Everything you ever wanted to know about small pupil phacoemulsification – Part 2.
My last column (EuroTimes December 2016/January 2017, Vol 21 Issue 12/Vol 22 Issue 1, Page 8-9) dealt with preoperative and intraoperative considerations for small pupil phacoemulsification. This column deals with the various pupil expander devices available for aiding surgery.
IRIS STRETCHING DEVICE:
The Beehler Pupil Dilator™ (Moria, USA) is a tri-pronged device that utilises three retractable micro-fingers together with an external micro-hook to stretch the iris. Once stretched, the instrument is removed and phacoemulsification continued. Cycloplegics must be given preoperatively. An irrigating model with two flexible U-shaped retractors, together with an external micro-hook, is also available that provides three-point stretch.
Prolene iris hooks were introduced by de Juan and metal hooks by Mackool. Prolene hooks are the most commonly used, are disposable, and the degree of dilatation depends on the amount that the silicone tyre is slid down over the hook.
Iris hooks should be introduced through small, short, peripheral paracenteses parallel to the iris plane in order to expand the pupil sideward towards the limbus. Creating paracenteses that are more clear corneal and angled downwards tents the iris upwards towards the cornea, causes obstruction to the passage of instruments, produces iris chafing, thermal damage and also shallows the anterior chamber.
The most commonly used configuration is that of four hooks applied in a square or diamond (Oetting et al) configuration, the latter having advantages of better visualisation and manoeuvre-ability of the phaco probe. Iris hooks may cause damage to the pupillary margin, especially in rigid pupils and also if the iris has been stretched excessively. Dilatation should therefore be done only to the degree required to uneventfully perform phacoemulsification, generally 5mm.
The Assia Pupil Expander (APX Ophthalmology Ltd, Israel) utilises two tiny, spring-loaded devices inserted 180 degrees from each other, perpendicular to the phaco incision. Each device is like a miniature blunt scissor, the arms of which open out to hold the iris expanded.
There are many ring designs available. These have advantages of being able to be inserted through the phaco incision and not requiring additional paracentesis incisions. These mechanically dilate the pupil and have advantages of creating the least amount of sphincter damage, providing vertical stability to iris tissue, preventing undue movement, iris billowing or iris prolapse during surgery. They are very useful in intraoperative floppy iris syndrome (IFIS).
Malyugin Ring® (MicroSurgical Technology, USA):
The Malyugin Ring, which has proven very popular, was designed by Boris Malyugin. It has a square design with loops at all four corners which engage the iris margin. It has the advantage of retaining a round pupillary shape when the device is in situ by giving eight points of fixation. It is available in two sizes – 6.25mm and 7mm and is also now available in a newer model that allows insertion through less than 2.2mm incisions. A special injector allows safe implantation and explantation. Care should however be taken while explanting that the edges of the loop go inside the injector before withdrawing the ring.
I-Ring® Pupil Expander (Beaver Visitec, USA):
This is a single-use pupil expander made of polyurethane. It gives uniform pupillary expansion of about 6.3mm. It has hinges that enhance flexibility and fold-ability, channels that safely hold the pupillary margin, four corners that hold the iris stroma in place and positioning holes for safe positioning with the Sinskey Hook. There is an inserter for easy implantation and explantation.
B-HEX Ring™ (Med Invent Devices, India):
Created by Suven Bhattacharjee, this has a uniplanar design that engages the pupil in the same plane as the device. It is wafer-thin (0.075mm) and comes in a preloaded carrier which presents the device sterile at the incision. Simple manoeuvers with a Sinskey Hook are used to glide the device through the incision (0.9–2.8mm) and tuck alternate flanges under the pupil margin. The eyelets and the micro-notches on the flanges help in engaging the pupil. At the end of surgery, the device is disengaged with a reverse Sinskey and explanted with a McPherson forceps.
The Graether Pupil Expander™ (Eagle Vision, USA) is an incomplete silicone ring with a groove on the outer surface that engages the pupillary margin to give an expanded inner pupillary margin of 6.3mm. The Morcher® Pupil Dilator 5S is a 300-degree, semicircular, elastic PMMA ring which gives a pupil size of about 5-6mm.
The Perfect Pupil® device (Milvella Ltd, USA) is made of flexible polyurethane with a small arm that remains externalised and provides a window for the phaco probe. It has a groove, scalloped tabs for 315 degrees, fenestrations for manipulation and gives dilatation to 7mm. The Siepser Iris Protector™ (Eagle Vision, USA) and the Clarke Ring are other models.
Stretching devices can cause sphincter tears as well as make the iris flaccid, leading to intraoperative iris prolapse. Devices creating circular expansion are more physiological than those with four-point dilatation. Intraoperatively, implantation and explantation of all devices should be done taking care not to damage other intraocular structures such as corneal endothelium, iris, angle and lens capsule, and these should be inserted only under viscoelastic cover.
If implanted after creating the rhexis, care should be taken not to unintentionally engage and stretch or tear the rhexis. Intraoperative disengagement may occur causing accidental iris aspiration. Explantation should be done gently to avoid iridodialysis from rough handling. Minimal damage to the iris sphincter may occur secondary to the stretch and can cause intraoperative bleeding and pigment dispersion.
Varying degrees of postoperative mydriatic pupil, pupillary atony or irregularity in the shape may be seen. These are more significant in patients with an atrophic or rigid pupil and fibrotic sphincter.
There may be an increased inflammatory response postoperatively with all pupillary dilators, especially in predisposed patients (uveitis, pseudoexfoliation, diabetes), and this should be anticipated and treated accordingly with topical steroids and nonsteroidal anti-inflammatory drugs. In case of a posterior capsular rent, care should be taken to avoid the device from dropping into the vitreous.
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India. She has a patent pending for the Glued Capsular Hook