Short-term outcomes of Tanito microhook ab interno trabeculotomy combined with phacoemulsification in primary open-angle glaucoma – A pilot study

Abstract

Purpose:

The aim of the study was to assess the early postoperative efficacy and safety of Tanito microhook (TMH) ab interno trabeculotomy combined with phacoemulsification in patients with primary open-angle glaucoma (POAG).

Methods:

This prospective interventional study was conducted on consecutive patients with visually significant cataract and mild-moderate POAG. All patients underwent a temporal clear corneal phacoemulsification combined with TMH ab interno trabeculotomy. Postoperative evaluation was done on day 1, 1 month, and 3 months. The outcome measures included intraocular pressure (IOP) at different follow-ups and postoperative complications.

Results:

In total, 30 eyes of 30 patients were included in the study. There were 16 (53.3%) females and 14 (46.7%) males with a mean age of 62.63 ± 6.7 years. The mean IOP reduced from 23.57 ± 1.65 to 17.33 ± 2.84 at 3 months (P < 0.001). All eyes had a corrected distance visual acuity ≥6/9 at 1 month postoperatively. Postoperative complications included corneal stromal edema in eight (26.7%) eyes, hyphema in four (13.3%) eyes, and IOP spike in one (3.3%) eye.

Conclusion:

TMH ab interno trabeculotomy combined with phacoemulsification in patients with mild-moderate POAG is an effective and safe procedure with fewer complications.

Glaucoma is the leading cause of irreversible blindness worldwide.[1] It is necessary to reduce the intraocular pressure (IOP) to treat glaucoma with medications or by surgery.[2,3] Trabeculotomy is a surgical method used to cleave the trabecular meshwork (TM) and the inner wall of the Schlemm canal (SC), which are considered the main sites of resistance for aqueous outflow.[4,5] Conventional trabeculotomy was done via the ab externo approach with a conjunctival incision. However, this may result in conjunctival damage, leading to failure when an additional trabeculectomy is performed later.[6,7,8] Recently, trabeculotomy techniques using the ab interno approaches have also been reported.[9,10,11]

Minimally invasive glaucoma surgery (MIGS) has emerged as an effective strategy, offering favorable outcomes and enhanced safety.[12] Tanito microhook (TMH) ab interno trabeculotomy is a MIGS procedure using a metal hook to incise the TM that has been noted to effectively reduce IOP and decrease dependency on antiglaucoma medications. TMH is a single-blade trabecular microhook with an oblique tip surface for effective tissue management and a unique hook with a circular edge for incising the TM. It is offered in three models: bent versions of left, right, and straight. Ab interno trabeculotomy surgery is often performed in combination with phacoemulsification.[9,10]

The purpose of the current study was to evaluate the surgical efficacy and safety profile of TMH ab interno combined trabeculotomy with phacoemulsification in Indian patients with primary open-angle glaucoma (POAG).

Methods

This was a prospective interventional single-center single-surgeon study conducted at our eye institute between January 2023 and December 2023 to evaluate the postoperative outcomes of TMH ab interno trabeculotomy combined with phacoemulsification. The institutional ethical committee approval was obtained before beginning the study. Written informed consent according to the tenets of the Declaration of Helsinki was obtained prior to inclusion in this study.

Patients with mild-to-moderate POAG and visually significant cataract with IOP between 21 and 28 mmHg at the time of presentation were included. POAG diagnosis was based on the presence of glaucomatous optic disc changes and retinal nerve fiber layer changes, with or without associated visual field changes and elevated IOP. Patients <50 years of age, on antiglaucoma medications, with corneal edema or opacities precluding gonioscopic angle view, any history of ocular trauma, and previous intraocular or glaucoma surgery were excluded.

Surgical technique

TMH ab interno trabeculotomy was preceded by phacoemulsification cataract surgery through a 2.8-mm wide, clear corneal incision at the temporal location. After intraocular lens (IOL) implantation, before washing away the dispersive viscoelastic, a straight tip TMH (RAICO LLC, USA) was used for the procedure [Video 1, Fig. 1a].

Figure 1.

