Research
Original Investigation
Effect of Cataract Extraction on the Visual Field Decay Rate in Patients With Glaucoma Ji-Woong Lee, MD, PhD; Esteban Morales, MS; Fei Yu, PhD; Abdelmonem A. Afifi, PhD; Eun-Ah Kim, MD; Niloufar Abdollahi, BS; Kouros Nouri-Mahdavi, MD, MSc; Joseph Caprioli, MD
IMPORTANCE A visual field parameter that is resistant to cataract formation and extraction would help monitor glaucomatous visual field progression in patients with coexisting glaucoma and cataract. OBJECTIVE To evaluate the effect of cataract surgery on the slow and fast components of visual field decay in a group of patients with glaucoma. DESIGN, SETTING, AND PARTICIPANTS Retrospective, interventional, longitudinal study. Eighty-five eyes of 68 patients with open-angle glaucoma who had cataract extraction were included. All patients had 5 or more reliable visual field measurements before and after surgery. INTERVENTIONS A pointwise exponential regression was used to perform trend analysis on
thresholds at visual field test locations before and after cataract surgery. The test locations were ranked according to the decay rate and were partitioned into slow and fast groups. MAIN OUTCOMES AND MEASURES The slow and fast visual field rate components were measured before and after cataract surgery and were compared. Linear regressions of the mean deviation and the visual field parameter were performed against time and were compared before and after surgery. RESULTS The mean (SD) mean deviation was −5.5 (5.1) dB before cataract surgery and −5.0 (4.9) dB after cataract surgery (P = .002). The mean (SD) Visual Field Index was 86.4% (13.5%) before cataract surgery and 86.6% (13.3%) after cataract surgery (P = .30). The mean (SD) slow component rate decreased from 0.48% (0.73%) per year before surgery to 0.26% (0.42%) per year after surgery (P = .04). No statistically significant difference was identified in the fast component mean (SD) rate per year before surgery (3.37% [4.05%]) vs per year after surgery (3.46% [3.56%]) (P = .29). CONCLUSIONS AND RELEVANCE Cataract progression seems to be the main determinant for the slow visual field rate component and does not change the fast visual field rate component. We conclude that the method used can help reduce the confounding effects of cataract progression and cataract extraction on measured perimetric progression in glaucoma. Author Affiliations: Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California (Lee, Morales, Yu, Kim, Abdollahi, Nouri-Mahdavi, Caprioli); Department of Ophthalmology, Pusan National University School of Medicine, Busan, Korea (Lee); Department of Biostatistics, Jonathan and Karin Fielding School of Public Health at the University of California, Los Angeles (Yu, Afifi).
JAMA Ophthalmol. 2014;132(11):1296-1302. doi:10.1001/jamaophthalmol.2014.2326 Published online July 31, 2014. 1296
Corresponding Author: Joseph Caprioli, MD, Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, 100 Stein Plaza, Los Angeles, CA 90095 ([email protected]). jamaophthalmology.com
Copyright 2014 American Medical Association. All rights reserved.
