Some patients show scarring at the level of the Descemet membrane (posterior limiting lamina), consistent in appearance with posterior polymorphous corneal dystrophy. This may be a posterior polymorphous corneal dystrophy variant. [21]

Paraxial (usually inferior to the pupil) stromal thinning may be appreciated.

Keratometry values typically increase to 45-52 D.

Distortion of the retinoscopy and direct ophthalmoscope red pupillary reflex may allow observation of "scissoring" or an inferior distortion termed the oil drop sign.

The Munson sign is noted when, upon downgaze, a "V" shape is visible in the cornea's profile against the lower lid margin. This is the accentuation of the conical shape of the modest to advanced keratoconus cornea.

Advanced keratoconus

Keratometry values are greater than 52 D.

Enhancement of all corneal signs, symptoms, and visual loss/distortion, including Vogt striae, Fleischer ring, and/or scarring, is present.

Acute corneal hydrops may occur.

Shape-based differentiation

Keratoconic eyes can also be divided by their shape.

Nipple cones have a diameter of 5 mm or less and are located in the center or slightly below the center of the cornea.

Oval cones are larger in diameter and reside inferonasally or inferotemporally to the center of the cornea.

Globus cones involve approximately 75% of the cornea and are the least common.

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Causes

Although not definitively identified, genetic inheritance, systemic and ocular associations, eye rubbing, atopy and specifically ocular allergies, and contact lens wear are proposed risk factors. [22, 23]

Several reports suggest, perhaps coincidentally, associations with keratoconus and other corneal dystrophies.

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Complications

Advanced keratoconus rarely progresses to acute corneal hydrops (acute keratoconus), wherein breaks occur in the Descemet layer that lead to central stromal edema and secondary severe corneal scarring.

Patients report a sudden loss of vision and some ocular discomfort or pain in one eye but usually not much conjunctival injection.

Acute treatment of hydrops is palliative; many corneas flatten secondary to hydrops, and both visual acuity and contact lens application may rarely improve following such events.

If secondary scarring is severe and central, corneal transplantation (ie, PKP) may be warranted.

Patients with keratoconus develop all complications of contact lens wear, especially abrasion [24] and giant papillary conjunctivitis. Contact lens–related secondary giant papillary conjunctivitis may be treated with topical mast cell stabilizers, antihistamine, and, occasionally, steroid drops.

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