One-year outcomes of trabeculotomy with 120°, 180°, or 360° Schlemm’s canal incision for primary open-angle and exfoliation glaucoma

doi:10.21203/rs.3.rs-2438072/v1

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One-year outcomes of trabeculotomy with 120°, 180°, or 360° Schlemm’s canal incision for primary open-angle and exfoliation glaucoma

https://doi.org/10.21203/rs.3.rs-2438072/v1

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Purpose: To investigate the surgical outcomes of trabeculotomy ab interno/externo with cataract surgery in patients with primary open-angle glaucoma (POAG) and exfoliation glaucoma (XFG) in a 12-month follow-up study.

Methods: This retrospective study enrolled 95 patients (121 eyes) with POAG or XFG who underwent trabeculotomy ab externo with a metal probe (M-LOT), ab interno with a Kahook Dual Blade® (K-LOT), or ab interno with a 5-0 nylon suture (S-LOT) between January 2015 and October 2022. Within these treatment groups, we assessed intraocular pressure (IOP), the number of IOP-lowering medications, the incidence of postoperative complications including hyphema with niveau and transient IOP spikes, and success rate using Kaplan–Meier survival analysis.

Results: Median IOP was significantly reduced from baseline (p < 0.05) in the three patient groups, but the number of IOP-lowering medications was only significantly reduced in the M-LOT group. Kaplan–Meier cumulative survival analyses showed a lower success rate for K-LOT. M-LOT had the lowest incidences of hyphema and IOP spikes while S-LOT showed the highest incidences of these.

Conclusions: M-, K-, and S-LOT had different surgical outcomes during the 12 months of follow-up, with M-LOT showing the fewest complications. These results will aid in choosing the most suitable trabeculotomy strategy for patients with POAG and XFG.

primary open-angle glaucoma

exfoliation glaucoma

trabeculotomy

ab interno

ab externo

metal probe

Kahook Dual Blade

suture

Glaucoma is a progressive disease and the second-leading cause of irreversible visual blindness worldwide due to functional and structural changes to the optic nerve associated with retinal ganglion cell death¹⁾. Elevated intraocular pressure (IOP) is known to be a major risk factor for the occurrence and progression of glaucoma^2,3). Maintaining a lowered IOP is thus considered to be the main treatment strategy for preventing both visual loss as well as the enlargement of visual-field defects in patients with glaucoma.

The aqueous humor is produced in the non-pigmented portion of the ciliary body and drains through the conventional outflow pathway, via the trabecular meshwork (TM) and the uveoscleral pathway, through the ciliary body to the suprachoroidal space. The main resistance to aqueous humor outflow in glaucomatous eyes is the TM and the inner walls of Schlemm’s canal (ISC)^4,5).

Topical treatments, including medical or laser treatments, are usually selected as the first-line therapy for patients with glaucoma. However, if topical treatments fail to sufficiently reduce the IOP, a second-line therapy with trabeculotomy may be used to relieve the aqueous outflow resistance from the anterior chamber to the collector channels by surgically opening the wall of the TM and ISC, thus reducing IOP without bleb formation. Conventional trabeculotomy is performed using metal trabecular probes in an ab externo approach, which involves extensive conjunctival and scleral incisions and sutures similar to trabeculectomy^6,7). However, since the introduction of minimally invasive glaucoma surgery (MIGS) procedures such as the ab interno approach initially described in 2012⁸⁾, new devices for MIGS have been developed and have become widely adopted globally over the last 10 years. The most common type of MIGS is gonioscopy‐assisted transluminal trabeculotomy using an ab interno approach with various surgical instruments, such as a Kahook Dual Blade⁹⁾(KDB; New World Medical, Rancho Cucamonga, CA, USA), iStent¹⁰⁾ (Glaukos, Laguna Hills, CA, USA), Trabectome¹¹⁾ (NeoMedix, Tustin, CA, USA), Microhook¹²⁾, and 5-0 nylon suture¹³⁾. MIGS as an ab interno trabeculotomy procedure has been emerging as an alternative to conventional ab externo trabeculotomy approaches for glaucoma, because of its relatively easy surgical procedures, short surgical time, and because it protects the conjunctiva and sclera in contrast to conventional trabeculotomy. There are now numerous strategies for trabeculotomy with ab interno and ab externo approaches, and glaucoma surgeons must select the appropriate type of surgery based on a complete understanding of the potential postoperative results of each procedure.

