Zonular weakness refers to compromise of the zonular fibers that suspend the lens capsule from the ciliary body, resulting in instability of the capsular bag-lens complex. This may present pre-operatively or intra-operatively and can complicate cataract surgery and intraocular lens (IOL) placement.
Zonular instability may arise from a variety of conditions, including mature cataracts, high axial myopia, previous ocular trauma, or prior ocular surgery. Systemic or genetic disorders such as pseudoexfoliation syndrome, Marfan syndrome, homocystinuria, and retinitis pigmentosa may also compromise zonular integrity.1
In the general population, the prevalence of zonulopathy ranges from 0.46% to 2.6%.2 Failure to recognize zonular instability can lead to increased risk of intra-operative capsule rupture, nucleus drop, vitreous prolapse, and IOL dislocation.3 Early recognition can allow surgeons to modify their surgical technique, use capsular support devices, reduce intra-operative complications, and improve refractive and visual outcomes.
The importance of pre-operative assessment
Thorough pre-operative evaluation is essential for identifying eyes at risk for zonular weakness. A comprehensive history should assess for prior ocular trauma or surgery, as well as systemic conditions such as connective tissue disorders. Patients with features suggestive of systemic disease, including increased height or known diagnoses such as Marfan syndrome, prompt further consideration of zonular instability.
Slit lamp examination may reveal subtle signs such as phacodonesis, poor pupillary dilation, or the presence of pseudoexfoliative material. Inadequate dilation, in particular, may indicate zonular dysfunction and should raise suspicion in the appropriate clinical context. Recognition of these findings preoperatively allows for appropriate surgical planning and preparation for capsular support.
Top 3 signs of zonular weakness
1. Phacodonesis or iridodonesis
Phacodonesis, or the abnormal movement of the crystalline lens with eye movement, is one of the most recognizable signs of zonular instability. This can be assessed with slit lamp examination. It is typically detected when the patient changes fixation or when the examiner shifts the slit beam across the pupil. The lens may demonstrate subtle wobbling due to loss of normal zonular tension. Phacodonesis may also be appreciated intra-operatively as excessive lens mobility during capsulorhexis or manipulation.
Video 1: Example of phacodonesis upon initiation of capsulorhexis.
Iridodonesis may also be present in more advanced cases and reflects secondary movement of the iris resulting from inadequate lens support. Additionally, subluxation or tilt of the crystalline lens, either identified pre-operatively or intra-operatively, should raise concern for underlying zonular insufficiency (Figure 1). Other associated findings include advanced cataract and pseudoexfoliative material.
Figure 1: Decentration of the lens–capsular bag complex is observed in the setting of zonular insufficiency.
Figure 1: Courtesy of Kamran Riaz, MD.
2. Abnormal capsule behavior
Abnormal capsular bag behavior during cataract surgery is an important intra-operative indicator of zonular weakness. Reduced zonular countertraction can cause the capsular bag to shift when traction is applied during capsulorhexis. Surgeons may observe the capsulorhexis drifting toward areas of zonular loss or note radial folds and wrinkling of the anterior capsule due to decreased zonular tension.
The use of trypan blue may improve visualization of the anterior capsule in these cases; however, it should be applied sparingly. Painting the capsule rather than forcefully injecting dye may reduce the risk of inadvertent staining of the vitreous in the setting of zonular compromise. Vitreous staining can make it difficult to distinguish prolapsed vitreous from surrounding structures, increasing the risk of unintended traction during surgical maneuvers.
Additional signs of capsular instability may become evident during later steps of the procedure. During hydrodissection or nuclear manipulation, the capsular bag may demonstrate excessive mobility as the remaining zonules fail to provide adequate support. Recognizing these intra-operative findings early is critical, as they may prompt the surgeon to modify surgical technique or consider capsular stabilization devices to prevent progression of zonular dialysis.
Video 2: Capsular instability during phacoemulsification.
3. IOL instability
IOL instability may be observed intra-operatively during IOL insertion and rotation (Video 3) or post-operatively. Inadequate zonular support can lead to IOL decentration, tilt, or rotation post-operatively.
