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First Author: S.Bhatta UK
Co Author(s): S. Longstaff
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To investigate the rate of peripheral anterior synechiae (PAS) formation in eyes following trabectome surgery for open angle glaucoma and its impact on the intraocular pressure (IOP) lowering effect.
This study was undertaken in the glaucoma unit of a tertiary university teaching hospital in the United Kingdom.
This was a retrospective study on patients who underwent trabectome surgery (NeoMedix, Inc, USA) in isolation or combined with phacoemulsification. All surgeries were performed by the same surgeon who had a special interest in glaucoma. The patients had pre- and post-operative intraocular pressures measured and gonioscopy performed. No eye with pre-operative PAS was included. A standard trabectome surgery was performed (under local anaesthesia) in the nasal quadrant over 3.5 clock hours (100 degrees) along the trabecular meshwork of the anterior chamber angle. When it was combined with phacoemulsification, trabectome surgery was performed following the cataract extraction. Phacoemulsification was performed through temporal clear corneal incision and trabectome was performed through the same wound. All patients were prescribed dexamethasone 0.1% four times daily and pilocarpine 2% three times daily for four weeks post-operatively. Post-operative PAS when present, was documented with anterior-segment OCT (Visante®) and / or slit-lamp gonioscopy pictures. Data was entered and analysed on Microsoft Excel spreadsheet.
19 eyes (of which 11 pseudophakic) underwent trabectome surgery and 15 eyes trabectome combined with phacoemulsification. The formation of PAS was higher (9 of 19, 47%) in the patients who underwent trabectome surgery in isolation than in those (6 of 15, 40%) who underwent combined surgery. Among 34 patients, there was no PAS formation in 19 eyes (56%, no-PAS group) while 15 developed PAS (44%, PAS group). The PAS was restricted to one-clock hour in the majority of patients (10 of 15, 66%). The mean overall pre-operative IOP was 27.7 + 4.5 mmHg and the mean IOP reduction was 8.2 + 6.5 mmHg (29.6% from baseline) after an average follow-up of 11 months. The mean IOP reduction in the no-PAS group was 9.5 + 5.4 mmHg (47% from baseline) and that in the PAS group was 6.6 + 7.6 mmHg (25% from baseline). Hence the IOP reduction in the no-PAS group was 2.9 mmHg lower than the PAS group but this was not found to be statistically significant (p=0.2). There was no major difference in the IOP reduction between those who underwent trabectome in isolation (29% reduction from baseline) from those who underwent the combined procedure (30% reduction from baseline).
We speculate that post-operative inflammation, hyphaema, shallowing of anterior chamber could be potential causes of PAS formation following trabectome surgery but it was outside the scope of this study to evaluate these factors. Our study showed that PAS formation occurred to a lesser degree when trabectome surgery was combined with phacoemulsification although majority of the eyes which underwent trabectome in isolation were pseudophakic from previous cataract surgery. Moreover there was no additional IOP lowering effect in those who underwent combined surgery. We would like to re-emphasise the hypothesis that drainage of aqueous which occurs directly into the collector channels through the cleft created by trabectome surgery remains functional independent of the development of PAS in post-trabectome eyes. While PAS formation following trabectome surgery was a relatively common occurrence in our study it did not adversely affect the lowering of the IOP in a statistically significant manner. It would be relevant to observe its clinical significance on a larger series of post-trabectome eyes.