Clinical Diagnosis and Management of Meibomian Gland Dysfunction

BY BEE-LENG ONG, B. OPTOM., PH.D
JUNE 1996

Complaints of "smeary" or "misty" vision among contact lens wearers may point to meibomian gland dysfunction. Here's how to identify and treat this disorder.With a better understanding of the function of meibomian lipids, along with a standardized system for grading meibomian secretions, we can develop a universally accepted definition for meibomian gland dysfunction (MGD). This will enable us to differentiate this condition from more serious meibomian disease and allow us to diagnose and treat it as a separate entity.

THE MEIBOMIAN GLANDS

The meibomian glands are lipid-producing glands in the tarsal plates of the
upper and lower eyelids. These holocrine glands are tree-like in structure with their orifices located along the mucocutaneous junction. There are approximately 30 to 40 glands in the upper eyelids and about 20 to 30 in the lower lids. Upon maturation, the cells burst and release the lipids they produce into the meibomian duct. During a blink, these lipids mix with the other components of the tear film. The different chemical components in the lipid layer are responsible for its
various roles as the outer layer of the precorneal tear film.

ROLES OF MEIBOMIAN LIPIDS

The meibomian lipids reduce the evaporation rate of the tear fluid. This lipid layer also:

• provides a smooth anterior surface to the precorneal tear film;
• lubricates between the lid margin and the cornea;
• prevents skin lipids from entering the tear film;
• acts as a hydrophobic seal for the closed lids during sleep;
• prevents tears from overflowing onto the skin; and
• stabilizes the tear film.

Because the lipid layer performs these important functions, any abnormalities of the glands will produce abnormal lipids that invariably will affect the tear film.

DEFINITION OF MGD

Despite continued research on MGD, there is no universally accepted definition of the condition. Korb and Henriquez called it "a syndrome that is characterized by reduced meibomian secretions," whereas Robin et al. defined MGD as "changes in the morphology of the meibomian gland." Hom et al., on the other hand, defined it as a condition where meibomian fluids become cloudy or are absent upon expression, and Bron et al. defined MGD as an infection of meibomian glands without necessary signs of inflammation.

As a clinician, and from an optometrist's point of view, I suggest we define MGD as a clinical condition where there is "a change in the meibomian secretions from the normal, clear state in the absence of clinically observable meibomian gland abnormalities." With this simple definition, we can use a slit lamp biomicroscope to detect MGD and differentiate it from other meibomian diseases such as meibomitis or chalazion where there is an inflammation or bacterial infection, or a more serious, albeit rare, carcinoma.

ETIOLOGY

Work on animal models shows that hyperkeratinization of the meibomian duct epithelium leads to MGD. In humans, however, the changes in surface and gland morphology could not be seen, but keratin proteins are detected in MGD fluids. Thus, we believe that the underlying cause of MGD is hyperkeratinization of meibomian ductal epithelium.

The actual mechanism leading to MGD is unknown, but it is hypothesized that after hyperkeratinization of duct epithelium occurs, the lipids mix with the cellular debris in the duct. The increased epithelial cells and cell debris in the duct cause thickening of the gland content and the meibum becomes stagnant as the flow is inhibited. The duct then becomes blocked allowing bacteria to feed on the dead cells in the duct, which eventually leads to meibomian gland diseases.

SIGNS AND SYMPTOMS

Not all MGD patients develop ocular symptoms. There is no inflammation or redness of the lid margins. The only clinical sign of MGD is the change in the lipid appearance upon expression. Although some studies report an absence of secretions upon expression in severe cases, I have found that if I apply digital pressure, I can squeeze out a waxy filamentary semi-solid. The tear films of MGD patients often appear foamy.

In MGD, there are no atypical symptoms that fall into specific classifications. The most common complaint is foreign body sensation. Other complaints include: dry eye; "gritty" eyes; watery eyes among elderly patients; and "smeary" or "misty" vision among contact lens wearers.

