Long Anterior Zonules

Key Points at a Glance

Key Points of This Disease

• Anterior zonular insertion is an anatomical variant in which the zonules attach anteriorly beyond the lens equator (≥1 mm anterior to the usual insertion site), with an estimated prevalence of approximately 2%.
• It has been associated with middle-aged Black women, hyperopia, and short axial length.
• Rarely, it is associated with late-onset retinal macular degeneration due to CTRP5 gene mutations.
• Associated with risk of pigment dispersion syndrome, angle-closure glaucoma, and plateau iris syndrome.
• Usually asymptomatic and often discovered incidentally during dilated slit-lamp examination.
• Cataract surgery requires a special surgical strategy due to the narrow zonule-free zone.

1. What is long anterior zonule?

Long anterior zonules (LAZ) are an anatomical variant in which the lens zonules (ciliary zonules) extend forward onto the anterior lens capsule beyond their normal attachment at the lens equator.

Normal zonules (Zinn’s zonules) arise from the epithelium of the ciliary processes, run toward the lens equator, and attach to the lens capsule in three regions: anterior, equatorial, and posterior. In long anterior zonules, this attachment site is located 1 mm or more anteriorly (closer to the visual axis) than usual.

The estimated prevalence is approximately 2%, making it a relatively rare variant. The exact cause is unknown, but it is more common in middle-aged Black women and has been associated with hyperopia and short axial length.

Q Do long anterior zonules adversely affect the eye?

A

In many cases, it is asymptomatic and does not cause direct visual impairment. However, it increases the risk of associated conditions such as pigment dispersion syndrome, angle-closure glaucoma, and plateau iris syndrome, and special surgical considerations are required during cataract surgery.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

The long anterior zonule itself is generally asymptomatic.

• Blurred vision and halos: When combined with pigment dispersion syndrome (PDS), temporary blurred vision and halos may occur due to intraocular pressure fluctuations caused by pigment release.
• Often asymptomatic: Incidentally discovered during routine eye examinations.

Clinical Findings

On slit-lamp examination under mydriasis, zonular fibers are observed extending onto the anterior lens capsule. Characteristically, the insertion is more than 1 mm anterior to the usual site (approximately 1.5 mm from the lens equator).

In some cases, pigmentation is observed on the anterior lens capsule, improving visibility.

In cases complicated by pigment dispersion syndrome, the following findings are observed.

• Positive transillumination of the mid-peripheral iris (radial spoke-like pattern)
• Krukenberg spindle (pigment deposition) on the corneal endothelium
• Increased pigmentation of the trabecular meshwork

The mechanism of pigment dispersion involves the release of melanin pigment from the iris pigment epithelium due to contact between the iris and zonular fibers. Melanin granules increase trabecular outflow resistance, leading to elevated intraocular pressure ²⁾.

The following are also assessed for evaluation of angle closure:

• Thick and anteriorly positioned lens
• Short axial length
• Position and morphology of the ciliary body (evaluated by anterior segment optical coherence tomography or ultrasound biomicroscopy)

If long anterior zonules may be associated with late-onset retinal macular degeneration, fundus examination is recommended to check for signs of macular degeneration.

3. Causes and Risk Factors

Etiology and Related Diseases

The pathophysiology of the anterior zonule is multifactorial, involving genetic and anatomical factors.

• Association with CTRP5 gene mutation: An association between late-onset retinal macular degeneration (L-ORMD) caused by mutations in the CTRP5 (C1QTNF5) gene and the anterior zonule has been reported. Since the ciliary epithelium and retinal pigment epithelium share the same embryonic origin, common developmental pathways may contribute to both the anterior zonule and late-onset retinal macular degeneration.
• Hyperopia and short axial length: Both are risk factors for angle-closure glaucoma.
• Racial predilection: More common in middle-aged Black women.

Mechanism of association with angle closure

Anteriorly positioned zonules may exert abnormal traction on the ciliary processes, rotating them forward and contributing to angle closure. Pupillary block is the most common mechanism of angle closure, accounting for up to 75% of all cases ¹⁾.

Long anterior zonules can anatomically mimic or exacerbate plateau iris syndrome, increasing the risk of angle narrowing.

Prevention and Daily Care

• If diagnosed with long anterior zonules, continue regular eye examinations to monitor intraocular pressure and angle status.
• Consult an ophthalmologist before using medications that cause pupillary dilation or are intended for light protection.
• If there is a family history of retinal degeneration (late-onset retinal macular degeneration), discuss genetic testing with your doctor.

4. Diagnosis and Examination Methods

Diagnostic Procedure

Examination	Purpose
Slit-lamp examination under mydriasis	Direct observation of zonular fibers extending onto the anterior lens capsule
Gonioscopy	Assessment of peripheral anterior synechiae and angle closure
Anterior segment optical coherence tomography / Ultrasound biomicroscopy	Quantitative assessment of ciliary body morphology and angle narrowing
Fundus examination	Evaluation for the presence of late-onset retinal macular degeneration (macular degeneration)
Genetic testing	Search for CTRP5 mutations in suspected late-onset retinal macular degeneration

Anterior segment optical coherence tomography provides noninvasive, high-resolution cross-sectional images and is excellent for evaluating functional angle closure. However, gonioscopy is essential for assessing peripheral anterior synechiae ¹⁾.

