Dyes/Staining Agents used in Ophthalmology

Dyes and staining agents used in ophthalmology used in various diagnostic techniques

1. Staining Agents and Dyes in Opthalmology Staining agents are used in assessing ocular conditions such as I ntegrity of the ocular surface P resence of hypersensitivity of the ocular surface L acrimal drainage problems . They are also used in certain procedures such as C ontact lens fitting. Goldmann tonometry . B lockage of the lacrimal system. O bservation of wound healing .

2. Commonly used staining agents include Fluorescein : stains epithelial lesions R ose bengal : stains degenerative cells Lissamine green : stains  mucus

3. Fluorescein: Fluorescein is a chemical dye that has the property to emit fluorescent light when exposed to light. It is orange-red in colour. Principle: The absorbed light energy in a dilute concentration of fluorescein excites the molecules to emit fluorescent light. The light appears green, having its highest intensity at a wavelength between 525 and 530 mm. The intensity of fluorescence is affected by factors such as the pH, concentration and other solutes in the solution. For best observation of the fluorescence , a cobalt blue filter is used. When used as a topical ophthalmic dye, fluorescein is in the form of a 2% solution or as 1 mg fluorescein-impregnated filter paper strips and is available in single-dose sterile pipettes to prevent bacterial contamination.

4. Clinical use: When examining the integrity of the ocular surface, one or two drops of the solution is instilled into the lower conjunctival fornix or the paper strip is moistened with sterile water or saline and the lower conjunctiva is gently touched with the strip . If the corneal epithelium is intact it will be impermeable so the fluorescein diffuses into the tear layer, which Is visible as a green layer, Staining of the tear film allows assessment of tear break-up time, tear flow and nasolacrimal duct patency. Fluorescein can also be used Identify foreign bodies in the eye as they will be surroundedby a green boundary.

5. Fluorescein is also used for performing Seidel's test to observe corneal wound healing after cataract or glaucoma surgery Fluorescein in solution is highly susceptible to bacterial con- tamination , especially by Pseudomonas aeruginosa . Preservatives used to prevent growth of microorganisms in fluorescein solutions include chlorobutanol and thimerosal . Sterile single does vials of fluorescein solution or filter paper strips are recommended for topical use if a preservative is clinically contraindicated. For combination of fluorescein-anaesthetic solutions, for example oxybuprocaine with fluorescein, such solutions are resistant to bacterial  contamination.

6. Rose Bengal: Rose Bengal stains devitalized epithelial cells of the cornea and conjunctiva. It also stains mucous strands of the pre corneal tear film. It is mainly used for ocular surface disease such as in the diagnosis of keratitis, keratoconjunctivitis sicca , abrasions and for the detection of foreign bodies. Rose Bengal is a derivative of fluorescein and is photo-reactive . It stains tissues with a vivid pink or magenta colour when viewed with white light. There is an initial irritation to the surface of the eye, especially in patients with dry eye. Rose Bengal has been formulated as a 1% solution and in the form of 1.3 mg sterile impregnated paper strips that require moistening with sterile saline or ocular irrigating solution.

7. Clinical use: Rose Bengal is used in the differential diagnosis of dry eye syndromes. In addition, it has also been recommended for the evaluation of corneal and conjunctival lesions, abrasions, ulcerations, detection of foreign bodies and dendritic ulcers. A mixture of stains containing 1% fluorescein sodium and 1% Rose Bengal was investigated by Norn (1970), who concluded that it was superior to the individual stains alone . Adverse reactions: M ild stinging, irritation and discomfort , particularly in higher concentrations. This discomfort may be relieved with a topical anaesthetic. Rose Bengal can also stain eyelids, cheeks, fingers and clothing. Accordingly, the eye should be irrigated and rinsed thoroughly to avoid subsequent staining of skin or clothing.

8. Lissamine green: Lissamine green is a vital stain that stains degenerative or dead cells and mucus in much the same way as Rose Bengal, and 1% of lissamine green is similar to 1% Rose Bengal. It is commonly used by practitioners in the convenient form of impregnated sterile paper strips. Lissamine green stains membrane-damaged epithelial cells and corneal stroma l ike R ose Bengal, it binds to the nuclei of severely damaged cells. However, the staining effect lasts longer than Rose Bengal. Lissamine green stains mucus strands in a bluish- green colour, and is particularly useful for assessing dry eye conditions. Lissamine green is better tolerated  by patients than Rose Bengal.