Pupil Expansion Devices and Mechanical Pupil Dilation
Key Points at a Glance
Section titled “Key Points at a Glance”1. Pupil Expansion Devices and Mechanical Pupil Dilation
Section titled “1. Pupil Expansion Devices and Mechanical Pupil Dilation”In cataract surgery (phacoemulsification: PEA), mydriasis of at least 6 mm is usually desirable to ensure an adequate surgical field. However, in cases of “small pupil” where the pupil diameter remains ≤5 mm after preoperative dilation, continuous curvilinear capsulorhexis (CCC) and nucleus emulsification become difficult. Performing PEA with a small pupil increases the risk of damage to the iris, anterior capsule, and posterior capsule.
The causes of small pupil are diverse. Aging, pseudoexfoliation syndrome, diabetes, uveitis, glaucoma, trauma, use of miotic agents, history of intraocular surgery, and use of α1-adrenergic receptor blockers (α1-blockers) are the main factors.
Pupil expansion devices and mechanical pupil dilation are collective terms for techniques and instruments developed and used to safely perform cataract surgery in such small pupil cases.
Intraoperative Floppy Iris Syndrome (IFIS)
Section titled “Intraoperative Floppy Iris Syndrome (IFIS)”IFIS is a specific condition that occurs during cataract surgery in patients taking α1-adrenergic receptor blockers (tamsulosin, terazosin, doxazosin, silodosin, etc.) for benign prostatic hyperplasia, characterized by the following triad:
- Billowing of the iris by irrigation fluid: The iris undulates with the flow of intraocular irrigation fluid.
- Progressive miosis: The pupil gradually constricts during surgery.
- Iris prolapse: The iris prolapses into the incision or side port.
IFIS occurs in approximately 1.1% of all cataract surgeries. The atrophic changes in the iris caused by α1-blockers are irreversible, and discontinuing the medication does not reduce the risk. It is essential to confirm the medication history preoperatively and approach surgery with anticipation of IFIS. If IFIS is not anticipated or recognized, the risk of complications increases significantly.
IFIS was first reported in 2005 by Chang and Campbell in association with tamsulosin.
Surgery is possible. However, preoperative preparation assuming IFIS (selection of appropriate pupil dilation strategy, adjustment of surgical fluid parameters, use of viscoelastic substances or pupil expansion devices) must be planned. Since the risk does not decrease even with drug discontinuation, surgery is performed while continuing oral medication.
2. Main Symptoms and Clinical Findings
Section titled “2. Main Symptoms and Clinical Findings”Subjective Symptoms
Section titled “Subjective Symptoms”Small pupil/IFIS is diagnosed during preoperative ophthalmic examination, and patients themselves do not complain of specific subjective symptoms before surgery. Postoperatively, the following points become issues.
- Photophobia (glare): Occurs when the pupil remains dilated after surgery
- Decreased visual acuity/discomfort: When excessive pupil dilation or iris damage occurs
Clinical Findings
Section titled “Clinical Findings”Preoperative evaluation points and intraoperative findings are shown below.
Preoperative findings (cases with poor mydriasis)
- Pupil diameter ≤5 mm after dilation
- Pseudoexfoliation material/fibrotic material attached to the pupillary margin
- Posterior synechiae
- Zonular weakness (lens instability/decentration)
Intraoperative Findings (IFIS)
Characteristic findings of IFIS include the triad of iris billowing with irrigation fluid, progressive miosis, and iris prolapse through the incision or sideport. Since the management of IFIS differs from that of small pupils due to other causes, accurate intraoperative recognition is important. The prevalence of IFIS is 0.5–2.0%, and the prevalence of iris/ciliary body damage is 0.6–1.2%.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”Causes of small pupil include the following:
- α1-adrenergic receptor antagonists: tamsulosin, terazosin, doxazosin, silodosin, and the herbal product saw palmetto. The greatest risk factor for IFIS.
- Pseudoexfoliation syndrome (PEX): Often associated with zonular weakness and poor pupillary dilation.
- History of uveitis: Posterior synechiae impair pupillary movement.
- Diabetes mellitus: Autonomic neuropathy and vascular changes reduce the mydriatic response.
- Aging: Fibrosis of the pupillary sphincter and reduction in pupil diameter.
- Use of miotics: Glaucoma medications, etc.
- Previous intraocular surgery or trauma: Structural changes to the iris.