Differential diagnosis

• Pigment dispersion syndrome: May present with intraocular pressure spikes after contact sports or pupillary dilation. Posterior bowing of the iris (reverse pupillary block) is observed²⁾.
• Plateau iris syndrome: Anterior displacement of the iris root is caused by anterior rotation of the ciliary processes. Characteristic ciliary body morphology is confirmed by ultrasound biomicroscopy.
• Pseudoexfoliation syndrome: Accompanied by degeneration and rupture of the zonular fibers. The mechanism differs from that of long anterior zonules.

Q When long anterior zonules are found, what other tests are needed?

A

Intraocular pressure measurement, gonioscopy, and anterior segment optical coherence tomography for angle evaluation are important. If there is a family history of retinal degeneration, fundus examination and genetic testing should also be considered. Iris transillumination test and evaluation of trabecular meshwork pigmentation are performed to assess for pigment dispersion syndrome.

5. Standard Treatment

Management Principles

Long anterior zonules are usually asymptomatic and do not require direct intervention. Management focuses on monitoring and treating associated complications.

Glaucoma Management

When angle-closure glaucoma is present, treatment should be based on the mechanism of angle closure (pupillary block, plateau iris).

• Laser iridotomy: Effective for pupillary block.
• Intraocular pressure-lowering medications: Used when an open-angle component remains.
• Miotics: Caution is needed in cases with posterior mechanism (plateau iris). Miotics for pupillary block may worsen angle closure ¹⁾.

Special Strategies in Cataract Surgery

In cataract surgery for patients with long zonules, the zonule-free zone (ZFZ: the area of the anterior capsule without zonular attachment) is narrow, so the following points require attention.

Choice of capsulorhexis:

• Small continuous curvilinear capsulorhexis (CCC) within the zonule-free zone: Ensures intraoperative and postoperative stability, but carries a risk of postoperative capsular phimosis.
• Large continuous curvilinear capsulorhexis (sacrificing long anterior zonular fibers): It has been shown that cutting the long anterior zonular fibers does not compromise intraoperative or postoperative lens stability. If radial extension of the capsulorhexis occurs, it can be corrected with the Little maneuver (a technique of pulling the capsulorhexis flap centrally).
• Capsular tension ring insertion: Another approach is to insert a capsular tension ring after performing a small continuous curvilinear capsulorhexis, and then enlarge the capsulorhexis to the desired size. For zonular weakness, a capsular tension ring reduces the risk of intraoperative zonular dialysis and improves postoperative centration of the intraocular lens³⁾.

There is no clear evidence indicating which capsulorhexis technique is superior.

Precautions during cataract surgery

• Preoperatively identify the presence of long zonules and plan the capsulotomy strategy in advance.
• If the zonule-free zone is narrow, radial extension of the capsulotomy is likely. Master the corrective maneuver (Little maneuver).
• Preparing for insertion of a capsule tension ring may be useful in some cases.
• Because there is a risk of postoperative capsular contraction, careful postoperative follow-up is required.

6. Pathophysiology and Detailed Mechanism of Onset

Anatomy of the Zonules and Mechanism of Abnormalities

Normal Zinn zonular fibers originate from the ciliary process epithelium and attach to the lens capsule in the anterior, equatorial, and posterior sections. The attachment site of the anterior zonules and the anterior capsule moves centrally with age, and the area of the anterior capsule not in contact with the zonules decreases with age.

In the long anterior zonule, this zonule extends forward to a position closer to the visual axis. This anatomical deviation causes:

1. Iris-zonule contact: The zonule has increased opportunity to contact the mid-peripheral iris, leading to friction-induced release of melanin pigment from the iris pigment epithelium (pigment dispersion)²⁾.
2. Abnormal traction on the ciliary processes: The anteriorly positioned zonule pulls the ciliary processes forward, and the forward rotation of the ciliary processes may form or worsen a plateau iris-like configuration.
3. Narrowing of the zonule-free zone: The area on the anterior capsule free of zonular attachment is reduced, limiting capsulotomy maneuvers during cataract surgery.

Association with Late-Onset Retinal Macular Degeneration

CTRP5 gene mutations may be involved in both late-onset retinal macular degeneration and long anterior zonules. Since the ciliary epithelium and retinal pigment epithelium share the same embryological origin, a common developmental pathway is thought to be involved in the formation of both structures.

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7. Latest Research and Future Perspectives (Reports at Research Stage)

For patients: Please read this

The following content is currently in the research or clinical trial stage and is not standard treatment available at general hospitals. It is reference information for professionals regarding future medical developments.

Establishment of optimal cataract surgery strategies

Research continues on the safest and most effective capsulotomy technique for long anterior zonules. Currently, there is no clear evidence that one surgical strategy is superior to another, and future comparative studies are expected.

CTRP5 Mutation and Screening for Late-Onset Retinal Macular Degeneration

Since long anterior zonules may serve as an early marker for late-onset retinal macular degeneration before retinal findings appear, research is underway on the significance of CTRP5 genetic screening in patients with long anterior zonules.

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8. References

1. European Glaucoma Society Terminology and Guidelines for Glaucoma, 5th Edition. The British journal of ophthalmology. 2021;105(Suppl 1):1-169. doi:10.1136/bjophthalmol-2021-egsguidelines. PMID:34675001.
2. European Glaucoma Society Terminology and Guidelines for Glaucoma, 5th Edition. The British journal of ophthalmology. 2021;105(Suppl 1):1-169. doi:10.1136/bjophthalmol-2021-egsguidelines. PMID:34675001. [Section 47: Pigmentary glaucoma]
3. Miller KM, Oetting TA, Tweeten JP, Carter K, Lee BS, Lin S, et al. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2022;129(1):P1-P126. doi:10.1016/j.ophtha.2021.10.006. PMID:34780842.