Among the various types of glaucoma, primary open-angle glaucoma (POAG) and exfoliation glaucoma (XFG) are the most common forms worldwide, with increasing incidences in elderly populations^14,15). Furthermore, a potentially large subset of patients will require treatment for both glaucoma and coexisting mild senile cataract. Several previous studies^16-20) have assessed the clinical use of ab interno and ab externo trabeculotomy with cataract surgery; however, these reports were lacking in some regards. First, patients were not classified according to the type of open-angle glaucoma, such as POAG, normal tension glaucoma (NTG), and XFG. Second, assessment of the surgical outcomes did not distinguish between trabeculotomy alone and trabeculotomy with cataract extraction. Third, the surgical techniques used for traditional ab externo trabeculotomy differed among the glaucoma surgeons. Traditional ab externo trabeculotomy involves either the incision of the TM and ISC only or that combined with the removal of Schlemm’s canal endothelium and deep sclerectomy (SER + DS). Notably, few prior reports, including our own^19,20) have assessed conventional ab externo trabeculotomy with SER and DS.

To select the appropriate trabeculotomy strategy among the various options with an ab interno/externo approach, glaucoma surgeons should understand the potential surgical outcomes of each procedure.

In this retrospective 12-month follow-up study, we compared the efficacy and complication rates of traditional ab externo 120° trabeculotomy with SER + DS, ab interno 180° trabeculotomy using a KDB, and ab interno 360° trabeculotomy using a 5-0 nylon suture in combination with cataract surgery in patients with POAG (excluding NTG) and XFG.

We enrolled patients who underwent ab interno or ab externo trabeculotomy with cataract surgery at Kansai Medical University Hospital, Japan, between January 2015 and October 2022. The study was conducted in accordance with the guidelines of the Declaration of Helsinki and was approved by the institutional review board of Kansai Medical University through a review of our electronic medical records. The study includeda statement confirming that informed consent obtained from all subjects. All patients underwent complete ophthalmic examinations including best-corrected visual acuity, slit-lamp biomicroscopy, gonioscopy, funduscopy, and IOP measurement by Goldmann applanation tonometry.

POAG was diagnosed as an IOP value > 21 mmHg with or without IOP-lowering medications, open angle (Shaffer grade 3 or 4) using gonioscopy, and optic neuropathy with matching optic disk and visual field defects. XFG was diagnosed if exfoliation materials adhered to the lens surface and/or the iris–pupil border as seen using slit-lamp biomicroscopy, the angle and Sampaolesi’s line were open (Shaffer grade 3 or 4) and present by gonioscopy, and optic neuropathy with a matching optic disk and visual field loss were confirmed. Patients with other pre- or co-existing ocular diseases, a history of steroid therapy, ocular trauma, or prior ocular surgery including laser treatment, narrow angle by gonioscopy, and complications during surgery were excluded. Patients with POAG or XFG who were followed-up for < 12 months were also excluded from the analysis. Surgery was indicated for cataract if the patient complained of glare or halos, had a nuclear grade ≥ 2 (Emery-Little grading), and best-corrected visual acuity ≤ 20/20. Patients with POAG or XFG combined with cataract were recruited from the hospital’s electronic medical records.

Surgical procedures

All patients underwent one of the following surgeries carried out by experienced glaucoma specialists (first and co-authors) under local anesthesia.

Surgical techniques

Trabeculotomy with an ab externo approach using a metal trabecular probe (M-LOT)

After incision of the conjunctiva and sub-Tenon tissue in the inferior nasal or temporal area, a first 4 × 4 mm superficial scleral flap was made. Similarly, an approximately 4 × 4 mm deep incision forming the second scleral flap was made. Corneal side ports were created at 3 and 9 o’clock using a 20-gauge (G) V lance, and a continuous curvilinear capsulorhexis (CCC) was then performed under conditions where the anterior chamber was filled with ophthalmic viscosurgical devices (OVDs). An inferior nasal or temporal 120° incision of the TM and ISC was then performed using a metal trabecular probe. SER and DS (i.e., removal of second scleral flap) were also performed. The first scleral flap and conjunctiva were then sutured using 10-0 nylon.

