Achieving Adequate Pupil Size in Cataract Surgery

Abstract and Introduction

Abstract

Purpose of review: Cataract surgery is the most common surgical procedure performed worldwide. Small pupils have been an eternal challenge for cataract surgeons; insufficient pupil dilation is associated with increased complication rates, including capsule rupture, vitreous loss, iris trauma or postoperative inflammation. The aim of the current review is to present the methods for pupil dilation and the risk factors for a small pupil in a cataract patient.

Recent findings: Risk factors for intraoperative small pupil include diabetes, intraoperative floppy iris syndrome, pseudoexfoliation syndrome, receiving glaucoma medications, having undergone previous ocular surgery and iris sphincter sclerosis from aging. There is a wide range of options to manage the small pupil, including pharmacological treatment, mechanical stretching, dilation with iris hooks or pupil expanders. We recommend a stepwise approach for intraoperative pupil dilation, from pharmacological mydriasis to pupil expanders.

Summary: The current article discusses risk factors for a small pupil and the methods for pupil dilation in a cataract patient. Every cataract surgeon needs to be ready to cope with a small pupil, both manifesting preoperatively and intraoperatively.

Introduction

Cataract surgery is the most common surgical procedure performed worldwide. With almost 20 millions surgery performed each year it could be considered as the most successful intervention in contemporary medicine.^[1] As the procedure has acquired technical advances, with sophisticated preoperative diagnostics and even more precise instruments, the patients' expectations have raised as well.

Small pupils have been an eternal challenge for cataract surgeons. A well dilated pupil is vital for cataract surgery including laser-assisted procedures, as it allows good access to the lens. Small pupils can be associated with increased complication rates, including capsule rupture, vitreous loss, iris trauma or postoperative inflammation.^[2] Difficulties to dilate the pupil are not an unusual finding; in a recent study on 1144 eyes undergoing cataract surgery, 6.8% of cases [95% confidence interval (CI): 5.2–8.8%] manifested a pupil size under 6 mm despite the application of the routine dilation regimen.^[3] Given that up to 4.0 million cataract surgeries are performed in the United States annually, and up to 20.0 million worldwide, would result in an annual rate of more than a million small pupil operations annually. According to Narendran et al^[2] the odds ratio of developing posterior capsule rupture (PCR), vitreous loss or both in eyes with small pupil is 1.45 (95% CI 1.1–1.91). Another study found that in cataract surgery complicated with vitreous loss 54.2% eyes had a pupil diameter of 6 mm or less, and only 38.6% of cases without vitreous loss manifested a small pupil (P = 0.003).^[4]

The aim of the study is to present the current methods for managing small pupils during cataract surgery.

Table 1. An overview of pupil expansion devices
Device	Producer	Additional information	Movie
Bhattacharjee pupil expansion ring	Madhu Instruments	Single-use, requires straight 23-G serrated forceps for insertion; options: square or hexagonal	N/A
Bhattacharjee pupil expansion ring (3rd generation)	Med Invent	Devices Single-use, requires straight 23-G serrated forceps for insertion	https://youtu.be/6XGgrIXhM40
Xpand NT	Diamatrix LTD	Pupil diameter 6.7 mm, incision width 2.5 mm	https://youtu.be/cpbw5TEsSAI
Malyugin Ring	MicroSurgical Technology	Single-use, introduced through a 2.2 mm incision with a dedicated injector	https://youtu.be/2K0fsuZWktA
Malyugin Ring 2.0	MicroSurgical Technology	Single-use, introduced through a 2.0 mm incision with a dedicated injector, available in 6.25 mm and 7.0 mm sizes	https://youtu.be/ABOd4cgYp5E
I-Ring pupil expander	Beaver-Visitec International	Single-use, preloaded	https://youtu.be/zzfGIx9AJk0
Assia Pupil Expander (APX) 200	APX Ophthalmology Ltd.	Single-use, does not require an injector	https://youtu.be/3OvxfcjqrZQ
OASIS Iris Expander	Oasis Medical Inc.	Single-use, packaged with easily loaded disposable injector, 6.25 or 7.0 mm version	https://youtu.be/G9GFjxTZZ4w
Graether 2000 Pupil Expander	Katena Products, Inc., NJ, USA	Single-use preloaded instrument, also pack includes an iris glide-retractor	https://youtu.be/9co0tlOPt3M
Morcher pupil dilator MR-5S	FCI Ophthalmics, MA, USA	Single-use, may be injected manually or with the Geuder pupil dilator injector	https://youtu.be/hjxAZkNo-7w
Perfect pupil device	Milvella limited	Single-use, engaged manually or with an injector	https://youtu.be/TCj8bAL2QTQ
Canabrava ring	AJL Ophthalmic S.A., Spain	Single-use, inserted with McPherson forceps	https://youtu.be/M8oHjg-JX8g

Table 2. Studies comparing mechanical methods for intraoperative pupil expansion
Reference	Design (number of eyes/patients)	Results and conclusion
Nderitu and Ursell [69]	Iris hooks (95) vs Malyugin ring (314)	Compared with no pupil expander, iris hooks were associated with an additional operating time of 14 min for consultants and 24 min for trainees, while pupil expansion ring with even more operating time of 4 and 6 min, respectively. The pupil expansion ring was associated with higher postoperative anterior uveitis and corneal edema rates. Pupil expander cases achieved equivalent visual acuity gains
Ghoneim and Wasfy [73]	Oasis ring (40) vs Manual stretching (40)	The mean pupil size was 6.00 ± 0.00 mm in the Oasis ring group, whereas it was 4.26 ± 0.48 mm in the nonmechanical device dilatation group (statistical significance). Time needed for pupil dilatation was longer in Oasis ring group (83–117 s) than with nonmechanical device dilatation (48–76 s). There was more liability for intraoperative difficulties as iris prolapse, minimal bleeding, and iris trauma in the nonmechanical device dilatation group. One month after surgery, in the Oasis ring group one eye (2.5%) manifested an oval-pupil and two eyes (5%) had minute tears; in the manual stretching group seven eyes (17.5%) had an oval-pupil and five eyes (12.5%) developed minute tears
Tian et al. [74]	Malyugin ring (1-right/1) vs I-Ring (1-left/1)	The circular I-ring resulted in smaller pupil distortion (ratio of the postoperative pupil area to the area of the circle of best fit) compared with the Malyugin ring. This was attributed to softer material, and less trauma to the iris
Wilczynski et al. [72]	Group 1: Malyugin ring (23/23) vs. Group 2: manual pupil stretching with 2 hooks (17/17)	Significant improvement in BCVA after the surgery in both groups, better postoperative BCVA in group 1. A significant difference in mean corneal endothelial cell loss measured 30 days postoperatively was 9.35 ± 11% in group 1, and 13.77 ± 8.0% in group 2 (P<0.05)