Regional distribution characteristics of eyelid Demodex in patients with squamous blepharitis

To investigate the regional distribution characteristics of different Demodex species in eyelash follicles of patients with squamous blepharitis, and to explore the correlation between Demodex distribution and ocular surface parameters.

Patients with squamous blepharitis who visited the ophthalmology outpatient clinic from December 2024 to May 2025 were enrolled in this cross-sectional study. Patients' information, Ocular Surface Disease Index (OSDI) scores, and meibomian gland (MG) dropout were recorded. Two eyelashes were collected from the inner row (conjunctival side) and outer row (cutaneous side) at the central part of each eyelid, respectively. Demodex folliculorum (DF) and Demodex brevis (DB) were identified according to their typical morphological features under a biological microscope. Ova, larvae, protonymphs and deutonymphs of DF and DB were collectively designated as pre-adult-stage (PAS) mites. Data from the patients' right eyes were selected for statistical analysis to explore the distribution characteristics of Demodex mites and analyze the correlations between Demodex infestation and OSDI scores as well as MG dropout. SPSS 22.0 software was used for all statistical analyses of the data.

A total of 100 patients with squamous blepharitis were enrolled in this study. The overall Demodex detection rate was 92% (92/100) in this study. DF had the highest detection rate (92%) with an average count of 2.78 ± 2.46 mites per eyelid, followed by PAS (detection rate: 42%, average count: 0.8 ± 1.63 mites per eyelid), and DB had the lowest detection rate (27%) with an average count of 0.26 ± 0.64 mites per eyelid (all P < 0.05). The counts of DF and PAS in the upper eyelids (3.72 and 1.34, respectively) were significantly higher than those in the lower eyelids (1.84 and 0.26, respectively) (both P < 0.001). The counts of DF, DB and PAS in the inner row (1.66, 0.2 and 0.67, respectively) were significantly higher than those in the outer row (1.13, 0.06 and 0.13, respectively) (P = 0.001, P = 0.001 and P < 0.001, respectively). Both MG dropout score and OSDI score were positively correlated with Demodex count (all P < 0.05). The MG dropout scores in the DB-positive group (upper eyelid: 2.15 ± 0.80, lower eyelid: 1.55 ± 1.00) were significantly higher than those in the DB-negative group (upper eyelid: 1.48 ± 0.76, lower eyelid: 0.99 ± 0.46) (P = 0.005 and P = 0.007, respectively).

Eyelid Demodex in patients with squamous blepharitis exhibits distinct regional distribution characteristics, with the inner row of upper eyelashes being the primary infestation site. DB in this specific region is an important risk factor for MG dropout in squamous blepharitis patients.