Factors Associated with Long Term Outcomes and Transient Intraocular Pressure Elevation in Minimally Invasive Glaucoma Surgery Using Kahook Dual Blades

doi:10.21203/rs.3.rs-2328014/v1

In this retrospective case-control study, we aimed to investigate the mid- to long-term outcomes and factors involved in minimally invasive glaucoma surgery using the Kahook dual blade (KDB). Of the 229 cases in which KDB was introduced as the glaucoma surgery since 2018 at the Tenri Hospital, 133 eyes of 98 patients who could be followed for more than 3 months were included. Intraocular pressure (IOP), drop scores, and reoperation need were evaluated on day(s) 1, 3, 6, 9, 12, 24, and 36 months postoperatively. Significant differences in IOP and drop scores were observed between the preoperative and 12-month postoperative time points (P < 0.001). The amount of IOP change was related to preoperative and day 1 IOP. Moreover, the drop score changes were related to the preoperative drop scores and age. Multivariate analysis of Spike's incidence factors showed a significant association with axial length, preoperative drop scores, and day 1 IOP. These results suggest that KDB is effective in lowering IOP or decreasing the drop score. Special attention to postoperative spike occurrence may be recommended for patients with a long axial length, high drop scores, and high IOP on day 1.

Health sciences/Diseases

Health sciences/Medical research

Glaucoma is a leading cause of irreversible blindness and affects patients’ quality of life and quality of view [1, 2]. Sufficient lowering of intraocular pressure (IOP) is important in glaucoma to prevent optic nerve injuries [3, 4]. Methods to reduce IOP include eye drops, laser therapy, and surgery. Generally, incisional surgeries are performed when other treatments are ineffective. Among them, trabeculectomy and tube-shunt implantation can provide greater IOP reduction than that of other treatments [5]. However, these surgeries require a high degree of expertise and frequent postoperative follow-up, with a high risk of complications such as excessively low IOP and infection [6–8]. Trabeculotomy is a method of incising the trabecular meshwork (TM) and lowering the resistance [9–11]. Conventional trabeculotomy can be performed using an ab externo approach, which requires conjunctival and scleral incisions, and sutures. However, this approach is invasive.

Recently, a faster and more effective technique for treating moderate glaucoma known as minimally invasive glaucoma surgery (MIGS) has been developed [12–14]. MIGS has gained popularity because of its favorable safety profile, ability to be combined with cataract surgery, and the reduction or elimination of adjunctive glaucoma medications. MIGS is particularly effective in reducing the number of eye drops required in patients with poor eye drop adherence and adverse eye drop reactions.

The Kahook dual blade (KDB; New World Medical, Rancho Cucamonga, CA, USA) is an ab interno trabeculotomy surgery that enables the removal of the TM and inner walls of Schlemm’s canal using dual blades to decrease resistance to aqueous outflow [15–22]. Preclinical studies show that nearly complete removal of the TM without damaging the sclera can be achieved [16]. Numerous studies have shown that the KDB is effective in lowering IOP and reducing the number of eye drops required. Recently, good results have been reported for 3-year long-term outcomes [22]. To the best of our knowledge, only a few reports have examined factors related to the treatment effects and complications in KDB over a medium-to-long-term period with a large sample size.

Study design

Of the 229 cases that underwent this procedure since the introduction of the KDB at our hospital in 2018, we included 133 eyes of 98 patients aged ≥ 18 years with no history of endophthalmic surgery except cataract (procedures such as laser iridectomy were also excluded) and who could be followed for at least 3 months after surgery. Baseline variables included age, sex, visual acuity, preoperative IOP, preoperative eye drop scores, incision range, mean deviation or mean defect (MD) value of the visual field test, presence of errors in the visual field test for poor fixation, disease type, and ocular axis length. Best corrected visual acuity immediately before surgery was used for visual acuity, which was converted to the logarithm of the minimum angle of resolution (logMAR) visual acuity for statistical analysis.

Preoperative IOP is the average of the IOP measured twice with a Goldmann applanation tonometer using the same eye drops as before KDB. The drop score was defined as one point for one component and two points for a fixed-dose combination. Oral IOP-lowering medications were considered one component and scored as one point. The incision range was determined from surgical records and divided into three quadrants: range 1 for cases narrower than the first quadrant, range 2 for cases between the first and second quadrants, range 3 for cases between the second and third quadrants, and range 4 for cases wider than the third quadrant. For visual field testing, we defined cases in which the MD value of the Humphrey visual field test immediately before surgery was greater than − 6 dB as mild, less than − 6 dB or greater than − 12 dB as moderate, and less than − 12 dB as severe. The presence or absence of errors of poor fixation in the blind spot check method was confirmed using the Humphrey visual field tests. The ocular axis length was measured using an optical coherence ocular axis length measuring device (IOLmaster 500™; Carl Zeiss Meditec, Jena, Thuringia, Germany).

