A randomized control study on post-operative iris distortion following small-pupil cataract surgery using B-HEX pupil expander versus Malyugin ring

Abstract

Background

The aim of the study was to evaluate postoperative pupil distortion following small pupil cataract surgeries performed using B-HEX and Malyugin rings (MR).

Methods

A randomized control trial was conducted from June 2020 to June 2023 at a tertiary eye-care hospital. The study consisted of 64 participants for cataract surgery with small pupil. There were two groups, one undergoing surgery with the use of B-HEX pupil expander and other with MR intraoperatively and the rest of the surgery was proceeded as per the convention. Areas of preoperative and postoperative images was calculated, put into an online software and pupil distortion was calculated in percentage. Two-tailed t-test was used to see the difference between the two groups.

Results

Mean age at presentation was 70.5 ± 10.12 years. Most common cause for small pupil was tamsulosin therapy. Mean size of small-pupil was 3.0 ± 1.1 mm. With the application of two rings, mean pupillary area preoperatively was 4178.23 ± 1589.46 and postoperatively was 6100.44 ± 2658.28 following the use of MR, respectively and 30,002.93 ± 13,193.40 preoperatively and 37,648.26 ± 15,207.01 postoperatively following the use of B-Hex ring respectively. Comparing baseline area from pupillary area at 1-month follow-up, a significant increase was noted for both the rings. Also, MR caused significantly more pupillary distortion compared to B-HEX ring (p < 0.05).

Conclusion

MR causes significantly more pupillary distortion in the postoperative period compared to B-HEX ring. Though, both the rings cause pupillary distortion, these devices expand the surgical area adequately, ease the procedure, decrease risk of complications achieving good functional visual outcomes.

Introduction

Phacoemulsification (phaco) cataract surgery in the presence of a small pupil presents a significant challenge in the cataract surgery. It not only poses difficulty during intra-operative procedures and manipulations but also increases the likelihood of post-operative glare due to pupillary distortion or iris trauma. Furthermore, patients with small pupils are more susceptible to complications like posterior capsule rupture (PCR), vitreous loss,^{1, 2, 3} iris sphincter damage, iris prolapse, bleeding, zonular damage and incomplete cortex removal.^{3, 4, 5, 6, 7}

The pharmacological agents like tropicamide with phenylephrine and combined intracameral mydriatic are helpful to dilate pupil preoperatively. Alternatively, mechanical pupil expansion techniques like synechiolysis, pupil stretching, sphincterotomies and use of pupil expansion rings are also recommended.⁸ Malyugin ring (MR) is currently the most widely used. It is a foldable and disposable square pupil-expansion device made of 5-0 polypropylene and features 4 circular coils or scrolls that engage the pupil edge to facilitate expansion.⁹ In the recent past, B HEX pupil expander is gaining increasing popularity due to ease of insertion and manipulation and achieving a circular expansion of pupil.^10,11

However, there is a lack of comprehensive studies in the literature comparing various pupil expansion rings and their effects on pupil size after phaco surgery.¹¹ Thus, this study aims at describing the behavior of pupil anatomy and quantifying the amount of distortion, specifically comparing postoperative pupil distortion after cataract surgeries with small pupils performed using the B-HEX and MR.

Materials and methods

A randomized control trial (RCT), registered in CTRI, was conducted from 30 Jun 2020 to 30 Jun 2023 at a tertiary eye-care hospital. The protocol was reviewed and approved by the institutional ethics committee. The research was conducted in accordance with the ethical standards mentioned in the Declaration of Helsinki. All patients provided informed written consent. The study consisted of 64 participants for cataract surgery with small pupil. Small pupil range starts from <6 mm and for experienced surgeons it may be even lesser.^{12, 13, 14} Thus, in our study, inclusion criteria included patients being worked up for phaco with PCIOL implantation with pupils dilating preoperatively to less than or equal to 4 mm. Patients were divided into two groups, one undergoing cataract surgery with the use of B-HEX pupil expander and other with MR. Patients requiring combined corneal, glaucoma or retinal procedure and patients with pre-existing macular oedema, post uveitis irregular pupils and harder cataracts (NS IV, mature cataract) were excluded from the study (Table 1). The intracameral dilators were used during the surgery and the cases who did not dilate intraoperatively despite intracameral dilators, surgery was continued as per the plan. The cases whose pupil dilated to a reasonable size intraoperatively following use of intracameral dilators were excluded from the study and underwent normal phaco.

