Phacoemulsification in eyes with preoperative non-dilating pupil or with intraoperative miosis is fraught with complications [1,2]. The following tips will help understand the small pupil and optimize strategy to deliver better outcomes.

1. Every eye is an IFIS candidate; Reduce threshold for using Pupil expansion devices:

Since its original association with tamsulosin intake, Intraoperative Floppy Iris Syndrome (IFIS) has been positively correlated with a plethora of risk factors which include: gender, age, hypertension, other a1-adrenergic receptor antagonists, finasteride, angiotensin II receptor inhibitors, benzodiazepines, antipsychotics, hypertension drugs and decreased dilated pupil diameter [1,3,4]. The risk of IFIS exists regardless of alpha antagonist treatment, in eyes with 7.0 mm or smaller pupil [5]. Hence, it would be prudent to consider every eye a potential IFIS candidate. Increased patient expectations, surgeon's desire to consistently deliver good outcomes, use of toric and premium lenses, and the availability of user-friendly pupil expanders have reduced the surgeon's threshold to use one [6].In IFIS, neither Iris Hooks nor Pupil Expanders can prevent Iris prolapse. These pupil expansion devices provide a valuable constant pupil size allowing adequate visibility for safe phacoemulsification. Iris prolapse in a particular case depends on the severity or grade of IFIS and is not a measure of the efficacy of the device used. The severity of IFIS depends on the extent of pathological damage to the stroma and muscles of the Iris.

2. Release posterior synechiae & peripupillary membranes completely:

Releasing the posterior synechiae and peeling the peripupillary membrane [7,8] followed by intracameral injection of combination mydriatics and/ or viscoelastic may dilate the pupil adequately. It is important to sweep the spatula under the Iris to release extensive or total posterior synechiae [9] which may be tying down the Iris to the lens capsule.

3.Intracameral injection of combination mydriatics and local anaesthetics:

Intracameral use of combination of epinephrine and lidocaine in fortified BSS as well as a combination of cyclopentolate, phenylephrine, and lidocaine has been shown to provide effective dilatation [10]. However, these “homemade” cocktails can lead to dilution errors and accidental use of medications containing preservatives, which can lead to toxic anterior segment syndrome [11,12,13]. Currently, commercially available combination drug products are Omidria (Omeros Corporation] and Mydrane (Thea Pharmaceuticals Limited).

4. Test and distinguish the elastic from the nonelastic rigid pupil:

Unlike with nonelastic miotic pupils, the IFIS pupil immediately snaps back to its original size following attempts at stretching it [14]. This means, small pupils are of two types, elastic & non-elastic (rigid). The elasticity of the pupil should be tested as soon as the paracentesis is made. As the anterior chamber (AC) is inflated with BSS, the elastic pupil expands momentarily and returns to its small size. On the other hand, a rigid pupil hardly enlarges. An elastic pupil is expandable like a rubber band. Whereas, a nonelastic rigid pupil is like a string and is not expandable but tearable. It will not expand until the pupil is stretched to tear the fibrous elements at the pupillary margin [15]. It would be logical to assume that pupils undergoing intraoperative miosis are elastic in nature because they were reasonably dilated to start with.

5.The elasticity of Pupil & Choice of Pupil Expander Device: OVD/ Iris hooks/ Pupil Expanders

In non-elastic pupils associated with pseudoexfoliation, the iris sphincter demonstrates fibrotic changes in the stromal and muscular elements [16,17]. For elastic pupils, ophthalmic viscosurgical devices (OVD), Iris hooks or Pupil expanders may be chosen depending on pupil size, pupil comorbidities and personal preference. However, rigid non-elastic fibrotic pupils can be expanded only after stretching or tearing the fibrotic sphincter at the margin with significant force either with two Kuglen hooks or with pupil expansion devices (Iris hooks or Pupil Expanders). When stretched bimanually to 5 mm with two Kuglen hooks in all directions, the stretching or tearing of the sphincter is symmetric and controlled resulting in round pupils postoperatively. This facilitates the placement of any pupil expander device. If Iris hooks or Pupil Expanders are deployed without a prior bimanual stretch, the pupil is torn irregularly due to uncontrolled asymmetric stretching. A stiff and bulky device like the Malyugin Ring (Microsurgical Technology), I-Ring (Beaver-Visitec International) or APX 200 pupil expander (APX Technology) may enlarge a rigid pupil but would be less manoeuvrable and cause uncontrolled disfiguring sphincter tears and glare [6,18,19]. The hair thin 0.075 mm (75 micron) B-HEX Pupil Expander (Med Invent Devices) can easily expand an elastic pupil but requires prior stretching of a non-elastic rigid pupil [6,15,20]. A bulky device occupies more space in the AC and obstructs movement of instruments. The vertical profile of the Malyugin ring at the corner scrolls is 0.7 to 0.9 mm which is significant in the presence of a shallow AC because the scrolls occupy the mid-peripheral AC, which is shallower than the central part [21]. The thinner B-HEX occupies very little space and allows unhindered instrument movement in the AC. The scrolls or pockets of some pupil expanders are thick biplanar structures. They snag the self‑sealing slit corneal incision during entry and exit and require an injector to circumvent this problem. The thin profile and uniplanar design of B-HEX allow it to glide through much smaller incisions without an injector using a 23 gauge Microforceps [6]. A 5.5 mm pupil provided by a pupil expansion device is good enough for safe and effective phacoemulsification [6]. A larger expansion requires a larger device which is unwieldy [6]. With present technology and fluidics, an assurance that the expander would maintain a 5.5 mm pupil without collapsing would encourage most surgeons to proceed with Phaco surgery [6]. Size for size a hexagon is much more efficacious than a square and is safer and practical. Geometrically, between an equal sized square and hexagon having equal incircles, the square has a larger circumcircle. Hence, a square device is more likely to injure the angle [6]. Apart from the additional incisions required, the additional operating time for iris hooks is more than that for pupil expansion rings [22]. When introducing instruments into the AC, it must be kept in mind that Iris hooks elevate the pupil margin anteriorly to the limbal plane. Permanent changes to the shape and/ or size of the pupil by damaging the iris sphincter is more common with iris hooks compared to Pupil expansion rings [23].

