Keratoconus Is Much More Prevalent Than We Thought
16:42If you're a long time reader, you'll know I've dedicated a lot of articles to writing about specialty contact lenses for keratoconus because its the specialty I've chosen to pursue in my own eyecare practice. In the five years that I have been out of optometry school, I've fit hundreds of patients with specialty contact lenses for irregular corneas, and over and over I found myself wondering, how could I be seeing so many? A new study out of the Netherlands in 2016 has revolutionized how common we believe keratoconus to be, reporting a prevalence of 1 in 375 people. Compare that to the previous estimated prevalence of 1 in 2000 reported in a 1986 study out of Minnesota, and you can see why the news has rocked the eyecare world.
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| An eye with keratoconus and corneal scarring via |
What is Keratoconus?
Eyecare specialists define keratoconus as "bilateral, asymmetrical, noninflammatory pathology characterized by progressive, localized thinning and protrusion of corneal tissue." In layman's terms, you'll often hear it described as a steepening of the cornea, causing the cornea to bulge forward and disrupt vision. One reason why we've struggled so much to both treat and properly define how prevalent keratoconus is in society is because we still have a poor understanding of what is happening in this disease. We know that the process of corneal thinning and protrusion usually starts around puberty, and progresses on average 10-20 years from there. Most people by age 40 have no further progression of the disease because of aging changes that stiffen and thus strengthen the cornea and prevent further prolapse. Keratoconus can be detected in its earliest stages with corneal topography, where the tell-tale surface steepening is visible creating a pattern of asymmetric and irregular astigmatism on the corneal surface.
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| Corneal topography showing normal (regular) astigmsim on the left and irregular astigmatism caused by keratoconus on the right. Note the lack of symmetry vertically in this map - a giveaway of corneal dystrophy. via |
What We Know and What We Don't
For years doctors have theorized that keratoconus had a genetic component, but there has never been a gene found that definitively proved this. And population studies looking at genetic prevalence show mixed results. Environmental factors like allergies and chronic eye rubbing also appear to contribute. So if you are looking for a definitive answer to why you have keratoconus, the answer is not so simple. It's probably a mixture of environmental and genetic risk factors.
Here's what we do know:
- Keratoconus is more common in India, the Middle East, and China than other countries around the world. It is unknown if this is due to environmental difference in temperature, oxidative UV damage from being closer to the equator, or diet and nutritional differences.
- The genetic prevalence of keratoconus differs based on ethnicity.
- In the US, the genetic prevalence of keratoconus is between 6 and 13.5% depending on the study you look at.
- When prevalence in a 2015 study was separated by ethnicity, Caucasians were found to have a genetic prevalence of 5% and Asians had 25% prevalence.
- Eye rubbing is an associated risk factor; chronic ocular allergies may be a risk factor (or is it just the rubbing?)
- People with keratoconus tend to rub their eyes longer and "more vigorously" than those with normal corneas. An average cornea patient tends to rub their eyes on average for 5 seconds and no longer than 15 seconds even when bothered by allergies; surveyed keratoconus patient rubbed their eyes between 10 and 180 seconds. Additionally, keratoconus is associated with:
- rotational knuckling motion with rubbing
- more forceful rubbing
- rubbing frequency greater than once a day
- rubbing year round (not just seasonal with allergies)
- Study results are mixed as to whether the risk of keratoconus is higher with a history of chronic allergies or atopic hypersensitivity like asthma and eczema. About 1/3 of patients with keratoconus self-report a history of allergies.
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| An eye with keratoconus via |
There is still much to learn about why keratoconus develops and we are no closer to a cure unfortunately. Luckily new treatments like corneal cross linking are showing excellent results at slowing progression of the disease. Early detection is key to stabilizing vision before the condition has progressed too far, and with the knowledge that keratoconus is so much more common than once believed, the hope is that doctors will be more active than ever in trying to detect early cases and get them referred for intervention and treatment as soon as possible.
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