A 45-year-old woman presents with pain, a foreign body sensation, tearing, photophobia, and decreased vision in her left eye for one day. A physician previously told her that there is “something wrong with her eye,” but she can't recall the diagnosis. She does not wear glasses or contacts, and denies a history of trauma, fever, eye crusting or pus, congestion, facial numbness, weakness, or lesions.
She cannot recall any exacerbating factors. Her physical exam is notable for a cone-shaped protruding cornea with an opacified tip. What is the diagnosis and what condition are you concerned about?
Keratoconus is a progressive noninflammatory condition that results in corneal thinning and subsequent cone-like protrusion of the cornea. Often bilateral but asymmetric, this condition can lead to progressive visual impairment typically starting in adolescence and progressing through the third and fourth decades of life. Occurring equally in men and women, the exact etiology of keratoconus is not known, and a genetic predisposition occurs in less than 10 percent of cases. (Am J Med Genet 2000;93: 403.) A number of gene loci have been recently implicated. (Middle East Afr J Ophthalmol 2010;17:15.)
Studies have shown that oxidative stress (Cornea 2008;27:1062) and subsequent proteolytic enzymatic processes are involved in the degradation of all corneal layers including the basement membrane (Curr Eye Res 2010; 35:185), but the exact mechanism of corneal destruction and thinning is not understood.
Keratoconus can be associated with other ocular conditions including vernal keratoconjunctivitis, retinitis pigmentosa, and Leber congenital amaurosis. It has also been associated with Down syndrome, mitral valve prolapse, atopic dermatitis, and some connective tissue disorders including Ehlers-Danlos and Marfan syndromes. Keratoconus most commonly occurs as an isolated ocular condition, however.
Patients who have a history of vigorous eye-rubbing including those with ocular allergies and hard contact lens wearers (Trans Am Ophthalmol Soc 1999;97:187), are also at increased risk for developing this condition, but most cases (more than 85%) develop spontaneously. (Cornea 1996;15:139.)
Vision loss is primarily the result of irregular astigmatism and myopia, but corneal scarring can result from corneal protrusion and also cause subsequent visual impairment. Corneal thinning is greatest at the apex of the protrusion, which makes it vulnerable to tear or rupture.
Other than the obvious cone-shaped protrusion of the cornea, other gross signs of keratoconus include Munson's sign, corneal scarring, and iron deposition in the epithelial cells at the base of the cone resulting in characteristic Fleischer ring formation. Other signs associated with keratoconus likely only to be appreciated by a trained ophthalmologist include Vogt striae and corneal ectasia. The diagnosis is clinical with no laboratory or imaging confirmatory studies required in the ED. Computer-assisted videokeratography may be performed as an outpatient procedure by a corneal expert.
Advanced cases may rarely progress to acute corneal hydrops (acute keratoconus). This results from the sudden development of corneal edema and scarring after the rupture of Descemet's membrane, the basement membrane between corneal stroma and endothelial layers, which allows an influx aqueous humor from the posterior cornea. This rare condition occurs in approximately three percent of patients with keratoconus. (N Engl J Med 2009;361:e32.) Patients present with a sudden decrease of vision, a painful red eye, photophobia, and profuse tearing. The etiology of acute hydrops is unknown, but occurs in patients with severe keratoconus.
The differential diagnosis of keratoconus is limited, and includes peripheral corneal thinning and protrusion and global corneal thinning (keratoglobus). Differential diagnosis of acute corneal hydrops is less finite, and includes acute infectious keratitis, corneal abrasion, laceration, ulceration, iritis, and ruptured globe.
Patients with keratoconus are at risk for infection and corneal perforation. The treatment of keratoconus is typically managed by an ophthalmologist, and includes instructions not to rub the eyes and use of rigid contact lens for visual impairment. In severe cases, corneal transplantation may be required. Patients with acute hydrops, however, may require treatment in consultation with an ophthalmologist. Treatment includes an eye shield or glasses to prevent rubbing, administration of cycloplegic agent (to dilate eye and prevent lens contraction), and artificial tears. Prophylactic topical antibiotics are recommended for any signs of corneal disruption to prevent infection. Corneal edema associated with acute hydrops typically resolves on its own within six to eight weeks. (N Engl J Med 2009;361:e32.)
Thanks to Christopher Carpenter, MD, for providing the case.
Comments about this article? Write to EMN email@example.com.
Click and Connect!Access the links in this article by reading it onwww.EM-News.com.