Risk Factors for Hyphema Following Kahook Dual Blade Goniotomy Combined With Phacoemulsification : Journal of Glaucoma

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Advances in Glaucoma: Original Studies

Risk Factors for Hyphema Following Kahook Dual Blade Goniotomy Combined With Phacoemulsification

Pratte, Eli L. MD*,†; Ramachandran, Maya BA*; Landreneau, James R. MD; An, Jella A. MD§

Author Information
Journal of Glaucoma 32(3):p 165-170, March 2023. | DOI: 10.1097/IJG.0000000000002142
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There is growing evidence that the surgical treatment of glaucoma may more effectively lower intraocular pressure (IOP) and prevent nocturnal fluctuations that contribute to glaucomatous optic neuropathy.1–4 Well-described issues with adherence to IOP-lowering drops are also addressed with surgical management.5–7 However, despite being uncommon, complications following glaucoma surgery can occur. Blood reflux into the anterior chamber is a common intraoperative finding whenever surgically bypassing Schlemm’s canal and has not been shown to negatively influence postoperative outcomes.8,9 Red blood cells (RBCs) are often noted in the anterior chamber (ie, microhyphema) on initial postoperative slit lamp exams but typically self-resolve within the first 2 weeks without any necessary intervention.10,11

Hyphema is an accumulation and layering of RBCs in the anterior chamber.12 More often seen as a result of blunt ocular trauma, layered hyphema is also a complication of glaucoma surgery, including trabeculectomy,13–15 Ahmed Glaucoma Valve implantation,16 Xen gel stent,17 Kahook Dual Blade (KDB) goniotomy,18 canaloplasty,19 and trabeculotomy.20 As opposed to the typical RBCs noted on initial postoperative slit lamp exams, layering of RBCs in the anterior chamber can occlude outflow pathways created by angle surgeries and cause a secondary spike in intraocular pressure (IOP). Layered hyphema can, therefore, negatively impact postoperative success following glaucoma surgery.13,16 A better understanding of the factors that lead to the development of hyphema after angle surgery may aid in preventing the complication. Therefore, this study was designed to determine any significant risk factors that predicted the development of hyphema in patients after Kahook Dual Blade (New World Medical, Rancho Cucamonga, CA) excisional goniotomy combined with phacoemulsification (KDB-phaco).


Data Collection

A waiver of informed consent was granted by the IRB at the University of Missouri due to this study’s retrospective nature (IRB #2041326). Any procedure performed was done in agreement with the ethical standards of the institutional and/or national research committee and the 1964 Helsinki declaration and its subsequent amendments or similar ethical principles.

Consecutive patients who received a KDB-phaco between February 21, 2017 and February 18, 2020 with a postoperative follow-up at day 1 and week 1 were included in this study. All patients who had hyphema were also followed up at month 1. Patients who received concomitant procedures other than adjunct viscocanalostomy (n=108) were excluded. In all, 202 eyes in 145 patients satisfied the inclusion criteria and were included in this study. Preoperative baseline characteristics in all patients were collected and included age, ethnicity, glaucoma severity, glaucoma type, axial length, IOP, IOP-lowering medications, surgeon training level (resident vs. attending surgeon), prior glaucoma surgery, and use of anticoagulation therapy (ACT) or antiplatelet therapy (APT). No other systemic risk factors (eg, hypertension) were collected or analyzed. Any patients on ACT or APT were advised to continue their therapy before and after surgery. The most common APT used in our patient population was 81 milligrams of Aspirin daily. Indication for KDB-phaco in our patient population was visually significant cataract and persistently elevated IOP refractory to medication or the desire to reduce the IOP-lowering medication burden. The primary outcome collected was the development of a hyphema in the first postoperative week.

Hyphema in this study was defined as the development of layered blood in the anterior chamber ≥1 mm. Asymptomatic, non-layered red blood cells floating in aqueous humor, also known as “microhyphema,” were excluded. Hyphema and microhyphema were graded in accordance with the well-known classification adapted from Brandt et al.12 The success of KDB-phaco was defined at each postoperative time point as patients with an IOP reduction ≥20% or ≥1 medication reduction from their preoperative values as well as having an IOP ≤18 mm Hg at that time point. Patients requiring an IOP-lowering procedure at any time during the postoperative period were considered a failure.

