Intraoperative IOP During Trabeculectomy Predicts Postop IOP
Intraoperative IOP During Trabeculectomy Predicts Postop IOP
This prospective observational study was conducted in 3 clinical centers: the Handan 3rd Hospital (Hebei Province, China), the Anyang Eye Hospital (Henan Province, China), and the Beijing Tongren Hospital from December 2009 to August 2010. The protocol and informed consent were approved by institutional review boards at all sites.
Primary glaucoma was defined as the presence of glaucomatous optic neuropathy combined with corresponding visual field defects in the absence of secondary causes.
The inclusion criteria were: (1) age between 18 and 80; (2) primary open-angle (including juvenile open-angle glaucoma) and closed-angle glaucoma (primary open-angle glaucoma, primary angle-closure glaucoma); (3) IOP ≥ 21 mm Hg; (4) evidence of optic nerve damage (combination of cup:disc ratio ≥ 0.7, asymmetry of cup:disc ratio ≥ 0.2, rim notch, rim:disc <0.1) and nerve fiber layer defects; (5) glaucomatous visual fields defect corresponding to optic disc damage; (6) primary trabeculectomy (no prior regular use of medical treatment).
The exclusion criteria were: (1) acute angle-closure glaucoma; (2) trabeculectomy combined with other procedures; (3) history of intraocular surgery or penetrating ocular trauma; (4) inability to attend follow-up due to serious systemic diseases, family issues, or other factors.
All trabeculectomies were carried out by glaucoma specialists. The speculum and drape were placed to minimize pressure on the eye. Surgery was performed using subconjunctival injection of 2% lidocaine supplemented with its topical usage. General anesthesia, peribulbar or retrobulbar anesthesia was not used in any cases. The choice of conjunctival flap was determined by the individual surgeon. For limbus-based flaps, a 10-mm incision was made through conjunctiva and the Tenon capsule approximately 8 to 10 mm posterior to limbus.
A partial thickness 4 × 3 mm rectangular scleral flap was fashioned. Mitomycin-c (MMC) was used at the discretion of the surgeon. Cellulose sponges soaked in MMC (0 to 0.4 mg/mL) were applied under the scleral flap and conjunctiva/Tenon as far posterior as possible for up to 4 minutes. This was followed by irrigation with balanced salt solution (BSS) to wash out any residual MMC solution. A paracentesis was performed and followed by a 2 × 1.5 mm trabeculectomy. We aimed for a 1-mm overlap of the opening by the scleral flap incision. An iridectomy was created and a minimum of two 10/0 nylon-fixed sutures were placed at the posterior portion of the scleral flap. Minimum tension was used to maintain a stable anterior chamber (AC) and to allow a gentle outflow when surgeon formed it with BSS. The superior rectus muscle traction suture was released and the AC was formed by injecting BSS through the paracentesis. Surgeons waited for at least 3 minutes. The objective was to achieve equilibrium (ooze with a formed AC).
For the limbus-based procedures, the conjunctival incision and the Tenon capsule was closed with a single running 10/0 vicryl suture. If a fornix-based flap was used, the procedure was the same except for the creation and closure of the conjunctival flap. The fornix-based flap was closed with a 2 tight wing sutures to the limbus/cornea. The integrity of wound closure was checked and any leak from the paracentesis was closed with a single 10/0 nylon suture. Subconjunctival tobramycin 10 mg + betnesol 4 mg was injected inferiorly to complete the procedure.
After closure of the scleral flap, the superior rectus muscle traction suture was released and patients were asked to look toward the microscope light before injecting BSS through the paracentesis. After about 3 minutes of achieving "equilibrium" with a formed AC, the IOP was measured 3 times with the Tonopen (Tono-Pen, Reichert Technologies, Depew, NY) before conjunctiva closure. Only readings with a variability of 5% were accepted and their mean was used for the analysis. Tonopen readings were obtained by the assistant surgeon; care was taken to avoid contamination of the field during the measurement, and gloves were changed after acquisition of the readings.
All patients underwent a comprehensive ophthalmic examination at baseline including visual acuity (Log MAR vision chart, Precision Vision, La Salle, TX), refraction, slit lamp, Goldmann applanation tonometry, static and dynamic gonioscopy using a Magnaview lens (Ocular Instruments, Bellevue, WA), and fundus examination. Automated perimetry was performed using the 24-2 threshold test with the SITA Fast program on a Humphrey Visual Field Analyzer 750 (Carl Zeiss Meditec, Dublin, CA).
Postoperative examinations and IOP measurements were performed on days 1, 7, and 30. Occurrence of complications and need for medications or further surgery were recorded at each visit. IOP measurements were performed twice by a trained clinical technician using an applanation tonometer. If the difference between the 2 measurements was >2 mm Hg, a third measurement was obtained and the mean of the 3 readings was recorded as the IOP for that visit.
Statistical analysis was carried out with SAS v8. If both eyes were included, 1 was randomly selected for analysis. Patients were stratified by intraoperative IOP readings into 3 groups: A (≤ 10.0 mm Hg), B (>10, ≤ 15.0 mm Hg), and C (>15 mm Hg). Mean IOP in each group were compared using analysis of variance and differences between each 2 groups were compared with LSD-t test.
Multiple regression and correlation models were used to predict the postoperative IOP from the intraoperative measurement and examine their associations. Variables with statistical significance (P < 0.05) in the univariable analysis and those with biological plausibility were included in the multivariable analysis. MMC use and concentration were entered in the analysis with "0" to indicate no MMC use. To establish equations for prediction, we used a stepwise method in selecting the variables. IOP < 20 mm Hg was considered IOP "control." α was set at 0.05.
