Kahook dual blade goniotomy combined with phacoemulsification in eyes with primary open angle glaucoma and pseudoexfoliation glaucoma: comparative study

Abstract

Purpose

To compare outcomes of phacoemulsification combined with a Kahook Dual Blade (KDB) goniotomy in eyes with primary open angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXG).

Methods

This retrospective comparative study was conducted in a tertiary medical center. Sixty eyes of 60 patients (27 with POAG, 33 with PXG) underwent phacoemulsification combined with a KDB goniotomy. Intraocular pressure (IOP), number of medications used, best corrected visual acuity preoperatively and at 1 day, 1 week and 1, 3, 6 and12 months postoperatively, surgical success, and surgical complications were reviewed. If IOP reduction was >%30 or postoperative IOP < 18 mmHg, the procedure was considered as surgical success.

Results

The mean IOP reduced from 26.4 ± 5.9 mmHg at baseline to 17.9 ± 6.1mmHg at 12 months for POAG (p < 0.01) and from 27.1 ± 7.9 at baseline to 15.1 ± 2.3 mmHg at 12 months for PXG (p < 0.01). Medication use reduced from 3.4 ± 0.9 to 2.0 ± 1.3 for POAG (p < 0.01) and from 3.7 ± 0.5 to 1.8 ± 1.3 for PXG (p < 0.01) at 12 months. Mean IOP was significantly lower in PXG than POAG at week 1 and months 1, 3, 6 and 12 (all p < 0.05). Surgical success rate was 74% for POAG and 84% for PXG (p = 0.30) at 12 months. No vision-threatening complications occurred.

Conclusion

KDB goniotomy combined with cataract surgery was safe and effectively reduced the IOP and drug burden in patients with POAG and PXG. In the first year, significantly lower IOPs were noted in PXG compared with POAG.

Introduction

Minimally invasive glaucoma surgeries (MIGS) stand out in glaucoma surgery due to their safer surgical profile compared to traditional surgical procedures [1]. Angle surgeries generally aim to lower IOP by reducing the aqueous outflow resistance in the trabecular meshwork (TM) and Schlemm’s canal (SC). Today, minimally invasive ab interno approaches with safer and faster recovery times are increasingly used [2,3,4].

The Kahook Dual Blade (KDB, New World Medical, Rancho Cucamonga, CA, USA) is a novel goniotomy blade that was designed for a more complete removal of TM through a minimally invasive approach. In traditional goniotomy, the incision of the TM is made with a microvitreoretinal (MVR) blade, while the KDB excises the TM. KDB is designed to protect surrounding tissues and allows avoiding deeper incisions [2]. Histological analysis in human cadaver eyes revealed that KDB allowed removal of TM without damaging the sclera, resulting in a more significant reduction in IOP compared to conventional goniotomy [2]. One of the disadvantages of traditional goniotomy is the risk of recurrence in the long term. Compared to traditional goniotomy, the excision of TM with KDB may prevent obstruction of aqueous outflow, and therefore, it can improve outcomes in the long-term follow-up. In addition, less damage to the surrounding tissues may induce less inflammation [5]. The aforementioned characteristics of KDB can provide long-lasting IOP control; however, long-term studies are needed to confirm this argument.

Pseudoexfoliative glaucoma (PXG) is the most common cause of secondary open-angle glaucoma and has a more aggressive clinical course than primary open-angle glaucoma (POAG) [6]. As such, patients with PXG usually require more frequent surgical intervention for IOP control [7]. The surgical outcomes of the KDB procedure have been previously reported by several studies [8,9,10,11,12]. However, long-term outcomes of cataract surgery, which is often combined with KDB, are needed. There are limited studies comparing the surgical outcomes of combined KDB and cataract surgery in eyes with POAG versus eyes with PXG [13,14,15]. The aim of our study was to evaluate the relatively long-term surgical outcomes of the KDB procedure and phacoemulsification and to compare the surgical outcomes of this combined approach between eyes with POAG or PXG.

