Methods for Achieving Adequate Pupil Size in Cataract Surgery

Andrzej Grzybowski; Piotr Kanclerz

Disclosures

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

In This Article

Risk Factors for Intraoperative Miosis

General Information

In general the pupil size decreases linearly with age, and such effect is found at all illumination level.[5] In older patients miosis has been associated with decreased sympathetic tone of the pupillary dilator muscle, and the muscle itself does not lose sensitivity to norepinephrine with age.[6] Moreover, the pupillary response to pupil dilators is associated with iris color. It is known that dark irises having a higher dose of melanin are more difficult to dilate with standard drug dosages.[7]

Diabetes

Alterations frequently seen in diabetic patients include small pupil size, light reflex disorder and difficulties in dilation with commonly used mydriatics.[8] The pupillary dysfunction manifested in diabetes is associated with autonomic neuropathy which predominantly involves the sympathetic innervation of the iris dilator.[9] Parasympathetic innervation of the iris sphincter is relatively spared. The loss of sympathetic tonus in people with diabetes limits the usefulness of commonly used topical anticholinergic agents, resulting in poor pupil dilation.[10] An addition of directly acting sympathomimetic, to which the pupil is hypersensitive, may provide sufficient mydriasis.[11] Importantly, sympathetic denervation is directly related to the duration of disease and to the development of systemic autonomic neuropathy.[12] In diabetic patients' eyes previously treated with retinal laser photocoagulation the pupils dilate less compared with eyes not treated with laser.[11] Such an effect is associated with damage of the short and ciliary nerves traversing the choroid; moreover chronic pupil dilation, loss accommodation and tonic pupils have been reported after panretinal laser photocoagulation.[13,14]

Pseudoexfoliation Syndrome

Pseudoexfoliation syndrome (XFS) is known to lead to poor pupillary dilatation, and in some cases might result in formation of posterior synechiae due to involvement of all cell populations of the iris.[15] The reduction of dilating properties of the iris is associated with tissue hypoxia and subsequent atrophy of the iris muscle cells, and the reduction of stromal elasticity.[16] Eyes with pseudoexfoliation manifest an increased risk of intraoperative complications also due to zonular laxity.[15,17,18] Although XFS is thought to be peculiar to Scandinavia, XFS was found in almost every ethnic group in which it has been looked for, except in Eskimos.[19] Moreover, in the Framingham Eye Study the female-to-male was determined as 2.3 : 1, and the prevalence increased with age from 0.6% for ages 52–64 years to 5.0% for ages 75–85 years.[20]

Medical Treatment

The intraoperative floppy iris syndrome (IFIS) is characterized by a triad of intraoperative symptoms including progressive constriction of the pupil during surgery, fluttering and billowing of the flaccid iris stroma during unremarkable intraocular fluid currents and a tendency for iris prolapse to the corneal incision.[21] IFIS can be graded as mild (good pupil dilation with iris billowing but without prolapse or intraoperative pupil constriction), moderate (iris billowing and some constriction of moderately dilated pupil) and severe. Due to the aforementioned characteristics IFIS is associated with a higher risk of surgical complications during cataract extraction.[22]

There is a causal relationship between the intake of sympathetic α1 antagonist agents and IFIS; this association is much stronger for antagonists that are selective for the α1A receptor subtype (e.g., tamsulosin or silodostin) compared with nonselective α1 blockers (e.g., doxazosin or alfuzosin).[22,23] Currently, systemic α1 antagonist are the most frequently prescribed medications for benign prostatic hyperplasia, which manifests in 50–60% of men in their 60s, and 80–90% of men in their 70s and 80s.[24] Also women are occasionally treated with tamsulosin for voiding difficulties or for facilitating the release of kidney stones.[25] Thus, IFIS is more commonly develops in male than in female patients (5.17 vs. 1.29% of cataract surgery cases, respectively, P < 0.0001).[26] Within the aforementioned study 72.2% of men with IFIS were treated with α1 antagonists, however, none of the women that developed IFIS received such treatment.[26] Importantly, the severity of IFIS is greater in female patients, resulting in higher intraoperative PCR rates (28% in females vs. 9.28% in males) and worse final visual acuity than in male patients.[26] A critical issue is that even after discontinuation of α1A antagonists (in the study by Pärssinen for 7–28 days), the iris remains floppy.[27]

Urologists should be aware systemic α1 antagonist treatment is associated with IFIS and manifests greater risk for complications during cataract surgery; particularly asking patients about their ophthalmic health should be considered at the initiation of treatment.

Ocular Surgery

Femtosecond laser-assisted cataract surgery is known to cause intraoperative pupillary miosis. The level of intraoperative miosis is correlated with the duration of lens fragmentation and of primary incision creation.[28] Moreover, the tendency for pupil constriction is associated with patient age, and the distance between the capsulotomy edge and pupillary margin.[28] According to Schultz et al.[29] the pupil size alterations are related to the release of aqueous humor prostaglandins, and the main trigger for their release is anterior laser capsulotomy. Optimizing energy settings to avoid miosis is recommended, as well as application of NSAIDs.

Importantly, some studies have reported that cataract surgery itself can induce postoperative pupillary miosis. In a study by Kanellopoulos and Asimellis[30] pupil size analysis showed a reduction in photopic pupil diameter by 11–13% 3 months after surgery; moreover, the pupil eccentricity was also reduced by 39%. The reduction was presumably associated with lower volume of the intraocular lens compared with the bulky crystalline lens, allowing more freedom of movement of the constrictor iris muscle and increasing the anterior chamber depth. In a study by Hayashi and Hayashi[31] the postoperative decrease in pupil size was temporary. It returned to preoperative size 1 month after surgery, both in diabetic, and in nondiabetic patients.[31] Rickmann et al.[32] noted that pupil size after cataract surgery decreases in scotopic, photopic, as well as mesopic static illuminance conditions. However, 4 weeks after surgery it returned to preoperative size in all illumination levels (0, 0.5, 4, 32 and 250 lx). The transient effect of pupillary reaction could be attributed to inflammatory reaction after cataract surgery via cyclooxygenase-1 (COX-1) and COX-2 enzymes and prostaglandins.[33] The inflammation cascade with prostaglandin synthesis leads to decreased pupil size, while nonsteroidal anti-inflammatory agents are commonly used for prevention of pupillary constriction. Similarly it can be expected that the pupillary size could decrease after other intraocular surgeries.

Other Medications and Causes

Miotics are the first widely used glaucoma medications. Long-term application of miotics might be associated with pupillary miosis due to hypertrophy of the pupillary sphincter or development of posterior synechiae.[34] Miotics are nowadays less commonly used, mainly for treatment of glaucoma and in the management of pediatric glaucoma.[35] Topical solutions of pilocarpine hydrochloride 0.25–4% and Echothiophate iodide 0.03–0.25% are currently available.

Other causes of small pupil include iris sphincter sclerosis from aging, uveitis or posterior synechiae, chronic syphilis, iridoschisis or previous trauma.[36]

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