Methods for Achieving Adequate Pupil Size in Cataract Surgery

Andrzej Grzybowski; Piotr Kanclerz


Curr Opin Ophthalmol. 2020;31(1):33-42. 

In This Article

Mechanical Enlargement of a Small Pupil

Manual Stretching

In moderate-to-severe small pupil cases pharmacological mydriasis might be insufficient, requiring mechanical stretching of the iris.

There are a variety of instruments available for iris-stretching. The simplest technique utilizes two hooks, for example a Kuglen or Y-hook (Figure 1).[54] After filling the anterior chamber with an ophthalmic viscosurgical device (OVD) one hook is placed through the main port and the other in the side port. When the iris is hooked, the instruments are spread apart towards the limbus in opposite direction. Such maneuver can be repeated 90° apart, if necessary.[55] Dedicated tools such those produced by ASICO (AE-2225) or Katena (K-3-4950) allow a multiple-point iris stretch through a single side port, while the one by Moria and Beehler (#18032) require a 3.0-mm incision. Manual stretching, both bimanual and with the Beehler dilator, were shown to be less time consuming the older expansion devices that is iris hooks and a polymethyl methacrylate (PMMA) pupil dilator.[56]

Figure 1.

Iris stretching. The pupil was very small and dilation was limited due to scarring. The pupil was stretched with two opposing metal instruments and then further dilated with the ophthalmic viscosurgical device. Reproduced with permission [57].

Importantly, it has been shown that manual pupil stretching might create micro-tears in the iris sphincter, particularly if performed too rapidly.[54] Damage to the iris sphincter may result in permanent mydriasis. Manual pupil stretching should be avoided in eyes with iris neovascularization as the fragile vessels can rupture and cause hyphema or intraocular bleeding. Moreover, stretching is ineffective in eyes with IFIS.

Multiple Sphincterotomies

In patients with a very small pupil or fibrotic irides another technique is to perform multiple sphincterotomies.[58] In this approach, after filling the anterior chamber with OVD six to eight radial equally spaced 0.5 mm incisions are performed (Figure 2). Following the sphincterotomy, the iris is stretched to its' root.[59] At the conclusion of the surgery, the pupil is usually mechanically returned to a configuration as small as possible. This technique allows achieving good cosmetic appearance and the sphincter to remain its' function. Moreover, it prevents or reduced tears that could eventually be induced by other mechanical techniques.

Figure 2.

Iris sphincterotomies. (a) Half-width sphincterotomy [60] (b) Postoperative appearance of an eye that underwent sphincterotomy, phacoemulsification and intra-ocular lens implantation [61]. Reproduced with permission [60,61].

Iris Retractors

Iris retractors are made nylon, polypropylene or titanium, and they employ silicone cinches to adjust the iris position (Figure 3). Nylon retractors although might be more difficult to handle, have less potential to induce injury to fragile ocular tissue.[62] Iris retractors are usually provided in packages containing four to six retractors. Four retractors are used most commonly during the surgery, while adding the fifth retractor reduces the pupil-opening circumference by 17%.[63]

Figure 3.

Iris hooks (a) the size and shape of the pupil are determined by the surgeon. (b) Micro-iris retractors shown with the appropriate amount of pupillary retraction. (c) The paracentesis is too high in the cornea. The iris is folded toward the cornea, making it impossible to pass the phaco tip into the anterior chamber without damaging the iris. (d) The paracentesis is too low. The iris is bunched up as the retractor is retracted. Passage of the phaco tip without iris damage is unlikely. (e) The correct placement of the paracentesis is demonstrated. Note the iris is retracted, and there is adequate space for the passage of the phaco tip. Reproduced with permission [36].

The retractors are usually placed at similar distance apart, slight malposition of the hooks increases the iris circumference.[63] The greatest iris circumference is achieved with displacement of two adjacent hooks in opposite directions, or two diametrically opposite hooks in the same clockwise direction. For each retractor a paracentesis is made, and proper placement of the paracentesis is a critical step. The paracentesis should be self-sealing made peripherally, very short, and narrow to prevent iris displacement. The stab incisions can be created with a microsurgical knife, or alternatively with a 25–27-G needle.[64] If the paracentesis is situated too anteriorly it will pull up the iris and cause difficulties with insertion of the phaco probe and intracameral fluid circulation. With iris retractors, the surgeon may manually modify the size of the pupil opening intraoperatively by adjusting the tension drawn by the retractors. It is important not to enlarge the pupil maximally, as this can lead to pupil irregularity, chronic inflammation and permanent damage of the iris.[65] Usually, an opening not larger than a 5.0 × 5.0 mm is recommended.[66] Iris hooks can also be used to stabilize the capsular bag, which might be particularly advantageous in removing subluxated cataractous lenses.[67,68]

One should consider that usage of iris hooks is relatively less invasive than application of pupil expanders. For example, in a study by Nderitu and Ursell[69] eyes with intraoperative application of a Malyugin ring more commonly manifested postoperative anterior uveitis (6.7 vs. 1.1% in iris hook cases, and 2.6% in cases with no pupil expander, P < 0.001) and corneal edema (7.0 vs. 2.1% in iris hook cases, and 1.8% in cases with no pupil expander, P < 0.001). Another advantage is the possibility to apply the hooks irrespective of the pupil size; for example, in moderate pupil dilation it might be impossible to apply a small expander. On the other hand, iris hooks cases take on average 10 min longer surgical time than Malyugin ring cases among consultants, and 18 min longer among trainees.[69] Reusable, polypropylene iris retractors might be the most cost-effective device for mechanical pupil expansion. Significantly, Li et al.[70] reported that it is possible to effectively dilate the pupil with a self-made iris retractors. The body of the retractor is made of a prolene suture, while the merocel sponge, which is usually supplied with the suture, is used as a the stopper.

