Study Population

This cross-sectional study was conducted at the Department of Ophthalmology in the Korea University College of Medicine. Two groups of subjects, the obstructive MGD group and the control group, were enrolled between June 1, and August 31, 2012 from our institute. This study adhered to the tenets of the Declaration of Helsinki and approval for retrospective review of clinical records was obtained from the Korea University Guro Hospital Institutional Review Board.

The obstructive MGD group contained subjects with clinical signs of MGD, terminal duct obstruction, plugging of the meibomian glands, turbid secretions or turbid secretions with clumps, inflammation and swelling of the eyelid margin, vascular injection of the posterior lid margin, and symptoms of MGD for at least 3 months. Participants in the control group did not have any clinical signs and/or symptoms of MGD, dry eye, or significant ocular surface disease and were not using eye drops or eye medications. Exclusion criteria included: (1) aged less than 18 years old; (2) presence of any uncontrolled systemic diseases; (3) previous ocular surgery; (4) use of contact lens; and (5) allergic to fluorescein sodium or topical anesthetic (eg, Alcaine, proparacaine hydrochloride 0.5%).

Study Protocol

All participants completed a patient history questionnaire. Afterward, an ophthalmic examination with slit-lamp biomicroscopy was performed for observation of lid margin and meibomian gland orifices. Clinical measurements were performed in the following order to remove the effect of previous measurement on the result of the other measurements: (1) lipid layer thickness; (2) corneal and conjunctival surface staining using fluorescein; (3) TBUT; (4) Schirmer 1 test; and (5) meibography. There was at least a 10-minute rest period between each test.

Subject Examination

Lipid layer thickness was measured using the LipiView interferometer (TearScience Inc, Morrisville, North Carolina, USA) ( Figure 1 ). The LipiView interferometer works according to the principle of white light interferometry, and the tear film is measured using an interferometry color assessment by specular reflection. The unit of measurement is interferometry color units (ICU), which is an index of thickness and is estimated on the basis of the observed mean interference colors. Participants were seated facing the LipiView interferometer, and the chin and forehead were positioned fully forward onto the chin rest and firmly against the forehead rest. Participants were instructed to maintain fixation on the internal target (3 light-emitting diodes). Camera adjustment was conducted until the pupil appeared in the center of the live video screen and the reflected tear film image was within the green targeting rectangle. The camera focus was then adjusted for the clear tear film image. During image capture, participants were instructed to blink naturally. Image capture typically takes 20 seconds.

The analyzed image by the LipiView interferometer. (Top) The image of specular reflections on the tear film in the anterior segment photograph. (Upper middle) The image of specular reflections on the tear film with the scale bar of interferometry color units (ICU) on the right. (Lower middle) Graph showing the change of the average, maximum, and minimum lipid layer thickness during 20 seconds. Interruptions in the graph indicate blinking. (Bottom) Table showing the data on the number of calculated frames; the average, maximum, and minimum values of lipid layer thickness; and the standard deviation. C-Factor represents the reliability of the measurements.

Grading of corneal and conjunctival surface staining was conducted according to the Oxford scoring scheme. Tear film stability was determined by TBUT using sodium fluorescein. Schirmer 1 test was conducted during 5 minutes without anesthesia.

Integrity of meibomian glands was assessed using a BG-4M Non-Contact Meibography System (Topcon Corp, Tokyo, Japan). The BG-4M Non-Contact Meibography System was mounted on slit lamps. This system employs a background illumination device with an infrared light transmittance filter that illuminates the meibomian glands to assess their integrity. Photographs of meibography were quantified with ImageJ (1.43u; http://rsb.info.nih.gov/ij/ ; National Institutes of Health, Bethesda, Maryland, USA). The ratio of meibomian gland dropout area to the total area (meibomian gland loss; %) was calculated using the polygon selection tool of ImageJ ( Figure 2 ). The area of the central two-thirds on both upper and lower tarsal conjunctiva, in which meibomian glands were best visible, was selected for analysis.

Analyses of the ratio of meibomian gland dropout area to the total area (meibomian gland loss; %) using the polygon selection tool of ImageJ.

To evaluate the intraobserver reliability of the LipiView interferometer, a second measurement was taken by the same examiner 10 minutes later. To assess interobserver reliability of meibomian gland dropout rate, the area of meibomian gland dropout was measured by another observer (J.S.L.). The observers were masked to the results of the other tests when measuring the area of meibomian gland dropout.

Statistical Analysis

Statistical analyses were performed using linear regression analysis, Mann-Whitney test, Fisher exact test, and Pearson correlation analysis in SPSS version 12.0 (SPSS Inc, Chicago, Illinois, USA). The intraclass correlation coefficient (ICC) was calculated to assess the intraobserver and interobserver reliability. Results were considered statistically significant if the P value was <.05.