Anterior segment parameters as predictors of intraocular pressure reduction after phacoemulsification in eyes with open-angle glaucoma

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ARTICLE

Anterior segment parameters as predictors of intraocular pressure reduction after phacoemulsification in eyes with open-angle glaucoma Yen C. Hsia, MD, Sasan Moghimi, MD, Paul Coh, BS, Rebecca Chen, BS, Marisse Masis, MD, Shan C. Lin, MD

Purpose: To evaluate intraocular pressure (IOP) change after cataract surgery in eyes with open-angle glaucoma (OAG) and its relationship to angle and anterior segment parameters measured by anterior segment optical coherence tomography (AS-OCT). Setting: University of California, San Francisco, California, USA. Design: Prospective case series. Methods: Eyes were placed into a narrow-angle group or openangle group based on gonioscopy grading. Biometric parameters were measured using AS-OCT (Visante) preoperatively, and IOP 4 months after surgery was obtained. The IOP change and its relationship to AS-OCT parameters were evaluated. Results: Eighty-one eyes of 69 patients were enrolled. The mean age of the patients was 76.8 years. The preoperative IOP was 15.02 mm Hg on 1.89 glaucoma medications. The average mean

umerous studies1–19 have shown that cataract surgery lowers intraocular pressure (IOP) in normal eyes. In glaucomatous eyes, the degree of IOP reduction varies depending on the type of glaucoma. In primary acute and chronic angle-closure glaucoma, cataract surgery can lead to a profound reduction in both IOP and glaucoma medications and is often offered early as surgical management.9 The IOP in eyes with pseudoexfoliation glaucoma has been shown to have up to a 20% reduction after cataract surgery.10,11 On the other hand, the effect of cataract surgery on open-angle glaucoma (OAG), the most prevalent type of glaucoma in the United States, is less pronounced, with a reported average IOP

N

deviation of preoperative visual field was 4.58 dB. The mean IOP reduction was 2.1 mm Hg (12.8%) from a preoperative mean of 15.0 mm Hg. The IOP reduction was significantly greater in eyes with narrow angles than in eyes with open angles (20.4% versus 8.0%) (P Z .002). In multivariate analysis, preoperative IOP (b Z 0.53, P < .001, R2 Z 0.40), angle-opening distance at 500 mm (b Z 5.83, P Z .02, R2 Z 0.45), angle-opening distance at 750 mm (b Z 5.82, P Z .001, R2 Z 0.52), and lens vault (b Z 0.002, P Z .009, R2 Z 0.47) were associated with IOP reduction postoperatively.

Conclusion: In eyes with OAG, IOP reduction after cataract surgery was greater in eyes with narrower angles. Preoperative IOP, angle-opening distance, and lens vault were predictors for IOP reduction. J Cataract Refract Surg 2017; 43:879–885 Q 2017 ASCRS and ESCRS

reduction of 13% postoperatively.1–7 In 2 prospective randomized controlled trials comparing cataract surgery alone to cataract surgery plus trabecular microbypass stent (iStent, Glaukos Corp.) or supraciliary microstent (CyPass, Alcon Laboratories, Inc.),12,13 at least 50% of the patients had a 20% postoperative reduction in IOP after cataract surgery alone. Thus, identifying preoperative predictors for postoperative IOP reduction in patients with OAG can be valuable in guiding ophthalmologists on whether to consider cataract extraction as a surgical method for IOP control. The most consistent predictor for IOP reduction after cataract surgery in normal eyes and glaucomatous eyes

Submitted: August 13, 2016 | Final revision submitted: March 19, 2017 | Accepted: March 28, 2017 From the Department of Ophthalmology (Hsia, Moghimi, Coh, Chen, Masis, Lin), University of California, San Francisco, California, and Case Western Reserve University School of Medicine (Chen), Cleveland, Ohio, USA; Farabi Eye Hospital (Moghimi), Tehran University of Medical Sciences, Tehran, Iran. Supported by core grant EY002162 from the National Eye Institute, Bethesda, Maryland, That Man May See, Inc., San Francisco, California, and Research to Prevent Blindness, New York, New York, USA. Presented at the annual meeting of the Association for Research in Vision and Ophthalmology, Seattle, Washington, USA, May 2016. Corresponding author: Shan C. Lin, MD, 10 Koret Way, Room K301 San Francisco, California 94143-0730, USA. E-mail: [email protected]. Q 2017 ASCRS and ESCRS Published by Elsevier Inc.

