Use of a specular microscope with pachymeter in ocular tolerance studies of eye drops in the rabbit. Evaluation of ocular tolerance of benzalkonium chloride in aqueous solution 0.01% and 0.1%.

Eye drops, unlike cosmetics or chemicals, only cause minor irritations which often prove difficult to objectively observe and assess. A specular microscope with pachymeter is used to measure corneal thickness, and to examine and photograph corneal endothelium in ocular tolerance studies in the rabbit. Rabbits were instilled 5 times a day for 16 days with BKC aqueous solution, 0.01% or 0.1% and subjected after anaesthesia to 4 corneal inspections (before treatment, 7th and 14th days of treatment, 5th day after treatment). Only the 0.1% concentration provoked an increase in corneal thickness. Thickening progressed during the treatment period (5.3% on day 7, 26% on day 14) and strongly regressed 5 days after treatment stopped (3%). A slit lamp examination revealed very light or light corneal opacities, but the correlation between corneal thickening ratio and opacity was poor (r = 0.62).