Trabeculotomy with an ab interno approach using a Kahook Dual Blade^® (K-LOT)

After creating a corneal side port at 9 o’clock using a 20 G V lance, the anterior chamber was filled with OVDs and CCC was then performed. The angle was visualized using an Ocular Swan Jacob Gonioprism (Ocular Instruments, Bellevue, WA, USA) after tilting the patient’s head and microscope. The tip of the KDB was inserted into Schlemm’s canal through the TM then moved circumferentially to excise the TM and ISC from 6 to 12 o’clock (nasal bisection: 180°).

Trabeculotomy with an ab interno approach using a 5-0 nylon suture (S-LOT)

Corneal side ports were created at 7 and 12 o’clock using a 20 G V lance. CCC was performed after filling the anterior chamber with OVDs, and a suture was then inserted into the anterior chamber through a corneal side port at 7 o’clock. Using a Swan-Jacob Gonioprism and/or Mori Upright Surgical Gonio Lens (Ocular Instruments, Bellevue, WA, USA), an approximately 1–1.5 mm incision of the TM was made through the corneal side port at 12 o’clock using a 20 G V lance. The tip of a 5-0 nylon (Mani Nylon, Mani, Tochigi, Japan) suture was inserted into Schlemm’s canal through the TM and then pushed forward circumferentially along the ISC using 23-G disposable microsurgical forceps (DSP forceps, Alcon, Tokyo, Japan). After passing the suture tip around the circumference of Schlemm’s canal, the distal edge of the suture was pulled out from the same opening and a 360◦ incision of the TM and ISC was performed.

Phacoemulsification

Standard phacoemulsification with insertion of an intraocular lens in the bag of the posterior chamber (PEA+IOLs) was performed after each trabeculotomy. After implantation of the IOLs in the capsular bag, OVD and blood were washed out from the anterior chamber by irrigation–aspiration. The anterior chamber was then inflated by injecting a balanced saline solution through the corneal side-port. The integrity of the wound was assessed for leakage using a medical quick absorber.

All patients received similar postoperative topical medications with 0.5–1.5% levofloxacin and 0.1% betamethasone phosphate for 3–4 weeks. We discontinued IOP-lowering medications after surgery and carried out additional postoperative follow-up visits if the IOP values were higher than the baseline values.

Parameters evaluated

We investigated the following parameters: sex, age, IOP, the number of IOP-lowering medications, and the incidence rate of early postoperative complications within 1 month. Baseline IOP was determined as the mean of the three most recent measurements prior to trabeculotomy. The most frequent early (< 1 month after surgery) postoperative complications were hyphema as niveau formation with blood higher than 1 mm in the anterior chamber as detected by slit-lamp biomicroscopy, and an IOP spike recorded as a transient elevation > 30 mmHg. Postoperative data on IOP and the number of IOP-lowering medications were collected at 1 week then 1, 3, 6, 9, and 12 months post-surgery.

Statistical analyses

All statistical analyses were conducted using JMP software version 15 (SAS Inc., Cary, NC, USA). Values are reported as the mean ± standard deviation for normally distributed data and as the median and interquartile range for non-normally distributed data. Dunn’s multiple comparison tests were used to compare pre- and postoperative IOP values. Dunnett’s test was adapted to compare the change in the number of IOP-lowering medications from baseline; if a combination of IOP-lowering medications was used, this was counted as two drugs. Kaplan–Meier survival curve analysis was used to evaluate the cumulative probability of success, and M-, K-, and S-LOT procedures were compared using the log-rank test. We defined surgical failure as < 20% reduction from the preoperative IOP value, a postoperative IOP > 21 or < 5 mmHg on two consecutive visits, and additional glaucoma surgery at least 1 month after the initial surgery. A p value < 0.05 was considered statistically significant.

A total of 121 eyes from 95 patients with open-angle glaucoma (POAG: 83 eyes, XFG: 38 eyes) who underwent M-, K-, or S-LOT with PEA+IOLs were included in this study. All patients fulfilled the inclusion/exclusion criteria during follow-up. M-, K-, and S-LOT with PEA+IOLs were performed in 35, 36, and 12 eyes in POAG patients and 24, 8, and 6 eyes in XFG patients, respectively. The clinical characteristics of all patients are summarized in Table 1.

