Human and Rabbit Eye Responses to Chemical Insult

An overview of current techniques for ocular toxicity testing

“…Since Draize assessments are based upon penlight or slit-lamp assessments, they provide very little information regarding the primary or secondary responses in the cornea, iris or conjunctiva (Maurer et al, 2002). Despite its "gold standard" status, Draize testing was never formally validated to any significant degree (Freeberg et al, 1986b). Since the anatomy of the rabbit eye differs from the human eye structurally, physiologically and biochemically, differences in sensitivity to irritants can occur.…”

“…As a result, LVET has yet to be adopted by any regulatory agency as an alternative test. The reluctance to adopt LVET may be due to the fact that it does not offer the element of "exaggeration" present in Draize testing, that helps to assure public safety (Freeberg et al, 1986b;Ubels and Clousing, 2005). However, retrospective LVET data is still useful to weight-of-evidence approaches.…”

“…Clinical studies using undiluted products raise both scientific and ethical concerns, so experiments have to be carefully controlled. In clinical studies, the test material (often very small volumes and/or diluted) is usually applied to the upper or lower conjunctival sac, as opposed to the apex of the cornea as in in vivo rabbit studies (Freeberg et al, 1986b). This in itself raises concerns about the comparability of the outcomes.…”

“…This in itself raises concerns about the comparability of the outcomes. In addition, human testing often investigates the "sting" more so than irritation (Freeberg et al, 1986b). Studies performed in the 1980s compared results from hundreds of accidental human exposures with Draize and LVET tests (Freeberg et al, 1984(Freeberg et al, , 1986a.…”

“…Studies performed in the 1980s compared results from hundreds of accidental human exposures with Draize and LVET tests (Freeberg et al, 1984(Freeberg et al, , 1986a. In such a study using human volunteers, household substances commonly associated with accidental exposure (shampoo, hand soap, fabric softeners), exposure data was collected under known, controlled conditions to establish the relationship between in vivo animal tests and human exposure effects (Freeberg et al, 1986b). It was demonstrated that Draize testing was a poor predictor of accidental human eye exposure, whereas LVET correlated well, although still over-predicted results.…”