Ocular Irritation: Pathological Changes Occurring in the Rat with Surfactants of Unknown Irritancy

Abstract

We believe the development and validation of in vitrr, alternatives to eliminate the need to use animals in ocular irritation testing must be based on a thorough understanding of the mechanisms of ocular irritation. We have recently undertaken the task of developing such an understanding for a panel of surfactants. The purpose of this study was to expand our current panel of surfactants for which the microscopic changes occurring over time have been Characterized. Macroscopic and microscopic findings regarding the ocular irritation of 6 surfactants of relatively unknown irritancy were compared to those of 6 surfactants of known irritancy. The right eye of each rat was treated by placing 10 ~1 of a surfactant directly on the cornea. Untreated left eyes served as the controls. At 3 hr and on days 1, 3, and 35, eyes and eyelids were collected for microscopic examination. Collectively, the macroscopic and microscopic findings revealed 3 surfactants to be similar to the mildly irritating surfactants previously studied, and' 3 surfactants to be similar to the moderately irritating surfactant previously studied. Information such as this will be important to develop mechanistically based in rirro alternatives to replace the use of animals for ocular irritation testing.

Pathology of Ocular Irritation with Acetone, Cyclohexanol, Parafl uoroaniline, and Formaldehyde in the Rabbit Low-Volume Eye Test

“…The principal approach of these validation efforts has been to statistically correlate the in vitro results to in vivo ocular irritation scores obtained from the Draize test and low-volume eye test (2,3,26,29,32,40). These irritation scores are based on the subjective scoring of descriptive changes observed during macroscopic examinations using a penlight (21,(26)(27)(28)(29)(30)32). Such parameters as corneal opacity, iridal injection and pupil responsiveness, and conjunctival reddening, swelling and discharge provide limited perspective regarding the cellular and molecular changes associated with initial injury and subsequent responses.…”

Microscopic Changes with Acetic Acid and Sodium Hydroxide in the Rabbit Low-Volume Eye Test

“…We have advocated that a better understanding of the critical cellular and molecular changes occurring in in vivo tests is needed in order to develop and validate alternative tests to replace the use of animals in ocular irritation testing (11,15,(17)(18)(19) (3,16,24).…”

“…We have proposed that differences in irritancy are related to differences in the extent of initial injury, and regardless of the processes leading to tissue damage, extent of injury is the principal factor determining the final outcome of ocular irritation (11,14,15,(17)(18)(19)(20)(21).…”

Quantitative Characterization of Acid- and Alkali-Induced Corneal Injury in the Low-Volume Eye Test

“…In a series of studies, we have shown that the ocular response and subsequent outcome for surfactant exposure are dependent upon the initial area and depth of corneal injury (4,5,8,13,14,16,17). Surfactants that were innocuous or that caused only slight irritation produced injury limited to the superficial corneal epithelium.…”

“…Prior to dosing, the eyes of all rabbits in both studies were examined macroscopically (with the aid of a penlight) by the same observer (R.D.P ). Each rabbit then received 10 [LI of each test material; this dose was directly applied to the right cornea by the same individual (R.D.P ) according to procedures described previously (4,5,8,13,14,16,17). Since in vivo confocal examination may lead to desiccation of the unobserved eye, poten-tially exacerbating the irritating effects of test irritants (5), only one eye of each rabbit was used for this study.…”