Abstract
BackgroundPeripheral iridectomy (PI), routinely performed during glaucoma filtration surgery, may contribute to scarring. This study aims to determine whether PI alters the concentrations of VEGF-A and TGF-β isoforms in the rabbit aqueous humour.MethodsAnterior chamber paracentesis (ACP) was performed in both eyes of six New Zealand white rabbits, with additional surgical PI performed in the right eyes. Eyes were examined on postoperative days (PODs) 1, 7, 30 and 60 by means of the tonopen, slit-lamp biomicroscopy, and bead-based cytokine assays for TGF-β and VEGF-A concentrations in the aqueous humor.ResultsACP caused a significant reduction in intraocular pressure (IOP) from mean preoperative 11.47 ± 1.01 mmHg to 5.67 ± 1.63 mmHg on POD 1 while PI did not cause further IOP reduction. Limbal conjunctival vasculature appeared slightly increased on POD 1 in both ACP and PI eyes with PI also causing mild bleeding from damaged iris vessels. Two PI eyes developed fibrinous anterior chamber reaction and/ or peripheral anterior synechiae. Aqueous VEGF-A levels were not significantly different between eyes treated with ACP and PI. Aqueous TGF-β concentrations distributed in the ratio of 4:800:1 for TGF-β1:TGF-β2:TGF-β3 respectively. While aqueous TGF-β2 was not significantly induced by either procedure at any time point, TGF-β1 and TGF-β3 were significantly induced above baseline levels by PI on POD 1.ConclusionPI increases the risk of inflammation. The combined induction of aqueous TGF-β1 and TGF-β3 by PI in glaucoma surgery may impact surgery success in glaucoma subtypes sensitive to these isoforms.
Highlights
Subconjunctival fibrosis is the most common cause of postoperative failure in glaucoma filtration surgery
Synopsis Peripheral iridectomy increases the incidents of inflammatory responses as well as induces aqueous TGF-β1 and TGF-β3, but not TGF-β2 or Vascular Endothelial Growth Factor (VEGF)-A
Anterior chamber paracentesis (ACP) alone caused a significant reduction in Intraocular pressure (IOP) by about 50% to 5.67 ± 1.63 mmHg on postoperative days (PODs) 1 (p = 0.00000080; 95% CI: 2.77–8.68; Fig. 1)
Summary
Subconjunctival fibrosis is the most common cause of postoperative failure in glaucoma filtration surgery. Excessive angiogenesis may contribute to the development of fibrosis [3]. The most potent proangiogenic molecules include members of the Vascular Endothelial Growth Factor (VEGF) family. VEGF-A was demonstrated to directly promote the growth activity of conjunctival fibroblasts, and further implicated in modulating scarring in a rabbit model of glaucoma surgery [6]. Higher preoperative VEGF levels in Tenon’s tissue are associated with a worse outcome following glaucoma surgery [7]. As VEGF-A levels are elevated in the aqueous humor of glaucomatous eyes [6, 7], and may be further upregulated following glaucoma surgery [6, 9], the surgical success may be dependent on limiting VEGF-A induction. Peripheral iridectomy (PI), routinely performed during glaucoma filtration surgery, may contribute to scarring. This study aims to determine whether PI alters the concentrations of VEGF-A and TGF-β isoforms in the rabbit aqueous humour
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