Table 1.

Distribution of patients and rings used for small pupil based on nucleus sclerosis.

Grade of cataract		Ring		Total
		Malyugin	B-HEX
	NS2	21	24	45
	NS3	11	8	19
Total		32	32	64

Detailed ophthalmic evaluation of the selected subjects was performed including best corrected visual acuity, anterior segment evaluation by slit lamp biomicroscopy, grade of cataract and posterior segment evaluation. Patients on tamsulosin therapy were asked to stop the drug a week prior to the surgery. Patients were then randomized into two treatment arms using computerized random table. Informed consent was taken from all subjects after explaining the risks and benefits of the surgery. The surgery was performed by experienced surgeon via clear corneal incision. Intraoperatively MR or B-HEX pupil expander was inserted as per the treatment arm allocation, to expand the pupil mechanically and rest of the surgery proceeded as per convention. Foldable intraocular lens was implanted. No other mechanical method of pupil dilatation was used.

Pupil shape was assessed. Quantitative assessment was carried out by measuring the longest and shortest horizontal axis (in mm) postoperatively at 1-month follow-up and computing for the eccentricity index (Fig. 1). Using an online Corel image analysis software, the areas of both the preoperatively and postoperatively images for each patient, was calculated. For example, area of image 3a is 68728px2 (preoperative) and area of image 3b is 137159px2 (postoperative) was calculated (in mm²), put into the software and pupil distortion was calculated in percentage. Thus, degree of pupil irregularity was assessed by estimating the percentage of pupil irregularity using photographs (Fig. 2, Fig. 3).

Fig. 1.

Images of pupil depicting quantitative assessment of area of preoperative (a) and postoperative pupil; (b) to compute for the eccentricity indices.

Fig. 2.

Slit-lamp photographs shows preoperative pupil and postoperative pupil (A–C) after the use of Malyugin ring.

Fig. 3.

Slit-lamp photographs of preoperative pupil and postoperative pupil after the use of B-HEX ring (A–C).

The data were collated in Microsoft Excel (2010) worksheet. Statistics Package for Social Sciences (SPSS) software 2016 was used to analyse the data. Categorical variables were presented as number (n) and percentage (%). Continuous variables were calculated as mean ± standard deviation (mean ± SD). Two-tailed t-test was used to see the difference between the groups. P < 0.05 was considered statistically significant.

Results

A total of 64 eyes of 64 patients were included in the study. Mean age at presentation was 70.5 ± 10.12 years. Patient demographic data and probable risk-factors for poorly dilating pupil are summarized in Table 2. There were 34 males (56.67%) and rest were females. Most common cause for small pupil was tamsulosin therapy followed by pseudoexfoliation syndrome. Mean size of small pupil was 3.0 ± 1.1 mm. After the instillation of standard topical mydriatic agents, the mean pupil diameter increased to 3.8 ± 1.1 mm.

Table 2.

Patient demographics and probable risk-factors for poorly dilating pupil.

Patient Characteristics (n = 64)		Frequency
Age (in years)	70.5 ± 10.12
Gender (n)	Males	34
	Females	30
Concomitant risk factors for poorly dilating pupil (n)	Tamsulosin therapy	22
	Diabetes mellitus	19
	PEX	21
	Others	02
Grade of cataract (nuclear sclerosis)	Grade 2	45
	Grade 3′	19
Size of small pupil (mm)	3.0	7
	3.5	13
	4	44
Preoperative visual acuity	6/18–6/24	36
	6/36–6/60	28

With the application of two rings randomly during the cataract surgery, the mean pupillary area preoperatively and postoperatively is described in Table 3. The follow-up was done at 1-month. There were 44 patients with 4 mm size of pupil and half of them were treated with Malyugin (22 cases) and other half with B-HEX (22 cases).

