Purpose
To evaluate the ocular biometric parameters associated with intraocular pressure (IOP) reduction after phacoemulsification.
Design
Prospective, observational case series.
Methods
The study included 999 patients who had undergone uncomplicated phacoemulsification. IOP and ocular biometric parameters were checked preoperatively and 3 months postoperatively using anterior segment optical coherence tomography, optical biometry, and ultrasonic biomicroscopy. The relationship between IOP change and the parameters, including preoperative IOP, anterior chamber depth, axial length, angle opening distance at 500 μm, anterior chamber area, corneal thickness, lens thickness, and iris thickness at 750 μm, was evaluated.
Results
The mean patient age was 67.1 ± 4.3 years. The average change in IOP was −1.6 mm Hg (−11.8%). In univariate analysis, axial length, corneal thickness, and iris thickness were not significantly associated with IOP reduction. However, preoperative IOP, anterior chamber depth, angle opening distance, anterior chamber area, and lens thickness were significantly associated with IOP change ( P < .05). Furthermore, changes in anterior chamber depth (standardized coefficient beta [ B ] = −0.082), angle opening distance ( B = −0.095), and anterior chamber area ( B = −0.380) were more strongly correlated with IOP change than were preoperative factors ( B = −0.078, B = −0.071, and B = −0.067, respectively). In multivariate analysis, preoperative IOP, lens thickness, angle opening distance change, and anterior chamber area change were significantly associated with IOP change ( P < .005).
Conclusion
In addition to preoperative IOP and lens thickness, parameters such as changes in anterior chamber area and angle opening distance were significantly associated positively with reduced IOP after phacoemulsification.
Cataract surgery is one of the most effective ways to control intraocular pressure (IOP) and reduce the number of antiglaucoma medications required to treat cataract-induced glaucoma, including phacolytic and phacomorphic glaucoma. Recently, cataract surgery has been shown to have many benefits related to the control of IOP, regardless of the type of glaucoma. Kim and Hyung reported that cataract surgery using phacoemulsification with intraocular lens (IOL) implantation was effective in reducing IOP among patients with chronic angle-closure glaucoma (ACG). Hayashi and associates confirmed that cataract surgery was effective in reducing IOP among patients with ACG. Tenzel et al . and Poley et al . reported that cataract surgery reduced IOP among patients with open-angle glaucoma (OAG), ocular hypertension, or normal tension glaucoma (NTG) and led to a decrease in the number of antiglaucoma medications required. However, few studies have examined the relationship between a reduction in IOP and ocular biometric or pathologic changes, although preoperative IOP and anterior chamber depth have been reported to influence postoperative reductions in IOP in previous reports.
Recent innovations in noninvasive high-quality image technology, such as anterior segment optical coherence tomography (AS-OCT) and ultrasonic biomicroscopy (UBM), enable the precise measurement of various ocular properties before and after surgery. Here, we attempt to determine the effects of cataract surgery on IOP and to identify ocular biometric parameters that affect the reduction in IOP after cataract surgery in nonhypertensive and nonglaucomatous eyes.
Methods
All subjects and their parents were informed appropriately and gave written informed consent to participate in this study in accordance with institutional guidelines. This study was approved by the Institutional Review Board at Veterans Health Service Medical Center in Seoul, Korea, and was in accordance with HIPAA regulations. All investigations in this study adhered to the tenets of the Declaration of Helsinki. In this prospective observational consecutive case series, we included 999 consecutive patients who had nonhypertensive IOP values (7-21 mm Hg) before surgery and who were scheduled to undergo cataract surgery between April 1, 2009 and December 31, 2011 at the ophthalmic department of Veterans Health Service Medical Center in Seoul, Korea. Patients who had been diagnosed with glaucoma, uveitis, severe retinal diseases, or congenital anomalies were excluded. Patients with a history of ocular trauma (including any intraocular surgeries) were excluded as well. Surgery was conducted by 1 skilled surgeon who used the same method for all surgeries. After making a 2.75-mm incision in the temporal cornea, phacoemulsification was performed. This was followed by the implantation of an I-Flex IOL (I-Medical, Heidelberg, Germany) in the posterior chamber. IOP was measured using Goldmann applanation tonometry 1 day before cataract surgery and 3 months after surgery. Anterior chamber depth, angle opening distance at 500 μm, anterior chamber area, corneal thickness, and iris thickness at 750 μm were measured following the technique described in a previous study conducted in our institute using ImageJ software (version 1.44; National Institutes of Health, Bethesda, Maryland, USA). The nasal and temporal quadrants were imaged using AS-OCT (Visante, version 2.0; Carl Zeiss Meditec, Dublin, California, USA). For each parameter investigated, angle opening distance at 500 μm or iris thickness at 750 μm measurements were obtained both nasally and temporally. Axial length was measured using an IOLMaster (Carl Zeiss, Jena, Germany). Lens thickness was determined using ultrasonic biomicroscopy (Optikon 2000; Optikon, Rome, Italy).
Before surgery, the patients were not treated with any topical medications, such as antibiotics, steroids, or antiglaucoma medications. After surgery, each patient was treated with ophthalmic 0.3% gatifloxacin, 0.1% fluorometholone, and 0.1% diclofenac sodium for 4 weeks. In treated eyes, the IOP was measured between 3 PM and 4 PM on the day before surgery, and between 9 AM and 4 PM 3 months after surgery. IOP was measured at the same time in nontreated fellow eyes to control for measurement errors. Best-corrected visual acuity (BCVA) was examined in treated eyes the day before surgery and 3 months after surgery. All biometric values were assessed by 1 physician (J.S.) who was masked to group assignment.
