*Seyed Javid Aldavood, Aliasghar Sarchahi, Rostam Behyar, Iraj Noroozian, Sadeghi
The effects of 3, 10 and 20% concentrations of acetylcysteine on corneal wound healing in dogs were evaluated. Corneal ulcers induced surgically, up to the depth of the anterior third of the stroma. It was created in both eyes of 18 dogs. One of the eyes was treated topically whit 0.9% NaCl Solution 3 times a day. The contralateral eye (the other one eye) was treated topically by Acetylcysteine 3%, 10% and 20% concentration in each 6 cases separately. Corneal ulcers measured by Fluorescein -staining every day. The mean time of healing in 3% group was significantly different of control eyes (6.17 ± 1.94 days). It was 7.19 ± 0.75 days in 20% group and 7±2 days in 10% group. The last two group were not significantly different from control (9.67 ± 3.01 days and 8.17 ± 3.60 days) respectively.
Dogs: 18 dogs of mixed breed both sexes (8 month to 5 years old) with normal eye examinations were selected. They were housed under lighting controlled at a dim level for comfort.
Surgical operation: The dogs were anesthetized with 10 mg ketamine HCl/kg + 1 mg Xylazine HCl/kg + 0.11mg acepromazine/kg combination. The dogs were placed in lateral recumbency. A pediatric eyelid speculum (Lid retractor) was placed for exposure to the cornea. Then a Muscle hook was placed under the ventral rectus muscle to control ocular movements during the trephination. A 6 mm calibrated corneal trephine was placed in the center of the cornea. The trephine depth was determined previously to be at a specific setting that would expose the anterior third of the corneal stroma. Trephination performed. A crescent bevel up blade was used to perform the keratectomy of the trephinated cornea .The corneal tissue buttons that were removed were then placed in formalin for histopathologic examination. This procedure was done on both left and right eyes of all dogs.
Experimental groups: The 18 dogs were divided to 3 groups of 6 dogs. The left eyes of all dogs were treated topically with 0.9% NaCl drops and used as controls. The right eyes of 6 dogs' in-group 1 were treated with acetylcysteine 20%, 6 dogs in-group 2 with acetylcysteine 10% and 6 dogs in group 3 with acetylcysteine 3% drops. It was given tree times a day, for 2 months.
Data of mean healing time and mean daily healing is shown in table 1, Figure 1 and 2. P values obtained by the student "t" test revealed the difference mean healing time between the controls and Acetylcysteine treated in 20% and 10% concentration. Although there was no statistically significant at the p < 0.05 level, but 3% concentration of acetylcysteine had significantly decreased in mean healing time compare to control group (P<0.05).
In other hand, mean daily healing in all groups was no significantly different between treatment and control groups.
Histopathological examination of the formalin-fixed corneal buttons revealed them to be of slightly variable thickness, but all of them were taken in the anterior third of the corneal stroma. The trephinated areas of the healed corneal epithelium in only some eyes demonstrated hypertrophy and hyperplasia (fig 3). In most eyes the epithelial basement membrane of the healed corneas was not distinct than the adjacent normal basement membrane. The subepithelial stroma seemed variably edematous (fig 4). The degree of stromal edema was independent of the treatment groups. Neovascularization was not seen in all healing corneas. The Descemet membrane and endothelium seemed normal in all eyes.
In general, corneal ulcers healed without any complications. Corneal transparency is dependent upon epithelial and stromal regularity. Stromal fibers must be of uniform diameter, and the distance between fibers must be less than half the wavelength of visible light to prevent the scattering of light (?). Clinically the healed corneas in the present study seemed variably opaque in the trephinated areas (in ophthalmoscopy and retinoscopy). The opacity in around the ulcer was the more sever than it in the center. In manual trephining a pressure of more than 40 pounds on the globe is necessary. This deforms the tissue and leads to irregular margins (18). The combination of the corneal epithelial hyperplasia and stromal edema and the more important than both, disarrangement of collagen fibers in this stage, account for this appearance. This opacity may have resolved during the time, because the histopathologic examination revealed no evidence of fibroplasia or neovascularization.
The corneal collagenases in the wounded cornea arise from several cell sources: the injured epithelium, the activated keratocytes, and invading inflammatory cells such as macrophages and polymorphonucleocytes. Whereas callagenolytic and gelatinolytic activity is essential for tissue remodeling and wound healing, downregulation of the response is essential to maintain tissue stability after initial wound healing (19).