Downloaded From: http://archopht.jamanetwork.com/ by a University of California - San Diego User on 06/01/2015
Cataract Extraction and Visual Field Decay Rate
C
ataract and glaucoma frequently coexist because the prevalences of cataract and open-angle glaucoma increase with aging.1,2 Trabeculectomy augments the risk of cataract formation by 78% in patients with glaucoma.3 Other treatments for glaucoma, including laser trabeculoplasty and medications, seem to increase this risk as well.4 Simulated cataract, minimally affecting visual acuity, can depress visual field sensitivities.5,6 The development of cataract causes diffuse visual field loss in patients with glaucoma, and differentiating perimetric deterioration caused by cataract from that caused by glaucoma worsening remains challenging.7 The visual field mean deviation (MD) and visual acuity improve significantly after cataract extraction,7-13 although some studies14,15 reported no significant changes in the MD. Similarly, changes in the pattern SD (PSD) and the Visual Field Index (VFI) have not been found to be significant after cataract extraction in some studies,8,11,13,14,16 whereas other studies9,10,12,17,18 have shown that the PSD worsened and the VFI improved after cataract extraction in patients with coexisting glaucoma and cataract. For example, the development or the worsening of cataract confounded the results of the Collaborative Normal-Tension Glaucoma Study.19 The favorable effect of intraocular pressure (IOP) reduction on visual field progression in patients with normal-tension glaucoma was detected only when the effect of cataract on the visual field results was removed.19 The measurement of the visual field decay rate is an important step to appropriate decision making to preserve vision in patients with glaucoma.20 While numerous studies have focused on the short-term effects of cataract extraction on visual acuity or the visual field parameters, little is known about the association between cataract extraction and decay rates in localized areas of the visual field. Our group developed a technique based on trend analysis that uses a pointwise exponential model to fit the behavior of individual test locations in a visual field series.21 This method separates slow and fast rate components of visual field decay, while preserving spatial information across a wide range of disease severity.21,22 The objective of this study was to evaluate the effect of cataract extraction on the slow and fast components of visual field decay as determined with a pointwise exponential regression model.
Methods Participants This study was conducted in accord with the tenets set forth in the Declaration of Helsinki and was approved by the UCLA Institutional Review Board. The institutional review board approved that informed consent from patients was waived because this is a retrospective study. A retrospective review of medical records of patients with open-angle glaucoma who underwent cataract surgery with intraocular lens implantation at the Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, between July 1, 2000, and June 30, 2010, was performed. Patients who underwent combined cataract and trabeculectomy surgery were excluded, as were any patients who jamaophthalmology.com
Original Investigation Research
underwent glaucoma surgery during the period of interest. All cataract surgery was performed by one of us (J.C.) with a temporal clear cornea, small-incision phacoemulsification technique using peribulbar anesthesia. The patients received a silicone foldable intraocular lens (STAAR Surgical) or an acrylic foldable intraocular lens (Alcon Laboratories Inc) implanted in the capsular bag.
Perimetric Tests All consecutive patients with open-angle glaucoma who had 5 or more reliable visual field measurements before and after surgery were included in the study. Reliability was defined as less than 30% fixation losses, less than 30% false-positive rates, and less than 30% false-negative rates. All visual field tests were performed using an automated visual field analyzer (Humphrey Field Analyzer; Carl Zeiss Ophthalmic Systems Inc) with a 24-2 test pattern, size III white stimulus with the Swedish Interactive Threshold Algorithm standard strategy. The last visual field before surgery and the first visual field after surgery were required to have been measured within 1 year of cataract surgery. The technique of measuring rates of visual field decay has been published in detail21,22 and is summarized herein. Rates of visual field decay were calculated by a pointwise exponential regression analysis of threshold sensitivities at 52 test locations, excluding the 2 locations corresponding to the blind spot. The association between the response variable (threshold sensitivity) and the explanatory variable (follow-up duration) was characterized by the following exponential regression models: y = ea + bx or, equivalently, ln y = a + bx, where a is the intercept, x is time, b is the mean annual rate of change in ln y, and eb represents the ratio of y in a given year to y in the year before. The decay rate is defined as 1 − eb. To facilitate an intuitive clinical understanding of the magnitude of decay rates, the coefficients of the exponential regressions were converted into percentage per year deterioration rates, where the percentage per year decay rate is (1 − eb) × 100. The 52 visual field test locations were ranked according to the decay rate and were clustered into 2 subgroups (slow and fast components) based on the P value for the difference in the mean rates between 2 clusters. For each possible partition, starting with a minimum number of 5 locations in a cluster, we computed a t test statistic, and the corresponding P values were adjusted for multiple testing. Because multiple simultaneous t tests were performed, it is desirable to correct the P values to control for false-positive results. Accordingly, BenjaminiHochberg correction was used to adjust the P values for multiple testing.23 For each eye, the mean slow and fast decay rates were calculated for the partitioned components during the preoperative and postoperative periods separately. The MD and VFI values for the preoperative and postoperative periods were also analyzed; univariate linear regression analyses of these values were performed against time, and corresponding regression slopes (in decibels per year and in percentages per year) were compared before and after cataract extraction. The MD, PSD, and VFI values of the last visual field measurement before surgery and the first visual field measurement after surgery were also compared. JAMA Ophthalmology November 2014 Volume 132, Number 11
Copyright 2014 American Medical Association. All rights reserved.