Surgical Procedure

Excisional goniotomy was performed by either a glaucoma specialist or a senior ophthalmology resident (PGY-4) directly supervised by the attending physician. Topical anesthesia was utilized for analgesia with mild sedation for patient comfort. Goniotomy was performed through a 2.4 mm temporal incision in the cornea before cataract phacoemulsification. The iridocorneal angle was visualized with a Swan Jacob-style gonioprism, and ~4 clock hours of the nasal trabecular meshwork (TM) was excised with the KDB.21 Microforceps were used to remove the excised portion of the TM from the anterior chamber. After the excisional goniotomy, a cannula was held at the outer wall of Schlemm’s canal, and viscocanalostomy was performed by injecting cohesive viscoelastic into the collector channel entrances. Following completion of the angle procedure, standard phacoemulsification with intraocular lens implantation was performed. Viscoelastic was subsequently removed from the anterior chamber and replaced with a balanced salt solution to maintain immediate postoperative IOP in the mid-20s to minimize the amount of postoperative blood reflux. Intracameral Moxifloxacin was injected into the anterior chamber. Patients were advised to sleep with the head of their bed elevated and to avoid activities that cause straining for the first 2 postoperative weeks. Prednisolone acetate 1% was prescribed 4 times per day for a week following surgery to reduce intraocular inflammation and was gradually tapered over the first postoperative month. Preoperative IOP-lowering medications were continued or held depending on postoperative IOP at the surgeon’s discretion.

Data Analysis

Logistic regression was used to determine risk factors of hyphema (age, axial length, day 1 IOP ≤12 mm Hg, sex, glaucoma type and severity, preoperative anticoagulation status (none vs. use of any ACT/APT), and surgeon training level (resident vs. attending surgeon)). Fisher exact tests were used to analyze the relationship between the development of hyphema and success at each postoperative time point. All values were reported as mean±SD for data with normal distribution and percentage (n) for analyzed categorical variables unless otherwise stated.


Baseline Demographic and Glaucoma Data

Overall, 202 eyes in 145 patients satisfied the inclusion criteria and were included in this study. The average age of patients included was 68.8±8.7 years, with 58.9% of eyes belonging to females. Primary open angle glaucoma was the most treated type (60.4%), and mild glaucoma was the most commonly treated severity (47.5%). Demographic and glaucoma status are reported in Table 1.

TABLE 1 - Baseline Demographic and Glaucoma Status Data (n=202)
Age (y), mean±SD 68.8±8.7
Range (y) 43–90
Sex, n (%)
 Female 119 (58.9)
 Male 83 (41.1)
Ethnicity, n (%)
 White 155 (76.7)
 Black or African American 35 (17.3)
 Other 12 (6.0)
 Baseline IOP (mmHg), mean±SD 17.4±4.6
 Baseline medications, mean±SD 2.0±1.3
Glaucoma type, n (%)
 POAG + NTG 122 (60.4)
 PACG + Combined 60 (29.7)
 PXG 14 (6.9)
 PDG 3 (1.5)
 Traumatic 3 (1.5)
Glaucoma severity, n (%)
 Mild 96 (47.5)
 Moderate 23 (11.4)
 Severe 83 (41.1)
 Patients on ACT/APT 75 (37.1)
ACT indicates anticoagulation therapy; APT, antiplatelet therapy; IOP, intraocular pressure; KDB, Kahook dual blade; NTG, normal tension glaucoma; PACG, primary angle closure glaucoma; PDG, pigment dispersion glaucoma; POAG, primary open angle glaucoma; PXG, pseudoexfoliation glaucoma.

