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Long-term Intraocular Pressure Fluctuation and Progressive Visual Field Deterioration in Patients With Glaucoma and Low Intraocular Pressures After a Triple Procedure
Samin Hong, MD;
Gong Je Seong, MD, PhD;
Young Jae Hong, MD, PhD
Arch Ophthalmol. 2007;125(8):1010-1013.
ABSTRACT
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Objective To evaluate the association of long-term intraocular pressure (IOP) fluctuation and visual field (VF) progression in patients with glaucoma and low IOP.
Methods Four hundred eight eyes with IOPs below 18 mm Hg after a triple procedure (phacoemulsification, posterior chamber intraocular lens implantation, and trabeculectomy) were included in this study. Measurements of IOP and VF were taken for at least 3 years after surgery. Based on the SD in postoperative IOPs, the sample was split into 2 groups (group 1: SD  2; group 2: SD >2). Change in VF at each test location was defined as a change in threshold sensitivity of 1 dB per year or higher, with P.01; pointwise linear regression analysis was applied.
Main Outcome Measures Intraocular pressure and VF progression.
Results The groups showed no differences in IOPs through the follow-up period and in the VF defect score 3 months after surgery. After 13 years, more patients with progressive VF deterioration were detected in group 2 than in group 1.
Conclusion Our results showed that larger long-term IOP fluctuation was associated with a progressive increase in the VF deterioration even though patients with glaucoma maintained their IOPs after the triple procedure.
Application to Clinical Practice The SD of long-term IOP should be less than 2 in patients with glaucoma, even if their IOPs drop below 18 mm Hg.
Trial Registration clinicaltrials.gov Identifier: NCT00428740
INTRODUCTION
Prevention of further visual field (VF) deterioration is a goal of glaucoma therapy. Previous studies reported that lowering intraocular pressure (IOP) slowed the advancement of VF damage in patients with glaucoma.1-9 However, even if the IOP can be substantially lowered, reduction of mean and peak IOP does not always prevent progressive VF deterioration.10-12
Several studies have reported that diurnal IOP variation is a risk factor for glaucoma.13-15 However, we believe that long-term IOP fluctuation may play a significant role in VF deterioration in patients with glaucoma and low IOPs.
Moreover, few reports appear in the literature regarding long-term IOP control and long-term progressive VF deterioration after a triple procedure (phacoemulsification, foldable posterior chamber intraocular lens implantation, and trabeculectomy).16-17
The aim of this study was to evaluate the association of long-term IOP fluctuation and progressive VF deterioration in patients with glaucoma and low IOPs after a triple procedure.
METHODS
SUBJECTS
The patients who underwent triple procedure for primary open-angle glaucoma (POAG) or chronic primary angle-closure glaucoma (CPACG) at Severance Hospital, Yonsei University College of Medicine (Seoul, Korea), between January 1, 1990, and September 30, 2002, were retrospectively identified from a patient database. From the original patient sample, 408 eyes of 408 patients meeting the following criteria were selected for this study: (1) at least 3 years of follow-up; (2) IOP less than 18 mm Hg at each postoperative visit; (3) a minimum of 5 VF examinations; (4) a reference VF defect score of 16 or less; and (5) good reliability indices (fixation loss of <20%, false-positive and false-negative rate of <15%).
One eye of each patient was randomly selected for the study, even if both eyes satisfied the entry criteria. In addition, patients with any other significant ocular diseases or intraocular surgical histories, diseases that may affect VF, or diabetes mellitus were excluded.
SURGICAL PROCEDURE
All operations were performed by the same glaucoma specialist (Y.J.H.) with the patient under peribulbar anesthesia. In some cases, separate surgical sites were used for the phacoemulsification and trabeculectomy procedures, and in others a single site was used.
In cases in which separate surgical sites were used, a fornix- or limbus-based conjunctival flap was created, and a rectangular half-thickness scleral flap measuring 4 x 4 mm was made. A continuous-tear capsulorrhexis was created, which was followed by hydrodissection and hydrodelineation. Phacoemulsification was accomplished through a corneal incision at a site separate from where the trabeculectomy was performed. Following implantation of a foldable posterior chamber intraocular lens, a sponge soaked in mitomycin, 0.04%, was applied under the scleral flap and subconjunctival space for 1 to 4 minutes (in cases of mitomycin application). After rinsing with isotonic sodium chloride solution, a trabeculectomy and peripheral iridectomy were performed. The scleral flap was closed with two to five 10-0 nylon sutures. The tenon and conjunctiva were sutured to be watertight.
When a single surgery site was used, phacoemulsification was performed through a scleral tunnel beneath a fornix-based conjunctival flap, followed by a trabeculectomy in which the scleral tunnel was used to create the half-thickness scleral flap.
DATA COLLECTION AND ANALYSIS
Preoperative and postoperative data were collected retrospectively. Patient follow-up occurred on the first postoperative day, and then according to clinical needs thereafter. During these visits, best-corrected visual acuity (as determined using the standard Snellen chart), IOP (measured using the Goldmann applanation tonometer), anterior segment examination, and fundoscopic examination (including cup-disc ratio) were evaluated. Based on the SD value of the postoperative IOP, the sample was split into 2 groups (group 1: SD 2; group 2: SD >2).
