Keratoconus
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Keratoconus, or "cone eye," is an eye condition in which the cornea thins and changes shape to be more like a cone than a parabola. Vision can become distorted quite badly, with "ghosting", "streaking", and light sensitivity all often reported. Keratoconus and the associated vision loss often affect the person's ability to function normally.
Keratoconus is a rare disease - it is estimated that 1 person out of 1,500 is affected - and seems to have genetic components. It is sometimes called the "academic's eye disease" because two-thirds of the people afflicted with it have IQs above 130. Keratoconus is also diagnosed more often in people with Down Syndrome, though the reasons for this link have not yet been determined. Keratoconus is a member of the family of atopic diseases, which include asthma, allergies, and eczema, and it is not uncommon for several or all of these diseases to affect one person.
Most people will have normal vision or mild astigmatism as puberty begins, but those who are affected by keratoconus are most frequently diagnosed as teenagers. Vision will seem to fluctuate over a period of months, driving patients to change lens prescriptions frequently but as the condition worsens, contact lenses are required. Traditionally, these have been "hard" or gas-permeable contact lens, although recently "soft" or hydrophilic lens have become available. Definitive diagnosis is obtained using corneal topography, a non-invasive visualization of the surface of the cornea.
Many special types of gas permeable contact lenses have been developed for keratoconus, and affected people should seek out both doctors specialized in conditions of the cornea, and contact-lens fitters who have experience with patients with keratoconus.
Some patients also find good vision correction and comfort with a "piggyback" lens combination, where gas permeable "hard" lenses are worn over soft lenses, both providing a degree of vision correction. Understandbly, fitting this lens combination requires experience on the part of the lens fitter, and patience on the part of the KC patient. Scleral lenses are also sometimes used; these lenses cover a larger portion of the corneal surface.
In the worst cases, where vision correction is not possible, thinning of the cornea has become advanced, or scarring as a result of contact lens wear causes problems of its own, a corneal transplantation (penetrating keratoplasty) is required. The recovery period can take four to six weeks and full post-operative vision stabilization often takes a year or more but most transplants are very stable in the long term.
Cornea transplants are usually done under sedation as outpatient surgery, and require careful follow-up with an eye surgeon for a number of years. Frequently, vision is greatly improved after the surgery, but even if the actual visual acuity does not improve, because the cornea is a more normal shape after the healing is completed, patients can more easily be fitted with corrective lenses.
Complications of corneal transplants are mostly related to vascularization of the corneal tissue and rejection of the donor cornea. Vision loss is rare, though difficult-to-correct vision is possible. When rejection is severe, repeat transplants are often attempted, and are frequently successful. Long-term outlook for corneal transplants is usually favorable once the initial healing period is completed and a few years have elapsed without problems.
The cornea does not have a direct blood supply, so donor tissue does not have to be blood type matched. Eye banks check the donor corneas for any disease or cellular irregularities.
See Also:
External links
- National Kerataconus Foundation (http://www.nkcf.org)
- Keratoconus Diagnosis & Management (continuing education material from Pacific University) (http://www.opt.pacificu.edu/ce/catalog/web013/course.htm)
- Helping the Keratoconus Patient Cope by Bezalel Schendowich, O.D., F.I.A.C.L.E. OCTOBER 1999 (http://www.clspectrum.com/archive_results.asp?article=11720&auth=816)
- International Center for Keratoconus (http://kcenter.org/)
- Vision Simulations: see what people with keratoconus see (http://www.visionsimulations.com/#)
- Julia Ziobro's Cornea Transplant Diary, right eye, 02/09/99 (http://www.ziobro.us/ODeye.html)
- Julia Ziobro's Cornea Transplant Diary, left eye, 05/25/04 (http://www.ziobro.us/OSeye.html)
- John Ackerman's transplant diary and excellent keratoconus resources (http://www.febo.com/eyes/)
- Mandy Patinkin, actor, describes his corneal transplant (http://www.mandypatinkin.net/TRANSPLANT/transplant.html)
- Dave Zimbrich's cornea transplant diary (http://home.comcast.net/~zimbricd/KCdiary.htm)