A Deeper Understanding of MGD

As knowledge of MGD and its effects have grown, so have our abilities to diagnose and educate patients

How does tear film stability affect visual acuity?

Ivan Mac, MD, MBA: A healthy tear film is one of the most important components of excellent vision. The eye contains three refractive interfaces: the tear film, cornea, and lens. Of the eye’s 60 diopters of refractive power, approximately two-thirds (40 diopters) are derived from the air-tear film interface and the cornea. Disturbances of the air-tear interface can have profound effects on vision.

The tear film itself has three layers: the lipid layer, which prevents tear evaporation; the aqueous layer, which makes up the bulk of the tear film and contains immune mediators; and the mucin layer, which helps the tear layer adhere to the ocular surface. Impairment of any layer of the tear film is known to affect visual acuity and visual quality.

Furthermore, disruption of the tear film is known to increase anterior corneal higher-order aberrations in normal eyes, and it does so more rapidly in patients with dry eye disease. We know that there appears to be a significant linear reduction in pre-corneal tear film stability that occurs between the ages of 8 and 80.

Steven I. Rosenfeld, MD, FACS: Back in our first year of ophthalmology residency, we learned that the primary refracting surface of the eye is the cornea. Specifically, the tear film on the corneal surface provides the main refracting surface based upon the significant difference in index of refraction between the air and the tear film. Any abnormality that disturbs the smooth and clear tear film diminishes the subjective and objective components of vision.

Anatomic defects, such as pterygia, corneal nodules, and anterior basement membrane corneal dystrophy, upset the smooth tear film and decrease visual acuity. Primary aqueous tear deficiency and Sjögren’s syndrome adversely affect the tear film and reduce visual acuity. Secondary dry eye syndrome caused by increased tear evaporation from meibomian gland dysfunction (MGD), anterior blepharitis, lid margin abnormalities, and lagophthalmos also cause problems with visual acuity, as do systemic medications that reduce tear production.

What role does MGD play in destabilizing the tear film?

Arthur B. Epstein, OD, FAAO: In my practice, MGD is a contributing factor in about 95% of dry eye cases. MGD is primarily a progressive, obstructive disease that advances from production of normal meibum the consistency of baby oil to thicker and thicker secretions with increased turbidity and stagnation. Untreated, the glands become totally obstructed, and a downward spiral of degeneration occurs. Reduced blinking due to changes in visual tasks and dietary changes are likely culprits.

Another contributor that has largely been overlooked until recently is the role of bacterial overpopulation of the lids and lid margins in MGD. Staphylococcus is the most common flora, and their production of exotoxin and lipase contribute to the burden of MGD. In particular, elaboration of lipase degrades the lipid component of the tears directly and also promotes saponification of tear lipids, which further attack the lipid layer and its ability to stabilize the tear structure.

Alice T. Epitropoulos, MD, FACS: MGD is the most common form of ocular surface disease. Meibomian glands, located on the lid margin posterior to the mucocutaneous junction, secrete meibum into the tear film when we blink. When these glands are unhealthy, the ocular surface suffers because the tear film is deficient of this lipid shield. The tear film subsequently evaporates prematurely, often causing eye fatigue, burning, and intermittent blurring of vision.

According to the MGD Workshop, MGD is a chronic, diffuse abnormality of the meibomian glands commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in the glandular secretion. MGD is a progressive disease. Without treatment, it can lead to irreversible glandular atrophy and loss of function.

Dr. Rosenfeld: MGD involves chronic and progressive obstruction of the meibomian gland orifices, usually due to keratinization, which results in a decreased delivery of lipids to the ocular surface. Other times, the Staph bacteria colonizing the lid margin will produce lipases that break down the lipids into less stable forms, or forms that irritate the ocular surface. Without the normal lipid layer to stabilize the tear film, the evaporation of tears on the ocular surface occurs at a much faster rate, thereby disturbing both the tear film and visual acuity.

Dr. Mac: The severity of dry eye symptoms appears to be correlated to lipid layer thickness. It is now generally recognized that increased evaporation as a result of a compromised lipid layer is one of the most common etiologies for hyperosmolarity of the tear film.

