Epidemiology of Keratoconus in Yazd Province

To determine the incidence and prevalence of clinical keratoconus (KCN) in Yazd province.

In this population-based survey, a surveillance program was established in Yazd province (population size=990,818). All new clinically diagnosed cases of KCN were registered and referred for topographic imaging during one year (2008-2009) by all local ophthalmologist and optometrists. People living less than 6 months in the province and those with known KCN before the beginning of the study were excluded. Diagnosis was based on topographic pattern (TMS-4a, Tomey, Japan) and indices including KPI, KCI and KSI and re-examination by an anterior segment subspecialist. Finally, referred patients were classified into 5 groups including, clinical KCN, early KCN, KCN suspect PMD (pellucid marginal degeneration) and non KCN corneal diseases. Incidence rate was calculated as the number of new cases divided by the province population and the prevalence was based on the Iranian life-expectancy (73 years).

During the study period, 685 patients were referred. Of these, 149 were excluded and 28 patients did not attend for topographic imaging (95% response rate). Topographic images showed suspect or definite patterns for KCN in 47.76% of participants (256/536 subjects). After re-examination the number of subjects with clinical and early KCN, PMD and suspect KCN was 108, 72, 9 and 20, respectively; 8 patients had other corneal disorders. Among 39 patients, not participating in the re-examination, based on topographic images 32, 6 and one person were classified as KCN, suspect and non-KCN groups, respectively. Consequently, the annual incidence rates of KCN in Yazd province were calculated as 22.3 (excluding suspects) and 24.9 (including suspects) in 100,000 and the prevalence was 1.4% and 1.55% excluding and including suspects, respectively.

The incidence of KCN in Yazd province is noticeable and consistant with other studies on Asian ethnic groups. This is much higher than the incidence in European Caucasians and warrants further genetic and environmental studies