IOP and drop scores at 1 day, and 1, 3, 6, 9, 12, 24, and 36 months after surgery were recorded as postoperative measurement points. Postoperative complications were checked for transient elevation of IOP (spike). Spike was defined as an increase in IOP of 10 mmHg or more from baseline within the first postoperative month.

The primary endpoint was a comparison of IOP and drop scores at baseline and at 12 months. Secondary endpoints included incisional extent, grading using visual field testing, and comparison of various scores after categorizing patients according to preoperative IOP value (≤ 20 mmHg vs. > 20 mmHg). Survival analysis was also performed, with death defined as two consecutive IOP drops < 20% or additional glaucoma surgery. This study was approved by the institutional review board of the Tenri Hospital (approval no: 1312), which waived the requirement for informed consent owing to the retrospective nature of the study and use of anonymized data. All methods were carried out in accordance with relevant guidelines and regulations. The study design, target patients, details of data to be used, and principal investigators are posted on the hospital's official website. Patients who refused to participate in the study were removed from the data set. The study adhered to the tenets of the Helshinki Declaration.

Surgical techniques

The patient was anesthetized using ophthalmic anesthesia with 4% xylocaine, incisions were made with the MVR knife at 10 o'clock and 2 o'clock positions, and space was secured at the corner angle with purified sodium hyaluronate/sodium chondroitin sulfate (Viscoat™ 0.5; Alcon Japan Ltd, Toranomon, Minato-ku, Tokyo). The patient's head was tilted, and the corner angle was checked using a corner angle speculum; the KDB was inserted into the TM, and the nasal, inferior, and auricular fibroblasts were removed. After confirming blood reflux, the anterior chamber was rinsed, and the wound was closed with intraocular fluid before the surgery was completed.

All postoperative patients were treated with 1.5% levofloxacin and 0.1% betamethasone valerate + gentamicin sulfate eye drops during hospitalization. After discharge from the hospital, 0.1% betamethasone valerate + gentamicin sulfate was changed to 0.1% fluorometholone and continued for approximately 1 month. Bromfenac sodium hydrate was also used for patients undergoing cataract surgery at the same time.

Statistical analysis

The Wilcoxon signed-rank sum test was performed to analyze each examination point preoperatively. Linear regression analysis was performed to analyze the factors involved in the change in IOP and drop score between preoperative and 12-month postoperative time points. Kaplan–Meier curves were drawn for the survival analysis. For grading by incisional extent and visual field testing, both IOP and ophthalmic score at 12 months were compared between the groups using the Kruskal–Wallis test. The survival rates were compared using the log-rank test for range 1 and 4 incisions. The Mann–Whitney U test was performed for each variable for the incidence of spike, and logistic regression analysis was performed for variables that were significantly different. Last observation carried forward was used to complete the missing values. The P-values were two-tailed, and the significance level was set at 5%.

Patient background

Ultimately, 133 eyes of 98 patients were available for analysis: 74 eyes of 56 male patients and 59 eyes of 32 female patients. The mean age of the patients was 73.4 ± 8.18 years, visual acuity was 0.198 ± 0.267 in logMAR, preoperative IOP was 19.2 ± 5.16 mmHg, preoperative drop scores were 2.85 ± 1.5, and MD was − 11.05 ± 7.74. Twenty-five patients had poor fixation (Table 1). In addition, 116 patients underwent simultaneous cataract surgeries and 17 underwent KDB procedures alone. The disease types included: 95 primarily open-angle glaucoma, 14 normal-tension glaucoma, 12 pseudoexfoliation glaucoma, 10 ocular hypertension, and 2 steroidal glaucoma.

Table 1

Baseline characteristics
	Total	IOP ≦ 20 mmHg	IOP༞20 mmHg
Number of eyes	133	89	44
Age (y), mean (SE)	73.4 ± 7.96	73.5 ± 7.02	73.2 ± 9.74
Sex, n(%)
Male	74(56)	49(55)	25(57)
Female	59(44)	40(45)	19(43)
IOP (mmHg), mean (SE)	19.2 ± 5.16	16.3 ± 2.64	25.0 ± 4.07
Drop score, n, mean (SE)	2.85 ± 1.5	2.75 ± 1.47	3.05 ± 1.54
BCVA (logMAR), mean (SE)	0.198 ± 0.267	0.189 ± 0.249	0.215 ± 0.304
MD (dB), mean (SE)	-11.05 ± 7.74	-11.3 ± 7.78	-10.6 ± 7.55
Poor-fixation, n	25	12	13
Axial length (mm), mean (SE)	24.8 ± 1.84	24.8 ± 1.81	24.6 ± 1.94

BCVA, best corrected visual acuity; dB, decibel; IOP, intra ocular pressure; logMAR, logarithm of the minimum angle of resolution; MD, mean deviation; mmHg, millimeters of mercury; SE, standard error.

