Short- to intermediate-term surgical outcome of Keiki Mehta valve implantation in refractory glaucoma

Abstract

Background:

Keiki Mehta body pressure (BP) valve is a glaucoma drainage device that works on the simple mechanism of body pressure.

Purpose:

To evaluate the short- to intermediate-term efficacy and safety of Keiki Mehta valve implantation in treating refractory glaucoma.

Methods:

This was a prospective, interventional, institution-based study. Adult patients (age >18 years) having refractory glaucoma who underwent Keiki Mehta valve implantation from May 2019 to December 2019 in a tertiary hospital in eastern India were followed up to 18 months.

Results:

Twenty patients (20 eyes) with refractory glaucoma who underwent Keiki Mehta valve implantation were followed up on postoperative day 1 and at 1, 3, 6, 12, and 18 months postoperatively. Visual acuity, intraocular pressure (IOP), antiglaucoma medications, and success rate were measured at every visit. There was significant reduction in mean IOP from the preoperative values at every postoperative follow-up (P < 0.05). Kaplan–Meier survival analysis demonstrated a probability of 50% complete success and 20% qualified success at 18 months. Hypotony was the most common postoperative complication.

Conclusion:

Keiki Mehta valve implantation is an effective and safe treatment for refractory glaucoma.

Glaucoma is a leading cause of irreversible blindness globally, which may affect up to 111 million people worldwide by 2040.[1] Refractory glaucoma is defined as uncontrolled intraocular pressure (IOP) with progressive optic nerve damage despite maximum medical treatment combined with/without failed filtration surgery or with high risk of failure of filtration surgery.[2]

Keiki Mehta body pressure (“BP”) glaucoma shunt is a glaucoma drainage device (GDD) developed by SURGIWEAR in association with renowned ophthalmologist, Dr. Keiki R. Mehta [Fig. 1a]. It has a valve mechanism based on body pressure, and so is known as BP valve. It has three parts, namely, a tube, a membrane valve, and a button, made of medical grade silicone. The button has a side-to-side length of 15 mm and a front-to-back length of 17 mm with “peaks” that keep the conjunctiva and tenon’s away from the button. When the pressure of fluid in eye is more than pressure of surrounding tissues, the valve opens, allowing the aqueous humor to flow out, reducing the IOP.[3]

Figure 1.

(a) Keiki Mehta BP glaucoma shunt device. (b) Anterior chamber entry 1–3 mm with 22 G needle parallel to the plane of iris. (c) Suturing of AM–UC graft to the sclera with 10-0 nylon. AM–UC = amniotic membrane-umbilical cord, BP = body pressure

Herein, we report the surgical outcome in a prospective study on 20 patients with refractory glaucoma who underwent Keiki Mehta valve implantation.

Methods

This is a prospective, interventional, institution-based study carried out at a tertiary referral hospital in East India. This study was approved by the Institutional Review Board and the Ethics Committee. All study procedures confirmed to the tenets of the Declaration of Helsinki for research involving human subjects. Informed consent (written) was obtained from all patients participating in the study.

Twenty patients (20 eyes) diagnosed with refractory glaucoma, that is, IOP uncontrolled on medications alone with chances of high risk of failure for trabeculectomy, underwent Keiki Mehta valve implantation between May 2019 and December 2019 and were followed up for 18 months. Uncontrolled IOP was defined as IOP >21 mmHg, even after maximal usage of antiglaucoma medications. Exclusion criteria were any previous ocular surgeries except phacoemulsification, preoperative visual acuity less than light perception, or age less than 18 years. A detailed preoperative examination was carried out for all the patients 1 week before the surgery. History of systemic disorders, type of glaucoma, and number of glaucoma medications used were noted. Slit-lamp biomicroscopic examination, lens status, IOP measurement using Goldmann applanation tonometry, gonioscopy using a Goldmann four-mirror lens, optic disc evaluation with a Volk 90 D lens, and indirect ophthalmoscopy using a Volk 20 D lens were performed. Visual acuity was measured using the Snellen’s chart, which was then converted to logarithm of the reciprocal of the minimal angle of resolution (logMAR). All the surgeries were performed by a single surgeon, while the postoperative evaluation was performed by a single clinician who was blinded to the intraoperative events.

