Pupil Expansion Devices and Mechanical Stretching of the Pupil
Nondilating or poorly-dilating pupils pose a significant challenge during cataract surgeries. Intraoperative difficulties include poor visualization of the peripheral cataract and capsulorrhexis/anterior capsular rim, iris prolapse, iris trauma, intraoperative further decline in dilation, and posterior capsular rupture. Various strategies have been employed in such patients to overcome the challenges. These strategies include ensuring maximal pupillary dilation with the use of tropicamide and phenylephrine drops, preoperative nonsteroidal anti-inflammatory drop to possibly prevent intraoperative miosis, viscodilation of the pupil, mechanical stretching, pupillary expansion devices, and iridectomy/sphincterotomy/pupilloplasty. This article discusses various available methods for pupillary stretching and mechanical pupil expansion devices/pupil expanders/ pupil enlarging devices.
Prerequisites before pupillary stretching and using pupil expansion devices
Maximal pharmacological dilation of the pupil should be achieved in such cases of poorly dilating or non-dilating pupils. Ophthalmic viscosurgical devices (OVDs) must be used in the anterior chamber to dilate the pupil to the maximum and to maintain the anterior chamber. Care should be taken to avoid overfilling the anterior chamber which may push iris backward and may cause difficulty in fixing the pupil expansion devices. Also, some OVD causing a mild separation of iris and the anterior capsule of the lens helps in the proper engagement of the expansion device. Any pupillary membrane should be removed using Utrata forceps or a similar instrument. Posterior synechia and all anterior capsular adhesions with the iris should be lysed using a blunt/smooth instrument. Care should be taken to avoid rupturing the anterior capsule and to avoid traumatizing the iris root (which can cause severe pain, hyphema, and iridodialysis in severe cases). As pupillary stretching may cause pain, it is prudent to augment the anesthesia using topical, intracameral, subtenon, or peribulbar anesthesia. Only after this, pupillary stretching methods or pupil expansion devices can be used. Very rigid and small pupils may need to be stretched bimanually with other instruments before pupil expansion rings can be engaged to the pupil.
Stretching of the pupil with 2 instruments
Frye popularized this technique originally described by Dr. Keener (Indianapolis, Indiana). This can be performed using 2 different instruments which may be Sinskey hooks Blunt choppers Graether collar buttons Y hooks Lester hook Kuglen hooks Fukasaku Small Pupil Snapper Hook
These 2 instruments are inserted from 2 different wounds at least 30° apart. The anterior chamber should be filled with OVD and should not collapse. The instrument tip is used to engage the pupillary margin 180° apart. Then the 2 instruments are carefully moved in the opposite direction (video 1) toward the iris root. This stretch is maintained for some time (around 3-5 seconds). Some minor bleeding points at the pupillary margin may be noted during this maneuver. If reasonable pupillary dilation is not achieved, similar pupillary stretching is performed at a line perpendicular to the previous location. Peters pupillary dilator (Rhein Medical Inc., Tampa, Florida) This has a J-like loop at the tip which helps in engaging the pupillary margin.
Brown pupillary dilator (Rhein Medical Inc., Tampa, Florida)
The tip has a curve to engage the pupillary margin. Both side port and main incision versions are available. Side port version has one c loop facing distally. Two such instruments can be used for pupillary stretching. The main incision (phaco incision) version has 2 c loops facing away from each other and these engage the sub-incisional and distal pupillary margin and the difference between 2 c loops can be increased leading to pupillary dilation.
Keuch Pupil dilator (Katena)
It is similar to the phaco-incision Brown pupillary dilator. The pupillary margin is caught at 2 places 180° apart, and then the 2 catches are separated maximally to dilate the pupil. https://www.katena.com/keuch-pupil-dilator-k3-4950
Beehler pupil dilator
This is used for stretching the pupil at 4 points. Initially, the dilator is introduced inside the anterior chamber through the single plane main wound (around 2.5 mm). The primary microhook engages the sub-incisional pupillary margin. The other 3 microhooks are also engaged at the pupillary margin and slowly simultaneous and symmetrical dilation at 4 points is achieved using this dilator. The pupil is held at maximal dilation for a few seconds and then the dilator is disengaged and removed. This creates multiple microsphincterotomies and makes the pupil to about 6-7 mm in diameter. Another version of the instrument with 2 microhooks is also available.
