Sensitivity and Specificity of Slit-Lamp Demodex Infestation Detection in Patients With Blepharitis

Purpose: To determine whether the sensitivity and specificity of detecting Demodex infestation using slit-lamp examination are comparable with those of light microscopy. Methods: We evaluated 22 eyelids of 22 patients with clinical signs and symptoms of blepharitis that suggested Demodex infestation. Two lashes with cylindrical dandruff were epilated from each lid and mounted on a glass slide. A coverslip was mounted on each slide, then placed on a strip of white paper, and examined on a slit lamp with a 90D lens attached. Number of mites per lash were documented. The slides were then examined under a light microscope. The same procedure was followed with a control group. Results were evaluated per lash and per patient. Results: Twenty-two patients were included, 11 were men, with an average age of 54.8 years. A total of 176 epilated lashes were examined. Mean total Demodex count per lash was 0.9 ± 1.3 mites by slit-lamp examination and 1.22 ± 1.73 by light microscopy. Corresponding values per patient were 7.3 ± 4.4 and 9.7 ± 7.18. Correlation between Demodex counts by slit lamp and light microscopy was mildly positive and statistically significant per patient (8 lashes, r= 0.69, P < 0.001). Analysis of positive/negative results yielded 43.2% with a positive result for slit lamp and 51.7% for light microscopy. The sensitivity of the slit-lamp examination for the presence of Demodex per patient was 96.6%, with a specificity of 90.9%; the positive predictive value was 91.6%, and the negative predictive value was 95.2%. Conclusions: Demodex infestation in patients with blepharitis and cylindrical dandruff can be confirmed using a slit lamp. This technique demonstrates diagnostic performance that is noninferior to that of light microscopy.