0886-3350/$ - see frontmatter http://dx.doi.org/10.1016/j.jcrs.2017.03.044

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ANTERIOR SEGMENT PARAMETERS AFTER PHACOEMULSIFICATION IN EYES WITH OAG

has been elevated preoperative IOP.14–19 In normal eyes, a narrower preoperative anterior chamber depth (ACD)2,15 and greater lens thickness14 have been associated with postoperative IOP reduction; however, the evidence is not consistent across studies.15,16 Because a deep ACD could compensate for lens thickness, Hsu et al.19 reported that lens position (ACD C one-half lens thickness) is a useful predictor because it reflects how anteriorly positioned the lens is within the anterior chamber. However, optical biometry performs less well than newer imaging technology, such as anterior segment optical coherence tomography (AS-OCT), in analyzing the anterior chamber anatomy and angle width.20 Anterior segment optical coherence tomography is a rapid noncontact method to assess the anterior chamber angle anatomy in high resolution.21 The cross-sectional images obtained by the AS-OCT can be processed by an automated program that breaks down the anatomic structures into quantifiable parameters, including anterior chamber width (ACW), anterior chamber volume (ACV), angleopening distance, iris thickness, trabecular–iris surface area, and lens vault. Our group16,17 previously found preoperative angle-opening distance and lens vault to be significant predictors for IOP reduction in normal eyes. Clinically, the ideal patient population that would benefit from the modest IOP reduction after cataract surgery would be those with mild to moderate glaucoma. Whether the preoperative predictors for normal eyes would apply to eyes with OAG remains unknown. At present, no studies have evaluated whether, and if so which, preoperative AS-OCT parameters predict postoperative IOP reduction in eyes with OAG. As a continuation of our previous work, this prospective study was performed to evaluate the preoperative predictors of postoperative IOP reduction in patients with OAG by analyzing the change in IOP at 4 months and its relationship with preoperative AS-OCT parameters. The glaucoma medications were unchanged after cataract surgery with the goal of evaluating the effect of cataract surgery on patients who are medically controlled. We also categorized the patients’ angle status into 2 groups (narrow angle and open angle) based on preoperative gonioscopy. We then evaluated the differences in preoperative AS-OCT parameters and postoperative IOP between those 2 groups. PATIENTS AND METHODS This was a prospective study approved by the institutional review board at the University of California, San Francisco, California, USA. Informed consent was obtained from all patients prior to enrollment. Patients were consecutively recruited from the glaucoma clinics from June 1, 2012 to December 31, 2015. Inclusion criteria were patients age 18 years or older with visually significant cataracts, uneventful routine cataract surgeries, and a diagnosis of glaucoma, defined by the use of glaucoma medications plus 1 of the following scenarios: glaucomatous visual field defect and the presence of glaucomatous optic disc excavation or a cup-to-disc ratio 0.9 or more if the patient was unable to perform the visual field. Exclusion criteria were intraoperative or postoperative complications (eg, posterior capsule rupture), previous intraocular surgery, presence of other ocular conditions that Volume 43 Issue 7 July 2017