Use of phaco sleeve
The phaco sleeve may be used to stretch the sub-incisional iris peripherally, thereby increasing the field of view. However, this maneuver may cause iris prolapse later in the surgery and may be associated with pigment loss/iris chafing/iris injury.
Using the lens or lens nucleus to keep the pupil dilated/ semi-dilated
This is a type of flip and chop. In very small pupils, after hydrodissection, a part of the lens is brought up to the anterior chamber while part of it remains in the bag. A sufficiently large capsulorrhexis is mandatory for safe manipulation of the lens in the pupil and for bringing it out of the capsular bag. This lens now mechanically keeps the pupil dilated, The corneal endothelium is coated with cohesive OVD and the lens is now chopped. The energy delivery in the eye may be reduced with phaco power modulations, and the phaco is performed at the iris plane, not at the anterior chamber. Such maneuvers may protect from posterior capsular damage, but care should be taken to protect the corneal epithelium also.
Mackool self-retaining titanium mechanical hooks
These have a defined length. Usually, 3-4 hooks are used via self-sealing peripheral corneal/limbal paracentesis (1.5mm) incisions leading to a triangular or square-shaped pupil. The pupil is stretched with another instrument (iris pusher) and then the pupillary margin is engaged in the hooks. The hooks are removed after the surgical procedure. Challenges with these hooks include increased surgical time and fluid loss through the incisions.
Nylon iris hooks with silicone sleeve
These are flexible J shaped iris retractors made of nylon which can be inserted through smaller paracenteses compared to Mackool retractors. A silicone sleeve is present to act as a stop or anchor. The design was attributed to De Juan. The various shapes of sleeve include disc, tube (encircling the iris retractor), and ????? The plane of the sleeves usually has a defined relationship with the plane of the hook so that the sleeve may give a clue to the orientation of the tip of the hook when it is not available.
The entry point for the iris hooks should be at the posterior limbus at the level of iris and anterior corneal wounds (which cause tenting of the iris) should be avoided. Most surgeons use at least 4 iris hooks. Four wounds are made 90° apart. All iris hooks are inserted and the pupillary margin is engaged. Then, the iris hooks are retracted causing pupillary dilation and the silicone sleeve is slid forwards. The sleeve helps in anchoring the hook so that it does not slide inside the anterior chamber making the pupil small. When tightening the hooks, the maneuvers should be gentle, otherwise, hyphema, iris injury, or anterior capsular injury may occur. It is suggested that the pupil should not be stretched to more than 5mm using iris hooks to avoid iris trauma, hyphema, and postoperative atonic and irregular pupil.''
Some surgeons make wounds for the iris hooks just behind the primary wound and side wounds. Iris hooks can be inserted at any stage of the cataract surgery if the pupil becomes small. However, since the ends of some iris hooks are quite sharp, care should be taken not to include the capsulorrhexis margin in the iris hook which can cause radial tear of the anterior capsule and even extension to posterior capsular tear. Adequate OVD should be injected inside the anterior chamber and also between the iris and lens capsule especially when the iris hook is inserted after the capsulorrhexis has been made. The iris hooks are removed after the implantation of the intraocular lens (IOL). For removal, the anterior chamber should be filled with OVD. The iris hook is first pushed inside to disengage the pupil. then it is drawn outwards. When the tip of the hook reaches the paracentesis, the plane of the hook is kept similar to the plane of the incision. Now, the body of the hook is made parallel to the limbus and pushed gently parallel to the limbus to manipulate the hook out of the wound.
Madlab Iris retractor
Pupil expansion devices
Hydroview Iris Protector Ring (Grieshaber)
This is a hydrogel device which in its dehydrated oval form can be placed in the anterior chamber through a 3 mm incision. The device engaged the pupillary margin via flanges and enlarges in size with hydration. It can be manipulated to aid in its expansion. It is removed after the placement of IOL through the same incision.