Every patient was followed up on postoperative day 1 and at 1, 3, 6, 12, and 18 months postoperatively. On each visit, best corrected visual acuity (BCVA) by Snellen’s chart and IOP measurement with the Goldmann applanation tonometry were done. Both anterior and posterior segments of the eye were examined thoroughly with slit-lamp biomicroscopy, 90 D, and indirect ophthalmoscopy. Any postoperative complication was noted. The number of antiglaucoma medications added for IOP control postsurgery was noted at each visit. If IOP was >21 mmHg, antiglaucoma medication was prescribed and patient was reviewed after 1 month. Patients were grouped as qualified success, complete success, or failure after each visit. Qualified success was defined as an IOP <21 mmHg with antiglaucoma medications, complete success as an IOP <21 mmHg without any antiglaucoma medication, while failure was defined as 1) an IOP >21 mmHg in spite of the use of maximum antiglaucoma medications, 2) requirement of revision surgery, and 3) devastating intraoperative or postoperative complication like expulsive suprachoroidal hemorrhage, endophthalmitis, or pthisis.

Surgical technique

Peribulbar anesthesia was used in all the patients. All the patients included in the study were operated upon by a single surgeon, while the postoperative evaluation was done by two other surgeons who were blinded to the preoperative and intraoperative events. Priming of the device was performed to check the integrity and patency of the valve by injecting 1 ml of balanced salt solution with 26 G cannula. A fornix-based conjunctival flap was created in the superotemporal quadrant between two adjacent recti muscles. The implant was sutured to the sclera 8–10 mm from the limbus with 9-0 nylon, and the drainage tube was trimmed to permit 2–3 mm insertion in the anterior chamber with a beveled cut at 30°. Anterior chamber paracentesis was performed and viscoelastic substance injected, following which the anterior chamber was entered 1–3 mm posterior to the limbus with a 22-G needle parallel to the plane of iris. The tube was entered through the needle tract with the bevel facing the corneal endothelium and then the drainage tube was covered with cryopreserved amniotic membrane–umbilical cord (AM–UC) graft sutured to the sclera by 10-0 nylon. In all patients, the tube was placed in the anterior chamber. Conjunctiva was then anchored to the limbus with 8-0 Vicryl sutures, and subconjunctival antibiotic with steroid was injected [Fig. 1b and c]. All antiglaucoma medications were stopped from postoperative day 1, and patients were followed up regularly as mentioned before.

Statistical methods

All statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) 21.0. For continuous variables, t-test or paired t-test was performed for data with normal distribution, while a corresponding nonparametric test was used for data with abnormal distribution. For categorical variables, Pearson’s Chi-square test or Fisher’s exact test was used. A P value of less than 0.05 was considered statistically significant.

Results

Twenty eyes of 20 patients with refractory glaucoma were included in this study. Majority of the patients (70%) had neovascular glaucoma due to proliferative diabetic retinopathy (PDR) or central retinal vein occlusion (CRVO). Fourteen (25%) had uveitic glaucoma and one patient had iridocorneal endothelial (ICE) syndrome. The demographic characteristics of the population are shown in Table 1.

Table 1.

Demographic characteristics

Baseline characteristics	n (%)
Age (years)
Mean	45.1±5.53
Range	35–56
Sex
Male:female	14:6
Laterality
Right eye: left eye	11:9
Lens status
Phakic (%)	6 (30%)
Pseudophakic (%)	14 (70%)
BCVA (logMAR)
Mean	1.2±0.21
Range	1–1.6
Baseline IOP (mmHg)
Mean	32.7±4.51
Range	28–42
No. of antiglaucoma medications
Mean	3.1±0.72
Range	2–4
Type of glaucoma
NVG (%)	14 (70%)
Uveitic glaucoma (%)	5 (25%)
ICE syndrome (%)	1 (5%)

BCVA=best corrected visual acuity, ICE=iridocorneal endothelial, IOP=intraocular pressure, logMAR=logarithm of the reciprocal of the minimal angle of resolution

The mean preoperative IOP was 32.7 ± 4.51 mmHg. At postoperative day 1 and at 1, 3, 6, 12, and 18 months after Keiki Mehta valve implantation, the mean IOP was 9.4 ± 1.96, 13.3 ± 1.86, 15.1 ± 2.78, 16.1 ± 2.38, 17.5 ± 4.67, and 17.3 ± 6.13 mmHg, respectively. The difference between the mean baseline IOP and IOP at each follow-up was statistically significant (P < 0.05) [Fig. 2].