could affect visual acuity or the IOP, history of ocular trauma, presence of peripheral anterior synechiae on gonioscopy, and evidence of pigment dispersion or pseudoexfoliation syndrome. Both eyes of patients were included in the study if they met the criteria. Eyes with history of laser peripheral iridotomy or laser trabeculoplasty were not excluded from the study. Patient demographic information was obtained via computer chart review. The preoperative assessment included visual acuity testing, IOP measurement, manifest refraction, central corneal thickness (CCT), gonioscopy, and complete slitlamp examination including dilated fundus evaluation. All IOP measurements were performed with the eye undilated using Goldmann applanation tonometry by the same clinician (S.C.L.) between 1 PM and 6 PM. The mean IOP from 2 preoperative visits was used in this study. If the IOP measurement from the 2 preoperative visits differed by more than 2 mm Hg, a third value was obtained and the median was chosen. Gonioscopy was performed by the same glaucoma specialist (S.C.L.) using a Zeiss-style 4-mirror lens (model OPDSG, Ocular Instruments, Inc.). The angles were graded based on the Shaffer grading system.22 Eyes with Shaffer grade 2 or less in at least 3 quadrants were defined as narrow angles and eyes with Shaffer grade 3 or 4 in at least 3 quadrants were defined as open angles. Surgical Technique Surgery was performed by the same surgeon (S.C.L.) using standard surgical techniques for phacoemulsification through a temporal clear corneal incision. A single-piece acrylic intraocular lens (IOL) (Acrysof SA60AT, Alcon Laboratories, Inc.) was implanted in cases. The postoperative eyedrop regimen included topical antibiotics 4 times daily for 1 week and prednisolone acetate 1.0% and ketorolac tromethamine 0.5% 4 times daily with a weekly taper. Postoperative Follow-up Postoperative follow-up visits were performed at 1 day, 1 week, 1 month, and 4 months. During each visit, visual acuity testing, IOP measurement, and a complete slitlamp examination were performed. Anterior Segment Optical Coherence Tomography Preoperative AS-OCT data were gathered using a Visante AS-OCT device (Carl Zeiss Meditec AG). Details of the imaging procedures and analysis have been described.16 Images were excluded if the scleral spurs were not identified. Only the nasal and temporal angle images were captured for analysis to prevent the mechanical influence on the superior and inferior angles for patients who might have needed eyelid manipulation. Definition of Anterior Segment Optical Coherence Tomography Parameters The lens vault is defined by the amount of lens (mm) anterior to the horizontal line connected by the 2 scleral spurs. The anterior vault is the sum of the lens vault and ACD in mm. The ACV is the cumulative cross-sectional area (mm3) of the anterior chamber. The ACW is the horizontal distance between 2 scleral spurs (mm). The angle-opening distance is defined by the perpendicular distance (mm) from the trabecular meshwork to the opposing iris 500 mm or 750 mm anterior to the scleral spur. The trabecular– iris surface area is defined by the cross-sectional area (mm2) bounded by the angle-opening distance 500 mm or 750 mm anteriorly, the inner corneoscleral wall superiorly, the iris inferiorly, and a perpendicular line from the scleral spur to the opposing iris posteriorly. The iris thickness is defined by the thickness of iris (mm) measured 750 mm or 2000 mm from the scleral spur. Iris curve is the perpendicular distance (mm) from the posterior central iris to a line connecting from the most peripheral posterior

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iris to the pupillary margin. The iris area is the cumulative crosssectional area (mm2) of the iris.

Table 2. Baseline AS-OCT parameters in all patients. Parameter

Statistical Analysis The Student t test was used to calculate statistical differences between paired continuous variables. Categorical variables were compared using the chi-square test. Linear mixed-effects regression analysis was used to assess the correlation between preoperative IOP, age, sex, and AS-OCT parameters with the IOP change (postoperative IOP minus preoperative IOP) in univariate analysis and multivariate analysis. The use of mixed models adjusts for the use of both eyes of some patients. To determine the most significant variable associated with IOP change, multivariate linear mixed-effects regression analysis adjusted for age, sex, and preoperative IOP was performed to assess the effect of variables from the univariate analysis with a P value less than 0.05. A P value less than 0.05 was considered statistically significant. All statistical analysis was performed using SPSS software (version 18, SPSS, Inc.).

