"The high proportion of asymptomatic patients should alert us to the possibility of unnoticed progression of meibomian gland dysfunction (MGD)," emphasized Dr Eloy Viso (Servico de Oftalmología, Complexo Hospitalario de Pontevedra, Pontevedra, Spain) when discussing the results of a recent study on a general Spanish adult population.  

A population-based approach was used to obtain a representative sample of the population noted Dr Viso. The possibility of selection bias was also evaluated to ensure the results were fair. "We used a stratified sampling procedure so a representative sample could be obtained in each age group and we performed a design based analysis to account for the stratified sampling and the unequal probability selection," added Dr Viso. "With respect to diagnostic criteria, which are an important cause of variability between studies, we included signs of the 2 categories described in the new MGD classification to reduce the number of false negatives and removed indirect indicators to reduce the number of false positives." 

Additionally, a standardized symptoms questionnaire was employed. "We used the questionnaire developed by Schein 

 because it was the most widely used in population-based studies and because it included symptoms such as eyes stuck shut that have been considered, in spite of a lack of sufficient evidence, more characteristic of MGD," he continued. "The biomicroscopic examination of the ocular surface, however, was performed without knowledge of the results of the questionnaire." 

A symptom-based approach may lead to an underestimation of MGD prevalence