Figure 2.

Preoperative and postoperative mean intraocular pressure after Keiki Mehta valve implantation plotted over time

The Kaplan–Meier survival curves for complete success and qualified success are shown in Fig. 3a and b. At the end of 18 months, the probability of complete success was 50%, while that of qualified success was 20%. Six eyes (30%) underwent failure and were planned for reimplantation of Keiki Mehta valve.

Figure 3.

(a) Kaplan–Meier curve showing the probability of complete success after Keiki Mehta valve implantation. (b) Kaplan–Meier curve showing the probability of qualified success after Keiki Mehta valve implantation

A reduction in the mean BCVA was seen from preoperative values (logMAR 1.2 ± 0.21) to postoperative day 1 value (logMAR 1.29 ± 0.25), which was statistically significant (P = 0.01). Three (15%) patients experienced a drop in vision by more than two lines on the first postoperative day, while the vision remained unchanged in 14 (70%) and the remaining three (15%) showed improvement in vision by more than two lines. At the final follow-up visit at 18 months, four patients (20%) had an improvement by more than two lines from preoperative vision, while six (30%) had a fall in vision by more than two lines [Fig. 4]. No significant difference in the mean BCVA was noticed between preoperative and 18 months follow-up visits (P = 0.08).

Figure 4.

Changes in vision from baseline at postoperative day 1 and the final follow-up

The mean number of antiglaucoma medications applied preoperatively was 3.1 ± 0.72, while that at 18 months follow-up was 1.75 ± 0.78. The was a statistically significant reduction in the number of antiglaucoma medications being used (P < 0.001).

Only one (5%) patient had hyphema, while three (15%) had shallow anterior chamber with hypotony on postoperative day 1 [Table 2]. Hyphema was seen in one patient with neovascular glaucoma and was managed conservatively with topical steroids and IOP-lowering agents, and it resolved within 7 days. The three patients who developed postoperative shallow anterior chamber with hypotony were managed with oral steroids and cycloplegic agents. Reforming the anterior chamber with viscoelastic substance was required in one patient.

Table 2.

Postoperative complications

	Total (%)
Immediate
Hyphema	1 (5%)
Shallow anterior chamber with hypotony	3 (15%)
Late
Cataract	3 (15%)
Tube exposure	2 (10%)
Bullous keratopathy with corneal edema	1 (5%)

Cataract was the most common complication in the late postoperative period (15%). Two patients having uveitic glaucoma and one patient with ICE syndrome developed cataract within 6 months and all three underwent phacoemulsification with foldable intraocular lens implantation. Two patients had tube exposure within 12 months of valve implantation and underwent scleral patch grafting. One patient who had valve failure developed corneal edema with bullous keratopathy due to high IOP at the end of 18 months and was planned for reimplantation of Keiki Mehta valve with optical penetrating keratoplasty.

Discussion

To our knowledge, there has been no study on Keiki Mehta valve implantation in refractory glaucoma. In our study, we observed a cumulative success rate of 70% at the end of 18 months, while the failure rate was 30%. For studies conducted with Ahmed glaucoma valve (AGV), a cumulative probability of success of 75% at 2 years was reported by Huang et al.,[4] whereas Ayyala et al.[5] reported a cumulative probability of success of 77% at 12 months. Souza et al.[6] reported the 1-year surgical success rate of AGV implantation in refractory glaucoma to be 80% and at 5 years, the success rate was 49%. The Ahmed Baerveldt Comparison (ABC) study[7] compared the long-term outcomes and complications between Baerveldt and Ahmed drainage devices. In the ABC study, at 1 year, treatment failure had occurred in 16% of patients with Ahmed valve and in 14% of patients with the Baerveldt device. The findings of our study were similar to what was observed in studies with Ahmed and Baerveldt GDDs.

