Zonulopathy (also called zonular dehiscence or rupture) refers to a condition where the supporting function of the zonular fibers (Zinn’s zonule) that support the lens capsule is insufficient. It may or may not be accompanied by lens position abnormalities (subluxation or dislocation).
The Zinn’s zonule has two main functions: (1) a positioning function that pulls the lens capsule equator in 360 degrees to fix the lens at the center of the visual axis, and (2) a shape-maintaining function that maintains the shape of the lens capsule by uniform tension. Depending on the extent and range of zonular rupture, either or both of these functions may be lost. As the rupture range expands, it progresses from partial rupture to subluxation, complete dislocation, and nucleus drop.
If recognized preoperatively during cataract surgery, countermeasures can be taken, but in many cases it is first discovered during surgery. Worsening during surgery can lead to serious complications such as nucleus drop and vitreous prolapse.
The incidence of general zonular rupture is about 1.1% in low-risk cases and increases to about 6.7% in cases with pseudoexfoliation syndrome 1). In a large surgical series using capsule expanders (CE) (14,394 eyes), lens phacodonesis or subluxation was observed in 92 eyes (0.6%), and PEA was completed in 90% of them 4). Late dislocation of the IOL-capsule complex occurs on average 8.5 years postoperatively, with pseudoexfoliation syndrome being the most common cause 3).
With appropriate preoperative evaluation and preparation, and using auxiliary devices such as capsular tension rings (CTR) or capsule expanders by an experienced surgeon, phacoemulsification (PEA) can be safely performed in many cases of zonulopathy. However, in cases of severe weakness, extracapsular cataract extraction (ECCE), intracapsular cataract extraction (ICCE), or IOL scleral fixation may be required.
Many patients are asymptomatic and are first identified during preoperative evaluation for cataract surgery. When significant subluxation or dislocation is present, the following symptoms occur.
Evaluation with slit-lamp microscopy is fundamental.
In patients with systemic sclerosis, zonular dehiscence may occur intraoperatively even in the absence of known risk factors. A case has been reported of a 55-year-old man with scleroderma who experienced intraoperative zonular dehiscence and iris prolapse during separate cataract surgeries in both eyes. Preoperative evaluation showed no pseudoexfoliation material, and the preoperative anterior chamber depth in the left eye was slightly shallow at 2.59 mm, later considered suggestive of zonular instability 1).
In spherophakia, due to severe zonular laxity, the IOL-capsule complex may subluxate downward (in the direction of gravity), and postoperative focal iris synechiae (PAS) and iris bombe may occur 2).
The causes of zonular weakness are diverse.
Ophthalmic Causes
Pseudoexfoliation syndrome: The most common cause. Abnormal accumulation of fibrillin-elastin fibers weakens the zonules. Surgical complication rate is 21.5%, and zonular dehiscence is 6.7% 1)
Trauma: Shearing force to the zonules from blunt ocular trauma
Iatrogenic: Cataract surgery, vitrectomy, repeated intravitreal injections
Hyper mature cataract, glaucoma, uveitis
Systemic Diseases
Marfan syndrome: Mutation in fibrillin-1 protein of the FBN1 gene. About 60% naturally develop lens dislocation. Zonular strength and elasticity are reduced.
Homocystinuria: Accumulation of abnormal glycoproteins weakens the zonules
Weill-Marchesani syndrome, Ehlers-Danlos syndrome
Systemic sclerosis (scleroderma)
History and findings predisposing to zonular weakness:
| History | Findings |
|---|---|
| Trauma or history of eye surgery | Lens tremors (phacodonesis) |
| Eyes with acute glaucoma attack | Pseudoexfoliation syndrome |
| After vitrectomy or laser iridotomy | Asymmetry in anterior chamber depth |
| Uveitis or congenital diseases | Narrow angle |
| Retinitis pigmentosa, atopic dermatitis, aging |
Zonular weakness is a clinical diagnosis, assessed through patient history and detailed preoperative examination.
Zonular weakness is assessed by the degree of lens wobble at the start of CCC (Taniguchi et al.’s ZW classification):
The Very Weak group (large wobble) in this subjective classification accounts for about 9% of all cases, and the rate of capsular support device use reaches 96.1%.