Intraocular pressure and drop scores preoperatively and at 12 months postoperatively

A significant difference was observed between the preoperative and 12-month postoperative IOP values (P < 0.001) (Table 2). The degree of IOP change was related to preoperative and day 1 IOP (P < 0.001 and P = 0.01, respectively), and a significant difference in eye drop scores was observed between the preoperative period and 12 months postoperatively (P < 0.001). Linear regression analysis showed significant associations between age and preoperative eye drop score (P = 0.01, P < 0.001, respectively) (Table 3). The survival rate was 27.8% at 12 months (Fig. 1).

Table 2

Result of IOP and drop scores at each measurement point compared with baseline
	Baseline	Day 1	Month 1	Month 3	Month 6	Month 9	Month 12
Number of eyes	133	133	133	133	120	96	86
IOP (mmHg), mean (SE)	19.2 ± 5.16	17.0 ± 7.46	16.6 ± 4.56	15.7 ± 3.4	15.4 ± 2.78	15.5 ± 2.51	15.4 ± 3.22
P-value (IOP mean change from baseline)	-	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001
Drop score, mean (SE)	2.85 ± 1.5	-	1.19 ± 1.4	1.67 ± 1.48	1.86 ± 1.59	1.91 ± 1.62	2.14 ± 1.74
P-value (drop score change from baseline)	-	-	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001
IOP, intra ocular pressure; SE, standard error

Table 3

Univariate linear regression analysis for the amount of change in IOP and drop score
Amount of change	IOP		Drop score
Amount of change	Coefficient (95% CI)	P-value	Coefficient (95% CI)	P-value
Age	-0.06 (-0.17–0.07)	0.38	-0.06 (-0.1-0.002)	0.01
Sex	-1.87 (-3.80–0.05)	0.06	-0.62 (-1.27–0.03)	0.06
With cataract surgery	0.7 (-2.62–4.04)	0.68	-1.1 (-2.18–0.03)	0.06
BCVA (logMAR)	-2.67 (-6.28–0.94)	0.14	-0.27 (-1.45–0.91)	0.65
MD classification	-0.96 (-2.15–0.23)	0.11	-0.04 (-0.45–0.36)	0.83
With poor fixation	0.25 (-2.34 − 2.83)	0.85	-0.62 (-1.52–0.27)	0.17
Incision range classification	-0.26 (-0.62–1.14)	0.56	0.03 (-0.33–0.27)	0.86
Day 1 IOP (mmHg)	-0.16 (-0.29–0.004)	0.01	-0.02 (-0.02–0.07)	0.26
Baseline IOP (mmHg)	-0.73 (-0.87–-0.59)	< 0.001	0.06 (-0.01–0.12)	0.1
Baseline drop score	-0.1 (-0.78–0.59)	0.78	-0.33 (-0.55–0.11)	< 0.001
Axial length (mm)	-0.11 (-0.43–0.65)	0.68	0.08 (-0.1–0.26)	0.39
Spike	-1.3 (-3.54–0.94)	0.25	0.18 (-0.67–1.13)	0.67

BCVA, best corrected visual acuity; CI, confidence, interval; IOP, intra ocular pressure; logMAR, logarithm of the minimum angle of resolution; MD, mean deviation.

Intraocular pressure and drop score categorization

IOP and drop scores were categorized into cases with preoperative IOP < 20 mmHg and those with IOP > 20 mmHg. In patients with preoperative IOP > 20 mmHg, a significant difference was observed between the preoperative and 12-month postoperative IOP values (P < 0.001, median − 6.5) (Fig. 2) and in drop scores (P < 0.001, median − 1) (Fig. 2). Survival analysis revealed a high survival rate of 54% at 12 months (Fig. 1). Moreover, a significant difference in IOP was observed between the preoperative period and 12 months postoperatively (P < 0.001, median − 1.3) (Fig. 2), even in patients with IOP < 20 mmHg. The eye drop scores were also significantly different (P < 0.001, median − 1.3) (Fig. 2).

