Alisa Sivak, MA(Ed) manages the development of educational publications produced by the Centre for Contact Lens Research at the University of Waterloo’s School of Optometry, Canada.
Meibomian gland dysfunction (MGD) is a common cause of the signs and symptoms of dry eye. The International Workshop on Meibomian Gland Dysfunction defines MGD as,
[A] chronic, diffuse abnormality of the meibomian glands, commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in the glandular secretion. This may result in alteration of the tear film, symptoms of eye irritation, clinically apparent inflammation, and ocular surface disease.1
What do we know about the quality and appearance of meibomian glands, and what causes their dysfunction? What is the best way to assess MGD, and are there any new treatment options? The following is a synopsis of new information reported about this condition at the 2011 meeting of the American Academy of Optometry.
Quality and appearance of meibomian glands
The Keratograph 4 – commonly used to image the cornea and assess contact lens fit – offers a quick and patient-friendly method of imaging the structure of meibomian glands, which can be difficult to observe clinically. Sruthi Srinivasan and colleagues at the Centre for Contact Lens Research (University of Waterloo, Canada) reported a positive correlation between OSDI scores and meiboscores captured with this device. 2
Research indicates that the quality of meibomian gland expression in the upper lid is similar to that of glands in the lower lids. Using a cotton-tipped applicator to express the glands of subjects with and without MGD, Jerry Paugh and Justin Kwan at the Southern California College of Optometry (USA) also reported that glands in the upper lid appear to atrophy less than those in the lower lid.3
The upper and lower eyelids have approximately the same mean total number of meibomian glands yielding liquid secretion (MGYLS), according to a pilot study conducted by Donald Korb and Caroline Blackie at Tear Science (USA). Dividing upper and lower lids into thirds (temporal, central, nasal) also revealed that the upper and lower lids have a similar distribution of MGYLS. Within each lid, the temporal third of each lid, however, had a significantly lower mean number of MGYLS.4
Assessing MGD
“MGD score” provides the most sensitive and specific diagnosis of MGD, according to Justin Kwan and Jerry Paugh at the Southern California College of Optometry (USA). This score comprises the sum of lid margin grade, gland expression grade and gland atrophy grade. This research team also found that standard clinical tests, including tear break-up time, lid margin evaluation, and ocular surface staining, surface regularity index, meibomian gland expression from lower lid, and meibography of the lower lid are also sensitive and specific in diagnosing this condition.5
Be cautious when relying on a photograph to interpret clinical findings, in evaluating MGD. Daniel Powell and others at The Ohio State University found variability between “real time” grading and retrospective image analysis.6
It may not matter whether you use a cotton-tipped applicator or a Meibomian Gland Evaluator (TearScience), when it comes to grading meibomian gland expression in those diagnosed with MGD, according to Jerry Paugh and colleagues at the Southern California College of Optometry. This team did find, however, that tool type made a difference with non-dry eye subjects.3
In vivo confocal microscopy is an effective method of visualizing inflammation underlying dry eye symptoms, particularly in the absence of clinical signs visible through a slit lamp microscope. Pedram Hamrah and colleagues at the Massachusetts Eye and Ear Infirmary (USA) and others found that five chronic MGD patients demonstrated subclinical signs only revealed via confocal microscopy, including subclinical inflammation of the palpebral conjunctival epithelium, substantia propria, and periglandular areas, as well as sub-epithelial conjunctival fibrosis.7
Causes and treatment of MGD
The LipiFlow® Thermal Pulsation System can be an effective treatment for meibomian gland dysfunction, according to Don Korb and Caroline Blackie at TearScience (USA). This 12-minute treatment unblocks the glands by applying controlled heat to the inner surfaces of the upper and lower palpebral conjunctivae and lid margins while simultaneously applying pulsating pressure over the outer eyelids. In a case study of a patient with long-term dry eye symptoms, this treatment improved both symptoms and signs: seven months after treatment, tear break-up time doubled and the number of meibomian glands yielding liquid increased.8
REFERENCES
1. Nelson JD, Shimazaki J, Benitez-del-Castillo JM, Craig JP, McCulley JP, Den S and Foulks GN. The International Workshop on Meibomian Gland Dysfunction: Report of the Definition and Classification Subcommittee. Invest Ophthalmol Vis Sci 2011;52(4):1930-1937.
2. Srinivasan S, Menzies K, Sorbara L, Jones LW. Imaging meibomian gland structures using the Oculus Keratograph. American Academy of Optometry 2011:e-abstract 110775.
3. Paugh JR, Kwan J, Nguyen A, Senchyna M, Christensen M, Meadows D. Comparison of upper and lower eyelid meibomian glands: Are they different? American Academy of Optometry 2011:e-abstract 115721.
4. Korb DR, Blackie C. Distribution of meibomian glands yielding liquid secretion in upper and lower eyelids and the correlation to dry eye symptoms. American Academy of Optometry 2011:e-abstract 115469.
5. Kwan J, Paugh JR. Diagnostic test efficacy in meibomian gland dysfunction. American Academy of Optometry 2011:e-abstract 115271.
6. Powell DR, Hopkins G, Jones-Jordan L, Nichols JJ, Nichols KK. Evaluation of interobserver agreement in meibomian gland dysfunction assessment. American Academy of Optometry 2011:e-abstract 110501.
7. Hamrah P, Qazi Y, Blackie C, Korb DR. An explanation for refractory dry eye symptoms despite significant improvement in dry eye signs post-treatment for meibomian gland dysfunction (MGD). American Academy of Optometry 2011:e-abstract 110010.
8. Korb DR, Blackie C. Lipiflow treatment of meibomian gland dysfunction secondary to meibomian gland drop out. American Academy of Optometry 2011:e-abstract 115313.