Downloaded From: http://archopht.jamanetwork.com/ by a University of California - San Diego User on 06/01/2015
1297
Research Original Investigation
Cataract Extraction and Visual Field Decay Rate
Table 1. Demographic and Clinical Characteristics Among 85 Eyes of 68 Patients With Open-Angle Glaucoma Who Underwent Cataract Surgery During the Follow-up Period Characteristic
Value
Age, mean (SD), y
70.2 (8.8)
Sex, No. Male
28
Female
40
Statistical Analysis
Study eye, No. Right
39
Left
46
Follow-up period, mean (SD), y Before surgery
5.6 (2.5)
After surgery
6.0 (2.1)
No. of visual field measurements, mean (SD) Before surgery
10.2 (4.3)
After surgery
9.5 (3.8)
Race/ethnicity, No. White
48
African American
4
Asian
9
Hispanic
7
The preoperative best-corrected visual acuity was recorded from the visit just before the surgery. All eyes were refracted within 1 month after cataract extraction. Snellen visual acuities were converted to a scale of the logMAR for comparison. The mean IOP and the mean number of medications were compared during the preoperative and postoperative periods.
All statistical analyses were performed with available software (SPSS for Windows 21.0; SPSS Inc). The normality of numerical data distribution was checked with KolmogorovSmirnov test. Differences between the preoperative and postoperative data were compared with Wilcoxon signed rank test. Spearman rank correlation coefficient was used to estimate correlations between various outcomes (eg, the preoperative and postoperative visual field decay rates) and each of the following continuous variables: age, vertical cup-disc ratio (VCDR), MD, PSD, VFI, mean IOP, and mean number of glaucoma medications. Multivariable linear regression analysis with a stepwise variable selection method was used to identify significant parameters that may explain the visual field decay rates in the slow and fast components.
Comorbidity, No. Hypertension
19
Diabetes mellitus
Results
7
MD, mean (SD), dB Baseline
−4.6 (4.5)
Final
−6.5 (5.5)
PSD, mean (SD), dB Baseline
5.5 (4.1)
Final
6.7 (4.1)
VFI, mean (SD), % Baseline
89.4 (11.7)
Final
82.4 (16.0)
Baseline vertical cup-disc ratio, mean (SD)
0.74 (0.11)
YAG laser posterior capsulotomy of eyes, No. (%)
28 (33)
Abbreviations: MD, mean deviation; PSD, pattern SD; VFI, Visual Field Index.
Eighty-five eyes of 68 patients with open-angle glaucoma who had cataract extraction were included in the study. The study eyes were followed up for a mean (SD) of 11.6 (2.9) years, and a mean (SD) of 19.7 (5.3) visual field measurements were available during the entire follow-up period. The demographic, clinical, and ocular characteristics of the study sample are summarized in Table 1. The mean (SD) logMAR best-corrected visual acuity significantly improved from 0.33 (0.19) before surgery to 0.14 (0.11) (P < .001) after cataract extraction (Table 2). The mean (SD) IOP decreased from 13.4 (3.2) mm Hg to 12.4 (3.7) mm Hg after cataract extraction (P = .002). Similarly, the mean (SD) number of glaucoma medications was reduced from 1.5 (0.9) to 1.0 (0.9) after cataract extraction (P < .001).
