Purpose:
Modern cataract surgery has been demonstrated to lower intraocular pressure (IOP). The underlying mechanism of this phenomenon is believed to be caused by an increase of outflow through the trabecular meshwork, but outflow facility changes following phacoemulsification had not been consistent in previous studies.
Methods:
Patients were recruited from clinics at St. Thomas’ Hospital. Cataract surgery was performed by a consultant surgeon (K.S Lim) under local or general anaesthesia. A clear corneal incision phacoemulsification was performed and an acrylic intraocular lens was inserted into the capsular bag. The viscoelastic was removed and a subconjunctival steroid and intracameral antibiotic given at the end.Inclusion criteria:1)Age ≥ 21 undergoing cataract surgery2) Diagnosis of POAG or normal healthy eyes. POAG is defined as IOP>21 mmHg on at least one occasion, glaucomatous optic neuropathy with corresponding visual field defects and a gonioscopic angle width of 3 or 4 and normal in appearance.Exclusion criteria:1) Previous intraocular surgery2) Previous ocular trauma3) Chronic use of systemic or topical steroids4) Any other concurrent ocular disease e.g. uveitis, diabetic retinopathy, corneal disease5) intraoperative complications6) persistent iritis at 3 months’ post-surgeryMeasurement:1) Outflow facility measured by electronic Schiotz tonometer at baseline and 3 month post-operatively2) IOP measured by Goldmann applanation tonometry at baseline, 1 day, 1 week and 3 months post-surgery
Results:
25 eyes of 23 patients were enrolled in the study. 7 black subjects and 16 white. POAG was found in 7 eyes. The mean age of the combined two groups of patients recruited was 70.7 (Range 50-82), mean baseline IOP was 15.6 mmHg ( SD ±3.8; range 10-26) and baseline outflow facility was 0.14µL/mmHg/min (SD±0.06; range 0.07-0.28). A significant IOP reduction was observed at 1 day (13.9 ± 2.5,p<0.05), 1 week (13.4 ± 3.3,p<0.05) and 3 month (13.7 ± 3.3,p<0.05) post operatively. The mean tonographic outflow facility increased significantly from baseline of 0.14 to 0.2 µL/mmHg/min at 3 month (p<0.05).
Conclusions:
This study confirmed that routine phacoemulsification reduced IOP at 3 months and this is caused by the associated increase in tonographic outflow facility.
Clinical Trial:
http://www.controlled-trials.com, CCT-NAPN-19240
Keywords: outflow: trabecular meshwork • treatment outcomes of cataract surgery • intraocular pressure