(a) Tanito microhook – straight tip (b) angle visualization before trabeculotomy using a direct gonioprism lens (c) ab interno trabeculotomy using Tanito microhook (d) minimal bleeding from the angle post trabeculotomy

For good visualization of angle structure, proper positioning of the patient’s head and surgical microscope is important. The patient’s head was tilted 30–40° to the nasal side, and the microscope was turned around 30° toward the temporal side. The TMH was inserted into the anterior chamber through the corneal port, and the angle opposite the port was observed using a Katena® or Swan Jacob gonioprism lens [Fig. 1b]. The tip of TMH was inserted into the SC and moved gently circumferentially in a sliding motion to incise the inner wall of SC and TM for approximately 120° (4 clock hours) at the opposite quadrant [Fig. 1c]. After insertion, the depth of the tip can be monitored by visualizing the tip through the TM. The inability to visualize the tip through the meshwork usually indicates that the tip has been inserted too deep. With adequate direction and depth, only minor resistance will be felt when moving the tip circumferentially; any resistance usually indicates that the tip has been inserted too deep. To avoid unintended tissue damage around the TM, the correct insertion, direction, and depth of the tip of the hook should be monitored carefully during the procedure. After TMH trabeculotomy, viscoelastic material was aspirated, and corneal ports were closed by corneal stromal hydration. Postoperatively, a combination of 0.5% moxifloxacin and 0.1% dexamethasone was applied topically four times and tapered gradually over 6 weeks.

The outcome measures included IOP at different follow-ups (day 1, 1 month, and 3 months) and postoperative complications.

Statistical analysis

Data were entered in the Microsoft Excel software in codes, and analysis was done using Statistical Package for Social Sciences (SPSS-23, IBM software computer package). Categorical variables were expressed as frequency and percentages. The test of normality was done using Kolmogorov-Smirnov and Shapiro-Wilk. Continuous variables were summarized with measures of central tendency. Repeated measures ANOVA and Bonferroni post-hoc analysis were used to compare the change in IOP over different follow-ups. For all the tests of significance, a P value less than 0.05 was considered statistically significant.

Results

Thirty eyes of 30 patients were included in the study. There were 16 (53.3%) females and 14 (46.7%) males. The mean age was 62.63 ± 6.7 years. Table 1 shows the demographic data.

Table 1.

Demographic data of study participants

Characteristic	n
n	30
Age (years)
Mean±SD	62.63±6.73
Gender (n)
Female	16 (53.3%)
Male	14 (46.7%)
Central corneal thickness (μm)
Mean±SD	525.17±15.88
Baseline IOP (mmHg)
Mean±SD	23.57±1.65

SD: standard deviation, IOP: intraocular pressure

The mean IOP reduced from 23.57 ± 1.65 to 17.33 ± 2.84 at 3 months (P < 0.001). Fig. 2 shows the change in IOP at different follow-up periods. The change in IOP from day 1 to 1 month and 3 months was not statistically significant [Table 2]. All eyes had a corrected distance visual acuity ≥6/9 at 1 month postoperatively.

Figure 2.

Change in intraocular pressure at different follow-up periods following combined Tanito microhook ab interno trabeculotomy with phacoemulsification

Table 2.

Bonferroni post hoc analysis of change in intraocular pressure at different follow-up periods

	Mean difference	SD difference	Change (%)	Bonferroni P
Baseline - day 1 IOP	5.73	4.16	24.33	<0.001
Baseline - 1 month IOP	5.87	3.35	24.89	<0.001
Baseline - 3 months IOP	6.23	2.97	26.45	<0.001
Day 1-1 month IOP	0.13	2.16	0.75	0.738
Day 1-3 months IOP	0.50	2.64	2.80	0.307
1 month - 3 months IOP	0.37	1.30	2.07	0.133

SD: standard deviation, IOP: intraocular pressure

Fig. 1d shows minimal bleeding after TMH trabeculotomy. Postoperative complications (day one) included corneal stromal edema in eight (26.7%) eyes, grade 1 hyphema (less than one-third of the anterior chamber) in four (13.3%) eyes, and IOP spike in one (3.3%) eye, which might be due to the surgical manipulation. Corneal edema and hyphema resolved at 1 month postoperatively. No re-bleeding was noted during the 3-month follow-up. Antiglaucoma medication (oral acetazolamide sustained release 250 mg twice a day for 5 days and topical timolol maleate 0.5% twice a day) was started in one patient with raised IOP (35 mmHg) postoperatively, following which the IOP came down to 18 mmHg at 1 month.

