Small Pupil—Big Problem

A Management Algorithm

Abstract

Small pupils pose problems for cataract surgery. The pupil is dilated with topical mydriatic drugs for all cataract surgeries to improve the surgeon’s access to, and visualization of, the lens nucleus, cortex, and capsular structures. Limited dilation poses a risk of surgical complications such as iris trauma or tearing of the anterior or posterior capsule. There are many ways and methods to achieve the appropriate pupil dilation, from pre-operative medications to intraoperative pharmacological and/or surgical methods. A management algorithm for small pupil will be discussed in this review. The various methods and maneuvers may work in isolation or combination to achieve adequate pupil dilation.

Small pupil will compromise visualization during cataract and vitreoretinal surgeries. It is not just a major challenge for a surgeon but also increases surgical complication rate substantially. Adequate mydriasis and its maintenance during the surgery are the best ways to prevent complications arising from a small pupil. There are many ways to achieve the desired mydriasis, which needs to be approached methodically, from preoperative medications to intraoperative pharmacological and/or surgical maneuvers. We would like to herein share our management algorithm for small pupil that could create a big problem if not handled properly (Fig. 1). The various methods and maneuvers may work in isolation or combination to achieve adequate pupil dilation.¹

FIGURE 1: Management algorithm for small pupil.

PREOPERATIVE MEDICATIONS

If patients are on miotics, we need to stop them preoperatively for at least 1 day. The use of nonsteroidal anti-inflammatory drugs for 3 days preoperatively contributes to maintenance of pupillary dilation by blocking the miotic effect of prostaglandins released because of iris manipulation. Pupillary dilation is maximized by a combination of drugs, which act on both the iris dilator muscles (adrenergic stimulants—phenylepherine), and those, which relax the iris sphincter (parasympatholitics—tropicamide and cyclopentolate).² A combination of 2.5% phenylephrine and 1% tropicamide every 15 minutes for 4 times before operation is safe and effective. Higher concentrations of phenylephrine are more effective but can be associated with a greater risk of increased blood pressure and other cardiovascular adverse effects. To prevent repeated instillations, one could use a cotton pledget or ocular inserts. Mydriasert (Spectrum Thea Pharmaceuticals Ltd, United Kingdom) contains both phenylephrine and tropicamide and can be inserted in the inferior fornix.² One-time topical application of 1% atropine preoperatively helps maintain pupillary dilation. Applying 1% atropine 2 times a day for 3 days will enhance its mydriatic effect. Preoperative use of intravenous mannitol helps dehydrate the vitreous and deepens the anterior chamber (AC), maximizing the chances of pupillary dilation. We do this as a routine for cases that have an AC depth of 2.5 mm or less.

CHOICE OF ANESTHESIA

Most cataract surgeries are done under topical anesthesia. However, retrobulbar, peribulbar, or subtenon anesthesia will help make the pupil larger and can be considered in selected cases especially when manipulation of iris tissue is anticipated. Our first choice of dilating is preopeative medications. However, for pupils that showed bad response to medications, retrobulbar, peribulbar, or subtenon anesthesia will be performed for any additional dilation effects in selected cases.

INTRAOPERATIVE MANAGEMENT

The common options for intraoperative mydriasis include pharmacologic dilation, viscomydriasis, surgical maneuvers such as membranectomy, separation of posterior synechiae, mechanical stretching of the pupil, sphincterotomies, and other options.

Pharmacologic Dilation by Intracameral Injection

Intracameral injection of various concentrations of diluted adrenaline and phenylephrine can been used. Both mydriatics need to be diluted (adrenaline, 1 mg/ml; 1:1000 to at least 1:4000 and phenylephrine, 2.5% at least 1:4 dilution with balanced salt solution (BSS), BSS plus, and/or preservative-free 4% lignocaine) to neutralize the pH and to dilute the bisulfite, which may cause endothelial damage.^3,4 There was no significant difference among the mean mydriatic responses to the epinephrine concentrations although better dilation and maintenance occur with concentrations greater than 1:25,000.⁵ The amount used for the intracameral injection is 0.1 mL and repeated injections can be used. Intracameral mydriatics have the advantage of more rapid mydriasis, lesser pupillary constriction, and iris billowing as compared with topical mydriatics alone.⁶ In case of bleeding from the iris, intracameral mydriatics due to their vasoconstrictive effect can help stop it. Intracameral mydriatics are safe and have no measurable systemic adverse effects.^7,8 Addition of 1 mg/mL adrenaline to the irrigating fluid helps supplement and maintain pupillary dilation. On the other hand, intracameral ketorolac combined with phenylepherine has undergone phase 3 clinical trials with encouraging results.⁹

Viscomydriasis

Pupillary mydriasis can be achieved by injection of an ophthalmic viscosurgical device (OVD). A combination of a viscoadaptive and a dispersive OVD works best because the viscoadaptive OVD (eg, Healon 5) mechanically stretches the pupil while the dispersive OVD (eg, Viscoat) will better resist aspiration and delay the evacuation.³ The mydriatic effect will be enhanced if the AC can be deepened. Preoperative intravenous mannitol is recommended if the AC depth is of 2.5 mm or less.