Postoperative VF tests were conducted with a Humphrey field analyzer II (Carl Zeiss Meditec Inc, Dublin, California) using the 30-2 Swedish interactive threshold algorithm standard strategy 3 months after surgery, and every 6 months thereafter. Scores of VF defect ranged from 0 (no defect) to 20 (advanced loss).18 A statistical software package (SPSS version 13.0; SPSS Inc, Chicago, Illinois) was used to perform pointwise linear regression analysis. Our method for definition of change vs stability at each test location, the 2-omitting regression algorithm, is described in detail elsewhere.19-21 In summary, a point was considered to be progressing or improving during the follow-up period only if the regression slope was significant (as defined later) in the following regression analyses: (1) after omitting the last threshold in a series and (2) after censoring the threshold before last for the same series. Regression slopes were considered significant if they measured –1 dB per year or less (progression) or 1 dB per year or more (improvement), with P.01. The change in a VF series was defined when at least 2 test locations belonging to the same glaucoma hemifield test cluster showed a change in the same direction.20-21
The VF defect score 3 months after surgery and at last follow-up and the proportion of patients with progressive VF loss were compared between the 2 groups.
RESULTS
A total of 408 eyes of 408 patients with glaucoma (246 eyes with POAG and 162 eyes with CPACG) were included in this study. The mean ± SD postoperative follow-up period was 9.21 ± 3.64 years. Mean ± SD age at the time of surgery was 66.5 ± 10.3 years, and 126 patients (30.9%) were male. The mean ± SD best-corrected visual acuity was 0.67 ± 0.45 logMAR before surgery and 0.44 ± 0.55 logMAR at last follow-up. The mean ± SD numbers of postoperative topical antiglaucoma medications used were 1.35 ± 0.74 (group 1) and 1.40 ± 0.92 (group 2) in patients with POAG (P = .70), and 1.10 ± 0.77 (group 1) and 1.14 ± 0.84 (group 2) in patients with CPACG (P = .76).
Preoperative and postoperative IOPs are shown in Table 1. The preoperative and postoperative IOP through the follow-up period did not differ between group 1 and group 2. Patients with POAG and CPACG showed a similar tendency.
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Table 1. Intraocular Pressure in Patients Receiving the Triple Procedure a
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Table 2 shows the data on VFs at the 3-month postoperative follow-up and at last follow-up. In group 1, the VF defect score at both follow-up times showed no significant difference (P = .75 for POAG; P >.99 for CPACG). However, the VF defect score at last follow-up was significantly worse than that at the 3-month postoperative follow-up in group 2 (P<.001 for POAG and CPACG). The number of patients with progressive VF loss was significantly higher in group 2 (30.0% for POAG; 28.6% for CPACG) than in group 1 (9.7% for POAG; 10.0% for CPACG). A similar tendency was observed in patients with both types of glaucoma.
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Table 2. Progression in Visual Field Loss in Patients Undergoing the Triple Procedure According to Long-term Intraocular Pressure Fluctuation
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COMMENT
Long-term IOP fluctuation was significantly associated with the progression of glaucomatous VF loss, even in patients in whom IOPs were maintained at low levels after a triple procedure, an effective approach for patients with coexisting glaucoma and visually significant cataracts. This study included patients with POAG and CPACG whose IOPs were maintained below 18 mm Hg after a triple procedure. The patients were split into 2 groups based on the SD value of the postoperative IOP (group 1: SD 2; group 2: SD >2). The VF defect score was significantly worse in group 2 than in group 1. More patients in group 2 showed progression of VF loss during the postoperative follow-up period than in group 1. Similar tendencies were noted in patients with POAG and CPACG.
The Advanced Glaucoma Intervention Study trial presented the relationship between IOP and progression in VF loss.3 It included patients with POAG whose IOPs remained uncontrolled despite maximum-tolerated medical therapy. They performed an argon laser trabeculoplasty or trabeculectomy, with the goal of maintaining an IOP lower than 18 mm Hg. Progression of VF was the primary study outcome. They classified eyes by the percentage of IOPs measuring lower than 18 mm Hg during the first 6 years of the postoperative follow-up period. Those eyes in which the IOP was lower than 18 mm Hg at all study visits had minimal mean change in VF status for 6 to 8 years. However, the other groups had substantial mean VF losses throughout the follow-up period. These differences were considered statistically significant beyond the first 5 years of follow-up, and the effect was greater in the following years.
The Advanced Glaucoma Intervention Study trial showed that the patients with POAG whose IOPs were maintained below 18 mm Hg did not experience a progression of their VF damage. Despite that finding, however, some patients apparently continued to lose portions of their VF after filtering surgery, even at IOP that are always considered excellent (<18 mm Hg). In our study, group 1 patients, who had little long-term IOP fluctuation, had very little progression in VF loss during the 13 years after the triple procedure. Our results suggest that glaucomatous VF damage cannot be stabilized by only lowering the postoperative IOP but also requires reducing the long-term fluctuation of the postoperative IOP.
If the diurnal variation of IOP were considered a risk factor for glaucomatous VF loss,13-15 the long-term fluctuation of IOP may play a significant role in VF deterioration even in those patients with glaucoma who have always maintained low IOPs. However, our long-term retrospective study did not consider the diurnal variation.
In conclusion, our study suggests that reducing the long-term fluctuation of IOP after glaucoma surgery is effective in slowing or preventing VF loss in patients with glaucoma.
AUTHOR INFORMATION
Correspondence: Young Jae Hong, MD, PhD, Department of Ophthalmology, Severance Hospital, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-752 Korea (yjhong0815{at}yumc.yonsei.ac.kr).
Submitted for Publication: August 30, 2006; final revision received December 3, 2006; accepted January 8, 2007.
Financial Disclosure: None reported.
Author Affiliations: Institute of Vision Research, Department of Ophthalmology, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
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