Materials and methods

In this retrospective comparative study, patients undergoing cataract surgery combined with KDB goniotomy for POAG or PXG at Gülhane Medical School, Department of Ophthalmology between 2019 and 2022 were evaluated. The study adhered to the ethical principles of the Declaration of Helsinki, and approval was obtained from the local ethics committee. All patients gave written informed consent for surgery after a detailed description of the study procedures. The patients with uncontrolled IOP and glaucoma progression despite maximum medical therapy, or those with intolerance to glaucoma medications underwent surgical intervention.

The patients were diagnosed with glaucoma through clinical examination, computerized visual field test, and optic coherence tomography of the optic nerve head and followed. All patients underwent a preoperative gonioscopy examination, which clearly revealed the angle structures and proved the presence of an open angle. To diagnose PXG, the presence of pseudoexfoliative material on the lens capsule, pupillary border, or angle was confirmed on biomicroscopic and gonioscopic examination. Exclusion criteria included patients with complicated cataract surgery (intraoperative posterior capsule damage and/or vitreous loss), mechanical complications of intraocular lens postoperatively, extensive peripheral anterior synechiae, neuro-ophthalmologic disease, uveitis, vascular disease, trauma history or corneal disease. None of the patients had a history of interventional surgery or laser trabeculoplasty.

Surgical procedure, postoperative protocol and data collection

A single surgeon (MTK) performed the surgeries. First, superior or temporal clear corneal incision of 2.4 mm was created to enter anterior chamber. Phacoemulsification and intracapsular lens implantation were performed. To bring the nasal angle into the surgeon’s focus, the patient’s head was rotated 30–45° away from the surgeon, while the microscope was tilted 30–45° towards the surgeon. Temporal corneal incision was created with a 20-G MVR blade. Intracameral carbachol (0.10 mg/mL) (Miostat, Alcon, Texas, USA) was used to induce myosis and intracameral trypan blue was used to increase visibility. The anterior chamber was maintained with a cohesive ophthalmic viscoelastic device (OVD). A direct surgical gonioprism (Swan-Jacob, Ocular Instruments, Inc.) was placed on the corneal surface. The KDB was inserted through the temporal corneal incision into the anterior chamber and directed to the nasal trabecular meshwork, then trabeculectomy was performed as targeted. Viscoelastic in the anterior chamber was removed by irrigation/aspiration. All corneal wounds were hydrated and checked for tightness.

Postoperatively, moxifloxacin hydrochloride 0.5% was prescribed for 10 days and prednisolone acetate 1% for 1 month. Patients continued to use anti-glaucomatous medications. When IOP decreased to targeted IOP at the related visit, glaucomatous medications stopped one by one. Patients were examined on the 1st day, 1st week, and 1st, 3rd, 6th and 12th months after surgery. Basic demographic characteristics such as age, gender, and primary diagnosis were recorded. During follow-up, patient data including glaucoma severity, best corrected visual acuity (BCVA), IOP values, number of glaucoma medications used, and postoperative complications were collected. The severity of glaucoma as assessed by the mean deviation (MD) score on Humphrey visual field test (MD ≥ − 6.0 dB, mild; −6.0 > MD ≥ -12.0 dB, moderate and MD < -12.0 dB, severe) was noted.

Outcome measures

Data included demographics, preoperative glaucoma status, IOP, the number of medications, visual acuity, and complication rates. The initial data were IOP and number of glaucoma medications. Secondary outcome measures were BCVA, surgical success, and complication rates. If IOP reduction was at least %30 compared to baseline IOP or postoperative IOP was lower than 18 mmHg, the surgical procedure was considered successful. IOP spike was defined as IOP > 21 mmHg after surgery.