Siepser iDeal iris ring (Eagle vision)
This ring has been devised by Dr. Steven B Siepser from Philadelphia, USA. This is similar to the Hydroview iris protector ring. It met FDA guidelines in 2016 and was clinically launched in 2017. This is an irregular oval hydrogel ring which expands on hydration. https://www.youtube.com/watch?v=wkrLH5L3m-w
Graether 2000 pupil expander system (Eagle vision, Memphis, Tenn/Katena Products, Inc., Denville, NJ, USA)
This is a soft silicone ring. It has a circumferential groove for engaging the pupillary margin. It is inserted inside the eye using a preloaded sterile device
Morcher Pupil dilator Type 5S
This is an incomplete elastic ring made of solid polymethylmethacrylate (PMMA) which can be injected into the anterior chamber with Geuder pupil dilator injector (2.5mm incision, #G-32970, FCI Ophthalmics, Marshfield Hills, MA) or manually. The maximal overall diameter of this device is 7.5mm and the thickness minimum thickness of the ring is 0.15 mm. At the sides, to engage the pupil the external area has a 0.6mm notch. The thickness of the device at the notch is 0.9mm. This device provides pupillary dilation of around 5-6mm. The device creates even tension at around 300° of the supported pupil and the chances of sphincter damage and postoperatively deformed pupil may be less. After insertion in the anterior chamber, the central segment of the device is manipulated to engage the distal pupillary margin. Then, the ends of the device are engaged in the pupillary margin with the help of the eyelets in the ring. For the removal of the device, first, the ends are disengaged. Then, the ring is removed with the use of forceps.
Malyugin ring (MicroSurgical Technology/MST Inc., Redmond, Washington, USA)
This ring is devised by Dr. Boris Malyugin from Moscow, Russia. The initial version was marketed in 2007. It is a square-shaped device made of 4-0 polypropylene with coils at its 4 corners which engage the iris. However, it has 8 points of fixation with the pupillary margin (at 4 coils and points located at the middle between the coils) and creates a round and dilated pupil. The device is injected inside the anterior chamber (via a 2.5mm incision) with a special disposable injector that is supplied with the ring. The coils may be engaged to the pupillary margin with Osher/Malyugin manipulator, Sinskey hook, Kuglen hook, Lester hook, or similar instruments. The current version is called Malyugin ring 2.0 can be inserted through a 2 mm incision using a modified injector. Other modifications from the previous model include thinner material (5-0 polypropylene), wider coil gap, and more soft and elastic material. This model was released in 2016. Two sizes are available 7 mm and 6.25 mm. The inventor recommends that high viscosity OVD like Healon 5 is used to create a space between the anterior lens capsule and the iris, as the material of the device is elastic. Thre coils (distal and 2 side coils) may be used to engage the pupillary margin automatically during insertion, leaving the proximal-most coil the only coil to be manipulated to hold the iris margin. Modifications Agarwal's modification- A suture is passed through the leading coil so that the device can be retrieved in cases with suspected posterior capsular rupture [Agarwal A, Malyugin B, Kumar DA, Jacob S, Agarwal A, Laks L. Modified Malyugin ring iris expansion technique in small-pupil cataract surgery with posterior capsule defect. J Cataract Refract Surg. 2008;34(5):724‐726. doi:10.1016/j.jcrs.2008.01.024]
For ectopic pupil- The ring can be used to dilate the pupil and an iris hook may be used to center the ring. [Malyugin B, Sobolev N, Arbisser LB, Anisimova N. Combined use of an iris hook and pupil expansion ring for femtosecond laser-assisted cataract surgery in patients with cataracts complicated by insufficient mydriasis and an ectopic pupil. J Cataract Refract Surg. 2016;42(8):1112‐1118. doi:10.1016/j.jcrs.2016.07.001]
In cases with zonular instability and small pupil, the side coils of the ring may be used to hold both the iris margin and the capsulorrhexis edge. Thus, a single device is used for both pupillary dilation and stabilization of the capsular bag [Zarei-Ghanavati S, Bagherian H. Stabilizing the capsular bag and expanding the pupil with a pupil expansion device. J Cataract Refract Surg. 2015;41(9):1801‐1803. doi:10.1016/j.jcrs.2015.08.010]
Milvella Perfect Pupil (Becton-Dickinson)
