26.2Questionnaires

Rose Bengal staining, once a standard test in this disease, is now used less frequently because the application of the ocular stain is intensely uncomfortable to patients with KCS.

Because gradual destruction of the lacrimal gland in SS leads to diminished levels of tear proteins (lysozyme, lactoferrin, tear-specific prealbumin), some authors have proposed to measure these proteins to identify patients with dry eyes [17, 18]. Other tests, such as the tear film osmolarity, tear evaporation, tear meniscus, and ocular surface impression cytology, and crystallization, have also been studied (Table 26.3) [19, 20]. Although all of these methods provide different qualitative information, they have not achieved general clinical acceptance because of their lack of broad accessibility and general applicability.

26.3.1Schirmer Test

The Schirmer test, a practical, semiquantitative method, is a commonly used initial screening procedure for SS [13]. Some studies have reported a good correlation between in vivo fluorometric measurement of basal tear turnover and tear flow [21], as well as with the rose Bengal test [22]. Other studies, however, have not [23–25].

The Schirmer test may be performed with or without topical anesthetic. In order to assess the maximal tear production, a cotton-tipped swab can be introduced gently into the nose to stimulate the nasolacrimal gland reflex (via the trigeminal nerve) while performing the Schirmer test [26]. This is known as a Schirmer-II test. For some authors, the Schirmer-II test has a better correlation with staining tests [24].

During the Schirmer test, a standardized tear test strip is placed between the eye and the lateral part of the inferior eyelid. The patient is then inclined forward in a resting position at 45°, with eyes closed. After 5 min, the length of the wetted strip area is measured (Fig. 26.1). Humidification of £5 mm at least in one eye is required for a test result to be positive. The sensitivity and specificity of the test are 76.9% and 72.4%, respectively, when this cutoff value is used [13]. When the first test is positive in both eyes, the test-retest reliability at 1 year is 77.4% for one eye and 84.2% for both [14].

One of the factors that influences the results of the Schirmer test is the tear clearance rate. Consequently, a tear function index (TFI) has been proposed as a better tear measurement. The TFI is derived from dividing the Schirmer’s test value by the tear clearance rate, which is calculated by instilling 10 mL of fluorescein into the conjunctival fornix [27, 28]. Although the TFI is theoretically useful, it is not as simple to perform as the Schirmer’s test and is not widely used in clinical practice.

Fig. 26.1 Schirmer-I test. Patient with absence of tear flow strip humidification after a time interval of 5 min. The lack of tear meniscus is also evident

26.3.2Vital Dyes

Vital dyes are any colored substance that contain auxochromes and are therefore capable of staining tissues. Vital dyes used in the field of ophthalmology have acceptable physiological and toxicological profiles. These dyes are used to detect abnormalities on the ocular surface. Positive staining is usually a relatively late manifestation of tear film disturbances or abnormalities of the ocular surface.

26.3.3Rose Bengal

The Rose Bengal method stains degenerated dead cells and cells that have a tendency to keratinization. Van Bijsterveld created a grading scale that divides the ocular surface into three zones: the nasal bulbar conjunctiva, cornea, and the temporal bulbar conjunctiva [29]. After instillation of the 1% Rose Bengal solution into the conjunctiva and asking the patient to blink one or two times, the intensity of staining of each area is scored. Each section is scored 1 (sparsely scattered), 2 (densely scattered), or 3 (confluent staining), such that a maximum score of 9 can be obtained.

KCS diagnosed when a grading Bijsterveld score ³4 in at least one eye is present (Fig. 26.2) [29]. The evaluation of the conjunctiva and cornea can be determined with an ophthalmoscope, although a more accurate evaluation with a slit lamp outfitted with a cobalt filter is preferred. Solutions of rose Bengal should not be left in the patient’s eye for a prolonged period, as this stain may be irritating and uncomfortable. In addition, it is important to remember that the specificity of the test is poor: Patients with infectious conjunctivitis or chronic, irritative conjunctivitis may also show an increased score [30]. The method has a sensitivity of 64.3% and a specificity of 81.7% [13].