〇 indicates cases where the preoperative IOP is < 20 mmHg; △ indicates cases where the preoperative IOP is > 20 mmHg. Error bar shows the standard deviation.

Comparison of intraocular pressure and drop scores among groups classified by the extent of incision

No significant difference was observed in IOP at 12 months postoperatively among the four groups classified by incision range (range 1: 60–100 °, range 2: 100–120 °, range 3: 120–130 °, range 4: 130–260 °) (P = 0.36). The same was true for eye drop scores, with no significant difference observed among the four groups (P = 0.285). No significant difference was found in the survival analysis between the groups of range 1 and range 4 (P = 0.44).

Comparison of intraocular pressure and drop scores among groups classified by preoperative mean deviation

No significant difference was found in survival rates among the three groups classified by preoperative MD (MD > − 6.0 dB, mild; − 6.0 > MD > − 12.0 dB, moderate; and MD < − 12 dB, severe) (P = 0.079). No significant difference was observed in eye drop scores and IOP at 12 months postoperatively (P = 0.8, 0.09; respectively).

Factors contributing to the occurrence of spik e

Univariate analysis of the incidence of spike showed significant differences in the preoperative drop scores, axial length, and postoperative day 1 IOP (P = 0.035, 0.002, 0.02; respectively) (Table 4). Logistic regression analysis similarly found significant associations among these three variables, with an odds ratio of 1.12 (95% confidence interval [CI], 1.05–1.19; P < 0.001) for postoperative day 1 IOP, 1.45 (95% CI, 1.02–2.06; P < 0.04) for preoperative drop scores, and 1.41 (95% CI, 1.06–1.88; P = 0.02 ocular axis length).

Table 4

Comparing baseline with presence and absence
With or without spike	Present	Absent	P-value
Number of eyes	25	108
Sex, n (%)
Male	17 (68)	57 (53)	0.19
Female	8 (32)	51 (47)
Age (y), mean (SE)	70.4 ± 10	74.1 ± 7.33	0.1
Baseline IOP (mmHg), mean (SE)	19.5 ± 4.93	19.1 ± 5.23	0.63
Day 1 IOP (mmHg), mean (SE)	22.1 ± 11.7	15.7 ± 5.4	0.035
Baseline drop score (n), mean (SE)	3.68 ± 1.44	2.66 ± 1.45	0.002
With cataract surgery, n (%)	23 (92)	92 (85)	0.62
Axial length (mm), mean (SE)	25.6 ± 2.23	24.5 ± 1.68	0.02
BCVA (logMAR), mean (SE)	0.23 ± 0.36	0.19 ± 0.24	0.83
Incision range classification			0.31
Range 1	7	25
Range 2	8	22
Range 3	4	30
Range 4	4	40

BCVA, best corrected visual acuity; IOP, intra ocular pressure; logMAR, logarithm of the minimum angle of resolution; SE, standard error. The incision area was classified by quadrant range

In this study, the KDB significantly improved IOP and drop scores, regardless of whether the preoperative IOP was high or low. In particular, a 54% survival rate was observed at 1 year in patients with high preoperative IOP. These results suggest that the KDB may have a relatively high IOP-lowering effect in patients with preoperative IOP > 20 mmHg, as previously reported [21]. Even in patients with preoperative IOP < 20 mmHg, there was a significant difference in IOP compared with the preoperative IOP. In comparison with the preoperative eye drop score, the median drop score was − 1, indicating a reduction of > 1 drop in many cases. Even when the IOP is relatively low, aggressive indications may be considered when the goal is to decrease the ophthalmic score. Linear regression analysis of the IOP change between the preoperative period and 12 months postoperatively revealed a significant association between the preoperative and postoperative day 1 in the amount of IOP change. Patients with high preoperative IOP and patients with high IOP on the first postoperative day may possibly have a certain degree of IOP reduction at 12 months postoperatively. Linear regression analysis of the change in drop score between preoperative and 12 months postoperative showed significant involvement of age and preoperative drop score. As the regression coefficient estimates were negative, patients may have been older and more surgeries may have been performed to reduce the number of eye drops in response to poor eye drop compliance and other factors. Additionally, the postoperative eye drop score may be higher in patients with high preoperative eye drop scores. However, no significant relationship was identified between the preoperative IOP and drop scores (P = 0.1).

