Topical fluorescein is a nontoxic, water-soluble, synthetic organic hydroxyxanthene dye that is available in several forms: as a 0.25% solution with an anesthetic (benoxinate or proparacaine) and a preservative, as a 2% nonpreserved unit-dose eyedrop, and in impregnated paper strips. Fluorexon, a related macromolecular compound, is available as a 0.35% nonpreserved solution that does not stain most contact lenses. Staining is easily detected with a cobalt-blue filter.
Fluorescein is most commonly used for applanation tonometry and evaluation of the tear film, including filaments. Tear breakup time (TBUT) is measured by instilling fluorescein, asking the patient to hold the eyelids open after 1 or 2 blinks, and counting the seconds until a dry spot appears. The appearance of dry spots in less than 10 seconds is considered abnormal. TBUT is further discussed in Chapter 3. Fluorescein detects disruption of intercellular junctions and stains punctate and macroulcerative epithelial defects (positive staining), such as herpetic dendritic lesions and dysplastic epithelium. It can also highlight nonstaining lesions that project through the tear film (negative staining), as in epithelial basement membrane dystrophy and Thygeson superficial punctate keratitis. Different disease states can produce various punctate staining patterns (Fig 2-21). Fluorescein that collects in an epithelial defect will diffuse into the corneal stroma and cause a green flare in the anterior chamber. Pooling of the dye due to an indentation or thinning of the cornea must be distinguished from actual staining. This can be done by anesthetizing the eye and using a wisp of cotton from a cotton-tipped applicator to absorb the fluorescein in the area of concern. If the epithelium is intact, the dye will be removed, with no staining noted in the base. In the dye disappearance test, the tear meniscus is observed for the disappearance of fluorescein. Prolonged presence of the dye suggests a blockage of the drainage system.
The Seidel test is used to detect seepage of aqueous humor through a corneal perforation (Fig 2-22) or a conjunctival defect, such as a leaking trabeculectomy bleb. The examiner applies fluorescein to the site of suspected leakage using a moistened strip or concentrated drop and looks for a flow of clear fluid streaming through the orange dye under cobalt-blue light.
Figure 2-21 Punctate staining patterns of the ocular surface.
(Illustration by Joyce Zavarro.)
Rose bengal and lissamine green
Rose bengal and lissamine green (both available as a 1% solution or in impregnated strips) are other water-soluble dyes. They stain the epithelial cells of the cornea and conjunctiva when a disruption occurs in the protective mucin coating. These dyes are routinely used for evaluating tear-deficiency states and for detecting and assessing various epithelial lesions, such as evaluating the extent of corneal intraepithelial neoplasia (Fig 2-23). Rose bengal is toxic to the epithelium. Lissamine green is better tolerated and has fewer toxic effects on cultured human corneal epithelial cells.
Figure 2-22 Leakage of fluid from the anterior chamber (arrow) following a corneal perforation, indicating a positive Seidel test result.
(Courtesy of Stephen E. Orlin, MD.)
Figure 2-23 Slit-lamp photograph from a patient with conjunctival intraepithelial neoplasia shows staining with lissamine green dye.
(Courtesy of Stephen E. Orlin, MD.)
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.