Risk Factors of Hyphema

Overall, 17/202 patients (8.4%) in our study developed a layered hyphema after KDB-phaco. No patient had more than 1 hyphema, and each occurred unilaterally. Eyes with a postoperative day 1 IOP ≤12 mm Hg were significantly more likely to develop a hyphema (13.7%) as compared with eyes with a postoperative day 1 IOP >12 mm Hg (5.4%) (P=0.049). Hyphema was significantly more likely to develop in male patients (14.5%) compared with female patients (4.5%) (P=0.008). Eyes with an angle closure component were significantly more likely to have postoperative hyphema (16.7%) compared with other glaucoma types (4.9%) (P=0.036). Eyes operated by resident surgeons were more likely to have postoperative hyphema compared with eyes operated by the attending surgeon, however, this difference was not significant when accounting for other variables, such as day 1 IOP, patient sex, and glaucoma type (P=0.172). Preoperative anticoagulation or antiplatelet use had no correlation with developing postoperative hyphema (P=0.538). Post-hoc analysis of the 17 patients with postoperative hyphemas did not reveal any diagnosed blood clots or bleeding disorders that could have contributed to this complication. No other factors studied in the patient cohort were predictive of hyphema development.

Each hyphema included in this study occurred on postoperative day 1 and all hyphema were resolved by 1 month postoperatively. One patient required paracentesis for an IOP spike, and 1 patient required AC washout at postoperative week 1. No other secondary surgical interventions were necessary due to complications of hyphema. All factors analyzed are included in Table 2. Graphical representation of analyzed categorical risk factors is included in Fig. 1.

TABLE 2 - Risk Factors of Hyphema After Kahook Dual Blade Excisional Goniotomy
Values P
Age (y), mean±SD 0.061
 Hyphema 69.1±8.9
 No hyphema 65.1±6.0
Race (cases with hyphema) 0.158
 White 15/155 (9.7)
 Black or Asian 2/47 (4.3)
Prior glaucoma surgery (cases with hyphema) 0.736
 No 12/135 (8.9)
 Yes (1 in 52 eyes, 2 in 15 eyes) 5/67 (7.5)
Axial Length (mm), mean±SD 0.340
 Hyphema 24.1±1.6
 No hyphema 24.4±1.9
Day 1 IOP (cases with hyphema), n (%) 0.049
 ≤12 mmHg 10/73 (13.7)
 >12 mmHg 7/129 (5.4)
Sex (cases with hyphema) 0.008
 Male 12/83 (14.5)
 Female 5/119 (4.2)
Glaucoma Severity (cases with hyphema) 0.605
 Mild & Moderate 10/119 (8.4)
 Severe 7/83 (8.4)
Glaucoma Type (cases with hyphema) 0.036
 ACG (1°, 2°, & combined) 10/60 (16.7)
 Other 7/142 (4.9)
Pre-op ACT/APT (cases with hyphema) 0.538
 Patient using 7/81 (8.6)
 Patient not using 10/121 (8.3)
Surgeon (cases with hyphema) 0.172
 Resident 9/62 (14.5)
 Attending 8/140 (5.7)
1°= primary.
2°= secondary.
ACG indicates angle closure glaucoma; anticoagulation therapy, ACT; antiplatelet therapy, APT; IOP, intraocular pressure; KDB, Kahook dual blade; mm, millimeters.

Risk factors of hyphema development after Kahook Dual Blade excisional goniotomy combined with phacoemulsification. IOP indicates intraocular pressure; ACG, angle closure glaucoma; ACT, anticoagulation therapy; APT, antiplatelet therapy. *, statistically significant difference, P<0.05.

Hyphema and Success

Patients with postoperative hyphema had the same likelihood of achieving the success criteria at each of the measured postoperative time points. Success was defined at each postoperative time point as an IOP reduction ≥20% or ≥1 medication reduction from preoperative values and IOP ≤18 mm Hg. Hyphema after KDB-phaco was not associated with an increased rate of failure at 1 week, 1 month, 3 months, 6 months, or 12 months postoperatively. Success rate graphed as a function of the presence or absence of postoperative hyphema is included in Fig. 2. Success rates at each postoperative time point for patients with and without post-KDB day 1 hyphema are included in Table 3.