Although it's not clear whether contact lens wear contributes to MGD, symptomatic patients should discontinue lens wear until the condition resolves. Some contact lens wearers become intolerant to their lenses.

CLINICAL DIAGNOSIS

Diagnosis of MGD is based on the appearance of the meibum. I recommend using a slit lamp biomicroscope with diffuse illumination and low magnification (X6). With the biomicroscope in position, hold the lid margin (upper or lower at one time) tightly between the index finger and the thumb. As you apply pressure, the fluids ooze out and you can observe them through the slit lamp. I rank meibomian secretions as follows:

• Grade 1: clear fluids expressed upon mild digital pressure;
• Grade 2: greasy fluids expressed upon mild digital pressure;
• Grade 3: opaque fluids expressed upon moderate digital pressure;
• Grade 4: waxy fluids expressed from some glands upon forceful digital pressure;
• Grade 5: fine filamentary wax expressed upon forceful expression.

Patients with grade 1 secretions are considered MGD-free whereas those with grade 2 to grade 5 secretions have moderate to severe MGD.

MGD may be more prevalent among contact lens wearers, but some studies have found no statistically significant correlation between lens wearers and nonwearers. There is also no correlation between patient gender or lens type (PMMA, soft or gas permeable) and MGD.

CLINICAL TREATMENT

The recommended treatment for MGD is application of hot compresses. This treatment melts the abnormal waxy lipids to facilitate the outflow from the glands. Some clinicians advocate the use of hot packs twice a day or lid massages four times daily. Patients should place a face cloth dipped in lukewarm water over the lids for five minutes, replacing the cloth as it cools, and repeating the procedure four times (20 minutes total) every morning, and again before going to bed, for two weeks. The same procedure should be carried out for both eyes (whether or not the fellow eye also suffers from MGD).

For contact lens wearers, the "misty" vision usually clears up after treatment with hot compresses. If symptoms persist, however, you may wish to recommend lid scrubs, lid massage, an antibiotic ointment such as bacitracin, or, if you're in the United States and are certified to do so, you can prescribe oral tetracycline twice daily to thin the lipids. These are safe alternative methods for relieving the symptoms of meibomian gland dysfunction. They do not, however, treat the condition.

For asymptomatic patients who do not wear contact lenses, it's usually not necessary to treat the condition. Patients who do not have symptoms frequently don't understand the benefits of treatment.

Occasionally symptomatic patients may complain that the treatment wasn't effective. In such cases, re-examine the patient to ensure that he or she is complying with the treatment procedure as well as to rule out other lid diseases. If the symptoms persist, the patient may be suffering from a more serious meibomian gland disease. By detecting the disease early, you play an important role in primary health care.


TREATMENT SUMMARY FOR MGD

• Hot packs
• Lid massage
• Antibiotic ointment
• Oral antibiotics (if necessary)

A WORD ABOUT VITAMIN A
& EPITHELIAL KERATINIZATION

Because MGD may be due to hyperkeratinization of meibomian ductal epithelium, and because vitamin A regulates epithelial keratinization and differentiation, some researchers now think that diet plays an important role in preventing and treating MGD.

However, research on the effect of vitamin A on MGD is incomplete. Use caution if asking the patient to go on a diet rich in vitamin A. Unlike water-soluble vitamins such as vitamin C that are routinely excreted from the body, vitamin A is a fat-soluble vitamin that is stored in the body so overdose is possible.

CLS

References are available upon written request to the editors at Contact Lens Spectrum. To receive references via fax, call 1-800-239-4684 and request Document #14. (Be sure to have a fax number ready.)

Dr. Ong is on the faculty at the Universiti Kebangsaan Malaysia, Deptartment of Optometry. From 1987 to 1991, she studied and conducted research on meibomian gland dysfunction at the University of Wales, College of Cardiff in the United Kingdom.