Making a Differential Diagnosis of MGD

Research suggests that 40% of patients seen clinically suffer from meibomian gland dysfunction (MGD).^1,2 Although the prevalence of the disease is high, diagnosis remains a challenge, especially in terms of differentiating MGD from other causes of dry eye.

Much of the difficulty in diagnosing MGD stems from variability in the clinical presentation of patients’ signs and symptoms and lack of consensus among eye care practitioners on exact diagnostic criteria. Despite these challenges, the importance of differentiating dry eye etiologies (eg, aqueous deficiency, environmentally caused, mucin deficiency, MGD) is becoming increasingly evident as the ophthalmic pharmacopeia expands to encompass tailored treatments.

THE IMPORTANCE OF DIFFERENTIATION

Historically, the terms meibomian gland dysfunction and posterior blepharitis were used interchangeably but were considered distinct from anterior blepharitis, which affects the lashes and lash follicles rather than the glands and their orifices.³ Research has now shown that, although the anatomic distinction exists, anterior and posterior blepharitis often present simultaneously, and MGD may arise independently as well. Obvious signs of MGD include gland inspissation, gland dropout, and inflammation of the eyelid, all of which are easily discerned with a quick slit-lamp examination. Evidence of subtle signs such as an abnormal quality and/or quantity of meibum requires gland expression.⁴ Because abnormal secretion is thought to be responsible for tear-lipid deficiency and the resultant symptoms of dry eye, its inclusion in a diagnostic evaluation is crucial.

Recognition of the need for established diagnostic criteria is evidenced by recent efforts within the ophthalmic community to illuminate the challenges of and to propose methods for diagnosis. In 2009, ophthalmic researchers in Japan published their evaluation of several criteria in both healthy patients and those diagnosed with obstructive MGD.⁵ The diagnosis of MGD was based on an ophthalmologist’s determination of ocular symptoms, lid margin abnormality (irregularity of the lid margin, vascular engorgement, plugged meibomian glands, apparent anterior or posterior movement of the mucocutaneous junction), and poor meibum expression. The criteria evaluated across study subjects included:

• Ocular symptom score from 0 to 14, based on the number of symptoms the patient indicated from a list of 14 (eg, discharge, foreign body sensation, dryness, sticky sensation);
• Lid margin abnormalities, graded from 0 to 4 depending on the presence of abnormal characteristics (see previous list);
• Meibomian gland change scored from 0 (no meibomian gland loss) to 3 (gland loss over two-thirds of total area of glands) determined using noncontact meibography on upper and lower lids (total sum scoring 0 to 6 per eye);
• Superficial punctate keratopathy graded from 0 to 3;
• Meibum volume and quality following expression using a digital pressure device, graded on a scale from 0 (clear and easily expressed) to 3 (no meibum expressed) per lid;
• Schirmer test as an indicator of tear production; and
• Tear film break-up time assessment, taking the median value of three consecutive measurements after fluorescein instillation.

Receiver-operating characteristics curve and areaunder- the-curve analyses demonstrated that the ocular symptom, lid margin abnormality, and meibum quality/quantity scores were the best indicators of patients’ disease state. The investigators recommended suspicion of MGD when two of the three scores are abnormal (ocular symptoms scoring 3 or higher, lid margin abnormality scoring 2 or higher, meibum scoring 3 or higher) and stated that MGD is highly likely if all three scores indicate abnormality.

Another effort to evaluate diagnostic challenges and patterns in MGD was executed by the Tear Film and Ocular Surface Society’s International Workshop on Meibomian Gland Dysfunction. The objectives of the workshop included an evidence-based evaluation of meibomian gland anatomy, physiology, and pathophysiology; the development of a comprehensive definition and classification of MGD; a review of appropriate aspects of clinical trial design; recommendations for the diagnosis and management of MGD; and the formulation of recommendations for future MGD research.⁵

A NEW ALGORITHM

The challenge of determining MGD during a patient’s visit demands a simpler yet effective algorithm. SET, or scan, express, and treat, is a new proposal for a three-step, quick assessment that many clinicians have started to adopt when dry eye or MGD is suspected:

(1) The clinician should scan the eyelid margin for signs of gland abnormality and query the patient for symptoms, especially dryness, caking, crusting, and excessive tearing early in the morning.

(2) The eye care practitioner can simply use either a sterile cotton swab or a clean fingertip to gently provoke the glands. Upon expression, he or she should look for discolored (ie, varying from clear) and noticeably small volumes of secretion. These characteristics are important, because abnormality generally translates to tear film instability and an unhealthy lipid layer. With older patients who are likely to have diminished elasticity in their eyelids, applying gentle, consistent force for up to 10 seconds may be required to elicit any secretions.

(3) Eye care practitioners should treat according to clinical presentation. If the patient exhibits the signs and symptoms of MGD, treatment should differ from that for other forms of dry eye syndrome (DES); the average ocular lubricant is not likely to affect lid health, and this may discourage patients. Because there is no US Food and Drug Administration (FDA)-approved treatment for MGD specifically, clinicians usually rely on current practices including hygiene using lid scrubs, warm compresses, or lid massage; nutritional considerations (eg, adequate omega-3 fatty acid intake); tear substitutes; and the off-label prescription of antibiotics, steroids, or combination products.

Giving patients the best chance for success with treatment may be simpler than expected. Adjusting the treatment to target the appropriate subset of DES is more likely to lead to success than a general protocol. Because the altered lipid composition destabilizes the tear film of eyes with MGD, a lipid-targeted ocular lubricant is often beneficial as a first-line therapy. Emollients in ophthalmic solutions may further assuage symptoms, and novel lubricants with these characteristics have become available.

CONCLUSION

The outcome of treatment and patient satisfaction are unmistakably linked to patients’ adherence to prescribed therapy. Meticulous diagnosis and treatment recommendations will benefit both patients and practitioners as the treatment and the disease progress.

Kelly K. Nichols, OD, MPH, PhD, is an Associate Professor at the Ohio State University College of Optometry in Columbus, Ohio. Dr. Nichols may be reached at email: knichols@optometry.osu.edu.

1. Hom MM,Martinson JR, Knapp LL, Paugh JR.Prevalence of meibomian gland dysfunction.Optom Vis Sci. 1990;67:710-712.
2. American Academy of Ophthalmology.Preferred Practice Pattern: Blepharitis.2008. http://one.aao.org/CE/PracticeGuidelines/PPP_Content.aspx?cid=080ac46b-ea4d-4556-893a- 2a63ba87ffcd.Accessed October 13, 2010.
3. McCulley JP,Dougherty JM,Deneau DG.Classification of chronic blepharitis.Ophthalmology. 1982;89:1173-1180.
4. Blackie CA, Korb DR, Knop E, et al.Nonobvious obstructive meibomian gland dysfunction [published online ahead of print September 15, 2010].Cornea.doi:10.1097/ICO.0b013e3181d4f366
5. MGD Workshop.The Tear Film and Ocular Surface Society Web site.http://www.tearfilm.org/ mgdworkshop/.Accessed Nov.8, 2010.

TAKE-HOME MESSAGE

• Anterior and posterior blepharitis often present simultaneously, and MGD may arise independently as well.
• Obvious signs of MGD include gland inspissation, gland dropout, and inflammation of the eyelid.
• Subtle signs include abnormal quality and/or quantity of meibum.
• Adjusting the treatment to target the appropriate subset of DES is more likely to lead to success than a general protocol.

SET: A NEW PROPOSAL FOR THE QUICK ASSESSMENT OF MGD

1. S = Scan the eyelid margins
2. E = Express and assess the meibum
3. T = Treat according to clinical presentation