- Femtosecond laser-assisted cataract surgery (FLACS): More intraoperative miosis due to prostaglandin release compared to conventional cataract surgery.
Miotics used for glaucoma treatment (e.g., pilocarpine) constrict the pupil, so even with frequent preoperative instillation of mydriatics, sufficient dilation may not be achieved. Additionally, beta-blockers and prostaglandin analogs can also affect the mydriatic response. It is important to report all medications used before surgery.
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”The diagnosis of small pupil and IFIS is based on preoperative history and slit-lamp examination.
Key Points of Preoperative Evaluation
- Confirmation of history of alpha-1 blocker use (for urinary disorders)
- Measurement of pupil diameter after dilation (pupil ≤5 mm is considered small)
- Assessment of pupillary margin: presence of fibrotic material or pseudoexfoliation deposits
- Presence of posterior synechiae
- Evaluation of zonular weakness (presence of lens instability or displacement)
Based on preoperative evaluation, plan which pupil dilation method to use in advance. In actual surgery, a step-by-step approach is often used, and the plan may be changed according to intraoperative findings.
Selection Criteria for Pupil Dilation Methods
Section titled “Selection Criteria for Pupil Dilation Methods”Refer to the following comparison to plan the surgery.
| Pupil Dilation Method | Reliability | Mydriasis Maintenance | Difficulty | Iris Injury Risk |
|---|---|---|---|---|
| Ophthalmic viscosurgical device (OVD) | Low | Limited | Easy | None |
| Hook | Slightly low | Limited | Difficult | Low |
| Iris retractor | High | Good | Slightly difficult | Low |
| Pupil expansion ring | High | Good | Difficult | Slightly high |
5. Standard Treatment
Section titled “5. Standard Treatment”Pharmacological Mydriasis
Section titled “Pharmacological Mydriasis”Preoperative mydriatic eye drops are the basic approach. The main drugs are as follows:
- Tropicamide 1% eye drops: Anticholinergic (cycloplegic)
- Phenylephrine 2.5% eye drops: α1-adrenergic receptor agonist
- Phenylephrine 1.0% + Ketorolac 0.3% intracameral injection: Useful for preventing intraoperative miosis
Preoperative NSAID eye drops (at least starting 1 day before surgery) are useful for suppressing intraoperative miosis caused by prostaglandin release. This is especially important in FLACS.
It has been reported that mydriatic devices are required in approximately 10% of cases. 1)
Mechanical Pupil Dilation Techniques
Section titled “Mechanical Pupil Dilation Techniques”Pupil Dilation with Ophthalmic Viscosurgical Device (OVD) (Viscomydriasis)
Section titled “Pupil Dilation with Ophthalmic Viscosurgical Device (OVD) (Viscomydriasis)”A method of dilating the pupil by injecting a dispersive OVD such as Healon V® or Viscoat® into the anterior chamber and behind the wound. The procedure is easy, but the OVD may be aspirated during PEA, causing the pupil diameter to decrease. In IFIS cases, it is also effective for local OVD placement when the iris is incarcerated in the wound.
Partial Pupil Dilation with Iris Hooks
Section titled “Partial Pupil Dilation with Iris Hooks”A method of securing the visual field by using push-pull hooks or Sinskey hooks to avoid the pupillary margin as needed. Since the pupillary margin is expanded at one location at a time, excessive stretching of the entire pupillary margin can be avoided. It is suitable for moderate mydriasis cases, but the dilation effect is limited in cases with small pupils.
Pupillary Sphincterotomy (Multiple Sphincterotomies)
Section titled “Pupillary Sphincterotomy (Multiple Sphincterotomies)”A method of making multiple short incisions of about 0.5 mm circumferentially along the pupillary margin, then injecting Healon V® to dilate the pupil. By making many short incisions, the pupillary response can be largely preserved. However, it is not indicated in IFIS or uveitis cases because the pupil does not dilate even when the iris is incised. Also, if the incisions are too long, there is a risk of intraoperative bleeding and postoperative posterior synechiae.
Iris Retractor (IR)
Section titled “Iris Retractor (IR)”A method of inserting four flexible wire hooks through corneal incisions or side ports and pulling the pupillary margin in four directions to fix it. This is one of the most reliable methods to dilate the pupil to any desired size. It is important to limit the dilation diameter to about 4–5 mm; excessive pulling can cause iris tears at the pupillary margin, postoperative irregular pupil, mydriasis, and posterior synechiae. In cases with zonular weakness, after continuous curvilinear capsulorhexis, the CE or IR can be repositioned onto the capsulorhexis edge to also support the lens capsule.
