Summary The purpose of this study was to evaluate the effects of different time combinations of dexamethasone and acetylcysteine on experimentally induced corneal ulcers in dogs. Experimental corneal wounds were created surgically to the anterior one third of the cornea in the center of all eyes of 15 mixed breed dogs. The eyes were divided into five groups according to planned post-operative medications: group 1, one drop of Nacetylcysteine 3% and one drop of dexamethasone 0.1% immediately after surgery; group 2, two drops of Nacetylcysteine 3% from day 1, one drop of N-acetylcysteine 3% and one drop of dexamethasone 0.1% from day 15; group 3, two drops of N-acetylcysteine 3%; group 4, two drops of dexamethasone 0.1%; group 5 (control), two drops of normal saline. When applied immediately after corneal ulceration, dexamethasone 0.1% (group 4) decreased corneal haze significantly and did not delay corneal wound healing. Addition of dexamethasone 0.1% to N-acetylcysteine 3% from day 15 (group 2) significantly suppressed opacity at two months after the beginning of the study, but when dexamethasone 0.1% associated to N-acetylcysteine 3% immediately after corneal ulceration (group 1), significant delay in corneal wound healing was induced. It is concluded that combination of dexamethasone 0.1% and NAC 3% immediately after surgery may delay corneal wound healing, also use of these drugs individually, has no obvious clinical effect on corneal haze. On the other hand, use of these drugs in combination with each other may reduce the corneal haze in later months after discontinuation of drugs. However, further studies using larger groups of animals are needed to demonstrate the effectiveness of these pharmacological modulators following experimentally induced corneal wounds in dogs.

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