The meibomian glands of the upper and lower eyelids are the major producers of a lipid material whose synthesis is dependent on factors such as stem cells, neurological stimulants, and hormones. This lipid material is fluid, spreads easily, is a surfactant as well as an aqueous barrier, and must remain functional after a blink. Before delivery, it can be modified by factors such as hormone abnormalities. After delivery, it might be modified by lipases produced by ocular bacteria.

Can patient questionnaires help point to a diagnosis of MGD?

Dr. Epitropoulos: I have patients fill out a dry eye questionnaire to screen for ocular surface disease. If they are symptomatic, I empower my technicians to obtain point-of-care testing, such as tear osmolarity, InflammaDry (RPS), and meibography.

Dr. Mac: One of the first aids to diagnosis can be the administration of a symptom questionnaire. Patients typically report burning and other symptoms, such as dryness, irritation, tearing, redness, a foreign-body sensation, or intermittent blurry vision. As part of the patient workup, a detailed review of medications is often helpful to aid diagnosis. For example, certain medications, such as docetaxel and isotretinoin, may cause dryness.

Do you express the meibomian glands as part of your exam?

Melissa Barnett, OD, FAAO: It is very important to express meibomian glands to evaluate for non obvious MGD. It is amazing how often gently expressing the glands reveals that MGD is present, even in normal-appearing eyelids.

Dr. Epstein: The most obvious way to diagnose MGD — slit lamp examination — is actually the least reliable. A significant number of patients who have MGD lack visible signs on cursory exam. Because close to half of MGD is non obvious, diagnostic expression is critical to the diagnosis. Diagnostic expression can be performed with a device, such as the Korb Meibomian Gland Evaluator (TearScience) or using a fingertip to apply pressure consistent with the force of a normal blink. Normal meibomian glands produce copious lipid with a baby oil consistency.

Dr. Rosenfeld: When patients have MGD, lid margin compression releases thickened, toothpaste-like meibomian gland secretions. Lid margin compression can be very helpful in making the diagnosis because a significant percentage of MGD patients have normal-appearing meibomian gland orifices.

What other strategies and tools do you use to diagnose MGD?

Christine W. Sindt, OD, FAAO: I evaluate the meibomian glands by observing the patient, performing a slit lamp examination, and using a meibographer. I watch the patient as we chat and discuss his medical history, noting how the patient blinks, if the eyelids look red, or if the patient rubs his eyes.

During the slit lamp examination, I look for signs of meibomian gland blockage and lid margin telangiectasia. I measure noninvasive tear break-up time, tear meniscus height, and infrared meibography with the Keratograph 5M (Oculus) if I suspect MGD. I find that imagery is vital to the patient’s understanding of the disease as well as symptom progression.

Dr. Barnett: With a careful slit lamp exam, I evaluate the lower and upper eyelids, conjunctiva, and cornea. I examine the adnexa for conditions such as dermatological inflammation, dermatochalasis, and rosacea, which is quite common. I evaluate the eyelids and margins for infectious, inflammatory, allergic, and physiologic conditions, such as lagophthalmos and eyelid laxity. I look for blepharitis, MGD, Demodex, lid-wiper epitheliopathy, and giant papillary conjunctivitis.

Dr. Mac: A slit lamp exam is essential to study the lid architecture, and I also directly express the glands with my thumb to evaluate the quality and consistency of the meibum. I measure the blink rate and calculate the blink interval, as well as the lower tear meniscus height. I instill fluorescein to measure the tear film breakup time and note the grade and pattern of corneal and conjunctival staining. Patients with MGD typically have linear staining along the inferior cornea.

LipiView (TearScience) is a commercially available interferometer that provides quantitative values of the tear film lipid layer thickness, an automated assessment for MGD. Video and infrared meibography can aid in diagnosis and quantification of MGD as well.

How do you explain MGD to your patients?

Dr. Sindt: I tell my patients that the front surface of the eye is like the windshield of your car. If you are out of windshield wiper fluid, have thick, dirty fluid, or your wipers are broken, it is hard to see through the window.

When the tear film is disrupted, the light passing through the tears is also disrupted, causing blur, halos, and glare. A smooth tear layer provides even refraction, minimizing scatter, and improving clarity. Maintaining a healthy tear film is vital to maintaining clear vision.

Dr. Epstein: Because my practice concentrates on dry eye, I see a lot of referred patients, almost all of whom think that they don’t make enough tears. This is rarely the case.