Figure 1 shows the baseline and postoperative IOP values at each time point for all groups. The changes in median IOP in the POAG group are described as follows. The median IOP in the M-LOT group was 18.5 (17–20) mmHg at baseline, and 15 (11–19; 18.9% reduction; p < 0.0001), 12 (10–14; 35.1% reduction; p < 0.0001), 12 (10-14; 35.1% reduction; p < 0.0001), 12 (10–14; 35.1% reduction; p < 0.0001), 13 (11–14; 29.7% reduction; p < 0.0001), and 12 (11–15; 35.1% reduction; p < 0.0001) mmHg at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. The median IOP in the K-LOT group was 20 (16–21) mmHg at baseline, and 22 (17.25–31.5; 10% increase; p > 0.95), 14.5 (12.25–16; 27.5% reduction; p = 0.0016), 14 (13–16; 30% reduction; p = 0.0004), 14 (12-17; 30% reduction; p < 0.0001), 15 (13–17; 25% reduction; p < 0.0001), and 14.5 (14–18; 27.5% reduction; p < 0.0001) mmHg at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. The median IOP in the S-LOT group was 18.6 (18.075–21.5) mmHg at baseline, and 21 (12.5–30.5; 12.9% increase; p = 0.7092), 13 (12.25–13.75; 30.1% reduction; p = 0.0069), 14 (12.25–15.75; 24.7% reduction; p = 0.0044), 13 (12.25–14.75; 24.7% reduction; p = 0.0007), 14 (12–15.75; 24.7% reduction; p = 0.0002), and 12.5 (11.25–15; 32.8% reduction; p = 0.0002) mmHg at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. Postoperative IOP was significantly reduced from 1 week to 12 months compared with baseline in all groups (M-, K-, and S-LOT) with POAG. The changes in median IOP in the XFG group are described as follows. The median IOP in the M-LOT group was 18.4 (17–24.5) mmHg at baseline, and 14.5 (12–24.5; 21.2% reduction; p = 0.0203), 12 (10.3–14; 34.8% reduction; p < 0.0001), 12.5 (10.3–13.8; 32.1% reduction; p < 0.0001), 12 (10–14; 34.8% reduction; p < 0.0001), 12.5 (11.3–14; 32.1% reduction; p < 0.0001), and 12.5 (11–15; 32.1% reduction; p < 0.0001) mmHg at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. Postoperative IOP was significantly reduced in the M-LOT group from 1 week to 12 months after surgery compared with baseline. The median IOP in the K-LOT group was 20 (15.6–23) mmHg at baseline, and 16 (9.8–25.5; 20% reduction; p = 0.5182), 11.5 (11–12; 42.5% reduction; p = 0.0023), 11.5 (10.3–12; 42.5% reduction; p = 0.0013), 13 (10–13.8; 35% reduction; p = 0.0282), 12.5 (11.3–13.8; 37.5% reduction; p=0.0495), and 12 (11–13; 40% reduction; p = 0.0137) mmHg at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. The IOP was significantly lower at 1, 3, 6, 9, and 12 months postoperatively compared with baseline in the K-LOT group. The median IOP of the S-LOT group was 21.2 (19.5–24.1) mmHg at baseline, and 24.5 (17.3–32; 15.5% increase; p > 0.95), 14.5 (12–17.3; 26.9% reduction; p = 0.2473), 11.5 (9.8–14.5; 45.8% reduction; p = 0.00214), 12.5 (9.8–16; 41.0% reduction; p = 0.0566), 12.5 (10.8–16; 41.0% reduction; p = 0.0627), and 12.5 (9–14.5; 41.0% reduction; p = 0.0248) mmHg at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. The IOP was significantly lower between 3 and 12 months postoperatively compared with baseline in the S-LOT group.

