Clinical experience with a mechanical pupil dilator
Cataract patients with small pupils present a particular challenge for surgeons. Using a pupil expansion device such as the Malyugin ring may help to reduce the complications associated with small pupil cataract surgery.
Reviewed by Jorge Alio
Cataract surgery in patients with small pupils is associated with a raft of complications including damage to and prolapse of the iris into a wound, the creation of a small anterior capsulorrhexis (leading to anterior capsule damage), incomplete removal of the cortical material, postoperative inflammation and a higher risk of posterior capsule rupture.1,2
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A small pupil also hampers visualisation of the peripheral capsule, making it difficult to ensure that the lens and haptics are placed completely in the bag.
Achieving and maintaining adequate mydriasis is crucial in preventing serious complications. However, we are fortunate to have more interventions and instruments available than ever before to help us deal with these difficult cases.
Managing small pupil size
There are a number of options for increasing pupil size, including the use of intracameral mydriatics such as Shugarcaine and epi-Shugarcaine, viscodilatation and pupil-expansion devices. The pupil-expansion devices available include plastic and metal iris hooks, Clarke and Siepser rings, the Graether expander (Eagle Vision Inc.), the 5S iris ring (Morcher GmbH) and Perfect Pupil (Milvella Pty Ld), to name just a few.
In the past, I nearly always used iris hooks in patients with small pupils. However, for my difficult cases, including patients with intraoperative floppy iris syndrome and pseudoexfoliation syndrome, I now almost always use the Malyugin ring (MicroSurgical Technology, Inc.).
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The brainchild of Boris Malyugin, professor of ophthalmology and deputy director general at the S. Fyodorov Eye Microsurgery State Institution in Russia, the Malyugin ring was designed to overcome some of the disadvantages associated with other pupil expanders, such as overstretching of the iris sphincter and extended surgery time. The Malyugin ring is a square-shaped device made from 5/0 polypropylene with a paperclip-scroll design that holds the iris at eight equidistant points.
The result is a round pupil, rather than the square one formed with four iris hooks, and circumferential protection of the iris (Figure 1). Helpfully, the device is available in two sizes, 6.25 mm and 7.00 mm, which offers a degree of flexibility. For example, while the 6.25 mm ring is suitable for most cases, the 7.00 mm ring is more suitable when placing an IOL with a large-diameter optic, or for surgeons who use the divide-and-conquer technique.
Key advantages
Key advantages of the Malyugin ring
As noted earlier, I used to employ iris hooks during cataract surgery in patients with small pupils. In doing so, it was necessary for me to create four or five corneal incisions.
Although I never experienced any problems with hooks, there is the risk that they might overstretch the iris sphincter and create iris defects. The main advantage of the Malyugin ring is that it can be inserted via the main clear corneal incision, eliminating the need for multiple incisions.
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There is no need to widen the main incision. I use a 2.2 mm incision and can easily place the Malyugin ring through it. This obviously saves considerable surgical time and is less invasive than using iris hooks.
The Malyugin ring also eliminates stretching or distorting of the pupil. Because it affords minimal contact with the iris, it is less likely to damage the iris sphincter than other rings or hooks. Perhaps not surprisingly, I no longer turn to hooks when I need to perform mechanical pupil expansion.
The Malyugin ring is very easy to use thanks to its disposable injector, which aids placement of the ring around the edge of the pupil. Typically, the first three of the four paperclip-like scrolls are very easy to insert.
However, to facilitate insertion of the fourth scroll close to the main incision, I would advise using the injector and an Osher micromanipulator (MicroSurgical Technology, Redmond, WA), which is designed for the specific geometry of the Malyugin ring, through a second incision.
After surgery, the same Osher micromanipulator can be used to remove the twelve o’clock scroll, while the injector can be used to quickly and smoothly remove the ring without trauma to the iris sphincter (Figure 2). Unlike other pupil-expansion devices, the injector can be disposed of once surgery is complete, eliminating the need for sterilisation and its associated costs.
Additional tools
Additional tools
Of course, I also use other pupil expanders and hooks, although perhaps less frequently than the Malyugin ring.
Alcon iris hooks (Alcon Laboratories, Inc., Fort Worth, TX) are useful in specific cases where I need to open the iris locally rather than globally. In cases of traumatic damage, some local pupillary defect or iris desinsertion may happen and iris hooks help ensure safer cataract surgery.
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Thankfully, small pupils are not very common so, for most surgeons, the need for hooks and mechanical dilators such as the Malyugin ring is somewhat limited.
However, to date and in my experience, the use of the Malyugin ring appears to be safe without any intraoperative difficulties or complications observed.
It undoubtedly provides greater confidence to the surgeon in offering safer and more effective cataract surgery to patients with small pupils.
References
1. J.D. Bartlett and K.M. Miller. Compr. Ophthalmol. Update 2003; 4: 171-176.
2. Malyugin B. Cataract Refr. Surg. Today Europe. 2013: 26-30.
Cedric Schweitzer, MD, is an ophthalmologist based at the University Hospital Bordeaux in France. Dr Schweitzer has no financial interests in MicroSurgical Technology, Inc.
E: cedric.schweitzer@chu-bordeaux.fr