Patients may present with decreased vision, monocular diplopia, or refractive changes resulting from IOL shift. Recognition of these findings should prompt evaluation for zonular insufficiency and consideration of surgical intervention if the instability is visually significant.
Video 3: Intra-operative IOL instability in zonular weakness.
Classification of zonular weakness
The severity of zonular weakness is commonly described according to the extent of zonular loss. This classification is typically expressed in clock hours:
- Mild: <3 clock hours of zonular loss
- Moderate: 3 to 6 clock hours of zonular loss
- Severe: >6 clock hours of zonular loss
More objective grading systems have also been proposed. Yaguchi et al. described a classification based on anterior capsule shift measured during capsulorhexis:4
- Grade I: Lens shift <0.20mm
- Grade II: Lens shift <0.20 to 0.39mm
- Grade III: Lens shift >0.40mm
Management strategies
Successful management of zonular weakness relies on careful surgical planning and anticipation of intra-operative challenges. Surgeons should be prepared to pivot from standard phacoemulsification to the use of capsular support devices, scleral fixation techniques, or anterior vitrectomy when necessary.
In cases of significant zonular compromise, referral to a surgeon with experience in complex cataract surgery may be appropriate.
Surgical technique recommendations
Capsulorhexis
Creation of a continuous curvilinear capsulorhexis (CCC) may be challenging due to reduced counter-traction from the zonules. Directing shearing forces toward areas of intact zonules and using a second instrument through a side-port incision for counter-traction may improve control.
Hydrodissection and nuclear removal
Gentle hydrodissection is important to mobilize the lens while minimizing stress on the zonules. Excessive hydrodissection or aggressive lens rotation should be avoided to minimize zonular dialysis. During nuclear disassembly, the chopping technique can limit rotational forces and reduce stress on remaining zonules.
Cortical removal
During irrigation and aspiration, tangential cortical stripping techniques can help reduce centripetal forces on the capsular bag and reduce traction on weakened zonules.
Anterior vitrectomy
In cases of significant zonular weakness, vitreous prolapse may be encountered, particularly in the area of zonular loss. When present, a limited anterior vitrectomy should be performed to remove prolapsed vitreous and minimize the risk of vitreoretinal traction and postoperative complications.
Capsular support devices
Capsular tension rings (CTRs) are commonly used to redistribute forces along the capsular bag in cases of mild to moderate zonular weakness (Video 4).5,6 In more severe cases, modified CTRs or capsular tension segments that allow scleral fixation may be required.5
Capsular stabilization devices should be placed early when instability is recognized, as early support may prevent progression of zonular dialysis. In cases of anterior or posterior capsular tear, CTRs are contraindicated.5 Insertion of a CTR can extend the capsular tear and potentially displace lens material into the vitreous cavity.
In addition, temporary capsular hooks can provide intra-operative support and stabilize the bag during phacoemulsification.7
Video 4: CTR placement for zonular weakness. A Sinskey hook is used to engage the leading eyelet, allowing controlled CTR insertion and minimizing stress on weakened zonules.
IOL selection
In cases with significant zonular compromise, surgeons should consider alternative IOL fixation strategies, including sulcus placement with optic capture, scleral fixation, or other secondary fixation techniques.8
While toric IOLs may still be considered in select cases, careful attention should be paid to the location of zonular weakness. If the intended axis of alignment corresponds to the area of zonular deficiency, rotational stability may be compromised. In such cases, alternative methods of astigmatism correction, including limbal relaxing incisions or corneal refractive procedures, may be preferred.
Key takeaways
- Zonular weakness results from compromise of the suspensory fibers supporting the lens capsule.
- It may be associated with ocular conditions such as trauma, prior surgery, or high myopia, as well as systemic disorders like pseudoexfoliation syndrome or connective tissue disorders.
- The three most useful clinical signs are phacodonesis, abnormal capsular behavior, and intraocular lens mobility.
- Classifying zonular loss by clock hours helps guide surgical planning.
- Early recognition allows surgeons to modify surgical techniques and utilize capsular support devices to improve outcomes.