Statistical analysis was performed using a commercially available statistical software package (SPSS, ver. 18.0; SPSS Inc, Chicago, Illinois, USA). The mean values are presented as means ± standard deviation. Paired t tests were used to determine the significance of changes in visual acuity, IOP, anterior chamber depth, angle opening distance at 500 μm, and anterior chamber area after surgery. We performed a univariate linear regression analysis with the change in IOP as a dependent parameter and ocular biometric parameters as independent parameters. To identify the factors most likely to predict a change in IOP, multivariate linear regression analysis was performed with the dependent parameter being change in IOP and independent parameters being the other parameters that were significantly associated with IOP change in univariate analysis. All P values were 2-sided and considered statistically significant when the values were less than .05; 95% confidence intervals are presented.
Results
Of the 999 patients included in the analysis, 913 were male and 86 female; their average age was 67.1 ± 4.3 (59-86) years. The average BCVA before surgery was 0.48 ± 0.14 (logMAR), and the average BCVA 3 months after surgery was 0.11 ± 0.09 (logMAR; P < .001). The average axial length before surgery was 24.02 ± 1.22 mm. The average IOP among all of the subjects was 13.5 ± 2.9 mm Hg, and the average change in IOP after surgery was −1.6 ± 2.6 mm Hg ( Table 1 ). The average IOP of nontreated fellow eyes before surgery was 13.6 ± 2.6 mm Hg, and the average IOP 3 months after surgery was 13.4 ± 2.6 mm Hg ( P = .329).
| Before Surgery | After Surgery | Paired t Test ( P Value) | |
|---|---|---|---|
| Age (y) | 67.1 ± 4.3 | 67.1 ± 4.3 | |
| M/F | 913/86 | 913/86 | |
| Best-corrected visual acuity (logMAR) | 0.48 ± 0.14 | 0.11 ± 0.09 | <.001 |
| Intraocular pressure (mm Hg) | 13.5 ± 2.9 | 11.9 ± 2.8 | <.001 |
| ACD (mm) | 2.60 ± 0.35 | 3.43 ± 0.43 | <.001 |
| AOD500 (mm) | 0.26 ± 0.03 | 0.44 ± 0.04 | <.001 |
| AA (mm 2 ) | 16.90 ± 1.03 | 22.19 ± 2.49 | <.001 |
| Axial length (mm) | 24.02 ± 1.22 | N/A | |
| Lens thickness (mm) | 4.28 ± 0.23 | N/A | |
| Corneal thickness (μm) | 539.00 ± 25.09 | N/A | |
| IT750 (mm) | 0.46 ± 0.03 | N/A |
When all IOPs before surgery were stratified into 5 IOP intervals (6-8, 9-11, 12-15, 16-18, and 19-21 mm Hg), the change in IOP was 11.1%, −2.0%, −11.2%, −19.3%, and −23.4%, respectively ( Table 2 ). Spearman correlation coefficient was 0.086 ( P < .001).
| Preop IOP Intervals (mm Hg) | Eyes | Mean IOP (mm Hg) ± SD | Change (%) at 3 Months | ||
|---|---|---|---|---|---|
| Preop IOP | Postop IOP | Change at 3 Months ∗ | |||
| 7-8 | 31 | 7.5 ± 0.6 | 8.4 ± 1.8 | 0.8 ± 2.0 a | 11.1% |
| 9-11 | 227 | 10.2 ± 0.8 | 10.0 ± 2.1 | −0.2 ± 2.3 | −2.0% |
| 12-15 | 506 | 13.4 ± 1.1 | 11.9 ± 2.4 | −1.5 ± 2.2 a | −11.2% |
| 16-18 | 182 | 16.9 ± 0.9 | 13.6 ± 2.6 | −3.3 ± 2.6 a | −19.3% |
| 19-21 | 53 | 19.7 ± 0.7 | 15.1 ± 2.7 | −4.6 ± 2.6 a | −23.4% |
| All eyes | 999 | 13.5 ± 2.9 | 11.9 ± 2.8 | −1.6 ± 2.6 a | −11.8% |
Table 3 shows the results of univariate linear regression analysis of the association between a reduction in IOP and various ocular parameters, including preoperative IOP. The univariate analysis of the association between IOP reduction and preoperative IOP showed that for a 1 mm Hg increase in preoperative IOP, the IOP decreased by 0.4 mm Hg. According to the standardized coefficient beta, increases in anterior chamber depth, angle opening distance at 500 μm, and anterior chamber area values were better predictors of a reduction in IOP than was preoperative IOP.
| P Value | Regression Coefficient B | 95% Confidence Interval | Standardized Coefficient Beta | |
|---|---|---|---|---|
| Preoperative IOP | <.0001 | −0.404 | −0.458 to −0.351 | −0.426 |
| Preoperative ACD | .013 | 0.457 | 0.096 to 0.819 | 0.078 |
| Preoperative AOD500 | .02 | 13.025 | 7.329 to 18.721 | 0.071 |
| Preoperative AA | .035 | 0.171 | 0.012 to 0.330 | 0.067 |
| Preoperative axial length | .359 | 0.063 | −0.072 to 0.198 | 0.029 |
| Preoperative lens thickness | <.0001 | −2.004 | −2.700 to −1.309 | −0.176 |
| Preoperative corneal thickness | .793 | 0.001 | −0.006 to 0.007 | 0.008 |
| Preoperative IT750 | .801 | −0.725 | −6.364 to 4.913 | −0.008 |
| Delta ACD | .009 | −0.516 | −0.904 to −0.128 | −0.082 |
| Delta AOD500 | .003 | −3.322 | −5.480 to −1.165 | −0.095 |
| Delta AA | <.0001 | −0.446 | −0.513 to −0.378 | −0.380 |
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