RESULTS The study enrolled 81 eyes of 69 patients with OAG. Twenty-one patients were men and 48 were women. Table 1 shows the baseline patient information. The narrow-angle group comprised 28 eyes of 24 women and 4 men. The open-angle group comprised 53 eyes of 36 women and 17 men. There was no statistically significant different in sex between the 2 groups (P Z .08, c2 test). Of the patients, 74 (91%) were using a prostaglandin analog (PGA), 32 patients (40%) a ß-adrenoceptor antagonist, 19 (23%) an a-adrenoceptor agonist, and 32 (40%) a carbonic anhydrase inhibitor. The same glaucoma medications were resumed the day after surgery except for PGAs. After 1 month, the same PGAs were resumed and study eyes were then back on the same glaucoma medication regimen. The study was designed in this way to isolate the outcome variable as the IOP change without a confounding effect from medication changes after the surgery. As a safety measure, the study protocol was suspended if persistent IOP less than 5 mm Hg was encountered. No patient was placed on oral carbonic anhydrase inhibitors. Four months after cataract surgery, the mean postoperative IOP was 12.9 G 2.7 mm Hg, with a mean reduction from baseline of 2.2 G 2.9 mm Hg or 12.3% (P ! .001). Table 2 shows the preoperative AS-OCT angle, iris, and anterior segment parameters in all eyes. Table 3 shows a Table 1. Baseline demographics of all patients. Parameter Age (y) Refraction (D) Cup-to-disc ratio Axial length (mm) CCT (mm) Preop IOP (mm Hg) Medications (n) Visual field mean deviation (dB) Postop IOP (mm Hg) IOP change (mm Hg) IOP change (%)

Mean ± SD 76.8 G 7.4 1.08 G 2.66 0.66 G 0.15 24.31 G 1.45 539.7 G 32.9 15.02 G 3.41 1.89 G 1.04 4.58 G 3.99 12.85 G 2.72 2.17 G 2.90 12.3 G 18.4

Range 60, 95 8.5, 2.75 0.40, 0.90 21.83, 29.43 471.5, 615.0 8.00, 23.00 0.0, 4.0 16.65, 2.42 6.50, 20.25 9.50, 4.50 59.3, 34.6

CCT Z central corneal thickness; IOP Z intraocular pressure

Angle AOD500 (mm) AOD750 (mm) TISA500 (mm2) TISA750 (mm2) Iris IT750 (mm) IT2000 (mm) I-area (mm2) I-curve (mm) Pupil diameter (mm) Anterior segment ACD (mm) ACV (mm3) Lens vault (mm) ACW (mm) Anterior vault (mm)

Mean ± SD

Range

0.250 G 0.095 0.344 G 0.137 0.101 G 0.040 0.186 G 0.063

0.040, 0.560 0.110, 0.840 0.020, 0.200 0.070, 0.380

0.43 G 0.10 0.41 G 0.06 1.68 G 0.29 0.32 G 0.16 3.93 G 0.77

0.16, 0.72 0.11, 0.56 1.08, 2.81 0.07, 0.98 2.17, 5.62

2.64 G 0.43 133.9 G 26.3 550.0.5 G 301.9 11.82 G 0.49 3.16 G 0.25

1.69, 3.87 65.3, 202.1 35.2, 1470.0 10.58, 13.14 2.67, 4.15

ACD Z anterior chamber depth; ACV Z anterior chamber volume; ACW Z anterior chamber width; AOD500 Z angle-opening distance 500 mm anterior to scleral spur; AOD700 Z angle-opening distance 700 mm anterior to scleral spur; I-area Z iris area; I-curve Z iris curvature; IT750 Z iris thickness 750 mm from sclera spur; IT2000 Z iris thickness 2000 mm from sclera spur; TISA500 Z trabecular-iris space areas 500 mm from scleral spur; TISA750 Z trabecular-iris space areas 750 mm from scleral spur

