Keratoconus (KCN) is a disease characterized by thinning and protrusion of the cornea, resulting in an irregular, conical shape (Figure 1 and 2). Irregular astigmatism occurs as the keratoconus progresses, and results in blurred vision, which can be impossible to correct with spectacles. Usually keratoconus occurs in both eyes, and involves the central cornea with the apex of the cone just below the visual axis.
Approximately 50 to 200 of every 100,000 people are afflicted with keratoconus. In the USA, a study found a prevalence of 54.5 per 100,000 people (Kennedy et al, Am J Ophthalmol 1986; 100:267-73).
Keratoconus occurs in all races and usually affects both eyes. Sensitive techniques, such as corneal topography, often detect keratoconus in both eyes in cases thought to be only in one eye based on physical examination and refraction. Keratoconus often starts in puberty and slowly progresses over decades and then stabilizes. In progressive cases, severe irregular astigmatism and scarring may require a corneal transplant in order to restore useful vision to the eye.
Heredity of keratoconus has not been clearly established. While there are families in which multiple persons are affected, factors such as allergic conditions and contact lens use make analysis difficult. As a general rule, chances of a blood relative developing clinical keratoconus are less than 10%.
Conditions associated with keratoconus include atopic disease (atopic or allergic dermatitis, allergic rhinitis, asthma), Down’s syndrome (5-8 % of Down’s patients), and connective tissue disorders (Ehlers-Danlos syndrome and osteogenesis imperfecta). Chronic eye rubbing is associated with keratoconus and may accelerate progression. Eye rubbing may be the common link between keratoconus and allergies, atopic disease and Down’s syndrome.
Findings in keratoconus include protrusion of the cornea, striae or wrinkles of the posterior cornea (Vogt’s striae), superficial scarring of the anterior cornea, and staining of the corneal surface epithelium with iron (Fleischer ring). Corneal hydrops, or marked swelling of the cornea in keratoconus, may occur when severe bulging of the cornea results in a tear in the deepest layer of the cornea (Descemet’s membrane), allowing fluid from the inside of the eye to permeate the cornea. Severe haziness, often accompanied by blister like lesions of the superficial cornea, results in impairment of vision and discomfort.
Cross-linking is the only FDA-approved treatment for halting the progression of keratoconus. Once the condition progresses, Intacs or a cornea transplant are more advanced treatment options.
Crosslinking for Keratoconus
The Cornea Research Foundation of America contributed to the recent US Food and Drug Administration (FDA) approval of cross-linking for halting or slowing the progression of keratoconus and corneal extasia after prior refractive surgery. These studies were designed to assess the safety and effectiveness of CXL for halting or slowing the progression of these conditions. Learn more about crosslinking here. The company that received te FDA approval expects to have the riboflavin and UVA light commercially available by the end of 2016. In the meantime, we are providing patients with continued access to cross-linking through an ongoing investigational study.
Treating visual focusing problems associated with keratoconus
In the early stages, patients with keratoconus can usually achieve adequate visual correction with spectacles. Anyone with keratoconus should be very careful to never rub their eyes, because that could make the keratoconus worse. Control of systemic allergies with antihistamines may decrease itching of the eye and eyelids and help make it easier not to rub the eyes. However, systemic antihistamines cause the eyes to become drier with less tear production, which can actually cause an increase in eye itching with allergies. Therefore we recommend using eye drops to control itching, instead of systemic antihistamines, in keratoconus patients.
When irregular astigmatism makes clear vision with spectacles impossible, rigid gas permeable (RGP) contact lenses are the next step. The rigid lens masks the underlying irregular cornea and functions as the new refractive surface of the eye, with the tear film filling in the space between the back of the contact lens and the front of the eye. However, in keratoconus the steep cone and irregular shape of the cornea makes fitting these lenses challenging, and the experience and expertise of the contact lens fitter is very important in determining the success of this intervention. Central corneal scars can also develop in keratoconus eyes. Usually this is caused by the contact lens rubbing or resting on the apex of the keratoconus cone. Proper fitting of the lens is very important to prevent or minimize scarring. When corneal scars in keratoconus limit vision or the ability to wear the contact lens, the scars can often be removed surgically without the need for a transplant.
Intacs for Keratoconus
If keratoconus progresses to the point where a contact lens cannot be fit or does not adequately correct vision, surgery may be indicated. Small plastic ring segments placed in the cornea can produce a more regular corneal surface in about 2 out of 3 keratoconus patients.
Cornea Transplants for Keratoconus
Historically, in about 1 out of 5 patients, keratoconus progresses to the point where a cornea transplant is needed to restore a more normal shape to the cornea. Data from the Cornea Transplant Database of corneal transplant shows that transplants performed for keratoconus are in the highest category for successful outcomes. In most cases, Dr. Price recommends the newer targeted transplant technique known as deep anterior lamellar keratoplasty (DALK) to help minimize the risk of graft rejection.