Evaluation of the effectiveness of topical insulin in the ocular surface epithelial defect model created by experimental chemical burn in rabbit eyes

Aim: Ocular chemical injuries are an ophthalmic emergency that can progress from simple irritation to eye loss. Topical insulin has recently become a popular treatment due to its healing effect on the corneal epithelium and its role in different ocular surface pathologies is being investigated. The aim of this study was to evaluate the efficacy of topical insulin on corneal healing in an experimental chemical burn induced epithelial defect model. Methods: In this study, an experimental chemical burn model was created by applying 1N NaOH to the right eye of 16 New Zealand breed rabbits and the rabbits were randomized into 3 groups. The control group consisted of 4 rabbits and the treatment groups consisted of 6 rabbits each. The left eye of one rabbit randomly selected from each group was taken as the healthy group. The rabbits in the control group received normal saline 4 times a day, the rabbits in the P group received polyvinyl alcohol and povidone 4 times a day, and the rabbits in the I group received insulin diluted at a dose of 1 IU/ml 4 times a day. All rabbits were also treated with topical moxifloxacin until epithelial closure. On days 1, 3, 5, 7, 14, 21 and 28, anterior segment photographs were taken and clinical findings (chemosis, conjunctival hyperemia, eyelid edema) were recorded. On day 28, after sacrification, corneas were evaluated histologically, immunohistochemically and electron microscopically. Results: There was no significant difference between the groups in the epithelial defect areas on the 1st day, but epithelial defects were closed on the 3rd day in all groups. There was no significant difference between the groups in terms of clinical findings, but chemosis and eyelid edema regressed completely on the 7th day and hyperemia on the 14th day. Histologic analysis revealed that epithelial disruption was higher in all groups compared to healthy eyes, and stromal edema was increased in both insulin and control groups compared to healthy eyes. There was no significant difference between the groups in terms of α-SMA staining, which is a myofibroblast marker, but it was higher in the insulin group compared to the other groups. In the electron microscopic examinations, it was found that collagen formation was more regular in the insulin group and telocyte-like cells, which play an important role in cell renewal and cell repair, were present in the stromal area. Conclusion: Stromal healing in insulin-treated eyes with corneal chemical burns was very similar to the physiologic structure, indicating that insulin is effective on stromal wound healing. The remodeling time in stromal wound healing may extend from 6 months to 1 year depending on the severity of the wound. Considering that the use of insulin increases epithelial cell proliferation and migration, improves the function of corneal epithelial cells and is beneficial for remodeling, topical insulin application in the early and late period seems to be beneficial in chemical burns. Our study is valuable because it is the first study to demonstrate the effects of insulin on corneal stroma wound healing under electron microscopy. More comprehensive studies with a larger patient group are needed.