ReviewNonobvious Obstructive Meibomian Gland DysfunctionBlackie, Caroline A OD, PhD; Korb, Donald R OD; Knop, Eric MD, PhD; Bedi, Raman MD; Knop, Nadja MD, PhD; Holland, Edward J MD Author Information From the *Korb Associates, Boston, MA; †TearScience Inc. Morrisville, NC; ‡Research Laboratory of the Department of Ophthalmology CVK, Charité, Universitätsmedizin Berlin, Berlin, Germany; §Iris Advanced Eye Centre, CMC Hospital, Chandigarh, India; and ¶Cincinnati Eye Institute, Edgewood, KY. Received for publication July 21, 2009; revision received January 11, 2010; accepted January 17, 2010. Sources of Support: Korb Associates, Boston, MA and TearScience, Morrisville, NC. C. A. Blackie is an employee of TearScience, Inc, D.R. Korb is a consultant for both Korb Associates and TearScience Inc., R. Bedi is a consultant for TearScience, Inc, and E. Knop, N. Knop, and E. J. Holland are not employees of either organization. Reprints: Caroline A. Blackie, Korb Associates, 400 Commonwealth Avenue, Unit #2, Boston, MA 02215 (e-mail: [email protected]). Cornea: December 2010 - Volume 29 - Issue 12 - p 1333-1345 doi: 10.1097/ICO.0b013e3181d4f366 Buy Metrics Abstract This review presents the rationale and supporting data for a recent paradigm shift in our understanding of meibomian gland dysfunction (MGD). The historical understanding of MGD has been that of an infectious hypersecretory disorder with obvious signs of inflammation, hypersecretion, and purulent excreta. The current understanding of MGD now includes the polar concept of a less obvious or nonobvious type of hyposecretory obstructive MGD, where inflammation and other signs of pathology may be absent unless special examination techniques are employed. A new term, nonobvious obstructive MGD (NOMGD), is used to describe what may be the most common form of obstructive MGD. Obstructive MGD is an area of growing importance because obstructive MGD is now recognized to be the most common cause of evaporative dry eye, and because NOMGD seems to be the precursor to obvious obstructive MGD, it is also an important area to understand. The prevalence of NOMGD seems to be very high but currently significantly underdiagnosed. This review presents the relevant anatomy and physiology, concepts of obstructive MGD, the usual absence of inflammation in obstructive MGD, nomenclature and classification of obstructive and NOMGD, clinical diagnosis of NOMGD emphasizing the necessity for diagnostic expression, the use of a new instrument for diagnostic expression providing a standardized method of assessing meibomian gland functionality, the complementary roles of the aqueous and lipid layers, and the specific treatment of NOMGD, emphasizing that the success of treatment of all forms of obstructive MGD is dependent on the relief of the obstruction. Copyright © 2010 Wolters Kluwer Health, Inc. All rights reserved.