The Use of Digital PCR for the Diagnosis of Demodex Blepharitis

Purpose: This was a pilot study to evaluate the efficacy of digital polymerase chain reaction detection of Demodex in eyelid margin swabs for the diagnosis of Demodex blepharitis. This study aims to explore the possibility of digital polymerase chain reaction detection to improve the diagnostic accuracy of Demodex blepharitis detection.Methods: Volunteers were prospectively recruited and classified by experienced doctors into suspected Demodex blepharitis or healthy controls using slit-lamp evaluation of the eyelid margin and an inquiry about symptoms. Three eyelashes from each eyelid were epilated from participants in each group for microscopic observation and mite counting. Then, swabs from the eyelid margins of each eye were collected after the eyelashes were epilated and stored at -80 degree celsius for future DNA extraction and digital polymerase chain reaction detection. The positive or negative results of both methods were compared for diagnostic accuracy, and the Kappa value was also calculated to evaluate their consistency.Results: The accuracy of the digital polymerase chain reaction detection was 71.6% and that of the mite counting method was 75%. Their combined accuracy was improved to 77.3%. The Kappa value of the two methods was 0.505, indicating moderate consistency.Conclusion: Digital polymerase chain reaction detection of Demodex from ocular surface swabs was painless and noninvasive and is a potentially accurate quantitative method available for diagnosing Demodex blepharitis. This method is also complementary to the conventional mite counting method, particularly when a sufficient number of eyelashes cannot be effectively epilated.