Statistical analysis

The IBM SPSS Statistics for Windows, Version 25.0 (IBM Corp., Armonk, NY) was used for data analysis. For the descriptive statistics, discontinuous variables were presented as numbers and percentages (%) and continuous variables were reported as mean ± standard deviation. For comparison of POAG and PXG groups, normality of the data was checked with Kolmogorov-Smirnov test. Chi-square test was used for categorical values. Student’s t-test was used for continuous variables with a normal distribution. Mann-Whitney U-test was used for continuous variables that were not distributed normally. Paired-sample t-test was employed to compare preoperative and postoperative values within the groups. A p value of 0.05 or less was considered statistically significant.

Results

We analyzed data from 60 eyes of 60 patients who underwent KDB combined with cataract surgery. There were 27 (%45) eyes with POAG and 33 (%55) eyes with PXG. The mean age of the patients was 68.1 ± 9.4 years for POAG group and 69.4 ± 5.9 years for PXG (p = 0.55). Preoperative clinical characteristics were similar between groups as shown in Table 1.

Table 1 Preoperative clinical characteristics for POAG group and PXG group

The mean preoperative IOP was 26.4 ± 5.9 mmHg for POAG and 27.1 ± 7.9 mmHg for PXG (p = 0.89). The mean postoperative IOPs were significantly lower at all visits for both groups compared to baseline (p < 0.01). The PXG group showed significantly lower mean IOPs at week 1, months 1, 3, 6 and 12 compared to the POAG group (p < 0.05). Mean IOPs at 1 day postoperatively were similar (p = 0.62). The mean IOPs at 12 months postoperatively were 17.9 ± 6.1 mmHg for POAG and 15.1 ± 2.3 mmHg for PXG (p = 0.02). Table 2 summarizes preoperative and postoperative IOPs.

Table 2 Intraocular pressure values before and after Kahook dual blade goniotomy combined with phacoemulsification for POAG and PXG

The mean number of preoperative glaucoma medications was 3.4 ± 0.9 for POAG and 3.7 ± 0.5 PXG (p = 0.43). Postoperative medication use was significantly lower at all visits for both groups compared to baseline (p < 0.01) but did not differ between POAG and PXG groups (p > 0.05). The mean number of glaucoma medications at 12 months postoperatively was 2.0 ± 1.3 for POAG and 1.8 ± 1.3 for PXG (p = 0.61). Table 3 shows the number of medications used preoperatively and postoperatively.

Table 3 Number of Glaucoma medications used before and after Kahook dual blade goniotomy combined with phacoemulsification for POAG and PXG

The mean preoperative BCVA was 0.23 ± 0.23 for POAG and 0.25 ± 0.23 for PXG (p = 0.85). The mean postoperative BCVA measurements were significantly higher at 1 week and 1, 3, 6 and 12 months postoperatively (p < 0.01) versus baseline but were comparable between POAG and PXG groups (p > 0.05). The mean BCVA measurements at 12 months postoperatively were 0.58 ± 0.33 for POAG and 0.63 ± 0.29 for PXG (p = 0.66). Table 4 displays preoperative and postoperative visual acuities.

Table 4 Best corrected visual acuity before and after Kahook dual blade goniotomy combined with phacoemulsification for POAG and PXG

At 12 months postoperatively, the percentages of patients with a 30% reduction in IOP compared to baseline were similar (p = 0.39) between the groups ( 59% (n = 16) for POAG and 69% (n = 23) for PXG). Surgical success rates were 20 (74%) for POAG and 28 (84%) for PXG (p = 0.30) at 12 months. Trabeculectomy was required in two patients with severe POAG because IOP regulation could not be achieved after KDB.

IOP spike was observed in 10 (%37) patients in the POAG group and in 8 (%24) patients in the PXG group at 1 day postoperatively (p = 0.28). It was observed that the cause of the IOP spike in the first 24 h was generally residual viscoelastic material. All IOP spikes resolved within a week. Microhyphema occurred in all subjects intraoperatively. At week 1, significant hyphema persisted in 3 (11%) patients with POAG and 3 (9%) patients with PXG (p = 0.79), which resolved spontaneously within a month. Cyclodialysis cleft occurred in 2 (7%) patients with POAG and in 1 (3%) patients with PXG (p = 0.44), all of which were < 2 clock hours and clinically insignificant.