Table 3.

Comparing the baseline area from pupillary area at 1-month follow-up for both the rings.

Rings		Mean	Std. deviation	95% Confidence interval of the difference		p-value
				Lower	Upper
Malyugin ring	Preoperative - Postoperative area	−1922.21	1330.45	−2401.89	−1442.53	0.000 (<0.05)
B-HEX ring	Preoperative - Postoperative area	−7645.33	3961.93	−9073.75	−6216.90	0.000 (<0.05)

Mean pupillary area (in mm²) preoperatively was 4178.23 ± 1589.46 and postoperatively was 6100.44 ± 2658.28 following the use of MR, and 30,002.93 ± 13,193.40 preoperatively and 37,648.26 ± 15,207.01 postoperatively following the use of B-HEX ring respectively. Fig. 2, Fig. 3 show slit-lamp photographs of preoperative pupil and postoperative pupil after the use of MR and B-HEX ring respectively. Comparing baseline area from pupillary area at 1-month follow-up, a significant increase was noted (p = 0.00) for both the rings (Table 3). Also, it was observed that MR causes significantly more pupillary distortion compared to B-HEX ring (p < 0.05) (Table 4).

Table 4.

Mean percentage pupillary distortion after use of Malyugin ring and B-HEX ring.

Findings of pupillary area	Mean ± SD
	Malyugin ring (n = 32)	B-HEX ring (n = 32)
Correlation between the two areas for the two rings (p-value)	0.00	0.00
Mean pupil distortion for the two rings (%)	45.73%	30.08%
Correlation between the pupil distortion for the two rings (p-value)	0.029 (< 0.05)

Application of both the rings was successful in all eyes (100%). They remained engaged and stable throughout the surgery. The rings were associated with an additional operating time of 1–2 min. In our experience, we found that placing the MR around the pupillary margin was relatively easier than placing the B-HEX ring, however, when it came to removal the situation was reversed. Neither pupil expander ring was associated with much of the intraoperative complications. With respect to safety, the only significant adverse event encountered was a single case of posterior capsular rupture in a case of MR, which was unrelated to the ring's application and culminated in successful placement of foldable IOL with good centration in the post op period.

There were only 3 cases of intra-operative iris prolapse (2 with B-HEX ring and 1 with MR), however, surgery could be completed without any untoward event in all the cases. All the cases had good post-operative recovery. Few cases had minimal corneal edema and anterior chamber reaction on the day 1 of surgery, which eventually got resolved. None of our case were detected to have macular edema, even the case who suffered PCR during the surgery.

Average rate of change at day 30 was loss of endothelial cell count of 4%–6% after the use of MR and BhR; with no clinically significant change in corneal morphology owing to the additional intraocular instrumentation due to their use in all the cases.

All the cases resulted in good visual recovery with best corrected visual acuity ranging between 6/9– and 6/6 at 1-month follow-up.

Discussion

The sense of achievement after a cataract surgery is greatly influenced by the postoperative results of a skilled surgeon, who had access to appropriate surgical instruments and an adequate degree of visualization and manipulation area during the procedure. While there is no universally accepted definition for a small pupil, for any experienced surgeon the threshold of pupil size to be able to perform phaco lies in the range of 4.5–5.0 mm.¹³ In another study from 2017, pupil size was characterized as normal (>6 mm), small (4–6 mm), or very small (<4 mm).¹⁴ If the pupil is smaller, various pupil expansion strategies are strongly recommended.

While the literature provides several risk-factors associated with small pupils like PEX, uveitis, diabetes mellitus, ocular trauma, prior ocular surgery, refractive surgery or use of certain pharmacologic agents like tamsulosin; our study found patients on tamsulosin therapy followed by PEX, as the most common cause for small pupil.

Iris hooks have been noted to be more cumbersome, laborious and time consuming.^9,15,16 However, with the introduction of MR and B-HEX, among others, the threshold for utilization of pupil expansion rings has been lowered.^15,17 In our study, these two specific rings, were used randomly for cases with small pupils instead of utilizing any other means of mechanical pupil dilation.