We observed a rise in IOP at 1 month postoperatively in 20% of the cases, which marked the hypertensive phase, similar to what was observed in AGV studies.[8] The hypertensive phase is defined as a transient rise in IOP and may be associated with encapsulated bleb seen in the early postoperative period. It is believed to be caused by increased inflammatory mediators causing congested, thickened, and encapsulated bleb around the plate of the implant, increasing the resistance to aqueous flow.[9] The mean IOP gradually tapered off after the hypertensive phase weaned in 3–6 months.

On the first postoperative day, a reduction in mean BCVA from the preoperative value was observed. This significant drop in BCVA can be attributed to Descemet’s folds due to the tube touching the cornea in patients with shallow anterior chamber and the anterior chamber reaction in patients with hyphema. However, the vision improved as the cornea cleared and hyphema resolved by 2 weeks. The mean BCVA at the final follow-up at 18 months showed a drop from the preoperative value, but it was not significant (P = 0.08). Six patients showed a worsening of vision by more than two lines. These six patients had valve failure with raised IOP and microcystic corneal edema, while one of them had bullous keratopathy. The drop in mean BCVA in failure cases can be explained by the corneal edema, bullous keratopathy, and can also be due to the progression of the underlying retinal pathology, namely, PDR, CRVO, etc.

Hyphema and shallow anterior chamber were the complications observed in the immediate postoperative period. The incidence of hyphema in GDDs is reported to be around 13%–16.9%, while that of shallow anterior chamber and hypotony is reported to be 3%–32%.[4,10] In our study on Keiki Mehta valve, we observed a 5% incidence of hyphema, while the incidence of shallow anterior chamber and hypotony was about 15%, consistent with the findings for Ahmed valve studies. The reason for reduced incidence of hyphema could be preoperative panretinal photocoagulation and intravitreal anti-vascular endothelial growth factor (anti-VEGF) given to all cases of neovascular glaucoma, which, on most occasions, reduced the neovascularization of iris (NVI), thereby reducing the chances of hyphema.[11]

The hypotony and shallow anterior chamber seen in three patients in the immediate postoperative period resolved within 3 weeks. There was no bleb leakage in these patients, and an ultrasonography B scan confirmed choroidal detachment. These patients were managed conservatively with steroid and cycloplegic agents, while one patient required reforming the chamber with viscoelastic substance. The condition resolved within 2 weeks, but all of these patients later on developed valve failure with raised IOP and one also had corneal edema with bullous keratopathy at the end of 18 months. The probable cause of the corneal edema and bullous keratopathy could be damage to the endothelium of cornea by the tube in the anterior chamber in the early postoperative phase due to shallow anterior chamber. Early postoperative complications are a probable risk factor for failure of glaucoma shunt devices. In case a patient shows a persistent shallow anterior chamber with hypotony for more than 6 months, an ultrabiomicroscopy scan (UBM) should be performed to rule out cyclodialysis cleft.

Cataract was seen in three patients in the late postoperative phase among the six patients having normal phakic lens preoperatively. The possible cause of cataract in these patients might be surgical maneuver during valve implantation. All the three patients underwent temporal clear corneal phacoemulsification with intraocular lens implantation. It has been reported that cataract surgery adversely affects IOP control in eyes with glaucoma drainage implant (GDI) and a possible cause might be the flow of lens debris/viscoelastic material through the GDI tube into the bleb.[12,13] However, in our study, we did not observe any significant change in IOP at 1 month postoperatively (P = 0.004).

Tube exposure was observed in 10% of the patients in our study at the end of 12 months. Ayyala et al.[5] reported tube exposure in six cases (7%) of their series in AGV implantation. It is important to note that unlike previous studies on GDDs where scleral patch graft or pericardial graft was used, here AM–UC graft taken from the junction of umbilical cord and placenta was used for tube shunt coverage. AM–UC has antifibrotic, anti-immunogenic, and antiangiogenic properties and provides good tectonic support of the tube shunt, allowing direct visualization of the tube.[14] Scleral patch graft was performed in the patients who had tube exposure.

Conclusion

Keiki Mehta BP valve implantation is an effective and safe GDD and may be used as an alternative to the other existing valved GDDs in patients with refractory glaucoma.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.