Epidemiology is the study of factors influencing the health of populations. Epidemiologists employ a range of research methods and analytic techniques to explore how disease occurs. Findings from epidemiologic research inform strategies to prevent disease and improve public health. Although the science of epidemiology is a relatively new discipline, epidemiology has made many significant contributions to public health. While early examples included understanding and controlling epidemic disease, later examples included landmark research such as the British doctors’ study which definitively proved the link between smoking and lung cancer (Doll & Peto 1976). Recommendations from epidemiological studies now play a central role in evidence-based health care. 

Contact lens-related microbial keratitis is a rare but acute condition and is the most severe complication of contact lens wear. Rare diseases such as microbial keratitis can only be studied in large population-based studies as prospective clinical trials would need prohibitively large sample sizes. Fortunately, several well-designed, population-based epidemiological studies have been conducted to evaluate the rates and risk factors for contact lens-related microbial keratitis, spanning the last 20 years. This body of literature has been summarised in several published reviews (Keay et al. 2007b, Stapleton et al. 2007a). Here, we revisit the epidemiological research to date and summarise the key findings that are relevant to those involved in contact lens practice. Armed with this information, optometrists can provide the best advice to limit serious complications in contact lens wear.