Discussion

We herein compared the surgical outcomes of cataract surgery combined with KDB goniotomy between the PXG and POAG groups. Our results showed that this procedure had a greater IOP-lowering effect in PXG than POAG at the end of the first year of follow-up. One of the reasons for this finding is that while the level of obstruction is mainly trabecular in PXG, more distal obstruction may be responsible in addition to TM dysfunction in POAG [1, 16]. Another explanation is that KDB goniotomy may provide an additional mechanical effect that clears exfoliative material from the areas where it accumulates mainly in the trabecular meshwork. The study showing IOP reduction in PXG with bimanual trabecular aspiration supports this argument [17].

Although there are studies reporting favorable results of KDB goniotomy surgery, data on the outcome of KDB goniotomy surgery in PXG eyes are insufficient. In a study by Greenwood et al. [8] in which they performed KDB and cataract surgery on 71 eyes, it was reported that this procedure successfully lowered IOP and reduced drug dependence at 6-month follow-up. They showed that the KDB procedure, when combined with cataract surgery, can achieve a significant IOP reduction of 4.6 mm Hg within 6 months after surgery. This represented a 26.4% reduction from baseline and a decrease of 20% or more in 58.3% of patients. Although 70% of the patients included in the study had POAG, specific results of PXG were not reported. In a study on 116 eyes, Wakil et al. [15] reported that KDB reduced IOP and the number of IOP-lowering medications at 12 and 18 months postoperatively. They reported that the mean decrease in IOP at 18 months was 13.1% in the group that underwent KDB combined with cataract surgery versus 31.4% in the group that underwent KDB alone. Comparing eyes with POAG or PXG, they noted a greater reduction in IOP from baseline in the PXG group, with a reduction in IOP-lowering drug use. Murakami-Kojima et al. [18] followed the effects of KDB trabeculotomy for six months in patients with POAG or PXG, including differences between KDB trabeculotomy alone and in combination with cataract surgery. In that study, IOP and the number of drugs used decreased in all four groups (PXG alone, combined with PXG, POAG alone and combined with POAG). The authors reported that the PXG-combined group achieved the lowest IOP between the PXG and POAG groups, and that KDB-phacoemulsification reduced the risk of postoperative IOP ≥ 20 mmHg. In a study evaluating the long-term surgical outcomes of combined KDB and cataract surgery, Iwasaki et al. [19] reported that there was no significant difference between the POAG and PXG groups in terms of the probability of success at 36 months after surgery. They found that IOP elevations and additional glaucoma surgery were significantly more common in the PXG group than in the POAG group. Iwasaki et al. [19] stated that discrepancies between the findings of their study and those of previous studies may be due to differences in sample size, patient characteristics (especially the severity of glaucoma), and the surgical procedures used (single or combined surgery). They noted that after KDB procedure combined with phacoemulsification, patients with PXG needed more glaucoma medication postoperatively than patients with POAG group. This result was explained by the greater number of severe glaucoma cases and the higher frequency of IOP elevations in the PXG group compared to the POAG group. Sieck et al. [20] reported that there was no difference between the POAG and PXG groups in terms of probability of success. They also found that the IOP lowering efficacy of KDB alone was similar to that of the phacoemulsification-KDB. In our study, IOP reduction was 69% and surgical success rate was 84% ​​for the PXG group at the end of 12 months. In the POAG group, IOP reduction was 59% and surgical success rate was 74%. So far, studies have reported differential outcomes of KDB alone or KDB combined with cataract surgery. In our study, there was no comparative group to reveal the effect of cataract surgery on the results.