comparison between the narrow-angle group and the open-angle group. There were no statistically significant differences in age, AL, CCT, number of preoperative medications, visual field mean deviation, or preoperative IOP between the 2 groups. There were significant differences in the preoperative AS-OCT parameters between the narrowangle group and the open-angle group. The narrow-angle group had a smaller angle-opening distance at 500 mm, angle-opening distance at 750 mm, trabecular–iris surface area at 500 mm, and trabecular–iris surface area at 750 mm than the open-angle group (all P ! .001). The angle-opening distance at 500 mm and angle-opening distance at 750 mm were 0.14 mm and 0.16 mm larger, respectively, in the open-angle group. Narrow-angle eyes also had a smaller ACD and ACV at baseline than open-angle eyes (P Z .018 and P Z .006, respectively). The lens vault was significantly greater in narrow-angle eyes (P Z .018). No statistical differences were found in iris parameters (iris thickness at 750 mm, iris thickness at 2000 mm, iris area, iris curve, and pupil diameter), ACW, or anterior vault between the 2 groups. The narrow-angle group had a greater absolute IOP reduction and percentage change than the open-angle group. The mean IOP reduction at 4 months was 3.4 G 3.0 mm Hg in the narrow-angle group and 1.5 G 2.6 mm Hg in the open-angle group (P Z .004), and the postoperative IOP differences between the 2 groups remained statistically significant after adjusting for age, sex, and preoperative IOP (P Z .005). The percentage of IOP reduction in the narrow-angle group (20.4%) was more than double that in the open-angle group (8.0%) 4 months postoperatively (P Z .004). Table 4 shows the results of univariate and multivariate linear mixed regression analysis of absolute IOP change with preoperative parameters. In the univariate linear Volume 43 Issue 7 July 2017

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Table 3. Comparison of the narrow-angle and open-angle groups. Mean ± SD Parameter Age (y) Axial length (mm) CCT (mm) Medications (n) Visual field mean deviation (dB) Preoperative IOP (mm Hg) Postoperative IOP (mm Hg) IOP change (mm Hg) IOP change (%) Angle AOD500 (mm) AOD750 (mm) TISA500 (mm2) TISA750 (mm2) Iris IT750 (mm) IT2000 (mm) I-area (mm2) I-vurve (mm) Pupil diameter (mm) Anterior segment ACD (mm) ACV (mm3) Lens vault (mm) ACW (mm) Anterior vault (mm)

Narrow Angle (n Z 28)

Open Angle (n Z 53)

P Value*

77.5 G 7.4 24.21 G 1.31 539.6 G 27.2 1.64 G 0.87 4.17 G 4.30 15.58 G 3.21 12.16 G 2.86 3.42 G 3.01 20.4 G 18.3

76.6 G 7.4 24.37 G 1.52 521.5 G 37.6 2.01 G 1.11 4.84 G 3.80 14.72 G 3.50 13.21 G 2.59 1.50 G 2.63 8.0 G 17.1

0.159 G 0.051 0.236 G 0.075 0.077 G 0.036 0.135 G 0.036

0.298 G 0.077 0.401 G 0.128 0.115 G 0.037 0.214 G 0.058

!.001 !.001 !.001 !.001

0.47 G 0.12 0.42 G 0.06 1.76 G 0.34 0.35 G 0.20 3.95 G 0.82

0.42 G 0.09 0.42 G 0.06 1.64 G 0.26 0.30 G 0.15 3.92 G 0.74

.05 .88 .09 .22 .89

2.49 G 0.41 122.8 G 29.6 656.8 G 261.8 11.79 G 0.41 3.14 G 0.25

2.73 G 0.43 140.1 G 22.3 490.2 G 308.7 11.84 G 0.45 3.17 G 0.25

.018 .006 .018 .66 .62

.61 .64 .05 .07 .51 .28 .09 .004 (.005†) .004 (.002†)