Surgical Techniques

If the various interventions fail to achieve adequate pupillary dilation, one needs to consider other surgical techniques or pupil-dilating devices.

Membranectomy

In cases where peripupillary membrane is causing the small pupil, a capsulorhexis forceps or intraocular forceps are used to grasp the membrane at the pupillary margin and remove it in a fashion similar to a capsulorhexis.⁹

Separation of Posterior Synechiae

Separation of the posterior synechiae should be attempted with OVD and a pair of blunt metal spatula specially designed for this purpose.

Pupil Stretching

This is particularly effective if the pupil is stiff and fibrotic, such as in patients who chronically use pilocarpine.³ It is a time-saving method and cosmetically acceptable because it preserves pupillary function at large with only tiny partial-thickness sphincter tears. However, the pupil size is smaller than other methods and some intraoperative miosis is expected.

Under OVD, using 2 Kuglen hooks engaging diagonally opposite points on the pupillary margin, stretch is performed in a slow sustained manner. It is subsequently repeated perpendicular to the initial stretch to cause maximal dilation. The Beehler pupil dilator (Ambler Surgical Corp), which has 3 microfingers and a hook, stretches the pupil in 4 symmetrical quadrants and achieves the same objective through a single entry.^2,10 In general, retracting the iris tissue rather than cutting it results in better postoperative pupil size and appearance.

Iris-Retracting Hooks

Iris hooks are safe and have a relatively easy learning curve. However, the technique is time consuming, with multiple limbal incisions. It requires careful planning because it can cause a tenting of the iris towards the cornea, thus reducing the AC depth.^2,3,10

Nylon iris hooks are inserted under OVD through multiple stab incisions close to the iris root plane. Usually 4 or 5 hooks are used to retract the pupil in a square or pentagonal opening.

Pupil Expansion Rings

There are various pupil expander rings made of different materials such as polymethylmethacrylate or silicone with different flexibilities. They capture the iris sphincter and also protect its margin preventing iris tearing or damage. The Malyugin ring (MicroSurgical Technology, Redmond, Wash) is made of 5 to 0 polypropelene, drapes the iris over its side and, depending on the size of the device used, creates a 6- or 7-mm-diameter pupil. The injector fits through a 2.5-mm incision and is used to place and remove the ring. The Bhattacharjee ring is made of nylon, can be inserted through a 0.9-mm incision, is 0.1-mm thick, and can be used in shallow ACs. It is single planar, easy-to-insert, and easy-to-remove and is less traumatic because it acts like a paper clip.¹¹

Sphinterotomies

Through limbal paracentesis sites, intraocular scissors (usually 23 g in size) are used to make multiple equidistant small-sized cuts (sphincterotomies) at pupillary margins. Deepening of the AC usually helps enlarge the pupil further. Sometimes, additional iris stretching with hooks is used to make the pupil larger. There are in general no uncontrolled sphincter microruptures, and the final pupil appearance and function can be more acceptable.¹²

Surgical Pearl

Intraoperative Floppy Iris Syndrome

Inadequate pupil dilation can be observed in cases of complicated intraoperative floppy iris syndrome (IFIS), which is associated with systemic administration of the α₁ antagonist. During operation, there are tendencies for iris prolapses through the incisions and progressive constriction of the pupil during surgery. Pharmacologic therapy including the combined use of strong mydriatics together with nonsteroidal anti-inflammatory eyedrops will help reduce the negative effect of IFIS.

Femtosecond Laser-Assisted Cataract Surgery

The femtosecond laser-assisted cataract surgery technique represents the frontier of modern cataract surgery. Applying this technique in a small pupil case can both customize the size of continuous curvilinear capsulorhexis and also reduce the manipulations in the AC, which may result in safer surgery.

Fluidics Adjustments

In small pupils, iris tissue is located closer to the high fluidic currents, which is why the iris is more likely to be aspirated into the ultrasound or irrigation/aspiration needles. Decreasing the flow parameters is an important factor in preventing iris damage during phacoemulsification. When employed with low aspiration, it averts in traocular pressure rise and AC deepening; with high aspiration, reduction of leakage takes place before the AC shallows.