Success of Kahook Dual Blade excisional goniotomy combined with phacoemulsification during the postoperative period compared with hyphema development.
TABLE 3 - Kahook Dual Blade Excisional Goniotomy Success in Patients With and Without Postoperative Day 1 Hyphema
Hyphema (n, %) No Hyphema (n, %) P
Week 1 7/17 (41.2) 73/178 (41.0) 1.0
Month 1 8/17 (47.1) 89/147 (60.5) 0.31
Month 3 10/14 (71.4) 103/145 (71.0) 1.0
Month 6 7/9 (77.8) 89/130 (68.5) 0.72
Month 12 8/12 (66.7) 64/105 (61.0) 0.77

Hyphema and ACT/APT

Hyphema development occurred irrespective of anticoagulation status in our study. In all, 9.3% (7/75) of patients on daily ACT or APT developed a postoperative hyphema, compared with 7.9% (10/127) of patients not on any blood-thinning therapy (P=0.538). Analysis of individual ACT/APT and its relation to hyphema development are included in Table 4.

TABLE 4 - Anticoagulation/Antiplatelet Therapy and Hyphema Development
ACT/APT Patients with Hyphema, n (%)
None 10/127 (7.9)
Aspirin 81 mg 6/60 (10.0)
Clopidogrel 2/5 (40.0)
Warfarin 1/6 (16.7)
Apixaban 0/6 (0.0)
Rivaroxaban 0/4 (0.0)


Kahook Dual Blade goniotomy is used as an interventional glaucoma surgery by removing the most common site of resistance to aqueous humor flow—the trabecular meshwork—while also more consistently limiting the diurnal IOP fluctuations that have shown to be a contributing factor to worsening complications of glaucoma.22,23 Clinically, the KDB excisional goniotomy has consistently proven efficacious with a limited complication profile.24,25 However, hyphema is a commonly reported complication of KDB excisional goniotomy and has been shown to negatively impact the success rates of related procedures, such as trabeculectomy.13 Further studies are needed to assess risk factors for hemorrhage and subsequent hyphema after other excisional procedures for patients with glaucoma, and no current study has assessed this for KDB goniotomy.

Blood reflux from Schlemm’s canal is a common intraoperative finding in angle-based surgery.26 Intraoperative visualization of episcleral venous blood reflux has been positively associated with success as it may represent an unobstructed outflow pathway.27,28 The authors believe that postoperative reflux hemorrhage is minimized by maintaining IOP in the mid-20s up to 2 weeks postoperatively and avoiding any activities that increase episcleral venous pressure (EVP), such as Valsalva maneuver or lowering the head below the level of the heart. In our study, patients with a postoperative day 1 IOP ≤12 mm Hg were significantly more likely to develop a layered hyphema. A review of human EVP performed by Sit et al29 reported an average EVP between 7.6 mm Hg and 11.4 mm Hg depending on the study. The average postoperative day 1 IOP of the 185 patients without hyphema was 15.8 mm Hg, while average postoperative day 1 IOP of the 17 patients with layered hyphema was 12.5 mm Hg. The relationship between the immediate postoperative IOP following phaco-KDB and EVP requires further investigation to determine new strategies to avoid layered hyphema.

Male sex was significantly associated with the development of layered hyphema after KDB-phaco in this study (P=0.008). There were 17 total postoperative layered hyphemas, 12 of which were found in male patients (70.6%). This trend is consistent with various studies on traumatic hyphemas, in which a male preponderance has consistently been reported.30,31 Interestingly, Iftikhar et al32 showed that traumatic hyphemas were significantly more likely in males (119/158, 78%), whereas spontaneous hyphemas secondary to neovascularization of the iris had no sex predominance (15/28, 54%). Male sex has also been associated with a higher rate of postoperative complications in orthopedic surgery that requires postsurgical activity limitation.33 Despite controlling for comorbidities, such as diabetes, male sex continues to be a risk factor for postoperative complications.33 This is consistent with psychosocial studies showing that men are more likely to engage in risky behaviors.34 This suggests that the sex differences in hyphema development in this study may be due to males being less likely to adhere to post-KDB-phaco activity limitations rather than any sex-associated physiological differences.

