That is a question often asked and the standard answer: 1 in 2,000 has become less plausible with publication of several recent papers.
The number 1 in 2000 was arrived at by counting the number of people living in Rochester, Minnesota diagnosed with KC between 1935 and 1982. (1)
Last year, NKCF reported a paper that used took advantage of new diagnostic technology as well as megadata. Using the nationwide health database, the authors looked at the medical records of 4.4 million individuals in the Netherlands and estimated the prevalence of keratoconus in this European country was closer to 1 in 375.(2)
The general belief among experts is that the rate of keratoconus is especially high among certain ethnic groups, including those of Middle Eastern descent. The British Journal of Ophthalmology is soon to publish a remarkable paper summarizing the results of a study conducted by King Saud University. (3)
Saudi children and young adults, between the age of 6 and 21, who were seen in emergency rooms at four Riyadh hospitals for non-ophthalmic reasons, were invited to be screened for evidence of keratoconus.
The researchers wished to avoid any bias that may come with screening only children who came to an eye clinic.
522 pediatric patients (average age 16) were evaluated using corneal tomography. The color coded maps of the front and back of the cornea created by tomography reveal a distinctive pattern, even for the mildest case of KC. Two examiners reviewed the corneal maps and graded them as (a) normal, (b) suspect, or (c) KC. Patients evaluated as suspect or KC were invited to a specialty eye center for follow-up consultation.
In this study of random young people from the Kingdom of Saudi Arabia, the reviewers estimated the rate of keratoconus to be 1:21 patients, or 4.79% of the population. This is almost a 100-times greater than the statistic most commonly quoted!
Technology helps with early diagnosis.
The paper points out that the technology is much more sensitive now and that is partially responsible for picking up disease in its earliest stages. They also acknowledged that the population studied was known to have a greater than average incidence of the disease.
Does this mean anything to individuals with KC in America?
If KC is much more prevalent than previously assumed, eye doctors should be fully trained in the diagnosis and treatment of this condition, and insurance companies should expect that a greater number of the lives they cover will have issues related to KC, from medical claims for crosslinking to coverage for contact lenses. Companies may be more willing to devote money to research and development of new treatments if they believe that the number of people who will benefit is larger than estimated.
While we still have not arrived at the incidence of keratoconus, learning that KC is not as rare as you may have believed is probably a good thing.
Resource:
1. Kennedy RH, et al, A 48-year clinical and epidemiologic study of keratoconus. Am J Ophthalmol 1986;101:267–73.
2. Godefrooij DA, et al, Nationwide reduction in the number of corneal transplantations for keratoconus following the implementation of cross-linking. Acta Ophthalmol 2016;94:675–8.
3. Torres Netto EA, et al, Prevalence of keratoconus in paediatric patients in Riyadh, Saudi Arabia, Br J Ophthalmol 2018 epub ahead of print.