Figure 2 shows the change in mean number of IOP-lowering medications before and after surgery in patients with POAG and XFG. The mean number of IOP-lowering medications in POAG patients in the M-LOT group decreased significantly from 3.7 ± 1.1 at baseline to 1.2 ± 1.2 at 1 week (p < 0.0001), 1.3 ± 1.1 at 1 month (p < 0.0001), 1.5 ± 1.2 at 3 months (p < 0.0001), 1.9 ± 1.2 at 6 months (p < 0.0001), 2.4 ± 2.4 at 9 months (p = 0.0042), and 2.4 ± 2.3 at 12 months (p = 0.0054) postoperatively. The mean number of IOP-lowering medications in POAG patients receiving K-LOT was 3.3 ± 1.3 at baseline, and 2.4 ± 1.5 (p = 0.0108), 2.3 ± 1.0 (p = 0.0079), 2.4 ± 1.1 (p = 0.0258), 2.5 ± 1.2 (p = 0.0570), 2.5 ± 1.2 (p = 0.0570), and 2.8 ± 1.1 (p = 0.3653) at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. The number of IOP-lowering medications was significantly lower at 1 week and at 1 and 3 months compared with baseline. The mean number of IOP-lowering medications in POAG patients in the S-LOT group was 3.7 ± 0.9 at baseline and 1.7 ± 1.3 (p < 0.0001), 2.0 ± 1.0 (p < 0.0001), 2.8 ± 0.9 (p = 0.0621), 3.1 ± 0.7 (p = 0.3972), 3.1 ± 0.7 (p = 0.3972), and 3.1 ± 0.7 (p = 0.3653) at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively. The number of IOP-lowering medications was significantly reduced at 1 week and at 1 month from baseline. The number of IOP-lowering medications in XFG patients who underwent M-LOT decreased significantly from 3.8 ± 1.3 at baseline to 1.3 ± 1.2 at 1 week (p < 0.0001), 1.4 ± 1.2 at 1 month (p < 0.0001), 1.8 ± 1.2 at 3 months (p < 0.0001), 1.8 ± 1.1 at 6 months (p < 0.0001), 1.9 ± 1.3 at 9 months (p < 0.0001), and 2.0 ± 1.3 at 12 months (p < 0.0001) postoperatively. The number of IOP-lowering medications in patients with XFG receiving K-LOT was 2.9 ± 1.4 at baseline, and 1.6 ± 1.2 (p = 0.0873), 2.0 ± 1.4 (p = 0.355), 2.5 ± 0.8 (p = 0.9485), 2.6 ± 0.7 (p = 0.9972), 2.6 ± 0.7 (p = 0.9972), and 2.6 ± 0.7 (p = 0.9972) at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively, with no significant differences from baseline at any time point. The numbers of IOP-lowering medications in XFG patients treated with S-LOT were 3.7 ± 1.0 at baseline, and 2.2 ± 0.8 (p = 0.0542), 2.5 ± 0.8 (p = 0.187), 2.7 ± 1.0 (p = 0.315), 2.5 ± 0.7 (p = 0.187), 2.5 ± 0.7 (p = 0.187), and 2.5 ± 0.7 (p = 0.187) at 1 week and 1, 3, 6, 9, and 12 months post-surgery, respectively, with no significant differences between any time point.

The Kaplan–Meier cumulative survival curves for patients with POAG and XFG in the three treatment groups (M-, K-, and S-LOT) are shown in Figure 3. The success rate of K-LOT (27.8%) was significantly lower than that of M- and S-LOT in patients with POAG (65.7%, 58.3%) and the success rate of S-LOT (100%) was significantly higher than that of M- and K-LOT in patients with XFG (70.8%, 75%) at 12 months post-surgery.

The occurrence of early postoperative complications including hyphema with niveau formation (> 1 mm) and transient IOP spikes (IOP increased > 30 mmHg) in all groups is shown in Table 2. Fortunately, hyphema and transient IOP spikes regressed spontaneously within 1–2 weeks without anterior chamber washing in all cases. Transient IOP spikes occurred within 2 weeks after surgery in three (8.6%), 10 (27.8%), and three (25%) eyes in the POAG M-, K-, and S groups, respectively, and hyphema with niveau formation was confirmed within 1 week in four (11.4%), four (11.1%), and four (33.3%) eyes, respectively. Hyphema and transient IOP spikes were significantly less frequent in the M-LOT group compared with the S- and K-LOT groups (p < 0.05) among POAG patients. Transient IOP spikes occurred within 2 weeks after surgery in four (16.7%), zero (27.8%), and two (33.3%) eyes in the XFG M-, K-, and S groups, respectively, and hyphema with niveau formation occurred within 1 week in three (12.5%), zero (10%), and two (33.3%) eyes, respectively. Hyphema and IOP spikes were significantly more frequent in the S-LOT group compared with the M- and K-LOT groups (p < 0.05) among XFG patients.

