dry eye

Non-Obvious Meibomian Gland Disease

New research reveals a non-obvious form of meibomian gland disease is preventing us from providing many of our patients with dry eye relief.

CAROLINE A. BLACKIE O.D., PH.D., F.A.A.O. AND DONALD R. KORB, O.D., F.A.A.O., Boston

A dry eye patient presents desperate for symptom relief. He tells you several other eyecare practitioners have attempted to treat him with "everything." "Everything," the patient explains, has consisted of placing warm washcloths over his upper eyelids, omega-3 fatty acid supplements, over-the-counter eye drops, prescription medications and punctal plugs.

To make matters worse, the patient's eyes and eyelids, upon external examination, don't look bad. In fact, the longer you observe them during his tortured report of one failed therapy after another, the more you wonder whether this patient is really one of "those" patients. You know — one of "those" patients who would benefit more from spending their time and money on psychological therapy because you and the eight other eye doctors he's seen can't identify the cause of his discomfort.

Keep in mind, however, that a large number of patients like this one aren't crazy. Instead, they have undiagnosed meibomian gland dysfunction (MGD). The reason it's undiagnosed: MGD can be non-obvious (NOMGD) and exist in the absence of inflamed and/or infected lids and gland orifices.¹ Unfortunately this is not widely known, and, therefore, we tend to skip the evaluation of the meibomian glands when the lids and gland orifices appear normal.

Here, we explain why the "normal appearance" rationale is frequently wrong and how you can ensure patients who have NOMGD, no longer go undiagnosed.

MGD despite "normal appearance"

From previous research, we know that the mechanism by which meibomian gland secretion is released onto the eyelid margin is via the blink.² Blinking is essential to the process. In the absence of a blink, the oil the meibomian glands are ready to express remain in the glands' terminal ducts and fails to contribute to the ever-so-critical oily layer of the tears.

Unfortunately, many of our daily tasks, such as computer work, reading, video games, television and contact lens wear reduce our blink rate.^3,4 This chronic, unconscious reduction in involuntary blinking significantly impedes the natural mechanism by which the meibomian glands release oil on to the lid margin. The result: a compromised lipid layer and, therefore, tear film instability.⁵

With increased evaporation (due to the compromised lipid layer), the likelihood of microtrauma to the lid wiper — the portion of the upper lid that is in contact with the ocular surface — is high.^6-8 This leads to inflammation of the lid wiper. Once the lid wiper is damaged and inflamed (lid wiper epitheliopathy), the very act of blinking itself causes discomfort, and the insidious cycle of MGD continues.

Throughout all this, however, the lids can appear quite normal, and the glands appear MGD free. As a result, we tend to miss the diagnosis. We may even diagnose lid wiper epitheliopathy, though fail to consider that the decline in the meibomian glands' function is likely the culprit. In failing to consider MGD, the use of artificial tears and other lubricants will only offer a potential short-term solution to the problem of reduced meibomian gland function.

Ensuring MGD diagnosis

To accurately determine the MGD diagnosis, you must diagnostically express the meibomian glands regardless of whether the patient lacks accompanying visible signs of MGD. Specifically, this means you must either apply a diagnostic expressor or apply small amounts of digital pressure (a light touch with your thumb or index finger just beneath the lashes of the lower lid) to evaluate whether the glands are ready to secrete oil upon deliberate blinking. (See figure 1.) If a gland has liquid oil available in its terminal duct, that gland and any glands you're diagnostically expressing simultaneously will release their liquid oily contents onto the lower eyelid margin. If a gland doesn't release any liquid contents, it could mean the gland is obstructed or doesn't have any available liquid oil at the time of the expression. If you increase the pressure, you may observe the gland expresses a cloudy liquid or inspissated material. In either case, these results reveal the gland contains some meibum, though you can't express it using very light pressure — as is experienced during normal blinking. Therefore, you'd consider these glands non-functional at the time of the expression.

Figure 1: Notice how the lid is slightly everted outward with diagnostic expression, yielding clear oil. Although, we used a diagnostic expressor here (see white area below the lashes), expression can be accomplished via thumb or index finger applying gentle digital pressure.

To determine whether this patient requires MGD therapy, such as therapeutic expression of the meibomian glands (explained below), you must determine how many of the glands are functional (e.g. releasing liquid oil) during your diagnostic expression. (See "MGD Treatment," below.) The lower eyelid contains approximately 25 glands. Previous research reveals that healthy, asymptomatic individuals have approximately 30% to 50% of their lower eyelid meibomian glands functional at any one time.⁹ Recent studies have confirmed this as well as the fact that symptomatic individuals tend to have fewer than five or six functional glands at any one time.¹⁰ As a result, if after performing diagnostic meibomian gland expression — in the manner described above — your patient's eyelids reveal fewer than five to six functional meibomian glands, the patient has MGD. If the lids appear otherwise normal but only five to six meibomian glands are functional, your patient has NOMGD.^1,11 (See figure 2.)

Figure 2: Here, we used a Mastroda paddle to therapeutically express the meibomian glands. Note that although the lid, lashes and lid margins are without inflammation or other pathological signs, the glands aren't expressing any material. This indicates significant obstruction of the glands in the absence of obvious clinical signs, or non-obvious MGD.

If the patient has fewer than five to six glands yielding liquid secretion with diagnostic expression but upon moderate or significant pressure over the glands, they release oily material, you should therapeutically express the glands. Therapeutic expression involves significant pressure over the glands using a topical anesthetic and a cotton swab, glass rod or Mastroda paddle to both "sandwich" the lid between a rigid surface on the rear surface of the lid and to protect the eyeball from the increased pressure. You may need to perform this therapeutic expression on multiple occasions throughout the year because some patients seem particularly prone to developing meibomian gland obstruction, though the literature on this topic is sparse.

Unfortunately, in cases of severe meibomian gland obstruction, patients can't tolerate the pain caused by the expression. A possible option in such cases is to terminate the manual expression on that day, and consider warm compress therapy in combination with lid scrubs and oral antibiotics for a few weeks. The purpose: to soften the obstructive material in the glands sufficiently for the patient to tolerate repeat manual expression on a followup visit. If you don't remove the obstructions in the meibomian glands, their function cannot be restored. The most effective way to remove the obstruction is manual expression of the glands.

"An old ophthalmology axiom states that the external exam is not completed until all four lids have been massaged for meibomian gland secretions and the lids averted," says Martin and colleagues.¹² "For some reason, while this axiom is truer than ever today, our clinical practices do not adequately reflect this."

If you want to help the patient who has failed to receive help from so many doctors before you — the one who reports symptoms of ocular surface discomfort with no accompanying visible signs of MGD — you must take the time to "diagnostically" express the meibomian glands. OM

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