This is described by Dr. John Milverton, of Sydney, Australia. This is a device with a 7 mm internal diameter made from polyurethane. It may be inserted inside the anterior chamber with a forceps or an injector through the main port which has to be mildly enlarged to accommodate both the photo/irrigation aspiration handpiece and the portion of the ring which protrudes outside the phaco wound. The device is first inserted into the anterior chamber which has been filled with OVD. The proximal-most area of the ring is first engaged, then adjacent areas are progressively engaged in the pupillary margin. The protruding portion of the ring helps in the removal of the ring after its use. https://www.youtube.com/watch?v=TCj8bAL2QTQ
This has been invented by Dr. Suven Bhattacharjee from Kolkata, India. B-HEX pupil expansion ring (Med Invent Devices, Kolkata, India) is a third-generation Bhatterjee ring.[Bhattacharjee S. B-HEX pupil expander: Pupil expansion redefined. Indian J Ophthalmol. 2017;65(12):1407‐1410. doi:10.4103/ijo.IJO_673_17] This is a hexagonal device made of 5-0 monofilament polyamide ring which dilates the pupil to 5.5mm (with 6.5mm model). Three models are available 6, 6.5, and 7mm. It has notches at the corners and flanges at the sides to hold the pupillary margin. Alternate flanges are tucked under the iris. It can be implanted through a 1 mm incision using the inserter provided with the ring. To engage the iris Sinskey hook or other instruments are needed to manipulate the device.
Assia pupil expander (APX Ophthalmology, Haifa, Israel)
This scissor-like device with a spring mechanism has been developed by Dr. Ehud Assia from Israel. The initial version (introduced in 2013), APX100 was made of metal and was reusable. APX200 is the second generation of the device which was introduced in 2015. It is made of plastic with a blue color. Two devices are used via opposite 19G paracenteses placed at 90° to the main wound. Exactly opposite paracenteses create a quadrangular opening, whereas if the angle between the paracenteses is not exactly 180°, it creates a trapezoidal opening. The corneal incision is made parallel to the iris. The closed device is inserted via the paracentesis. The device is opened slowly only when the pivot pin is inside the anterior chamber, or at least within the incision. The pupillary margins are engaged on to the tip of the device one by one in the half-opened stage of the device. Then it is opened fully and the special forceps are released (see video). The pupillary opening is usually 6x6mm and intraocular manipulations are not required. Also, only 2 paracenteses suffice compared to 4 or 5 in cases with iris hooks. One end of the APX hook in each side is bent downwards for a good hold of the pupillary margin. https://youtu.be/jjXSKRl0QL0
==I-Ring pupil expander (Beaver-Visitec International, Waltham, MA, USA)==
This is a circular soft ring made of polyurethane which causes a circular dilation of the pupil to 6.3 mm. There are 4 outward projecting triangular portions with holes in each which help in positioning the device properly. The device may give a more circular appearance of postoperative pupil compared to the Malyugin ring.[Tian JJ, Garcia GA, Karanjia R, Lu KL. Comparison of 2 pupil expansion devices for small-pupil cataract surgery. J Cataract Refract Surg. 2016;42(8):1235‐1237. doi:10.1016/j.jcrs.2016.07.002]
Xpand NT iris speculum-X1 (Diamatrix Ltd, Woodlands, Texas, USA)
It is prepared from thin nitinol wire and dilates the pupil to around 6.75mm. To position the device, manipulation with other instruments is needed.
Oasis Iris Expander (Oasis Medical Inc. Glendora, California, USA)
This square-shaped device is made of polypropylene and comes in 2 sizes 6.25 mm and 7 mm.
This was developed by Dr. Sergio Canabrava from Brazil. https://www.youtube.com/watch?v=dvkGztkCSqM
After using these hooks/methods, multiple sphincterotomies may be noted and the pupil may appear dilated. The pupil in such cases may be constricted intraoperatively using gentle centripetal strokes over iris with blunt instruments including Lester hook and intraoperative miotic agents (including pilocarpine). However, in most cases, the pupillary sphincter is not damaged till the full radial extent, and pupils retain a good cosmetic appearance and good pupillary response to light and accommodation. In the immediate postoperative period, miotic agents may be considered to prevent iridocapsular adhesion/synechia.