In this retrospective study, we evaluated and compared the surgical outcomes of 360° trabeculotomy ab interno with sutures, nasal 180° trabeculotomy ab interno with KDB, and 120° trabeculotomy ab externo with a metal probe in combination with cataract extraction during 12 months of postoperative follow-up in patients with POAG or XFG.

Whether the reduction in IOP is correlated with the extent of the TM and ISC incisions, used to allow the aqueous humor to drain from the anterior chamber into the collector channels during trabeculotomy, remains unclear. Postoperative efficacy in relation to the incision range in LOT procedures was found to vary in previous reports. Manabe et al.²¹⁾ reported that an incision in the TM and ISC of ≥ 150◦ did not significantly affect the reduction in IOP compared with the 1-year outcome of S-LOT with an ab externo approach. Sato et al.¹⁶⁾ also showed that neither a 180° nor a 360◦ incision in the TM and ISC resulted in a significant IOP reduction. In enucleated human eyes, 120° trabeculotomy caused an 85% IOP reduction in outflow resistance²²⁾. These prior experimental and clinical results^16,21,22) suggest that incisions > 120–180° may not contribute to a reduction in IOP. In contrast, 360° suture trabeculotomy achieved lower IOP values than 120° metal trabeculotomy in a study by Chin et al.¹³⁾ However, it is difficult to evaluate the surgical outcomes based on the extent of the TM and ISC incisions due to the different incision approaches used. Our current study demonstrated that the extent of the TM and ISC incision might not correlate with the reduction in IOP or the number of IOP-lowering medications in the S-LOT group. Moreover, patients in the M-LOT group, with the smallest TM and ISC incisions, had the lowest postoperative IOP values compared with the K- and S-LOT groups. However, differences among the incision approaches makes it difficult to evaluate the surgical outcomes based on the extent of the TM and ISC incisions. In this study, we could not accurately evaluate the correlation between IOP reduction and the extent of TM and ISC incision among our three groups because our M-LOT procedure included SER and DS, which can certainly promote a filtration effect. The correlation between the extent of the TM/ISC incision and IOP reduction should thus be compared between the K- and S-LOT groups, excluding the M-LOT group. However, a wider TM and ISC opening may contribute to IOP reduction, given that the 360° incision in the S-LOT group was associated with better outcomes than the 180° incision in the M-LOT group in the present study.

Hyphema with niveau formation and transient IOP spikes are the most frequent early complications after trabeculotomy. Hyphema with niveau formation occurs as a result of blood reflux from the episcleral veins after incision of the TM in Schlemm’s canal, while transient IOP spikes are related to prolonged hyphema with niveau formation in the anterior chamber. There was a significant difference in the occurrence of postoperative hyphema with niveau formation among the three groups in the present study. The incidence rates of both hyphema with niveau formation and transient IOP spikes were higher in the S-LOT group compared with the other two groups. Longer incisions in the TM and ISC may result in greater blood reflux, which would in turn lead to a higher frequency of postoperative hyphema with niveau formation and transient IOP spikes. From this point of view, a 360° incision of the TM and ISC might be too invasive to attain lower IOP. Consistent with this, the incidence rates of these postoperative complications were lowest in the M-LOT group. Moreover, the filtration effects of SER and DS may have contributed to the low rate of postoperative complications in the M-LOT group.

In our study, M-LOT with an ab interno approach showed lower postoperative median IOP, a lower number of IOP-lowering medications, and lower rates of hyphema with niveau formation and transient IOP spikes during the 12 months of postoperative follow-up, suggesting that conventional M-LOT with an ab externo approach was more effective than S-LOT or K-LOT with an ab interno approach for patients with POAG or XFG. However, the success rate of S-LOT in patients with POAG and XFG according to Kaplan–Meier survival analysis was 58.3% and 100%, respectively. While there was no significant difference in the success rate of S-LOT and M-LOT in POAG patients, the success rate of S-LOT was significantly higher than that of M-LOT in XFG patients.

