Effect of benzalkonium chloride on the stability of the precorneal tear film in rabbit and man.

Abstract

The tear film is important both as a lubricating and protective layer and because it provides the outer, optically-smooth, refracting surface of the cornea. The tear film has a thickness of about 6 ,um and appears to be able to maintain its integrity during long periods between the respreading and replenishing action of the blink, by two means: I. The corneal epithelium holds the tear film on its surface, probably aided by mucus from conjunctival cells, which encourages spreading of the film (Lemp, Holly, Iwata, and Dohlman, 1970) purpose (Brown, Foster, Norton, and Richards, I964). Since BZA is a surface-active agent (and indeed may owe its antibacterial activity at least in part to this detergent property), the present experiments were undertaken to examine its effect on the stability of the tear film in rabbit and man. A significant hastening effect of BZA on corneal drying was observed in both species. Methods and results RABBITDutch rabbits were anaesthetized with halothane (3 per cent) in nitrous oxide-oxygen (3:i). The animals to be tested were placed in front of a small fan to hasten drying of the comea, and any tendency of the eyelids to droop was overcome by clipping back the fur on to the top of Address for reprints: Dr W. S. Wilson, Department of Pharmacology, University of Glasgow, Glasgow G12 8QQ the skull. The eyes were equally illuminated by similar 6o watt lamps placed on each side of the animal.Saline (3 drops of o-9 per cent) was applied to both eyes at zero time; the excess fluid was removed from the conjunctival sac by means of paper tissue without allowing the eyelids to blink. The time taken for the development of a dry spot on each cornea was measured and this was taken as the zero-time control value. The tear film was immediately restored by blinking the eyelids tlhree times. BZA solution (3 drops of o-oooi per cent w/v in o09 per cent saline) was then applied, the excess fluid removed as before, and the time for the appearance of a dry spot measured again. This procedure was repeated for successive threefold increases in concentration of BZA. Finally, the cornea was irrigated with saline, and the eyelids repeatedly blinked during a period of about IO minutes, after which another control determination was made 'end control'.These experiments were so straightforward that they were mainly carried out by one person. Since the possibility of observer bias existed, a second series of experiments was conducted in which an entirely impartial observer judged the times of dry spot appearance; another observer administered the eyedrops and operated the stop-clocks.The statistical significance of the results was evaluated using the paired Student's t test.The dry area usually appeared first as a well-defined pit or spot about i mm in diameter. If drying had been allowed to continue, other spots would soon have appeared, enlarged, and coalesced until the entire cornea eventually would have appeared dry and dull. Occasionally, the cornea would dry more uniformly, changing gradually from the norma...

Improved Corneal Toxicity and Permeability of Tranilast by the Preparation of Ophthalmic Formulations Containing Its Nanoparticles

“…of 5 independent samples. BAC is a quaternary ammonium compound that has been shown to hasten the drying of the tear film 29,30 , worsen preexisting dry eye 31 , and affect both the cornea and conjunctiva 32 . In addition, BAC is a pro-inflammatory or proapoptotic mediator 33 because it induces oxidative stress 34 36 or significantly alters precorneal mucins 37 .…”

Eye irritation and environmental factors in the office environment-hypotheses, causes and a physiological model

“…Eye make-up should be used with care (13). The use of artificial tears may be beneficial in alleviating symptoms, but they should be without preservatives, which destabilize the tear film (10,163,205). The use of oral contraceptives (93,153) and hormonal treatment for postmenopause (161) may increase the risk of dry eyes.…”

“…It is known that direct instillation of compounds, surfactants [eg, benzalkonium chloride (73,163), paraffin oils, and silicone emulsion (34)] may induce a reduction in surface tension, reduce the lipid layer and break-up time, or enhance epithelial damage of the conjunctiva. However, such outcomes of high local exposure of the eyes are unlikely in the office environment.…”

Effect of chronic anti-glaucoma medications and trabeculectomy on tear osmolarity

“…11 The lipid-destruction properties in BAK extend to the lipids in the tear film, which solubilizes during interaction with BAK. 12 Tear lipids are responsible for the stabilization and evaporation control of the tear film. Its disturbance is a major cause of dry eye 13 -a common condition among patients being treated for glaucoma.…”