Vital Staining
Vital staining implies applying stains to the eye in-vivo. As different stains make it possible to differentiate anomalies, this method has gained wide acceptance. The most commonly used dyes include Fluorescein, Rose Bengal and Lissamine Green.
Fluorescein
Fluorescein retention has been observed in normal corneas of both humans as well as animals. This retention has been suggested to be due to the normal desquamation of corneal epithelium, as desquamating epithelial cells have increased permeability (Kikkawa 1972). Fluorescein staining is increased by rapid stromal diffusion and can manifest whenever there is disruption of cell to cell junctions; Fluorescein is highly water soluble and diffuses via intercellular fluid spaces (Feenstra and Tseng 1992a). Both Fluorescein as well as Rose Bengal stains healthy living cells; cell degeneration or death can increase membrane permeability to these dyes and enhance staining (Feenstra and Tseng 1992a). The lipophilic epithelium of the cornea as well as Descemet's membrane do not stain with Fluorescein, since Fluorescein dye is water soluble (Gelatt 1978). Any disruption of the corneal epithelium, as an ulcer of the cornea, will thus cause a positive staining of the cornea with Fluorescein. Fluorescein is used to detect corneal defects, foreign bodies and leaking ocular wounds. The eye should be examined immediately after application of Fluorescein as the rapid diffusion through the corneal stroma may cause over-estimation of the size of an ulcer( Gelatt 1978).
Rose Bengal
Slatter (1973) found no Fluorescein retention in normal canine eyes, but experienced Rose Bengal retention in many normal eyes. Rose Bengal stains mucus, degenerating and dead cells (Gelatt 1972). Removal of excessive stain with normal saline or artificial tears is necessary (Gelatt 1972). Blepharospasm and tearing occurred most frequently after application of Rose Bengal in normal canine eyes (Gelatt 1972). Slatter(1973) found increased numbers of neutrophils in conjunctival scrapings on the day following Fluorescein-Rose Bengal instillation. Gelatt (1972) found Rose Bengal retention associated with trichiasis, distichiasis, entropion and ectropion. Rose Bengal retention was evident on the conjunctiva and the cornea in cases of KCS (Gelatt 1972). Experimentally induced reduction in tear flow resulted in increasing the number of minute punctate areas of the cornea with Rose Bengal retention, and the staining was a more intense red (Slatter 1973). Uptake of Rose Bengal was seen prior to any histopathological lesions in KCS (Slatter 1973). Recent studies showed that Rose Bengal uptake is inhibited by albumin, mucin or carboxy cellulosis. Thus Rose Bengal stains whenever there is insufficient protection of pre-ocular tear film as a result of either decreased tear components or abnormal surface epithelial cells (Feenstra and Tseng 1992a). After staining(in-vitro) of cells with Rose Bengal, cells lost vitality, as evidenced by instant morphologic changes, subsequent loss of cellular motility, cell detachment, and cell death (Feenstra and Tseng 1992b).
Lissamine Green
Norn (1973) introduced Lissamine Green as a vital stain of the cornea and conjunctiva. He found that the dye stained degenerate cells, dead cells and mucus. A study of 171 eyes (Norn 1973) concluded that Lissamine Green had properties very similar to Rose Bengal, but did not cause irritation to the eye. Manning et al (1995) found that there was no difference in objective staining scores between Lissamine Green and Rose Bengal. Rose Bengal causes significantly more pain after application in human patients with KCS, and this pain is of a significantly longer duration than that of Lissamine Green (Manning et al 1995). A resent study of Lissamine Green (Chodosh et al 1994) concluded that Lissamine Green stained membrane-damaged epithelial cells, and that Lissamine Green stains the corneal stroma. Lissamine Green cannot be blocked by mucin in the way mucin prevents Rose Bengal uptake (Chodosh et al 1994). Lissamine Green and Fluorescein are vital dyes, but Rose Bengal is not a vital dye (Chodosh et al 1994). Lissamine Green does not stain healthy, normal cells in vitro (Chodosh et al 1994).
This page was authored by T. F. Evans October 2000.