Table 2. Changes in the Visual Acuity, Intraocular Pressure, Number of Glaucoma Medications, and Global Visual Field Parameters After Cataract Extraction Among 85 Eyes of 65 Patients With Open-Angle Glaucoma Mean (SD) Variable
P Value
Before Surgery
After Surgery
Difference
logMAR
0.33 (0.19)
0.14 (0.11)
−0.19 (0.19)
Original Investigation
Effect of Cataract Extraction on the Visual Field Decay Rate in Patients With Glaucoma Ji-Woong Lee, MD, PhD; Esteban Morales, MS; Fei Yu, PhD; Abdelmonem A. Afifi, PhD; Eun-Ah Kim, MD; Niloufar Abdollahi, BS; Kouros Nouri-Mahdavi, MD, MSc; Joseph Caprioli, MD
IMPORTANCE A visual field parameter that is resistant to cataract formation and extraction would help monitor glaucomatous visual field progression in patients with coexisting glaucoma and cataract. OBJECTIVE To evaluate the effect of cataract surgery on the slow and fast components of visual field decay in a group of patients with glaucoma. DESIGN, SETTING, AND PARTICIPANTS Retrospective, interventional, longitudinal study. Eighty-five eyes of 68 patients with open-angle glaucoma who had cataract extraction were included. All patients had 5 or more reliable visual field measurements before and after surgery. INTERVENTIONS A pointwise exponential regression was used to perform trend analysis on
thresholds at visual field test locations before and after cataract surgery. The test locations were ranked according to the decay rate and were partitioned into slow and fast groups. MAIN OUTCOMES AND MEASURES The slow and fast visual field rate components were measured before and after cataract surgery and were compared. Linear regressions of the mean deviation and the visual field parameter were performed against time and were compared before and after surgery. RESULTS The mean (SD) mean deviation was −5.5 (5.1) dB before cataract surgery and −5.0 (4.9) dB after cataract surgery (P = .002). The mean (SD) Visual Field Index was 86.4% (13.5%) before cataract surgery and 86.6% (13.3%) after cataract surgery (P = .30). The mean (SD) slow component rate decreased from 0.48% (0.73%) per year before surgery to 0.26% (0.42%) per year after surgery (P = .04). No statistically significant difference was identified in the fast component mean (SD) rate per year before surgery (3.37% [4.05%]) vs per year after surgery (3.46% [3.56%]) (P = .29). CONCLUSIONS AND RELEVANCE Cataract progression seems to be the main determinant for the slow visual field rate component and does not change the fast visual field rate component. We conclude that the method used can help reduce the confounding effects of cataract progression and cataract extraction on measured perimetric progression in glaucoma. Author Affiliations: Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California (Lee, Morales, Yu, Kim, Abdollahi, Nouri-Mahdavi, Caprioli); Department of Ophthalmology, Pusan National University School of Medicine, Busan, Korea (Lee); Department of Biostatistics, Jonathan and Karin Fielding School of Public Health at the University of California, Los Angeles (Yu, Afifi).
JAMA Ophthalmol. 2014;132(11):1296-1302. doi:10.1001/jamaophthalmol.2014.2326 Published online July 31, 2014. 1296
Corresponding Author: Joseph Caprioli, MD, Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, 100 Stein Plaza, Los Angeles, CA 90095 ([email protected]). jamaophthalmology.com
Copyright 2014 American Medical Association. All rights reserved.