ACD Z anterior chamber depth; ACV Z anterior chamber volume; ACW Z anterior chamber width; AOD500 Z angle-opening distance 500 mm anterior to scleral spur; AOD700 Z angle-opening distance 700 mm anterior to scleral spur; CCT Z central corneal thickness; I-area Z iris area; I-curve Z iris curvature; IOP Z intraocular pressure; IT750 Z iris thickness 750 mm from sclera spur; IT2000 Z iris thickness 2000 mm from sclera spur; TISA500 Z trabecular-iris space areas 500 mm from scleral spur; TISA750 Z trabecular-iris space areas 750 mm from scleral spur *Student t test † Linear mixed model, adjusting for age, sex, and preoperative intraocular pressure

mixed-effects regression analysis, the significant predictors of IOP reduction were preoperative IOP, angle-opening distance at 500 mm, angle-opening distance at 750 mm, trabecular–iris surface area at 750 mm, and lens vault. After adjusting for preoperative IOP, age, and sex, the multivariate analysis showed preoperative IOP, angle-opening distance at 500 mm, angle-opening distance at 750 mm, and lens vault to be significant predictors for IOP reduction. There were no associations between IOP reduction in eyes with OAG and the preoperative AL, ACD, ACV, ACW, or anterior vault.

DISCUSSION In this prospective study, in eyes with medically controlled mild to moderate OAG, phacoemulsification with IOL implantation led to a mean IOP reduction of 2.17 mm Hg, or a 12.3% decrease from a mean preoperative IOP of 15.02 mm Hg, without adjusting the glaucoma medications postoperatively. The amount of IOP reduction was significantly greater in eyes with a narrower angle grading based on preoperative gonioscopy than in eyes with more open angles. Preoperative AS-OCT parameters that were significant predictors of a postoperative IOP reduction were higher preoperative IOP, narrower angle-opening distance, and greater lens vault. Volume 43 Issue 7 July 2017

The reduction in IOP 4 months after phacoemulsification in eyes with OAG is consistent with published reports that cataract surgery results in a IOP reduction in both normal eyes and glaucomatous eyes.1–19 Several studies1,4,7 have reported an average reduction in IOP of 2 mm Hg or 13% reduction after uncomplicated phacoemulsification with IOL implantation in eyes with OAG, with a preoperative IOP ranging from 15 mm Hg to 17 mm Hg. This is comparable to our prospective group of OAG eyes, which had a mean preoperative IOP of 15.0 mm Hg and a mean reduction of 2.2 mm Hg, without adjustment of glaucoma medications postoperatively. Few studies5,12,13 have reported postoperative IOP reduction up to 20% in eyes with OAG; however, these studies included patients with higher preoperative IOP (O20 mm Hg), which likely contributed to the greater IOP reduction. Narrower preoperative angles based on gonioscopy grading have been shown to have a greater IOP reduction after cataract surgery than angles that were more open.17,18 Similarly in our study, the narrow-angle group had a significantly greater absolute IOP change after phacoemulsification than the open-angle group (3.4 mm Hg versus 1.5 mm Hg). The AS-OCT parameters reflected the anterior chamber differences between the narrowangle group and open-angle group. Specifically, the narrow-angle group had a narrower angle-opening

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Table 4. Univariate and multivariate analysis of the association between preoperative parameters and changes in IOP. Univariate Analysis Parameter Age (y) Sex (male/female) Preop IOP (mm Hg) Axial length (mm) AOD500 (mm) AOD750 (mm) TISA500 (mm2) TISA750 (mm2) IT750 (mm) IT2000 (mm) I-area (mm2) I-curve (mm) ACD (mm) ACV (mm2) Lens vault (mm) ACW (mm) Anterior vault (mm)

b 0.266 5.287 2.755 2.730 45.177 35.701 83.549 77.027 23.030 31.999 8.022 21.237 7.081 0.092 0.013 0.085 2.251

95% CI 0.805, 0.274 14.580, 4.006 3.798, 1.713 0.140, 5.601 3.301, 87.054 6.707, 64.696 17.808, 184.905 13.837, 140.217 64.362, 18.302 42.629, 106.627 22.615, 6.570 46.332, 3.857 2.268, 16.431 0.70, 0.253 0.026, 0.00001 8.154, 8.345 14.359, 18.861