Discussion

In this pilot study, TMH ab interno trabeculotomy combined with phacoemulsification decreased the IOP from the preoperative value of 23.57 ± 1.65 to 17.33 ± 2.84, a 26% decrease at the final 3 months of evaluation. Although most of the surgical complications are relatively minor and resolve spontaneously, the decision to perform TMH ab interno trabeculotomy should not be considered in eyes with advanced glaucoma as post-surgical IOP spike can be related to a decrease in visual acuity.

Conjunctival and scleral sparing with the ab interno technique, short surgical time (<10 minutes), moderate IOP reduction, and no bleb-related complications fulfill the conditions of MIGS, similar to the recent techniques of gonio-bypass surgeries such as the Trabectome (NeoMedix Corp., Tustin, CA, USA),17 iStent (Glaukos, Laguna Hills, CA, USA), gonioscopy-assisted transluminal trabeculotomy (GATT), canaloplasty, and dual-blade trabeculectomy (New World Medical Inc., Rancho Cucamonga, CA, USA).[12,13,14,15,16,17,18,19]

Studies have compared goniotomy using a Kahook dual blade (KDB) with TMH and found similar IOP reduction effectiveness between TMH and KDB.[20,21] Compared to a Kahook dual blade, the TMH tip is small, reducing tissue damage with less chance of damaging the iris root and corneal endothelium. A recent multicenter study by Asaoka et al.[22] showed comparable IOP reduction effectiveness and safety profiles between TMH and iStent inject W.

Rosenquist et al.,[23] in their study on perfused autopsy eyes, showed that incisions in the TM at width corresponding to 1, 4, and 12 clock hours led to a decrease in outflow resistance by 30%, 44%, and 51%, respectively, under a perfusion pressure of 7 mmHg, and by 30%, 56%, and 72%, respectively, under a pressure of 25 mmHg. This suggests that different extents of trabeculotomy can result in varying levels of IOP reduction. Nevertheless, other studies found no differences in IOP reduction based on the extent of trabeculotomy.[24,25,26,27,28,29,30] In our study, around 4 clock hours of TM was incised.

Tanito et al.,[31] in their single-center retrospective study including cases with POAG and exfoliation glaucoma, observed that the surgical success rate of TMH ab interno trabeculotomy at 1 year was 44.6% (IOP ≤18 mmHg and IOP reduction ≥20% with the use of antiglaucoma medications) and 69.1% (IOP ≤18 mmHg and IOP reduction ≥20% with the use of antiglaucoma medications). Another multicenter retrospective study by Mori et al.,[32] including all types of glaucoma, reported a success rate of 74.2% (IOP = 5–21 mmHg, IOP reduction ≥20%, and no additional glaucoma surgery) at 1 year with TMH trabeculotomy. However, in our pilot study, we assessed only the reduction in IOP and did not define surgical success.

Maheshwari et al.[33] conducted a prospective comparative study including 114 patients with mild-moderate open-angle glaucoma who underwent phacoemulsification with TMH trabeculotomy and phacoemulsification alone. They found that the reduction in IOP was greater in the TMH trabeculotomy-phacoemulsification group (P < 0.001) than in the phacoemulsification group at 12 months, respectively.

Postoperative complications were noted in 30% of eyes in our study, which is similar to other studies.[10,20,21,30,31] Hyphema is a common postoperative complication following angle surgeries.[25,28,29,30,31] A higher incidence of hyphema was noted in eyes undergoing TMH than in those receiving first- and second-generation iStent implants during the early postoperative period.[34,35] However, complications such as corneal edema and hyphema did not impact other safety profiles or the final visual function, although they likely influenced the early visual recovery. Postoperative IOP spike >30 mmHg was seen only in one eye (3.3%) in the present study, similar to the incidence reported in other studies.[9,10,21,30]

As this was a pilot study, the major limitations include the small sample size and short follow-up, which could be overcome in a large-scale study. The study included only cases with POAG, predominantly involving an elderly population, which may limit the generalizability of the findings. The need for more information on the use of anticoagulants and antiplatelet agents, which could contribute to postoperative hyphema, was another drawback.

Conclusion

TMH ab interno trabeculotomy with phacoemulsification was effective in lowering IOP with minimal complications and could be an option worth considering for mild-moderate POAG.

Conflicts of interest:

There are no conflicts of interest.

Funding Statement

Nil.