Pupil Expanders

Currently, this is a wide variety of pupil expanders available on the market (Table 1, Figure 4). Nevertheless, single studies have compared outcomes of application of different pupil dilation strategies (Table 2). As a rule, all pupil expander should be used with the anterior chamber filled with OVD to protect the corneal endothelium. One of the most popular pupil expander is the Malyugin ring. Each ring comes with a disposable injector, and the ring itself is inserted through the main cataract incision. The ring contacts the iris at four points forming a diamond or square opening. The second version of the Malyugin ring is made of 5–0 prolene, instead of 4–0, and can be inserted through a 2.0 mm main incision. The Malyugin ring generates significantly less stress on the iris sphincter compared with iris hooks.[71] Moreover, Wilczynski et al.[72] presented that manual stretching of the pupil with two hooks resulted in a greater endothelial cell loss 1 month after surgery compared with Malyugin ring. Consequently, in their study the Malyugin ring group presented a better outcome in best-corrected visual acuity.

Figure 4.

Pupillary rings. Open rings: (a) Perfect pupil; (b) Morcher pupil dilator. Closed rings: (c) Graether 2000; (d) Malyugin ring; (e) Oasis iris expander; (f) Xpand NT Iris Speculum. Reproduced with permission [36].

The Visitec I-ring is another pupil expander, which is made of resilient polyurethane material. Similarly to the Malyugin ring, it is inserted through the main cataract incision. Its' outer border is circular in shape, however, has a wide-flange and positioning holes to engage the Sinskey hook. In a single case report of a patient with the I-ring inserted in one eye, and the Malyugin ring in the other, the I-ring resulted in smaller pupil distortion compared with the Malyugin ring. This was attributed to softer material, and less trauma to the iris.[74] On the other hand, introducing a soft pupil expander requires a step-by-step engagement of the iris margin, which might introduce excessive dragging and could be traumatic to the iris.[71]

The Oasis iris expander (Oasis; Oasis Medical Inc., Glendora, California, USA) is a disposable polypropylene device available in a 6.25 and 7.0 mm version. The device is foldable, and each unit is packed with its' own injector. Ghoneim and Wasfy[73] presented that mechanical dilatation with an Oasis iris expander device requires more time than pupil stretching (83–117 vs. 48–76 s). However, in most cases it resulted in a steady and sufficiently dilated pupil with less liability for intraoperative complications.

Other pupil rings include the Graether 2000 pupil expander (Katena Products, Inc., Parsippany, New Jersey, USA) and open rings: the Morcher pupil dilator (Morcher GMBH, Stuttgart, Germany), the Perfect pupil device (Milvella, Sydney, Australia) or Canabrava ring (AJL Ophthalmic S.A., Vitoria-Gasteiz, Araba, Spain). The Graether 2000 pupil expander is made of silicone and creating a 6.3 mm aperture. It is provided in a preloaded injector.[75] The Perfect pupil device is a 315° polyurethane ring, with an internet arm kept in the main incision and a 0.24 mm flanged groove for stabilizing the iris. The ring is open for 45°, to enable easy access for the phacoemulsification tip.[76] The Morcher pupil dilator ring is a semi-circular plastic ring made of PMMA. The Morcher pupil dilator may be inserted manually or using a reusable capsular tension ring injector. It was shown that the PMMA ring combines as much surgical time as iris hooks, however, cause less iris trauma.[56] The Canabrava ring is made of PMMA, with a semi-arch opening of 60° and internal diameter of 6.3 mm.[77]

Another approach is employed in the Assia Pupil eXpander (APX). The APX is a scissors-like device which is inserted into the anterior chamber parallel to the iris plane. Two devices are used in each case and are inserted through opposite 1.1 mm incisions. When released, the APX's distal curved tips are placed behind the iris and slowly open when being released. An advantage of this device is that no intracameral maneuvers are required. Moreover, a large 'device-free' area is left for the phaco tip and second instrument, so they do not intersect any element of the pupil dilator. The first version of the device (APX-100) was made of metal and is reusable, while the second generation (APX-200) is disposable. In a numerical model by Tan et al.,[71] the APX generated the higher stress on the iris sphincter muscles, compared with iris hooks and the Malyugin ring. On the other hand, the study had several limitations and was rather designed to provide guidance for development of next-generation pupil expanders than to assess the utility of current ones.