About 1.2% of the individuals of Australia’s The Raine Study’s Generation 2 (Gen2) birth cohort — or about 1 in 84 Australian adults, all 20-years-old — have keratoconus, a disease that causes noninflammatory corneal thinning and abnormal corneal thickness distribution, as seen with Scheimpflug imaging, researchers found in a population-based cross-sectional study published in Ophthalmology.
“This has important public health implications and suggests that eye care professionals should be screening individuals at a younger age, given the presence of keratoconus at a younger age is associated with a greater risk of disease progression,” according to the researchers. “This is particularly so, as corneal cross-linking has been demonstrated to be effective at halting and slowing disease progression, thus reducing vision impairment in young adults.”
The researchers sought to determine the prevalence of keratoconus in the Australian population because no previous study had reported that data, they said. They also wanted to determine the disease’s associations with systemic conditions in the hopes that this would give ophthalmologists a better chance to diagnose keratoconus prior to the onset of vision loss and to stabilize the disease early.
The data the researchers collected was from the 20-year follow-up study of The Raine Study’s Gen2 population of 2868 Western Australians who were born between 1989 and 1992.
The Gen2 participants underwent an eye exam and completed a self-administered health questionnaire that included demographic questions (race was determined by each parent’s reported ethnicity and subjects were categorized as non-White if 1 parent was non-White). It also asked about family history of ocular disorders, history of allergic disease, smoking status, and pregnancy. Researchers also obtained the participants’ visual acuity, height, weight, and corneal topography and tomography.
The researchers obtained adequate Scheimpflug imaging from 1262 of the 1344 participants who completed the eye exam at the 20-year follow-up. They excluded 3 participants who had a history of ocular surgery or a disorder that might have affected imaging.
Subjects who had a Belin/Ambrόsio Enhanced Ectasia Display (BAD-D) score of 2.6 or greater were determined to have keratoconus (false positivity rate, 0.1%). The higher BAD-D score was recorded in cases where both of the patient’s eyes had keratoconus.
Of the 1259 remaining subjects (620 males), 2 had a pre-existing diagnosis of keratoconus, 7 had a BAD-D score of 2.6 or greater in at least 1 eye, and 8 had a BAD-D score of 2.6 or greater in both eyes. The prevalence of keratoconus was therefore 1.2% (95% CI, .7-1.9) or 1 in 84 subjects.
Of the 15 subjects, 12 were White, 2 were categorized as East Asian, and 1 had 1 Indian parent and 1 White parent. More individuals who had BAD-D scores of 2.6 or greater (38.5%) than those individuals who had BAD-D scores less than 2.6 (14.6%, P =.04) reported regularly smoking cigarettes.
Althoughthere is no consensus on the diagnostic criteria for keratoconus, abnormal posterior elevation, abnormal corneal thickness distribution, and clinical noninflammatory corneal thinning are mandatory findings when diagnosing the disease, the study explains. In the absence of diagnostic criteria, the true prevalence of keratoconus cannot be determined. Until that criteria is established, clinicians can rely only on machine-derived indices and image analysis by experts to diagnose the disease.
The researchers do point to evidence that suggests the prevalence of keratoconus is higher in ethnic groups such as Black and Hispanic communities in the United States, and Maori and Polynesian populations in New Zealand, compared with White populations. Data from the United Kingdom show that Asian patients present at a younger age and with more advanced disease compared with non-Asian patients. This contrasts with research from the United States, where Asian Americans had reduced odds of keratoconus compared with White patients. These investigations may represent differences in the demographics of Asian populations in the United Kingdom-based study, who were primarily of Pakistani and Indian descent, and the United States-based publication, where Americans of Chinese and Indian descent are predominant.
Limitations of the study included that because of the higher percentage of subjects who were White, the prevalence in the cohort may not reflect the prevalence of the disease in non-White populations and BAD-D scores are typically insufficient for diagnosis of keratoconus. However, the researchers noted, the likelihood of false-positive high BAD-D scores is low in this age-group, and two ophthalmologists qualitatively examined the scans with a BAD-D score of 2.6 or greater to verify their inclusion.
Chan E, Chong EW, Lingham G, et al. Prevalence of keratoconus based on Scheimpflug imaging: The Raine Study. Ophthalmology. Published online Aug 26, 2020. doi: 10.1016/j.ophtha.2020.08.020