Similar results were reported by studies with gonioscopy-assisted transluminal trabeculotomy (GATT) in PXG. Sharkawi et al. [21] performed GATT in 103 patients with PXG and followed the patients for 24 months. At the end of this period, they observed a 51% IOP reduction and 89% success rate. The authors suggested that GATT might yield more successful results in PXG. Aktas et al. [1] shared the long-term results of GATT surgery in 111 eyes with PXG. At the end of the second year, they reported the IOP reduction rate as 42% and the surgical success rate as 91%.

In our study, although postoperative medication use was significantly lower in both groups compared to baseline at all visits, there was no difference between the POAG and PXG groups. In the long-term, re-deposition of exfoliation material is predicted to reduce the IOP reduction and surgical success rates achieved in the early stages of surgery in PXG. Therefore, long-term follow-up of this patient population is important. Using GATT, Aktas et al. [1] showed that the advantage of IOP reduction in PXG versus POAG observed in the first year disappeared in the following years, with equal results found in the third year. This was attributed to the re-accumulation of exfoliation material over time. Although our study is consistent with the aforementioned report in terms of more successful first-year results in PXG, we do not have longer-term follow-up results.

The findings of our study are consistent with previous reports regarding the effectiveness of KDB goniotomy surgery. Another critical consideration is safety profile. Studies on safety of this procedure demonstrated that it is a safe method [18,19,20]. Hyphema and transient IOP elevations were reported as the most common complications. The use of steroids in the postoperative period is necessary to suppress inflammation and prevent the formation of peripheral anterior synechia. One study reported that topical corticosteroids increased the incidence of IOP elevations within 3 months after GATT [22]. Therefore, a less potent steroid should be used to shorten the steroid tapering period after surgery or to reduce the risk of postoperative IOP elevation. In our study, IOP increase at 1 day postoperatively was 37% for the POAG group and 24% for the PXG group. All IOP elevations resolved within one week. Hyphema was present in 11% of the eyes with POAG and 9% of the eyes with PXG at 1 week postoperatively but all resolved within one month without the need for surgical intervention. Clinically insignificant cyclodialysis also occurred in 2 eyes with POAG and 1 eye with PXG in our study. No devastating complication that threatened vision was observed.

The limitations of our study include its retrospective nature, limited sample size, lack of long-term follow-up, and the absence of a control group to evaluate the effect of cataract surgery on the outcomes. In addition, the severity of glaucoma and cataract will affect postoperative results. KDB goniotomy surgery in advanced glaucoma is still a controversial issue. However, some reports have been reported in the literature with a limited number of patients [23]. Severe glaucoma is often resistant to treatment. Differences in glaucoma severity may have affected surgical outcomes. In advanced cataracts, the postoperative inflammatory response may be excessive. Postoperative inflammation and peripheral anterior synechiae may affect surgical outcomes due to increased resistance to aqueous outflow. For this reason, there is a need for prospective studies in which patient characteristics are standardized before surgery, with wider participation, and to observe the dynamic changes that may occur in the long-term follow up. Complications of cataract surgery have not been reported. Exfoliative glaucoma is associated with an increased risk of zonular dialysis, capsular tears, and vitreous loss. Therefore, future studies on this subject should take this into account.

In conclusion, this study showed that KDB goniotomy as a combined procedure with cataract surgery safely and effectively reduces IOP and drug burden in patients with POAG and PXG. Although surgical success rate is higher in PXG at the end of the first year than in POAG, it would be useful to observe long-term changes. The contribution of our study to the literature is important in terms of KDB goniotomy results in eyes with PXG, which have a more aggressive clinical course. There are studies reported in the literature in this field with a limited number of patients. The results obtained in previous reports, including our study, need to be supported with larger samples. Studies to be conducted from different centers in this field will make the reported results more understandable and trustworthy. Additionally, studies evaluating comparative results with trabeculectomy will be an important step in demonstrating effectiveness.