I explain that tears provide an optically smooth surface, and the engineering that supports a functional, stable tear film is complex. I compare it to a building with a foundation, walls, and a roof. I ask them to think about how much stability the roof contributes to the overall structure of a house. Most patients easily grasp that, allowing me to explain how the lipid layer plays such a critical role in tear structure and stability.

I show patients images of their non-invasive tear breakup time and explain that it’s a measure of their tear film stability. I also review their meibography and discuss the role the glands play. At this point, patients almost intuitively understand the importance of the tears for comfort and good vision.

Dr. Barnett: I like to explain the tear film in simplified terms, including the lipids, mucin, and aqueous. For patients who want more detailed information, I go into greater depth describing the tear film. The tear film provides a smooth, liquid outer layer on the eye in order to provide optimal visual acuity. I use the analogy of a clean windshield and clean and new (not old and cracked) windshield wipers, which provide a pristine view, just as the tear film does on the ocular surface to improve both vision and comfort.

I describe the importance of having clean eyelids and meibomian glands to enhance the ocular surface. I want patients to understand that it is critical to have a healthy, functional tear film, and clean eyelids with intact meibomian glands are imperative. In addition, I review the inflammatory role of allergies and dry eye and the importance of treating both conditions.

Dr. Rosenfeld: MGD can be diagnosed in a variety of ways, both at the slit lamp and with newer diagnostic modalities. Upon walking into the examination room, the external exam may reveal the typical facial stigmata of rosacea, including telangiectasia, erythema, pustules, papules, hypertrophic sebaceous glands, and rhinophyma.

Slit lamp examination in MGD will often demonstrate any combination of findings, including lid margin redness; bulbar conjunctival injection; tear film cloudiness and debris; inspissated meibomian gland orifices; telangiectatic blood vessels surrounding the meibomian gland orifices; pouting of the meibomian gland orifices; increased viscosity and cloudiness of meibomian gland secretions; foaming of the orifices; and atrophy of meibomian gland acini with loss of normal glandular architecture.

Diagnostic modalities that can assist in making this clinical diagnosis include fluorescein-assisted tear breakup time and characteristic inferior punctate corneal staining; abnormal tear film osmolarity testing; abnormal LipiView images; abnormal tear film MMP levels; and imaging of the meibomian gland architecture that reveals structural problems.

Dr. Epstein: I evaluate the glands using meibography with the Keratograph 5M, and I also use LipiView to measure lipid layer thickness — an indirect measure of meibomian gland function — and blink dynamics. The Keratograph 5M has a dry eye testing suite that includes meibography, noninvasive breakup time, and several other useful tests. Also, transillumination of the glands can show gross abnormalities.

Dr. Epitropoulos: As expectations in our surgical patients continue to rise, we need to look at the tools available to us to achieve the best results for our patients. Current options for evaluating and diagnosing dry eye have changed significantly throughout the last several years in specificity and objectivity. If patients are symptomatic on the dry eye questionnaire, my techs obtain tear osmolarity and InflammaDry. Using the LipiView, meibography produces high-definition images of the meibomian glands, which help me determine whether there is dilation, truncation, or atrophy of the glands. It is an excellent tool to identify these patients early, as well as a good opportunity to educate them and guide the discussion about the disease. Patients can visualize healthy versus unhealthy glands, which helps our patients understand the disease. ■

	Melissa Barnett, OD, FAAO, is a principal optometrist at the UC Davis Eye Center in Sacramento and President of The Scleral Lens Education Society.
	Alice T. Epitropoulos, MD, FACS, practices at Ophthalmic Surgeons and Consultants of Ohio at The Eye Center in Columbus, Ohio, and is a clinical assistant professor at The Ohio State University.
	Arthur B. Epstein, OD, FAAO, is the director of cornea external disease and clinical research at Dry Eye Center of Arizona in Phoenix.
	Ivan Mac, MD, MBA, is medical director and CEO at Metrolina Eye Associates in Charlotte, N.C.
	Steven I. Rosenfeld, MD, FACS, is in private practice at Delray Eye Associates in Delray Beach, Fla., and is a voluntary clinical professor at the Bascom Palmer Eye Institute, University of Miami School of Medicine.
	Christine W. Sindt, OD, FAAO, is the director of the Contact Lens Service and a clinical associate professor at the University of Iowa, Department of Ophthalmology and Visual Sciences.