6. Viscomydriasis:

Healon 5 (2.3% sodium hyaluronate) has been found to be useful to achieve viscomydriasis in patients with a small or constricted pupil especially in patients with IFIS and an atonic iris [24]. Viscomydriasis alone should be used with caution, as the limited duration of this effect will likely not last throughout phacoemulsification if other pupil-related pathologies exist [25].

7.General Techniques to facilitate use of Iris Hooks & Pupil Expanders:

Inflating the AC with viscoelastic flattens the iris against the lens capsule and makes it difficult to engage iris hooks or pupil expanders to the pupil margin. A deep AC would also require the devices to be inconveniently angled in an attempt to engage the pupil margin. It is preferable to keep the AC a little shallow and inject viscoelastic under the pupil margin so that the iris is bowing anteriorly and the pupil margin is lifted off from the anterior lens capsule [26].

8.Iris Hooks Tips:

A 0.5 mm incision is adequate to insert 4-0 or 5-0 Polypropylene or Nylon iris hooks. Larger incisions may leak and allow Iris prolapse. A mark to identify the incisions either by nicking the conjunctiva or applying Trypan blue saves embarrassment as they can be very difficult to find. If a hook is to be placed at the phaco incision it should be planned well in advance. Limbal incisions bevelled towards the endothelium help keep the Iris at a posterior plane. The stopper should be retracted in advance to allow the hook enough length to reach the pupil margin. Using the tented part of the pupil margin created by a previous hook makes engagement of every subsequent hook much easier. Over retraction and asymmetric retraction of hooks is to be avoided. When used after a capsulorhexis, a second instrument or spatula may be used to tent up the pupil margin to ensure that the capsulorhexis margin is not engaged. In deep set eyes, the redundant part of the hooks beyond the stopper may be trimmed to allow unhindered movement of the eyeball and instruments. The flexible hooks can be just pulled out because they can straighten momentarily.

9.Pupil Expander Tips:

Malyugin Ring: It may be possible to engage the pupil margin in three scrolls in the first pass but this should not be an obsession because the success depends on the pupil size, WTW, AC depth, anterior lens contour etc. If the ring is lying on the iris, the possibility of endothelial touch should be considered because the scrolls are at the mid periphery where the AC is shallower than the centre. When the Malyugin ring is used after capsulorhexis, the gaps in the scrolls on the sides of the device are not directly visible in the top view. Aligning these gaps to the pupillary margin may be slightly difficult [21]. When the Malyugin ring is deformed during retraction, the scrolls can unpredictably crush or release the pupil margin. This is because the scrolls behave like a torsional spring and compression spring with narrowing of the gap as the arms are moved towards each other and vice versa [21]. Pressing down on the scrolls with a spatula as they are retracted into the Injector tube prevents snagging of the scroll.

B-HEX Pupil Expander: The flanges should be held at the tabs with the tip of the jaws such that the tips of the jaws are within the outer limit of the flange. In other words, when tucking, the flange should be leading and not the Jaws. This allows the B-HEX to be carried to the maximum extent into the AC in the first pass without the jaws knocking the angle or the Cornea and the tucking is easier too. If the Pupil is suspected to be non-elastic, stretching it to 5 mm is very helpful in engaging the B-HEX. If stretching is inadequate and the B-HEX buckles, the B-HEX-Pupil complex can also be stretched bimanually with two Kuglen hooks. In rigid pupils, the flanges can also be tucked bimanually using a 23-gauge forceps and a metal iris hook [21, 27]. For removal through the main incision or side-port, the flange closest to the incision is held and the notches on either side are disengaged and the B-HEX may be drawn out. The trailing notches disengage spontaneously [6,26,28].

10.Post-operative Medications & Follow Up:

The use of pupil expansion devices may predispose eyes to increased risk of clinically significant Pseudophakic cystoid macular edema (CME) due to perioperative manipulation of the iris. Effective anti-inflammatory treatment and follow-up are warranted in eyes with pupil expansion device. [29] The possibility of CME must be kept in mind and OCT should be performed at the slightest suspicion.

Summary:

The elastic and non-elastic pupil needs to be differentiated. The choice of techniques and pupil expansion devices should be timely and judicious. The threshold for using a pupil expansion device should be very low because it could save serious complications.

References:

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