Won Jun Lee¹, Minjeong Kim¹, Seung Hyeun Lee¹, Yeoun Sook Chun¹ & Kyoung Woo Kim ^1,2*

This study aimed to investigate the impact of ocular demodicosis on dry eye disease (DED) and meibomian gland dysfunction (MGD) across different age populations: young (20 to < 40), middle-aged (40 to < 60), and elderly (≥ 60), based on the retrospective medical chart review. In each age subgroup, Demodex infestation and its count were correlated with clinical parameters of DED and MGD. Among the total of 351 subjects, 52.7% had ocular demodicosis, with a mean of 2.31 ± 1.39 mites per four eyelashes (0.58 per lash) in a unilateral eye. In the age subgroup 1 (age < 40; N = 44), subjects with Demodex had significantly higher meibum quality grades. In subgroup 2 (40 ≤ age < 60; N = 122), subjects with Demodex had higher ocular surface disease index scores and higher MG expressibility grades. However, in subgroup 3 (age ≥ 60; N = 185), demographics and all parameters did not differ according to Demodex infestation. Moreover, the number of mites did not correlate with MGD severity in any of the subgroups. In conclusion, age may act as a significant confounding factor in the relationship between ocular Demodex infestation and clinical features of DED and MGD, despite older patients aged 60 years and above being at a higher risk of Demodex infestation and experiencing more severe MGD.

Demodex mites are parasitic creatures measuring 150–350 μm in length that are commonly found in the eyelid area. While there are several Demodex species, Demodex folliculorum (D. folliculorum) and Demodex brevis (D.brevis) inhabit the human body¹. The former resides in eyelash follicles, while the latter is found in meibomian and sebaceous glands of the eyelashes, particularly on the ocular surface². The infestation of these mites has been linked to conditions such as anterior blepharitis, meibomian gland dysfunction (MGD), and even corneal abnormalities³.

D. folliculorum has been identified as a vector for bacteria, fungi, and viruses⁴, and may directly penetrate cell membrane to feed, potentially inducing allergies⁵. Moreover, Demodex infestation may cause superficial corneal neovascularization, phlyctenule-like lesions, corneal infiltration, and opacity^6–9. A recent study, conducted by ocular surface disease experts agreed that itching is the most common symptom in Demodex blepharitis¹⁰.

The relationship between Demodex infestation and meibomian gland health remains debated, with studies suggesting both associations and non-associations. A study indicated that ocular Demodex infestation might contribute to ocular surface discomfort, inflammation, and meibomian gland dropout in MGD patients⁵. Conversely, a study found no significant association between the expressibility and drop-out of meibomian glands and Demodex infestation³. Additionally, D. brevis, which usually inhabits the meibomian glands, has been suggested as a possible cause of repeated chalazia and hordeola rather than MGD in the posterior eyelid¹¹. A recent randomized clinical trial used lotilaner ophthalmic solution to treat Demodex blepharitis, using the cure of collarette as a primary end point, a clinical marker of Demodex-associated anterior blepharitis¹².

Earlier studies have shown that the prevalence of ocular Demodex increases with age13– 15, and one study reported a demodicosis frequency of 77% in individuals aged over 70 years, compared to 8% in those aged 25 years or younger¹⁶. Furthermore, it was observed that the higher prevalence of ocular Demodex in elderly

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