A pupil expansion device that achieves a 5.5 mm pupil size is considered adequate for carrying out phaco safely and effectively.¹⁷ An area of 5.5 mm diameter provides enough space for performing capsulorrhexis and nucleus disassembly during the surgery.

MR evenly expands the pupil and needs an injector. With the introduction of B-HEX ring the small pupil game has been revolutionized for ophthalmic surgeons especially in developing countries like India. Nevertheless, the use of pupil expansion devices may necessitate the acquisition of additional skills, instruments and potential expenses.

According to the recommendation of Bhattacharjee, it is preferable to bimanually stretch nonelastic pupils smaller than 4 mm–5 mm before placement of the device. This technique induces controlled micro-tears of the fibrosed pupil margin and minimizes the need for extensive manipulations of the B-HEX ring.¹⁰ In our study, the primary objective was to compare the rate of post operative pupillary distortion following the use of MR versus B-HEX ring. The specific maneuver of stretching the pupil before placement of B-HEX ring is already known to cause some degree of pupillary distortion on its own merit.¹⁰ This additional distortion could have potentially confounded our results; hence, we intentionally omitted this step in our study.

Our study included cases of small pupils irrespective of the depth of anterior chamber and we had a reasonable mix of patients, however, we didn't encounter any trouble during any step of surgery per se due to the presence of B-HEX or MR in the eye further validating our findings.

To remove the B-HEX ring, a notch is simply disengaged allowing the ring to be decoupled from the iris before carefully extracting the ring from the eye. The trailing notches let go of the iris margin in a gentle manner without causing any unnecessary pulling or trauma. Alternatively, two flanges can be disengaged prior to removal. Owing to its flexible nature, the ring gently glides through the incision without hitching or snagging it. Importantly, the B-HEX ring demonstrated remarkable durability, remaining intact without breaking and buckling during introduction or revocation. Nevertheless, removal of MR does necessitate specific skills to retract it into the injector system prior to its extraction.

The pupil has a propensity to heal postoperatively, but unlikely to become more distorted. Pupil dilation with iris hooks or manual stretching result in distortion postoperatively because of the limited points of contact between the device and the iris. The rings offer an advantage of evenly distributing the force, either between 8 points in MR or 6 points in B-HEX ring and were considered to be causing much lesser pupillary distortion postoperatively otherwise. Nonetheless, in our study, it has been observed that the use of these rings causes significant amount of iris distortion in the post operative period.

In our study involving 64 eyes with small pupils, successful insertion and positioning of the two rings, the rings effectively maintained adequate visualization throughout the surgical procedure, eliminating the need for additional maneuvers to achieve an adequate field of view while performing cataract surgery.

Our study revealed pupillary distortion following the utilization of both types of rings. However, a greater degree of distortion was seen with the MR, compared to that of B-HEX ring. Notably, there has been scarcity of studies in the existing literature that directly compares the rate of post-op pupillary distortion between the readily employed pupil expansion rings and establish the superiority of one over the other. A previous study done by Tian et al. reported increased pupillary distortion after the use of MR.¹¹

It was observed in our study that the rate of post operative pupillary distortion was more with MR as compared to B-HEX ring, however, both the rings resulted in a significant amount of pupillary distortion from the baseline. Moreover, the disparity in the rate of pupillary distortion following the use of MR and B-HEX ring was statistically significant. It is worth noting that we did not encounter any case of spontaneous ring disengagement, bleeding, iris tears or capsulorrhexis tears during the surgical procedures.

Conclusion

Both the rings affect pupil anatomy and cause distortion of pupil postoperatively. MR causes more pupillary distortion when compared to B-HEX. Despite the fact that both the rings cause pupillary distortion, these devices equip a surgeon with a surgical tool, which expands the surgical area adequately, ease the procedure, decrease risk of complications and results in good functional visual outcomes.

Disclosure of competing interest

The authors have none to declare.