The incision range was grouped by quartile range and analyzed; however, no significant difference was found in the IOP and drop scores in each group In a previous report using optical coherence tomography with Tabectome™, no significant relationship was found between the incisional area and IOP reduction [23]. This is due to the fact that aqueous humor flows through the TM, SC, and collector channels and then flows into the episcleral vein [11]. Although the TM and SC are located around nearly the entire angle of the corneal perimeter, there are only a limited number of collector channels, and even if the outflow resistance of the TM is reduced, the collector channels may become a bottleneck, limiting the degree of IOP reduction. Therefore, even if the TM outflow resistance is lowered, the drop in IOP is limited. Therefore, theoretically, a significant difference in IOP reduction may occur between a very small area and a 360° TM incision. In fact, many reports on 360° TM incisions have been conducted, some with favorable results from the viewpoint of complications [24, 25]. In contrast, a report comparing the results of suture LOT 360° incision with those of a KDB found no significant difference in IOP reduction [26]. Based on these results, the KDB may not necessarily require extremely large incisions although may be an option for extensive incisions only in cases where reoperation is difficult due to age or background.

The analysis classified according to preoperative MD values showed favorable results regardless of the degree of glaucoma progression, which is consistent with previous reports [20]. Outflow-tract surgery may also be indicated in cases of severe visual field defects. Another report that found no significant difference between cataract surgery alone, and combined KDB and cataract surgery in glaucoma patients with moderate-to-mild visual field impairment and good IOP control [17]. In cases with good IOP control, cataract surgery alone may be acceptable, except in cases where there is a strong objective to reduce the use of drops, whereas in cases with poor IOP control, the use of the KDB may be recommended even in cases of moderate-to-severe visual field impairment. However, a spike may occur at a certain rate, and the spike risk should be fully explained.

A significant association was found between the preoperative drop scores, postoperative day 1 IOP, and axial length regarding the occurrence of spike. The results for postoperative day 1 IOP were similar to those previously reported [27]. In patients whose condition is controlled using multiple medications preoperatively, eye drops are expected to strongly suppress aqueous humor production and promote outflow. Generally, eye drops are discontinued postoperatively. The timing of spike occurrence varies from case to case; however, it is thought that spike occurs when the timing of recovery of the individual's own aqueous humor postoperatively coincides with a decrease in aqueous humor outflow for some reason that has increased after surgery. Notably, most of the patients who had spikes were able to reduce their IOP with medication within 1–3 months, and only a few patients required reoperation owing to persistently high IOP caused by spikes. For patients with high preoperative IOP scores, frequent observation during the first month after surgery is recommended. Previously, the length of the ocular axis is also reportedly involved in the occurrence of spikes after cataract surgery [28]. Another report suggested that high myopia may lead to prolonged inflammation in the anterior chamber [29], the outflow resistance of the collector channel in the sclera may be increased due to the irregular shape of the eye [30], and that the depth of the anterior chamber may be deep enough to leave behind the viscoelastic material used during the surgery. Although an increase in IOP is often observed on postoperative day 1 in cases where viscoelastic material is left behind, multivariate analysis of the occurrence of spikes in our study showed no collinearity between ocular axis length and postoperative day 1 IOP; both variables were significantly different on multivariate analysis (P = 0.02, P < 0.001; respectively). Further studies on the effects of anterior chamber inflammation and ocular shape are warranted.

The limitations of this study include the fact that it was a single-center study; therefore, future studies should be conducted with a larger number of patients. Missing values were supplemented by last observation carried forward. The incision range was treated as an ordinal variable using the interquartile range rather than a continuous variable because it is a subjective finding of the surgeon based on the surgical record and may lack reliability. Therefore, quantitative evaluation of the incision range is insufficient.

KDB may be effective in improving IOP and drop scores regardless of preoperative IOP, and the extent of TM incision may have little effect on the postoperative course. Preoperative IOP and drop scores, IOP length, and postoperative day 1 IOP are suggested to be involved in the risk of spike occurrence.

Acknowledgements

We would like to thank Hitoshi. Obayashi. for their guidance with the statistical analysis. We would like to thank Editage (www.editage.com) for English language editing.

Author contributions

TS and HN have designed the study. TS aquired and analyzed the data. TS wrote the manuscript. HN revised the manuscript. All authors read and approved the final version of the manuscript.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing interests.

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No competing interests reported.

Factors Associated with Long Term Outcomes and Transient Intraocular Pressure Elevation in Minimally Invasive Glaucoma Surgery Using Kahook Dual Blades

Status:

Journal Publication

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Abstract

Figures

Introduction

Methods

Study design

Surgical techniques

Statistical analysis

Result

Patient background

Intraocular pressure and drop scores preoperatively and at 12 months postoperatively

Comparison of intraocular pressure and drop scores among groups classified by the extent of incision

Comparison of intraocular pressure and drop scores among groups classified by preoperative mean deviation

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1