A method of placing one retractor under the wound to prevent iris prolapse has also been reported.
Pupil Expansion Ring
Section titled “Pupil Expansion Ring”The Malyugin Ring is a representative pupil expansion ring. It was developed by MicroSurgical Technology, and following its success, several manufacturers have released various designs of pupil expansion devices. Each device differs in material, mechanism of fixation to the pupillary margin, and ease of insertion and removal.
The first choice of auxiliary device for IFIS is iris retractors or these pupil expansion rings. 1)
Capsule Expander (CE)
Section titled “Capsule Expander (CE)”This is a good indication for cases where the lens shakes during continuous curvilinear capsulorhexis and zonular weakness is evident. It can support the lens capsule while also dilating the pupil, enabling stable PEA.
Methods that should NOT be performed in IFIS: Pupillary margin incision (full-thickness iridotomy) is ineffective in IFIS cases and should not be performed. Similarly, mechanical pupil stretching and sphincterotomy are ineffective in IFIS. 1)
Both are excellent methods in terms of reliability and maintenance of mydriasis. Iris retractors can be adjusted to any size and can also be used for capsular support in cases with zonular weakness. Pupil expansion rings (e.g., Malyugin ring) offer superior maneuverability and uniformity of dilation. Choose according to the surgeon’s proficiency and the case situation (iris characteristics, zonular status, etc.).
6. Pathophysiology and Detailed Mechanism
Section titled “6. Pathophysiology and Detailed Mechanism”Mechanism of IFIS
Section titled “Mechanism of IFIS”The core pathology of IFIS is dysfunction of the iris dilator muscle due to alpha-1 adrenergic receptor blockers and atrophy of the iris stroma.
The iris dilator muscle expresses alpha-1A adrenergic receptors. Alpha-1A selective blockers such as tamsulosin bind to these receptors for a long time, causing muscle atrophy and fibrosis. This change persists even after drug discontinuation (irreversible). As a result, the tone and elasticity of the iris are lost, making it prone to billowing under the flow of irrigation fluid during surgery.
Furthermore, alpha-1 blockers also block alpha-1 receptors on iris blood vessels, impairing the vasoconstrictive response to shear stress from irrigation fluid, which promotes edema and flaccidity of the iris stroma. This leads to progressive miosis and iris prolapse.
IFIS can also occur with alpha-1 blockers other than tamsulosin (e.g., terazosin, doxazosin) and even in patients not using alpha-1 blockers, but the incidence is highest with tamsulosin (alpha-1A selective).
Complication Risk Due to Small Pupil
Section titled “Complication Risk Due to Small Pupil”A small pupil is one of the most important risk factors during surgery. Continuing surgery with a small pupil increases the risk of incomplete continuous curvilinear capsulorhexis, intraoperative bleeding, iris sphincter rupture, posterior capsule rupture, vitreous loss, and corneal endothelial cell loss. Some reports indicate that when an experienced surgeon performs surgery with minimal iris manipulation, results similar to those in normal dilated eyes can be achieved, but appropriate measures including adjustment of fluid parameters (lowering bottle height, reducing aspiration flow rate) are necessary.
7. Latest Research and Future Perspectives (Research-stage Reports)
Section titled “7. Latest Research and Future Perspectives (Research-stage Reports)”Continuous irrigation of intracameral mydriatics
Section titled “Continuous irrigation of intracameral mydriatics”A method of continuous irrigation of a mixture of phenylephrine and ketorolac during surgery is attracting attention. While bolus injection dilates the anterior chamber, continuous irrigation is used to prevent intraoperative miosis. It is also expected to suppress miosis caused by prostaglandin release during FLACS.
Development of new pupil expansion devices
Section titled “Development of new pupil expansion devices”Following the success of the Malyugin ring, various pupil expansion devices with improved materials, fixation mechanisms, and operability have been introduced to the market. The combination of pharmacological mydriasis and pupil expansion devices enables safe and effective cataract surgery in the majority of cases with poor mydriasis.
8. References
Section titled “8. References”- American Academy of Ophthalmology. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2021;128(1):P1-P228.