The results of this study suggest that the ideal trabeculotomy strategy for each patient could be selected based on the following criteria. In patients with POAG, the use of M-, K-, or S-LOT should be determined according to the target postoperative IOP. In cases with a target postoperative IOP of 12–13 or 13–14 mmHg, M-, S-, and K-LOT are selected, respectively. In patients with XFG, the postoperative median IOP was similar (12 mmHg) among the three groups. When choosing M-LOT, glaucoma surgeons should keep in mind that this procedure requires conjunctival and scleral dissection because this surgery is performed using the ab externo approach. The main advantage of the ab interno approaches, other than M-LOT, is that they do not require conjunctival and scleral dissection and allow the option for subsequent filtration surgeries if necessary. M-LOT, featuring conjunctival and scleral dissection, should be selected in patients who do not require filtering devices, including Baerveldt^®, Ahmed^®, Express^®, etc. in the future. M-LOT may also be selected to avoid transient IOP spikes and/or worsening visual acuity due to hyphema with niveau formation because of severe glaucoma or occurrence in the dominant eye. K-LOT may be chosen because a second ab interno trabeculotomy could be recommended in the future due to the residual 180° at the temporal area of the TM and ISC. Although trabeculectomy should initially be performed based on the severity of the POAG or XFG, S-LOT may be preferred because of difficulties in postoperative management, especially in patients with dementia or poor ADL due to other systemic disease.

Our study has several limitations that should be noted. First, this was a retrospective study, and the 120°, 180°, and 360° TM and ISC incisions were therefore not assigned randomly to the subjects. Medication withdrawal was at the investigator’s discretion rather than via a pre-specified approach. However, selection bias was limited by selecting all cases that met the minimal eligibility criteria within the specified time frame. Second, patients were recruited regardless of the severity of their glaucoma. Given that severe glaucoma may impact surgical outcomes, differences in severity among the three groups may have affected the study results. Third, cataract surgery reduces IOP via several mechanisms. Increased postoperative outflow due to anatomical changes such as angle width or traction of the ciliary zonules in pseudophakic eyes after cataract surgery may increase the aqueous outflow. Notably, our study population included cases of combined trabeculotomy and cataract surgery.

In conclusion, the goal of glaucoma management is to preserve the patient’s quality of life by maintaining their visual field and visual acuity, and to minimize any adverse effects of the treatment. Differences in the extent and location of Schlemm’s canal incisions during ab interno and/or ab externo trabeculotomy, including 360°, 180°, and 120° incisions, showed good surgical outcomes during a 12-month follow-up period in patients with POAG and XFG. To our knowledge, there have been no previous reports comparing the range of postoperative results for trabeculotomies with ab interno and externo approaches, as described in our present study. Although we are entering the era of MIGS for glaucoma patients, M-LOT is still a highly utilized surgery. A better understanding of the outcomes of the different procedures will allow for the selection of optimal trabeculotomy strategies for patients with POAG and XFG in the future.

intraocular pressure :IOP

trabecular meshwork :TM

inner walls of Schlemm’s canal :ISC

minimally invasive glaucoma surgery :MIGS

Kahook Dual Blade:KDB

primary open-angle glaucoma :POAG

exfoliation glaucoma :XFG

normal tension glaucoma :NTG

Schlemm’s canal endothelium and deep sclerectomy :SER + DS

gauge :G

continuous curvilinear capsulorhexis :CCC

ophthalmic viscosurgical devices :OVDs

phacoemulsification with insertion of an intraocular lens in the bag of the posterior chamber :PEA+IOLs

Acknowledgements

None

Author Contributions

Research was designed by Hidetsugu Mori.

Data analysis was performed by Hidetsugu Mori.

Surgeries were performed by Hidetsugu Mori, Tomoyuki Chihara, Hideyuki Yoshida, Ikuko Kaga, Shimpei Oba, and Ryusuke Takezawa.

Hidetsugu Mori wrote the paper with support from Haruhiko Yamada and Kanji Takahashi.

Disclosure of potential conflicts of interest
All authors declare no conflicts of interest.

Funding

None

Disclosure Statement

The authors declare that they have no conflicts of interest and no financial interests.

Data availability” statements

The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.

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Table 1. Patient characteristics

Trabeculotomy	POAG (eyes)	XFG (eyes)
M-LOT	35	24
K-LOT	36	8
S-LOT	12	6

Table 2 is available in the Supplementary Files section.

No competing interests reported.

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One-year outcomes of trabeculotomy with 120°, 180°, or 360° Schlemm’s canal incision for primary open-angle and exfoliation glaucoma

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