MGD AND LENS WEAR
Meibomian Gland Dysfunction and Contact Lens Wear
Does contact lens wear cause MGD—or does MGD cause contact lens discomfort?
By William Ngo, OD, FAAO
Meibomian glands (MGs) are modified sebaceous glands embedded within the tarsal plate of the eyelids. These glands consist of a long central duct surrounded by grape-like structures called acini. The acini produce oils (meibum) into the long central ducts, and the meibum then travels out of the orifices located near the eyelid margin (Figure 1). At the eyelid margin, the meibum comes into contact with the tear film. With individual variation in consideration, there are approximately 31 MGs in the upper lid and 26 in the lower lid (Knop et al, 2011).
Figure 1. Meibomian gland orifices along the eyelid margin as indicated with white arrows.
A Closer Look at Meibomian Gland Dysfunction
Healthy MGs are able to produce and deliver meibum to the tear film unobstructed. However, this delivery could be disrupted in a variety of ways, e.g., keratinization of the orifice opening or increased meibum viscosity. Obstruction of the MG orifice causes a stasis in meibum flow and increases the pressure within the ductule system. The decreased delivery of meibum to the tear film results in evaporative dry eye (Knop et al, 2011), which has been suggested to be the most common form of dry eye disease (Castillanos et al, 2008). Long-term obstruction and inflammation causes MGs to atrophy. This process is called meibomian gland dysfunction (MGD). The recommended definition of MGD by the International Workshop on Meibomian Gland Dysfunction is as follows:
“Meibomian gland dysfunction is 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,” (Nelson et al, 2011).
The prevalence of MGD can range from 3.5% to approximately 70%, with a higher prevalence in the Asian population (Schaumberg et al, 2011). Some of the risk factors that are hypothesized to correlate with MGD include, but are not limited to, aging, chronic blepharitis, isotretinoin use, and contact lens wear (Schaumberg et al, 2011).
Patients who have MGD may or may not experience dry eye symptoms (irritation, soreness, itchiness); assessment of symptoms is subjective and is conducted using validated symptom questionnaires (e.g., Ocular Surface Disease Index [OSDI], McMonnies) (Tomlinson et al, 2011). The advantage with questionnaires is that they are the only method in which symptoms can be quantified. However, due to their subjective nature, it can be difficult to compare between two individual scores because of subjective interpretation of questions and discomfort tolerance. Another issue is that symptom scores do not always correlate well with dry eye signs (Hay et al, 1998; Pult et al, 2011; Schein et al, 1997).
In addition to symptoms, various physical aspects of MGD can be assessed. A slit lamp biomicroscope can be used to observe changes in lid morphology, extent of lid telangiectasia, vascularity, and hyperkeratinization of the lid margin (Tomlinson et al, 2011).
MG obstruction is often assessed by applying pressure to the lower lid, either digitally or using a standardized instrument. A standardized device controls the pressure exerted by applying the same amount of pressure every time, which makes it useful in tracking changes to MG expressibility (Figure 2).
Figure 2. This device applies consistent pressure along the eyelid margin to express meibomian glands.
The volume of meibum expressed from the gland openings provides information about the degree of secretory activity and/or obstruction. The quality of meibum—which can range from clear and oily (i.e., normal) to white, opaque, and thick (i.e., altered state, Figure 3)—can also be observed simultaneously.
Figure 3. Poor-quality meibum is white, opaque, thick, and can be seen when the glands are expressed.
Meibography is a procedure that is less commonly used in clinical practice but can be used to observe the morphology of MGs (Tapie, 1977). Meibography can be conducted using a variety of techniques (Ngo et al, 2013). In one technique, the eyelid is transilluminated using white light, and the palpebral side is viewed through an infrared filter (Robin et al, 1985). Alternatively, the morphology of MGs can be viewed by illuminating the palpebral side of the eyelid with infrared light, then viewing the MGs through an infrared sensor (Arita et al, 2008). MGs appear as an array of vertically aligned threads that travel along the tarsal plate (Figure 4).
Figure 4. Under infrared illumination, meibomian glands appear as white thread-like structures. The loss of these structures represents gland atrophy.
There are numerous grading scales currently available for grading the eyelid margins, meibum appearance, gland expressibility, and meibography.
MGD is often underreported, and treatment methods are highly variable among practitioners. Regardless, lid hygiene, warm compresses, artificial tears, antibiotics, and anti-inflammatory therapy remain the primary methods for treating MGD (Geerling et al, 2011). The International Workshop on Meibomian Gland Dysfunction has provided a staged management algorithm for treating MGD based on the severity of clinical presentation. To summarize:
• Early-stage MGD is characterized by no symptoms and only minor alterations in meibum quality. Manage this stage by informing patients about their environment and medications and by considering eyelid hygiene.