Multivariate Analysis* P Value .33 .26 !.001 .06 .03 .01 .10 .02 .27 .39 .27 .10 .13 .26 .04 .98 .78

b 0.251 7.178 0.53 d 5.83 5.82 d 6.17 d d d d d d 0.002 d d

95% CI 0.687, 0.185 14.568, 0.212 0.69, 0.37 d 0.85, 10.90 2.48, 9.17 d 4.14, 16.49 d d d d d d 0.004, 0.0006 d d

P Value

R2

.25 .05 !.01 d .02 .001 d .2 d d d d d d .009 d d

d d 0.40 d 0.45 0.52 d d d d d d d d 0.47 d d

ACD Z anterior chamber depth; ACV Z anterior chamber volume; ACW Z anterior chamber width; AOD500 Z angle-opening distance 500 mm anterior to scleral spur; AOD700 Z angle-opening distance 700 mm anterior to scleral spur; CI Z confidence interval; I-area Z iris area; I-curve Z iris curvature; IOP Z intraocular pressure; IT750 Z iris thickness 750 mm from sclera spur; IT2000 Z iris thickness 2000 mm from sclera spur; TISA500 Z trabeculariris space areas 500 mm from scleral spur; TISA750 Z trabecular-iris space areas 750 mm from scleral spur *In multivariate analysis, preoperative intraocular pressure was adjusted for age and sex, while other AS-OCT parameters were adjusted for age, sex, and preoperative intraocular pressure

distance, smaller trabecular–iris surface area, reduced ACD, lower ACV, and a higher lens vault than the open-angle group. Our group previously found that nonglaucomatous eyes with a higher lens vault, narrower trabecular–iris surface area, and shallower ACD were more likely to have a greater angle-opening distance that widened after cataract removal, and a preoperative lens vault that correlated with the degree of IOP reduction.16,17 The findings in our study suggest that mild to moderate medically controlled OAG eyes without previous intraocular surgeries behave similarly to nonglaucomatous eyes in that a narrower anterior chamber anatomy benefits from cataract surgery, resulting in the widening of the anterior chamber angle and improved aqueous outflow. Furthermore, the results suggest that the mechanism of IOP reduction after cataract surgery in patients with OAG is likely the mechanical widening of the angle, leading to better aqueous outflow.17 Another proposed theory of how phacoemulsification cataract surgery leads to IOP reduction includes the activation of an interleukin-1a pathway in the trabecular meshwork secondary to ultrasound (US) energy during surgery.23 However, a prospective randomized controlled trial comparing manual small-incision cataract surgery and phacoemulsification cataract surgery in normal eyes8 showed equivalent IOP reduction 6 months after surgery, suggesting the mechanism of IOP reduction is more likely due to the anatomic widening of the drainage angle rather than a US-related pathway. The multivariate analysis showed that the preoperative IOP, angle-opening distance, and lens vault were significant predictors of IOP reduction in eyes with OAG after cataract surgery. Multiple studies14–19 have shown that the

preoperative IOP is a strong predictor of IOP reduction after cataract surgery in normal eyes and glaucomatous eyes. Our study confirmed that the preoperative IOP is a strong predictor of post-phacoemulsification IOP reduction in eyes with OAG. One concern regarding high preoperative IOP as a predictor for IOP reduction after cataract removal is the effect of regression to the mean. To control for this in our study, the mean of 2 preoperative IOP readings was used. The time of the IOP measurement was also restricted to account for the diurnal fluctuation in IOP. The angle-opening distance and lens vault have been shown to be strong AS-OCT parameters in determining eyes with a narrow angle width in Asian populations.20,24,25 The value of the angle-opening distance and lens vault as parameters in predicting IOP reduction after cataract surgeries has been shown in prospective studies of eyes without glaucoma.14,16,17 This is first study reporting that the preoperative angle-opening distance and lens vault can be useful predictors for IOP reduction in eyes with medically controlled mild to moderate OAG. There are several limitations to this study. First, the glaucoma medications were unchanged before and after cataract surgery to keep the medication effect constant. Thus, the IOP reduction effect is likely blunted by the lower preoperative IOP. As mentioned earlier, in other prospective studies that included a preoperative medication washout period, IOP reduction after cataract surgery was shown to be up to 20%.12,13 Because our analysis aimed to analyze the correlation between IOP change and baseline parameters, the reduction in IOP change with glaucoma medication might have influenced the magnitude of the statistical correlation. Second, our study did not evaluate Volume 43 Issue 7 July 2017