Not necessarily. Even for experienced surgeons, it is not uncommon for zonular weakness to become apparent only during surgery. In pseudoexfoliation syndrome, sudden rupture may occur intraoperatively even if there is no wobble during CCC. All anterior segment surgeons must be proficient in intraoperative management techniques.
For cases with zonular rupture, considering long-term prognosis, it is most ideal to complete the procedure with IOL scleral suture fixation. Since a technique for suturing a 7.0mm IOL through a small incision is now established, the challenge is how to perform the preceding total lens extraction through a small incision (a corneoscleral incision of about 3.0mm and two corneal ports of about 2.0mm). Use of a CTR requires a completed continuous curvilinear capsulorhexis.
In cases with fragile zonules, countertraction is reduced, making CCC difficult.
Alternative techniques that minimize manipulation and rotation of the nucleus may be appropriate.
Modified nylon iris hooks. The looped support end distributes force over a wide area on the capsule, reducing the risk of anterior capsule rupture. Inserted through a limbal or paracentesis incision parallel to the iris. Easy to insert and remove. In cases of partial zonular dialysis due to trauma, placing two hooks at the dialysis site can stabilize the capsular bag.
An open-ring PMMA device, approximately 12–14.5 mm in diameter (compressed about 2 mm within the capsule). Effective for Zinn zonule breaks up to about 150 degrees. Covered by insurance.
Indications: ① Zinn zonule breaks of about 1/3 circumference or less, ② Mild to moderate zonular weakness (Guidelines for Use of Capsular Tension Ring, March 2014 version) 4)
Contraindications: Anterior capsule rupture, discontinuous capsulotomy, posterior capsule rupture, severe Zinn zonular weakness without planned scleral fixation
Insertion timing (three patterns: early, mid, late) 4):
Note that there is no evidence that CTR placement prevents late IOL-capsule complex dislocation 3). However, if early support is needed, a capsular tension segment (CTS) is an alternative option.
Modified CTRs:
Introduced by Ike Ahmed (2002). Made of PMMA, covers 120 degrees of the zonular damage area, and the anterior fixation eyelet is sutured to the sclera. Its greatest advantage is that it can be inserted before lens removal.
Composed of a T-shaped pad hook with a total length of 12 mm and a tip width of 2 mm, a 5-0 polypropylene thread body, and a silicone fixation part. It can be applied to a wide range of cases from mild zonular weakness to lens dislocation/subluxation into the anterior chamber. It may enable PEA even when the zonules are detached 360 degrees 4).
CE non-indication (conversion to ICCE): Hard nucleus (grade 4-5), massive vitreous prolapse into the anterior chamber, lens vitreous sinking, irregular CCC, difficulty in CE placement, inability to maintain capsular shape during surgery4).
Create scleral pockets at two locations 180 degrees apart posterior to the corneal limbus (Brian Hoffman, 2006), and tie the sutures within the pockets. Advantages include no need for conjunctival incision, improved postoperative comfort, and reduced risk of suture exposure.
Select IOL fixation method according to the degree of zonular weakness and surgical approach.
In spherophakia, the zonules are severely lax, and the IOL-capsule complex may continue to subluxate downward (in the direction of gravity) postoperatively. In some cases, localized iris bombe, shallow anterior chamber, and angle synechiae may occur, which can be prevented by performing an additional iridotomy during surgery 2). Postoperative follow-up and intraocular pressure management are important.
Structure and function of the zonules of Zinn:
Mechanisms by major disease:
Mechanisms of iatrogenic injury during surgery:
Femtosecond laser-assisted cataract surgery (FLACS) with capsulotomy and nuclear softening has been reported to achieve over 90% success in preserving the lens capsule and enabling in-the-bag IOL implantation. The role of FLACS in cases with zonular weakness, where standard intraoperative techniques carry high risk, will be studied further.
For extremely elderly patients aged 90 years or older with severe zonular laxity, a technique using bimanual manipulation to lift central cortical fibers and aspirate toward the periphery has been introduced. This approach is noted for ensuring a clear visual axis while avoiding excessive zonular stress on the periphery.
