Healing modulation in glaucoma surgery after application of subconjunctival triamcinolone acetate alone or combined with mitomycin C: an experimetal study

Objective: to study the efficacy and safety of the use of subconjunctival triamcinolone acetate alone or in combination with mitomycin C as a modulator of trabeculectomy healing in rabbits. Methods: we submitted thirty male, albino, New Zealand rabbits to bilateral trabeculectomy. We divided the animals into four experimental groups with 15 eyes per group: control, mitomycin C, triamcinolone acetate and triamcinolone acetate + mitomycin C. We performed aplanation tonometry and clinical analysis of the bleb through the Moorfields Graduation System in the postoperative period. For the evaluation of healing, we carried out the quantitative analysis of the inflammatory infiltrate (polymorphonuclear) through Hematoxylin & Eosin staining, and vascular proliferation, through immunohistochemistry. Results: we observed a significant decrease in postoperative intraocular pressure in all groups compared with the preoperative pressure (p<0.001). However, there was no difference between groups (p=0.186). The triamcinolone + mitomycin C acetate group presented better indices as for the maximum bleb height and vascularization of the bleb central area (p=0.001); in addition, there was a lower inflammatory response (p=0.001) and lower vascular proliferation (p=0.001) in the intermediate phase of the study compared with the monotherapies. Conclusion: the combination of mitomycin C and triamcinolone acetate resulted in a synergistic action between these agents, with broader and more diffuse blebs, less inflammatory infiltrate and less vascular proliferation in the intermediate stages of follow-up in this animal model.


INTRODUCTION
G laucoma is an optic neuropathy that causes irreversible blindness if not treated properly. It is a public health problem, being the second largest cause of blindness in the population 1 . The objective of its treatment is the reduction of intraocular pressure, through topical medications, laser and/or surgical procedures 2,3 . Since the first description, in 1968, trabeculectomy has become the standard procedure in the surgical treatment of glaucoma. It aims at forming a fistula that provides an alternative route for the drainage of aqueous humor from the anterior chamber to the subconjunctival space, to reduce intraocular pressure (IOP) 3,4 .
Unlike many types of surgery in which complete healing is the desirable outcome, trabeculectomy aims to achieve a partial healing response, to allow continuous drainage of the aqueous humor through the fistula 4 . Modulation of the healing response in glaucoma surgery is often necessary, to achieve adequate pressure, maximizing surgical success 5 . There are a variety of agents available that can modify this response.

Original Article
Healing modulation in glaucoma surgery after application of subconjunctival triamcinolone acetate alone or combined with mitomycin C: an experimetal study

Modulação da cicatrização na cirurgia do glaucoma após aplicação de acetato de triancinolona subconjuntival isolado ou em associação à mitomicina C: estudo experimental
In ophthalmologic practice, antimetabolites, 5-fluorouracil (5-FU) and mitomycin C (MMC), have revolutionized the history of glaucoma surgery and are therefore the drugs most used in modulating healing 4,6 . Although they have enhanced the surgical success rate in trabeculectomy, the non-specific mechanism of these agents may result in various ocular complications, such as corneal toxicity, avascular blebs, endophthalmitis, hypotonia and, in some cases, they are just ineffective 7 . Therefore, there is still a need for alternative strategies to prevent surgical failure secondary to over-healing.
Anti-inflammatory agents are already part of the strategy to modulate inflammation and wound healing in the eye. Steroid hormones are the prototype 4 . Triamcinolone Acetate (TA) is a corticosteroid in the form of an injectable suspension already used for the treatment of neovascular, proliferative and edematous diseases in ophthalmology. Its anti-inflammatory potential is approximately five times that of cortisol 8,9 . The anti-inflammatory and antifibrotic action of TA is largely mediated by suppression of leukocyte concentration and functionality, as well as its effects on vascular permeability. This leads to less local inflammation, reduced release of growth factors, and production of clot and fibrin. As a result, there is a decrease in the fibroblast activity and in the cicatricial response 8,10 .
Although there are already some studies evaluating the use of TA in glaucoma surgery, there is still a need to assess whether TA can be used in monotherapy or only in association with MMC. Therefore, in this research, the objective was to evaluate the efficacy and safety of the use of TA isolated or associated with MMC in trabeculectomy in rabbits.

Experimental model
We used thirty male, albino rabbits of the Oryctolagus caniculus species, New Zealand breed, weighing between 2kg and 3kg in the study. angiogenesis. From each slide, we took three photos in sequence of the area of interest, with a 400-fold increase, which were then evaluated by a pathologist who also did not know the groups.

Statistical analysis
We used the SPSS software, version 19.0. We applied non-parametric tests in the clinical analysis of the bleb. We performed the comparison between independent groups with the Kruskal-Wallis test. In the comparison between the phases, we used the Friedman test. To evaluate the influence of the groups and of the study phases on the intraocular pressure, we used the Variance Analysis based on a Repeated Measures planning.
We carried out the evaluation of the influence of the group and the time of evaluation until death of the animals (phase) in the immunohistological variables, as well as the interaction between these two factors (group and phase) using the two-way Analysis of Variance. We considered the results significant for a probability of significance of less than 5% (p<0.05).

RESULTS
There was no significant difference regarding the animals' initial weight between groups   3 and 4).

DISCUSSION
The healing process is a physiological, complex, dynamic event that comprises a cascade of different processes closely linked and not yet fully