Downloaded From: http://archopht.jamanetwork.com/ by a University of California - San Diego User on 06/01/2015
Cataract Extraction and Visual Field Decay Rate
C
ataract and glaucoma frequently coexist because the prevalences of cataract and open-angle glaucoma increase with aging.1,2 Trabeculectomy augments the risk of cataract formation by 78% in patients with glaucoma.3 Other treatments for glaucoma, including laser trabeculoplasty and medications, seem to increase this risk as well.4 Simulated cataract, minimally affecting visual acuity, can depress visual field sensitivities.5,6 The development of cataract causes diffuse visual field loss in patients with glaucoma, and differentiating perimetric deterioration caused by cataract from that caused by glaucoma worsening remains challenging.7 The visual field mean deviation (MD) and visual acuity improve significantly after cataract extraction,7-13 although some studies14,15 reported no significant changes in the MD. Similarly, changes in the pattern SD (PSD) and the Visual Field Index (VFI) have not been found to be significant after cataract extraction in some studies,8,11,13,14,16 whereas other studies9,10,12,17,18 have shown that the PSD worsened and the VFI improved after cataract extraction in patients with coexisting glaucoma and cataract. For example, the development or the worsening of cataract confounded the results of the Collaborative Normal-Tension Glaucoma Study.19 The favorable effect of intraocular pressure (IOP) reduction on visual field progression in patients with normal-tension glaucoma was detected only when the effect of cataract on the visual field results was removed.19 The measurement of the visual field decay rate is an important step to appropriate decision making to preserve vision in patients with glaucoma.20 While numerous studies have focused on the short-term effects of cataract extraction on visual acuity or the visual field parameters, little is known about the association between cataract extraction and decay rates in localized areas of the visual field. Our group developed a technique based on trend analysis that uses a pointwise exponential model to fit the behavior of individual test locations in a visual field series.21 This method separates slow and fast rate components of visual field decay, while preserving spatial information across a wide range of disease severity.21,22 The objective of this study was to evaluate the effect of cataract extraction on the slow and fast components of visual field decay as determined with a pointwise exponential regression model.
Methods Participants This study was conducted in accord with the tenets set forth in the Declaration of Helsinki and was approved by the UCLA Institutional Review Board. The institutional review board approved that informed consent from patients was waived because this is a retrospective study. A retrospective review of medical records of patients with open-angle glaucoma who underwent cataract surgery with intraocular lens implantation at the Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, between July 1, 2000, and June 30, 2010, was performed. Patients who underwent combined cataract and trabeculectomy surgery were excluded, as were any patients who jamaophthalmology.com
Original Investigation Research
underwent glaucoma surgery during the period of interest. All cataract surgery was performed by one of us (J.C.) with a temporal clear cornea, small-incision phacoemulsification technique using peribulbar anesthesia. The patients received a silicone foldable intraocular lens (STAAR Surgical) or an acrylic foldable intraocular lens (Alcon Laboratories Inc) implanted in the capsular bag.
Perimetric Tests All consecutive patients with open-angle glaucoma who had 5 or more reliable visual field measurements before and after surgery were included in the study. Reliability was defined as less than 30% fixation losses, less than 30% false-positive rates, and less than 30% false-negative rates. All visual field tests were performed using an automated visual field analyzer (Humphrey Field Analyzer; Carl Zeiss Ophthalmic Systems Inc) with a 24-2 test pattern, size III white stimulus with the Swedish Interactive Threshold Algorithm standard strategy. The last visual field before surgery and the first visual field after surgery were required to have been measured within 1 year of cataract surgery. The technique of measuring rates of visual field decay has been published in detail21,22 and is summarized herein. Rates of visual field decay were calculated by a pointwise exponential regression analysis of threshold sensitivities at 52 test locations, excluding the 2 locations corresponding to the blind spot. The association between the response variable (threshold sensitivity) and the explanatory variable (follow-up duration) was characterized by the following exponential regression models: y = ea + bx or, equivalently, ln y = a + bx, where a is the intercept, x is time, b is the mean annual rate of change in ln y, and eb represents the ratio of y in a given year to y in the year before. The decay rate is defined as 1 − eb. To facilitate an intuitive clinical understanding of the magnitude of decay rates, the coefficients of the exponential regressions were converted into percentage per year deterioration rates, where the percentage per year decay rate is (1 − eb) × 100. The 52 visual field test locations were ranked according to the decay rate and were clustered into 2 subgroups (slow and fast components) based on the P value for the difference in the mean rates between 2 clusters. For each possible partition, starting with a minimum number of 5 locations in a cluster, we computed a t test statistic, and the corresponding P values were adjusted for multiple testing. Because multiple simultaneous t tests were performed, it is desirable to correct the P values to control for false-positive results. Accordingly, BenjaminiHochberg correction was used to adjust the P values for multiple testing.23 For each eye, the mean slow and fast decay rates were calculated for the partitioned components during the preoperative and postoperative periods separately. The MD and VFI values for the preoperative and postoperative periods were also analyzed; univariate linear regression analyses of these values were performed against time, and corresponding regression slopes (in decibels per year and in percentages per year) were compared before and after cataract extraction. The MD, PSD, and VFI values of the last visual field measurement before surgery and the first visual field measurement after surgery were also compared. JAMA Ophthalmology November 2014 Volume 132, Number 11
Copyright 2014 American Medical Association. All rights reserved.