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the long-term effect of the IOP reduction; postoperative data was limited to 4 months. However, several studies indicate the long-term effect of phacoemulsification in glaucomatous patients. Vold et al.13 found an IOP reduction at 2 years after phacoemulsification cataract surgery compared with the baseline IOP, while Shingleton et al.6 reported an IOP reduction up to 5 years. Third, our sample was relatively small, with a total of 81 eyes and only 28 eyes in the narrow-angle group. Finally, our study was of patients with mild to moderate OAG (mean deviation 4.58 dB on preoperative visual field) who were medically controlled, who had no previous glaucoma incisional surgeries, and who were taking on average 1.89 medications. Therefore, the results might not be applied to cases of advanced OAG with uncontrolled IOP. In summary, routine phacoemulsification with IOL implantation led to a modest IOP reduction in patients with medically controlled mild to moderate OAG and visually significant cataracts, indicating it might be a potential surgical option for patients needing additional IOP control. The amount of reduction was greater in patients with narrow angles based on gonioscopy grading and AS-OCT parameters. The OAG patients with a higher preoperative IOP, narrower angle-opening distance, and greater lens vault were more likely to achieve a larger IOP reduction after cataract surgery. These findings can help better determine the predictability of IOP reduction after phacoemulsification with IOL implantation in patients with OAG.

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WHAT WAS KNOWN

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 Cataract surgery lowers IOP in normal eyes and in eyes with glaucoma.  The preoperative IOP is a strong predictor of IOP reduction after cataract surgery.

16.

WHAT THIS PAPER ADDS  The preoperative angle-opening distance and lens vault were predictors of IOP reduction after cataract surgery in eyes with mild to moderate OAG.

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18.

REFERENCES 1. Poley BJ, Lindstrom RL, Samuelson TW, Schulze R Jr. Intraocular pressure reduction after phacoemulsification with intraocular lens implantation in glaucomatous and nonglaucomatous eyes; evaluation of a causal relationship between the natural lens and open-angle glaucoma. J Cataract Refract Surg 2009; 35:1946–1955 2. Kashiwagi K, Kashiwagi F, Tsukahara S. Effects of small-incision phacoemulsification and intraocular lens implantation on anterior chamber depth and intraocular pressure. J Glaucoma 2006; 15:103–109 3. Hayashi K, Hayashi H, Nakao F, Hayashi F. Changes in anterior chamber angle width and depth after intraocular lens implantation in eyes with glaucoma. Ophthalmology 2000; 107:698–703 4. Mathalone N, Hyams M, Neiman S, Buckman G, Hod Y, Geyer O. Longterm intraocular pressure control after clear corneal phacoemulsification in glaucoma patients. J Cataract Refract Surg 2005; 31:479–483 5. Hayashi K, Hayashi H, Nakao F, Hayashi F. Effect of cataract surgery on intraocular pressure control in glaucoma patients. J Cataract Refract Surg 2001; 27:1779–1786 6. Shingleton BJ, Pasternack JJ, Hung JW, O’Donoghue MW. Three and five year changes in intraocular pressures after clear corneal

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Disclosure: None of the authors has a financial or proprietary interest in any material or method mentioned.

First author: Yen C. Hsia, MD Department of Ophthalmology, University of California, San Francisco, California, USA

Volume 43 Issue 7 July 2017