In addition, our study showed that having glaucoma with an angle closure component was a significant predictor of hyphema (P=0.036). In our patient population, 16.7% (10/60) of patients with angle closure glaucoma versus 4.9% (7/142) of patients with open angle glaucoma developed a postoperative hyphema. Of the patients with angle closure, 11.7% (7/60) had primary angle closure glaucoma, 10.0% (6/60) had secondary angle closure glaucoma, and 78.3% (47/60) had combined open angle glaucoma and phacomorphic angle closure secondary to lens rise. Goniosynechialysis was performed in 2 patients with primary angle closure glaucoma (28.6%), 2 patients with secondary angle closure glaucoma (33.3%), and 14 patients with combined-mechanism glaucoma (29.8%). In addition, 1/18 patients receiving concomitant goniosynechialysis with KDB-phaco developed postoperative hyphema (5.6%). In our study, resident surgeons were more likely to perform KDB on patients with angle closure (23/62, 37.1%) compared with the attending surgeon (37/140, 26.4%). In addition, there were 2 small iridodialyses induced in our study, each in resident-performed cases with an angle closure component (2/23, 8.7%). One iridodialysis resulted in a small grade 1 hyphema that had resolved spontaneously at the 1-week follow-up appointment, while the other did not result in a layered hyphema or have any further complications. Therefore, it is possible that the increased hyphema risk in patients with narrow iridocorneal angles is attributable to difficulty visualizing TM and surgeon inexperience. However, despite significantly higher rates of hyphema in the resident surgeon cohort compared with the attending surgeon group (14.5% vs. 5.7%, P=0.044), training level itself was not significantly correlated to hyphema development when controlling for other variables (P=0.172).

Whether to stop anticoagulation or antiplatelet therapy before incisional glaucoma surgery remains under investigation. Cobb et al35 retrospectively analyzed 367 consecutive trabeculectomies, which showed that continued preoperative aspirin use increased the risk of layered hyphema after trabeculectomy, but did not affect surgical outcome. However, Nakatake et al13 showed that layered hyphema was in fact, a significant risk factor for surgical failure of trabeculectomy in patients with neovascular glaucoma. Therefore, anticoagulation is often stopped before filtering surgery due to the risk of bleeding complications (eg, layered hyphema and suprachoroidal heme), but typically continued for XEN gel stent or tube procedures with lower risk of significant IOP fluctuations. Our study showed that patients on anticoagulation or antiplatelet therapy had higher rates of layered hyphema, but the difference was not statistically significant (9.3% vs. 7.9%, P=0.539).36 A limitation of our study is that we were unable to stratify our analysis by individual blood-thinning therapy. In addition, most patients in our studied cohort were taking low-dose aspirin, which may have less risk of reflux hemorrhage and consequently lowered the rates of hyphema development in this cohort. On the basis of the results of this study, remaining on necessary preoperative ACT/APT may not preclude patients from receiving KDB excisional goniotomy, however, future prospective studies could support this conclusion and allow for more supported recommendations. Further study with a larger cohort of patients is needed to determine true hyphema rates in this patient population.

The presence of hyphema during the postoperative period did not significantly impact the long-term success of KDB-phaco in our study. The majority of hyphemas included in this study were small, grade I hyphemas that did not require additional procedural intervention (12/17, 70.6%). One grade III hyphema occurred in a patient who engaged in a wrestling match with his son on postoperative day 1 and required an uncomplicated AC washout. His vision recovered to 20/30 at the postoperative month 1 follow-up without a recurrence of hyphema. The remainder of hyphemas were grade II (4/17, 23.5%). Because of its microinvasive nature, hyphemas resulting from excisional goniotomy performed with the KDB were small and uncommonly required surgical intervention, likely the reason for the lack of impact on outcomes. However, further study with a greater number of hyphemas may be necessary to adequately determine any association with success.

Our study helps to provide relevant information to surgeons to aid in preventing bleeding complications inherent to excisional angle surgery performed with the KDB. Adopting new strategies to ensure transiently elevated early postoperative IOPs may prevent episcleral venous reflux. Employing added caution and ensuring good identification and visualization of the TM during goniotomy in narrow iridocorneal angles may also limit intraocular trauma contributing to hyphema formation. Lastly, discontinuing ACT/APT before excisional surgery or excluding patients on blood-thinning medications may not be necessary, although further research is needed before recommendations can be made.


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Kahook Dual Blade; MIGS; risk factors; hyphema; bleeding

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