Downloaded From: http://archopht.jamanetwork.com/ by a University of California - San Diego User on 06/01/2015
1297
Research Original Investigation
Cataract Extraction and Visual Field Decay Rate
Table 1. Demographic and Clinical Characteristics Among 85 Eyes of 68 Patients With Open-Angle Glaucoma Who Underwent Cataract Surgery During the Follow-up Period Characteristic
Value
Age, mean (SD), y
70.2 (8.8)
Sex, No. Male
28
Female
40
Statistical Analysis
Study eye, No. Right
39
Left
46
Follow-up period, mean (SD), y Before surgery
5.6 (2.5)
After surgery
6.0 (2.1)
No. of visual field measurements, mean (SD) Before surgery
10.2 (4.3)
After surgery
9.5 (3.8)
Race/ethnicity, No. White
48
African American
4
Asian
9
Hispanic
7
The preoperative best-corrected visual acuity was recorded from the visit just before the surgery. All eyes were refracted within 1 month after cataract extraction. Snellen visual acuities were converted to a scale of the logMAR for comparison. The mean IOP and the mean number of medications were compared during the preoperative and postoperative periods.
All statistical analyses were performed with available software (SPSS for Windows 21.0; SPSS Inc). The normality of numerical data distribution was checked with KolmogorovSmirnov test. Differences between the preoperative and postoperative data were compared with Wilcoxon signed rank test. Spearman rank correlation coefficient was used to estimate correlations between various outcomes (eg, the preoperative and postoperative visual field decay rates) and each of the following continuous variables: age, vertical cup-disc ratio (VCDR), MD, PSD, VFI, mean IOP, and mean number of glaucoma medications. Multivariable linear regression analysis with a stepwise variable selection method was used to identify significant parameters that may explain the visual field decay rates in the slow and fast components.
Comorbidity, No. Hypertension
19
Diabetes mellitus
Results
7
MD, mean (SD), dB Baseline
−4.6 (4.5)
Final
−6.5 (5.5)
PSD, mean (SD), dB Baseline
5.5 (4.1)
Final
6.7 (4.1)
VFI, mean (SD), % Baseline
89.4 (11.7)
Final
82.4 (16.0)
Baseline vertical cup-disc ratio, mean (SD)
0.74 (0.11)
YAG laser posterior capsulotomy of eyes, No. (%)
28 (33)
Abbreviations: MD, mean deviation; PSD, pattern SD; VFI, Visual Field Index.
Eighty-five eyes of 68 patients with open-angle glaucoma who had cataract extraction were included in the study. The study eyes were followed up for a mean (SD) of 11.6 (2.9) years, and a mean (SD) of 19.7 (5.3) visual field measurements were available during the entire follow-up period. The demographic, clinical, and ocular characteristics of the study sample are summarized in Table 1. The mean (SD) logMAR best-corrected visual acuity significantly improved from 0.33 (0.19) before surgery to 0.14 (0.11) (P < .001) after cataract extraction (Table 2). The mean (SD) IOP decreased from 13.4 (3.2) mm Hg to 12.4 (3.7) mm Hg after cataract extraction (P = .002). Similarly, the mean (SD) number of glaucoma medications was reduced from 1.5 (0.9) to 1.0 (0.9) after cataract extraction (P < .001).
Table 2. Changes in the Visual Acuity, Intraocular Pressure, Number of Glaucoma Medications, and Global Visual Field Parameters After Cataract Extraction Among 85 Eyes of 65 Patients With Open-Angle Glaucoma Mean (SD) Variable
P Value
Before Surgery
After Surgery
Difference
logMAR
0.33 (0.19)
0.14 (0.11)
−0.19 (0.19)
