Blepharitis is a relatively common disorder that manifests various clinical signs such as foreign body sensation, tearing and dry sensation, etc. The complete treatment of this condition is believed to be difficult because of abnormal meibomian gland function and changes in the normal flora of conjunctiva. Consequently, the course is often chronic, frustrating both clinicians and patients. Meibomian gland dysfunction is a common type of chronic blepharitis and although it is so common it can be easy to overlook clinically. Because symptoms can improve with appropriate treatment, it is very important to identify the disorder in patients who complain of dry eye symptoms.Chronic meibomian gland dysfunction particularly affects the lipid layer of tear film, destabilizing the tear film and quickening the tear film's evaporation, and ultimately causes many disorders of the external eye, including dry eye syndrome. 1In order to treat this dysfunction, physicians have reported prescribing 200 mg twice-daily doxycycline (α -6 deoxy-5 hydroxytetracycline), a long acting analogue of tetracycline that inhibits collagenase and also has antichemotactic effects, thus improving patients' symptoms by stabilizing the lipid layer of tear film. Recently, in the field of dentistry, low-dose doxycycline hyclate (20 mg) has been used to treat and prevent periodontitis by inhibiting collagenase. 3 The authors wanted to investigate the effectiveness of such therapy in the chronic meibomian gland dysfunction patients.One hundred fifty patients were selected (55 male, 95 female) that reported to the department of ophthalmology between January and December of 2003 and newly diagnosed with chronic meibomian gland dysfunction with grade 2 or worse meibomian gland destruction or meibomian gland Department of Ophthalmology, Dankook University College of Medicine, Cheonan, KoreaPurpose: The aim was to investigate the effect of low dose doxycycline (20 mg) therapy in patients with chronic meibomian gland dysfunction that were refractory to conventional therapy. Methods: The randomized prospective study enrolled 150 patients (300 eyes) who have chronic meibomian gland dysfunction and who didn't respond to lid hygiene and topical therapy for more than 2 months. All topical therapy was stopped for at least 2 weeks prior to beginning the study. After conducting the tear break up time test (TBUT) and Schirmer test, the authors randomly divided the patients into three groups a high dose group (doxycycline, 200 mg, twice a day), a low dose group (doxycycline, 20 mg, twice a day) and a control group (placebo). After one month, the author repeated the TBUT and Schirmer tests, and analyzed the degree of symptomatic improvement. Results: Compared to the control group, both the high and low dose group showed statistically significant differences after treatment in TBUT, Schirmer test, the number of symptoms reported and the degree of improvement of subjective symptoms. However, there was no statistically significant difference between the high and low dose ...