• In moderate stages, patients may feel minimal to moderate ocular discomfort. Eyelid margins begin to vascularize, and MG orifices show plugging. Meibum is thicker, turbid, and more difficult to express. Warm compresses, lid hygiene, and oral tetracycline may be used at this point along with a lubricant ointment prior to sleeping.
• In more severe stages, MGD is characterized by marked ocular discomfort. Eyelid margins are irregular and vascularized, and orifices are obstructed. Expressed meibum is thick and opaque. The International Workshop on Meibomian Gland Dysfunction recommends that all of the aforementioned treatments be used in combination with anti-inflammatory therapy (e.g., doxycycline, minocycline, etc.) in more severe stages.
A Link Between Contact Lenses and MGD?
Two questions that remain unanswered are whether contact lens wear can cause MGD, and whether MGD can cause contact lens discomfort. Over the past 30 years, only a handful of studies have observed the relationship between contact lens wear and MGD.
Henriquez and Korb (1981) conducted bacteriological and cytological studies to examine MGs and found that stagnated secretions and obstructed orifices would alter meibum secretions, which alters the tear film dynamics and may contribute to contact lens intolerance. Another mechanism proposed was that toxins originating from bacteria residing within the MGs could be delivered to the tear film. The toxins could then be transported behind the precorneal tear film and cause discomfort.
Ong (1996) conducted a comparative cross-sectional study to determine whether lens wear had any effect on the MGs. The population (n = 231) that he studied had 81 lens wearers. He found that 49% of the lens wearers had MGD, and 39% of the non-lens wearers had MGD. After conducting a χ2 analysis, he found that there was no significant difference between these two groups. This study was unable to establish a relationship between contact lens wear and MGD.
Paugh et al (1990) observed the effect of MGD therapy (lid scrubs and warm compresses) on patients who had contact lens intolerance (not attributable to lens wear, care system, or health factors). In 16 of the 21 patients, tear breakup time (TBUT) significantly improved, and the glands became easier to express. Although not statistically proven, there was anecdotal support for improved subjective comfort after therapy.
Marren (1994) conducted a study (n = 50) that investigated the relationship between eye rubbing and cosmetics use with lens wear. She found no significant correlation between eye rubbing and MGD, nor between MGD and lens wear.
Robin et al (1986) conducted a study (n = 28) and observed that subjects who repeatedly deposited on extended wear lenses also tended to have moderate-to-severe lid abnormalities. This would suggest that MGD may contribute to lens deposition. However, other studies (Subbaraman et al, 2012; Omali et al, 2013) have shown that protein deposition on contact lenses is not strongly correlated to subjective comfort.
Arita et al (2009) used infrared meibography to examine and compare MG atrophy in lens wearers (n = 121) to non-lens-wearing healthy participants (n = 137). Partial or complete loss of the MGs was scored for each eyelid using four grades (meiboscores): grade 0 (no loss of MGs) through grade 3 (the area characterized by gland dropout was more than 66% of the total area containing the MG). They found that MG atrophy was statistically higher in the lens wearers (mean meiboscore = 1.72) compared to the non-lens wearers (mean meiboscore = 0.96). Furthermore, a regression analysis showed that MG atrophy correlated significantly with duration of lens wear, but not with TBUT, lid margin features, and corneal staining.
The Jury Is Still Out
Currently, only a limited number of studies examine the evidence relating contact lens wear and MGD. There is not strong enough evidence to state that contact lens wear causes MGD, or that MGD alone would cause lens discomfort. More research into this area is needed before any conclusions can be made. In the meantime, other mechanisms such as osmolarity and lens water content must also be considered. CLS
This article was prepared with financial support from Alcon.
For references, please visit www.clspectrum.com/references and click on document #232.
Dr. Ngo is a clinical researcher at the Centre for Contact Lens Research (CCLR), University of Waterloo School of Optometry & Vision Science, Canada. His research area of interest involves the management of dry eye and meibomian gland dysfunction. He obtained his Doctor of Optometry at the University of Waterloo School of Optometry & Vision Science in 2011, and he is currently pursuing a PhD in Vision Science under the supervision of Dr. Lyndon Jones. Dr. Ngo is a member of the Association for Research in Vision & Ophthalmology. He continues to be involved with patient care in the Greater Toronto Area.