What causes blepharitis due to eyelash mites (Demodex)?

Causes of Demodex Blepharitis

Demodex blepharitis is primarily caused by an overpopulation of Demodex mites (Demodex folliculorum and Demodex brevis) that naturally inhabit the eyelash follicles and meibomian glands. 1

Pathophysiology of Demodex Blepharitis

Demodex mites contribute to blepharitis through several mechanisms:

1. Direct mechanical damage to eyelid tissues and follicles
2. Vector for bacteria - carrying and introducing bacteria to the eyelid margin
3. Inducing hypersensitivity and inflammatory responses in the host 2

The presence of cylindrical dandruff or "collarettes" (waste products of Demodex mites) at the base of eyelashes is pathognomonic for Demodex infestation. 1, 3

Risk Factors

Several factors increase the risk of developing Demodex blepharitis:

• Age - Prevalence increases significantly with advancing age 2
• Rosacea - Strong association with ocular rosacea 1
• Diabetes - Higher susceptibility to Demodex overgrowth 2
• Immunocompromised states - Allows for proliferation of mites

Clinical Presentation

Demodex blepharitis presents with:

• Collarettes at the base of eyelashes (diagnostic hallmark)
• Eyelid margin redness and inflammation
• Itching and irritation of the eyelids
• Foreign body sensation
• Crusting and scaling of the eyelid margin
• Eyelash abnormalities including loss, breakage, or misdirection 1

Diagnostic Approach

The diagnosis of Demodex blepharitis involves:

1. Slit-lamp examination - To identify collarettes and eyelid margin inflammation
2. Eyelash epilation - Microscopic examination of epilated eyelashes can reveal Demodex mites
   • Place epilated eyelashes on a glass slide
   • Add a drop of fluorescein
   • Cover with a coverslip
   • Examine under microscope or with slit lamp using a 90D lens 1

The severity of ocular surface discomfort has a strong positive correlation with the number of Demodex mites per eyelash. 1

Impact on Ocular Health

Untreated Demodex blepharitis can lead to:

• Meibomian gland dysfunction - Blockage and atrophy of meibomian glands
• Dry eye disease - Worsening of symptoms due to tear film instability
• Corneal complications - Including epithelial defects and keratitis 3

Treatment Options

Recent advances in treatment include:

• Lotilaner ophthalmic solution 0.25% - First FDA-approved therapy specifically for Demodex blepharitis

  • Eradicates mites in 50-67% of patients
  • Shows continued benefits through 1 year of follow-up 3, 4

• Tea tree oil preparations

  • 50% tea tree oil lid scrubs or 5% tea tree oil lid massages
  • Effective in reducing mite counts and inflammation 5

• Eyelid hygiene

  • Warm compresses to soften crusts and warm meibomian secretions
  • Gentle massage of eyelids to express meibomian secretions 6

Clinical Pearls and Pitfalls

• Don't overlook Demodex - It's responsible for more than two-thirds of all blepharitis cases in the US 3
• Look for collarettes - Their presence is pathognomonic for Demodex blepharitis
• Consider comorbidities - Especially rosacea, which has a strong association with Demodex infestation 1
• Recognize treatment limitations - Traditional treatments like tea tree oil and metronidazole have shown variable efficacy 7
• Address underlying causes - Treating Demodex may improve other ocular surface diseases 3

By identifying and treating Demodex blepharitis appropriately, clinicians can significantly improve patient outcomes and potentially reduce the need for chronic therapy for associated ocular surface diseases.