Evaporative Dry Eye
The symptoms in evaporative dry eye consist of burning, foreign-body sensation, redness of the eyelids and conjunctiva, and filmy vision that is worse in the morning. The clinical signs associated with evaporative disease are usually confined to the posterior eyelid margins, although patients may occasionally have associated seborrheic changes on the anterior eyelid margin. The posterior eyelid margins are often irregular and have prominent, telangiectatic blood vessels coursing from the posterior to anterior eyelid margins. The meibomian gland orifices may pout or show metaplasia, with white material extending through the glandular orifice (Fig 3-12). They also may become posteriorly displaced on the eyelid margin. In active disease, meibomian secretions may be turbid, more viscous, or even cheesy.
Table 3-6 Systemic Diseases and Other Conditions Associated With Dry Eye
As discussed, the primary abnormality in evaporative dry eye is meibomian gland dysfunction (MGD), which the International Workshop on Meibomian Gland Dysfunction has classified as high delivery (ie, hypersecretory) or low delivery. Low delivery is further divided into hyposecretory or obstructive. Obstructive MGD can be cicatricial (eg, trachoma, mucous membrane pemphigoid, or atopy), or noncicatricial (eg, seborrheic dermatitis, rosacea, or atopy). MGD is more common in people of Asian ethnicity than it is in whites.
Occasionally, a patient is symptomatic but lacks obvious clinical signs of meibomian gland disease. The meibomian glands appear normal; however, with mild compression, obstruction of the glands is detected. More forceful expression produces a thin filamentous secretion, which is due to narrowing of the distal portion of the ducts, near the orifice. This condition is believed to be a precursor to clinically apparent disease. Gland expression can be performed using a cotton swab or a commercially available handheld device.
Figure 3-12 Meibomian gland dysfunction.
Extensive atrophy of the meibomian gland acini may develop after years of inflammation from MGD, so that eyelid compression does not result in expression of meibomian gland secretions. Atrophy of meibomian gland acini and derangement of glandular architecture can be demonstrated by shortening or absence of the vertical lines of the meibomian glands, which may be revealed by transillumination of the everted eyelid using a muscle light or infrared photography (see Chapter 2).
Tear breakup is a functional measure of tear film stability. In MGD, the stability is disrupted, causing a rapid tear breakup time (TBUT). After a fluorescein strip moistened with sterile saline has been applied to the tarsal conjunctiva, the tear film is evaluated using a broad beam of the slit lamp with cobalt blue illumination. This should be done before any manipulation of the eyelids or instillation of other drops. Fluorescein-anesthetic combination drops are not recommended for this purpose, because excessive fluorescein is typically instilled and the anesthetic may affect the ocular surface. The time lapse between the last blink and the appearance of the first randomly distributed dry spot on the cornea is the TBUT. The appearance of dry spots in less than 10 seconds is considered abnormal.
Additional clinical findings in MGD include foam in the tear meniscus along the lower eyelid, bulbar and tarsal conjunctival injection, papillary reaction on the inferior tarsus, linear staining along the inferior cornea and inferior conjunctiva, episcleritis, marginal epithelial and subepithelial infiltrates, corneal neovascularization or pannus, and corneal scarring or thinning. Corneal vascularization is more typical of MGD, while punctate staining is more typical of staphylococcal blepharitis.
Patients with MGD frequently have acne rosacea. Rosacea is discussed later in this chapter.
American Academy of Ophthalmology Cornea/External Disease Panel. Preferred Practice Pattern Guidelines. Blepharitis. San Francisco: American Academy of Ophthalmology; 2013. Available at www.aao.org/ppp.
Foulks GN. Meibomian gland dysfunction. Focal Points: Clinical Modules for Ophthalmologists. San Francisco: American Academy of Ophthalmology; 2014, module 12.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.