Lacrimal and meibomian gland evaluation in dry eye disease: A mini-review

Abstract

Lacrimal and meibomian glands contribute to the aqueous and lipid components of tear film, respectively. Their evaluation remains central to diagnosing and managing dry eye disease (DED). The review discusses the differences and reliability of various diagnostic tests and commercially available devices used for DED diagnosis. Slit-lamp-based techniques are direct palpebral lobe and tear flow assessment, Schirmer test, meibum quality and expressibility, and evaluation of tear meniscus height. Non-invasive tear meniscus height (TMH), tear break-up time (TBUT), lipid layer thickness (LLT), and meibography are machine-based diagnostic tests. The structure-function correlation of the tear-producing glands gives more comprehensive details than either information alone. Many devices are available in the market, which make DED diagnosis an easy feat, but the tests should be interpreted keeping in mind the intra-observer and inter-observer repeatability. Also, the tear film displays a huge variability as per the environmental conditions and impact of blinking. Hence, the examiner should be well versed with the techniques and repeat the test two to three times to obtain an average reading, which is more reliable. The recommended sequence of tests for diagnosing DED is a dry eye questionnaire, TMH, LLT, NIBUT (FBUT if non-invasive test is unavailable but should be performed after osmolarity), tear osmolarity, meibography, and ocular surface staining. Invasive tests such as Schirmer should be performed after the non-invasive tear film diagnostic testing.

Keywords: Dry eye disease; lacrimal gland; lipid layer thickness; meibomian glands; tear break-up time; tear meniscus height.

Figure 1

Schematic shows the location of lacrimal and meibomian glands in the eye. Also, the three components of the tear film, superficial lipid, middle aqueous (blue), and mucin layer (green), can be seen

Figure 2

Tear meniscus height obtained using Oculus keratograph 5M and measured manually in nasal, central, and temporal quadrants

Figure 3

Palpebral lobe of lacrimal gland in normal and DED patients. a & e, Right palpebral lobe of a young healthy individual (Schirmer 27 mm) shows four secretory ductules (marked with an arrow) having a tear flow rate of 1.21 μl/min. b & f, Normal tear flow seen in a patient with MGD with three secretory ductules. c & g, Reduction in tear flow (0.23 μl/min) and secretory ductules in a patient with Sjogren’s syndrome. d & h, A Stevens–Johnson syndrome patient (Schirmer 0 mm) has flattening of the contour, whitish conjunctival scarring, and no secretory opening

Figure 4

(a) Lid margin of a normal adult showing clear meibum quality when expressed from the upper eyelid. (b) Thick, whitish, and cloudy meibum expressed from a patient with MGD. (c) Increased lid margin vascular congestion in a patient with MGD with inflammation around meibomian gland openings

Figure 5

A1 & A2, Infrared meibography of upper and lower eyelids of a normal adult showing vertically running meibomian glands reaching up to convex tarsal border. In DED patient, there is gland loss involving 1/3^rd to 2/3^rd of tarsal area (B1 & B2)

Figure 6

Lipid layer thickness output from a LipiView interferometer giving minimum, average, and maximum thicknesses along with blink rate

Figure 7

Non-invasive tear break-up time captured with Oculus keratograph in a patient with meibomian gland dysfunction