Effect of tetracaine on intraocular pressure in normal and hypertensive rabbit eyes

Purpose: To evaluate the effect of tetracaine on intraocular pressure [IOP] in normal and hypertensive rabbit eyes

Methods: The study was conducted on 12 healthy rabbits as controls and 6 healthy rabbits in which an experimental model of ocular hypertension [OHT] was induced by administration of 70 mL/kg of tap water through an orogastric tube. One drop of tetracaine was instilled in the left eye while a drop of normal saline [placebo] was applied to the right eye of the control group. IOP was measured before and 0, 5, 10, 15, 20, 25, 30, 35 and 40 minutes after drop administration in this group. The OHT group also received one drop of tetracaine and normal saline in the left eyes and right eyes respectively, immediately after water loading; the instillation of drops was repeated after 55 minutes. IOP was measured before and 0, 5, 10, 15, 20, 25, 30, 35, 40, 55, 70, 85, 100 and 115 minutes after water loading in this group

Results: Tetracaine treated eyes in both groups [ocular hypertensive and normal controls] demonstrated significant IOP reduction at time zero [immediately after drop instillation] which was sustained up to 20 minutes, as compared to placebo treated eyes [P<0.05]. In ocular hypertensive rabbits, repeat instillation of tetracaine significantly reduced IOP at 55 minutes up to 30 minutes thereafter

Conclusion: Topical tetracaine can reduce IOP; this fact should be considered in experiments evaluating IOP reducing agents

Effect of different treatment regimen with dexamethasone and acetylcysteine on corneal wound healing in rabbits

The effect of corticosteroid therapy on corneal wound healing is controversial. The objective of this study was to evaluate the effects of combination therapy with dexamethasone and acetylcysteine at different times and duration on experimentally-induced corneals wounds and haze in rabbits. Eighteen adult New Zealand white rabbits were divided into three groups of six each. Under anesthesia corneal wounds were created surgically in the center of all eyes. The right eyes of rabbits in group 1 were treated topically with acetylcysteine and dexamethasone immediately after surgery, those in group 2 were treated with acetylcysteine from day 8, and those in group 3 were treated with acetylcysteine from day 1 and with acetylcysteine and dexamethasone from day 1 and with acetylcysteine and dexamethasone from day 15. The left eyes were assigned as controls and were treated with normal saline. All eyes were treated six times a day for 28 days. Corneal wounds were measured by fluorescein staining every day. The combination of acetylcysteine and dexamethasone in group 1 significantly increased mean healing time, but did not change that in groups 2 and 3. Clinical and histopathologic examinations revealed that one month after the ulceration in groups 1 corneal haze was greater in treated than in the control eyes. Moreover, there was no significant difference between the control and treated eyes of group 1, 2, or 3 in terms of corneal haze at two or three months after the ulceration. The findings of the present study show that the association of 3% concentration of NAC and 0.1% concentration of dexamethasone immediately after corneal ulceration can delay corneal wound healing, and consequently produce more corneal haze. Thus, the use of 0.1% concentration of dexamethasone should be delayed at least until the completion of the epithelial defects