Materials and Methods
This prospective observational study was conducted in 3 clinical centers: the Handan 3rd Hospital (Hebei Province, China), the Anyang Eye Hospital (Henan Province, China), and the Beijing Tongren Hospital from December 2009 to August 2010. The protocol and informed consent were approved by institutional review boards at all sites.
Primary glaucoma was defined as the presence of glaucomatous optic neuropathy combined with corresponding visual field defects in the absence of secondary causes.
The inclusion criteria were: (1) age between 18 and 80; (2) primary open-angle (including juvenile open-angle glaucoma) and closed-angle glaucoma (primary open-angle glaucoma, primary angle-closure glaucoma); (3) IOP ≥ 21 mm Hg; (4) evidence of optic nerve damage (combination of cup:disc ratio ≥ 0.7, asymmetry of cup:disc ratio ≥ 0.2, rim notch, rim:disc <0.1) and nerve fiber layer defects; (5) glaucomatous visual fields defect corresponding to optic disc damage; (6) primary trabeculectomy (no prior regular use of medical treatment).
The exclusion criteria were: (1) acute angle-closure glaucoma; (2) trabeculectomy combined with other procedures; (3) history of intraocular surgery or penetrating ocular trauma; (4) inability to attend follow-up due to serious systemic diseases, family issues, or other factors.
Surgical Technique
All trabeculectomies were carried out by glaucoma specialists. The speculum and drape were placed to minimize pressure on the eye. Surgery was performed using subconjunctival injection of 2% lidocaine supplemented with its topical usage. General anesthesia, peribulbar or retrobulbar anesthesia was not used in any cases. The choice of conjunctival flap was determined by the individual surgeon. For limbus-based flaps, a 10-mm incision was made through conjunctiva and the Tenon capsule approximately 8 to 10 mm posterior to limbus.
A partial thickness 4 × 3 mm rectangular scleral flap was fashioned. Mitomycin-c (MMC) was used at the discretion of the surgeon. Cellulose sponges soaked in MMC (0 to 0.4 mg/mL) were applied under the scleral flap and conjunctiva/Tenon as far posterior as possible for up to 4 minutes. This was followed by irrigation with balanced salt solution (BSS) to wash out any residual MMC solution. A paracentesis was performed and followed by a 2 × 1.5 mm trabeculectomy. We aimed for a 1-mm overlap of the opening by the scleral flap incision. An iridectomy was created and a minimum of two 10/0 nylon-fixed sutures were placed at the posterior portion of the scleral flap. Minimum tension was used to maintain a stable anterior chamber (AC) and to allow a gentle outflow when surgeon formed it with BSS. The superior rectus muscle traction suture was released and the AC was formed by injecting BSS through the paracentesis. Surgeons waited for at least 3 minutes. The objective was to achieve equilibrium (ooze with a formed AC).
For the limbus-based procedures, the conjunctival incision and the Tenon capsule was closed with a single running 10/0 vicryl suture. If a fornix-based flap was used, the procedure was the same except for the creation and closure of the conjunctival flap. The fornix-based flap was closed with a 2 tight wing sutures to the limbus/cornea. The integrity of wound closure was checked and any leak from the paracentesis was closed with a single 10/0 nylon suture. Subconjunctival tobramycin 10 mg + betnesol 4 mg was injected inferiorly to complete the procedure.
Intraoperative IOP Measurement
After closure of the scleral flap, the superior rectus muscle traction suture was released and patients were asked to look toward the microscope light before injecting BSS through the paracentesis. After about 3 minutes of achieving "equilibrium" with a formed AC, the IOP was measured 3 times with the Tonopen (Tono-Pen, Reichert Technologies, Depew, NY) before conjunctiva closure. Only readings with a variability of 5% were accepted and their mean was used for the analysis. Tonopen readings were obtained by the assistant surgeon; care was taken to avoid contamination of the field during the measurement, and gloves were changed after acquisition of the readings.
Clinical Examination
All patients underwent a comprehensive ophthalmic examination at baseline including visual acuity (Log MAR vision chart, Precision Vision, La Salle, TX), refraction, slit lamp, Goldmann applanation tonometry, static and dynamic gonioscopy using a Magnaview lens (Ocular Instruments, Bellevue, WA), and fundus examination. Automated perimetry was performed using the 24-2 threshold test with the SITA Fast program on a Humphrey Visual Field Analyzer 750 (Carl Zeiss Meditec, Dublin, CA).
Postoperative examinations and IOP measurements were performed on days 1, 7, and 30. Occurrence of complications and need for medications or further surgery were recorded at each visit. IOP measurements were performed twice by a trained clinical technician using an applanation tonometer. If the difference between the 2 measurements was >2 mm Hg, a third measurement was obtained and the mean of the 3 readings was recorded as the IOP for that visit.
Statistical Methods
Statistical analysis was carried out with SAS v8. If both eyes were included, 1 was randomly selected for analysis. Patients were stratified by intraoperative IOP readings into 3 groups: A (≤ 10.0 mm Hg), B (>10, ≤ 15.0 mm Hg), and C (>15 mm Hg). Mean IOP in each group were compared using analysis of variance and differences between each 2 groups were compared with LSD-t test.
Multiple regression and correlation models were used to predict the postoperative IOP from the intraoperative measurement and examine their associations. Variables with statistical significance (P < 0.05) in the univariable analysis and those with biological plausibility were included in the multivariable analysis. MMC use and concentration were entered in the analysis with "0" to indicate no MMC use. To establish equations for prediction, we used a stepwise method in selecting the variables. IOP < 20 mm Hg was considered IOP "control." α was set at 0.05.
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