Fig. 26.2 Rose Bengal staining. Staining is mainly present at the medial bulbar conjunctiva and cornea

26.3.4Fluorescein

Fluorescein stains denuded areas of the epithelium (Fig. 26.3). This method is an alternative for Rose Bengal. The same grading Bijsterveld score ³4 is considered positive for the presence of KCS [31].

26.3.5Lissamine Green

Like fluorescein, lissamine green stains corneal and collagenous stroma and can demonstrate epithelial defects within the corneal and conjunctivae (Fig. 26.4). Its capacity to stain membrane-damaged epithelial cells, combined with its ability to stain denuded corneal stroma, makes this dye a useful alternative to Rose Bengal and fluorescein. Lissamine green also causes less irritation than these other two dyes, but requires a slit lamp examination for adequate quantification of the staining [32].

26.3.6Tear Break-Up Time

The tear break-up time measures the stability of the tear film and is useful in the evaluation of an evaporative dry eye. The tear break-up time is defined as the interval between a complete blink and the appearance of the first randomly distributed dry spots. In order to perform the test, a 1% fluorescein solution is instilled in the inferior fornix of both eyes. After blinking, the interval in seconds between the last and first bead in the tear film is measured. A tear film break-up time of less than 10 s is considered positive [33].

The break-up time depends on variables such as the concentration of fluorescein, age, and the number of blinks [30]. The method has a sensitivity of 77.8% and a

specificity of 38.9% [13, 34]. The use of this test is generally limited to ophthalmological practice because the need for a slit lamp to assess the results.

26.3.7Tear Osmolarity

Reduction of aqueous secretion and increased evaporation in patients with SS can combine to produce a tear film with an increased osmolarity. This has been shown to damage the ocular surface in and of itself. The normal tear osmolarity value varies around 304±1.4 mOsm/L. Values greater than 320 mOsm/L have a sensitivity of 94% and a specificity of 97% in the detection of dry eye [19].

26.3.8Tear Meniscus

Most of the tear film is located at the lacrimal meniscus area that is found between the ocular surface and the lower lid margin. This zone has been used as a measurement of the basal lacrimal basal volume. Its normal height is approximately 0.3 ± 0.1 mm. The ideal means of measuring the tear meniscus is through the use of a video meniscometer, but subjective assessments (visible, poor, absent) have also been employed [16, 19].

26.3.9Tear Proteins

Diminished lactoferrin or lysozyme content usually signals impaired lacrimal gland function. The most frequent cause of decreases in the lactoferrin or lysozyme concentrations is related to aging. The normal concentrations of lysozyme and lactoferrin are 1–3 mg/mL and 2.05 ± 1.2 mg/mL in normal subjects respectively [17–19].

26.3.10Ferning Test

Saliva crystallizes in the form of ferns when it is dried at room temperature and observed by polarized light microscopy. This is known as the “ferning phenomenon.” Patterns of crystallization can then be identified based on the uniformity, integrity, and spreading of the ferning phenomenon. Grade I ferning (uniform arborization, without spaces among the ferns) is normal. Grades II (shorter and thicker ferns), III (smaller ferns and incompletely formed), and IV (absence of ferning phenomenon) are abnormal patterns seen in patients with SS [20].