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Studies shed light on mystery surrounding keratoconus
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COLUMBUS, Ohio - Most practitioners should be able to relate to the patients enrolled in the ambitious Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.
"It feels like we have an intuitively representative sample," said Karla Zadnik, OD, PhD, an assistant professor at the Ohio State University College of Optometry here and chairman of the 5-year study, which is being sponsored by the National Eye Institute, a division of the National Institutes of Health.
A total of 1,209 eligible keratoconus patients enrolled in the CLEK Study between May 1995 and June 1996. "This is the largest prospective sample of keratoconus patients ever assembled," said Dr. Zadnik, who presented baseline data at the American Academy of Optometry annual meeting in San Antonio.
She noted that the study has exceeded its originally projected recruitment goal of 1,000 patients by 20% and achieved its goal in only 10 months. Furthermore, "All previous studies have been retrospective," she said.
Keratoconus is a progressive corneal disease that affects about 1 out of every 2,000 people. Subjects entered the CLEK Study in various stages of keratoconus and are to be followed annually for 3 years. Inclusion criteria for the purely observational study included an irregular cornea in at least one eye, a slit lamp sign of keratoconus in at least one eye and no bilateral transplants or bilateral crystalline lens-related or posterior segment disease.
Balanced racial make-up
In terms of race, 69% of study patients are Caucasian, 20% are African-American, 8% are Hispanic and 3.5% are Asian. "Earlier on, we were concerned about under-representation of Hispanics, so we added a clinic in Texas and a clinic in Miami," Dr. Zadnik said. Overall, "I think we've come up with ethnic demographics that are fairly indicative of the United States."
The mean age is about 40. "This probably reflects what most optometrists find among the keratoconus patients they take care of in their practices," Dr. Zadnik said. Approximately 45% of the sample are women.
As for pre-existing ocular conditions, 118 patients entered the study with a unilateral corneal transplant.
The study also seeks to assess how practitioners are treating their keratoconus patients. "Three-quarters of the sample wear rigid gas-permeable lenses in both eyes," Dr. Zadnik said. "That is the mainstay of visual correction in this disease."
However, two-thirds of these contact lens wearers also use spectacles in some capacity. "So keratoconus patients tend to mostly use rigid gas-permeable lenses but glasses as an adjunct," she said. Furthermore, about 75% of the contact lens wearers reported them as comfortable.
Eye rubbing
Half of the patients said they rub both eyes vigorously, while fewer than 2% of patients rub only one eye vigorously. About half of patients reported no eye rubbing in either eye.
As for the connection between keratoconus and family history, about 13% of patients reported the disorder as affecting either a parent, sibling, child, aunt or uncle.
Because there have been several rare diseases associated with keratoconus, patients were asked if they had a positive history of conditions such as Down's syndrome, Marfan's syndrome, focal dermal hypoplasia and Ehlers-Danlos syndrome. Surprisingly, "compared to previous reports, we did not find a single patient with any of those exotic conditions," Dr. Zadnik said.
More than half of the patients, however, reported having hay fever or allergies, and 15% reported having asthma. About 8% reported having atopic dermatitis.
Patient dropout has been minimal. "For the most part, people are interested and motivated to learn more about the condition they have," said Dr. Zadnik, who is hopeful that upon completion of the CLEK Study in 1999, a treatment trial will commence. "We first need to learn about the natural history of this condition, which should allow practitioners to better counsel their patients."
Contributing factors
At the same Academy meeting, Adrian S. Bruce, BScOptom, PhD, a senior optometrist from the Victorian College of Optometry in Melbourne, Australia, presented the results of an independent survey of 227 keratoconus patients and 100 age-matched and sex-matched control subjects. "By looking at the frequency with which various systemic conditions occurred, we tried to determine a cause of keratoconus," he said.
Allergy and genetic predisposition were the two major factors that appeared to contribute to keratoconus. Nearly two-thirds of the keratoconus group (62%) had a positive allergy history, while only 27% of the control group did. Moreover, a positive family history of keratoconus was present in 22% of keratoconus subjects, but in only 4% of controls. Nevertheless, the nature of the link between keratoconus and allergy remains a mystery.
"A theory of genetic mutation was not supported, because the age of the parents at the time of the subjects' birth were similar for both the test and control groups," Dr. Bruce explained. There was also no difference in the number of children in the family for the two groups. "The theory that keratoconus is a random, genetic mutation could not be validated. But the study does support the claim of a recessive genetic basis to the condition," he said.
The survey found a history of persistent styes in 28% of keratoconus subjects and in only 2% of controls. In addition, the common age of keratoconus onset was between 10 and 20.
"One practical result of the study was finding no indication that contact lens wear or eye rubbing actually causes keratoconus. That's a reassuring finding," said Dr. Bruce. "As far as we can tell, keratoconus is primarily a genetically determined condition that patients have little control over."
For Your Information:
- Karla Zadnik, OD, PhD, can be reached at the Ohio State University College of Optometry, 338 West 10th Ave., Columbus, OH 43210-1240; (614) 292-6603; fax: (614) 292-4705; e-mail: zadnik.4@osu.edu. Dr. Zadnik has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- Adrian S. Bruce, BScOptom, PhD, can be reached at Victorian College of Optometry, Cnr Keppel and Cardigan Sts., Carlton, VIC 3053, Australia; (61) 3-9349-7471; fax: (61) 3-9349-7499; e-mail: a.bruce@optometry.unimelb.edu.au. Dr. Bruce's research colleagues were graduate student James Armitage and Adelaide optometrist Tony Phillips. Dr. Bruce has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.