Long Anterior Zonules
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Disease Entity
Long Anterior Zonules (LAZ) represent a distinctive anatomical variation where the lens zonules extend anteriorly beyond their usual attachment at the lens equator.[1] This atypical positioning of the zonules leads to a more central insertion of the fibers onto the lens capsule, which may have implications for associated ocular conditions, such as glaucoma and cataract surgery.
Etiology and Epidemiology
LAZ is considered relatively rare, with an estimated prevalence of approximately 2%. While the exact etiology remains unclear, LAZ appears more frequently in middle-aged black women and has been associated with hyperopia and shorter axial lengths.[2] In rarer cases, LAZ may be observed in younger individuals and correlate with late-onset retinal and macular degeneration (L-ORMD), a rare retinal disorder caused by mutations in the protein C1QTNF5.[3]
Pathophysiology
The pathophysiology of LAZ may be multifactorial, involving genetic and anatomical influences.
LAZ has been observed in association with L-ORMD, a retinal disorder linked to mutations in the CTRP5 gene. The embryonic origin of both the ciliary epithelium and the retinal pigment epithelium (RPE) could underlie a shared developmental pathway, contributing to both LAZ and L-ORD in certain individuals.[4]
In LAZ, the zonules extend anteriorly beyond their usual location, attaching to the lens closer to the visual axis. This anterior positioning may increase the risk of iris-zonule contact, particularly at the midperipheral iris, which could lead to pigment dispersion from iridozonular contact.[5] LAZ has also been associated with anatomical configurations such as plateau iris syndrome and angle-closure glaucoma. Anteriorly placed zonules may create abnormal traction on the ciliary processes, potentially rotating them forward and contributing to angle closure.[6] Additionally, LAZ is associated with hyperopia and shorter axial lengths, both risk factors for angle closure.
Diagnosis
Physical examination
LAZ is typically asymptomatic and often discovered incidentally during routine eye examinations.
Diagnosing LAZ requires careful biomicroscopy with pupil dilation. On slit-lamp examination, the zonules can be observed extending onto the anterior lens capsule, often more than 1 mm anterior to their typical insertion point, which is normally around 1.5 mm from the lens equator.[7]
In some cases, the anterior zonules can exhibit pigment deposition, making them more visible. Pigment Dispersion Syndrome (PDS) related findings may include midperipheral iris transillumination, Krukenberg spindle on the corneal endothelium, and increased pigmentation of the trabecular meshwork.[5]
Because LAZ is associated with angle-closure mechanisms, the examination should assess contributing anatomical factors such as a thicker, anteriorly positioned lens and a shorter axial length. LAZ has also been hypothesized to alter ciliary body configuration by exerting anomalous traction on the ciliary processes. This traction may lead to forward rotation of the ciliary processes and potentially creating or exacerbating a plateau iris configuration. Together, these structural variations increase the risk of crowding in the anterior chamber angle and may predispose patients with LAZ to angle-closure glaucoma.
A thorough fundoscopic evaluation is recommended to check for signs of macular degeneration, especially given LAZ’s association with L-ORMD, where LAZ may precede retinal findings.[8]
Symptoms
LAZ is generally asymptomatic. However, if pigment dispersion syndrome (PDS) coexists, some patients may experience intermittent blurred vision or halos around lights, particularly with fluctuations in intraocular pressure (IOP) due to pigment release.
Laboratory test
Genetic testing can be considered in patients with LAZ and a family history of retinal degeneration, particularly if L-ORMD is suspected.
Management
Management of LAZ primarily involves monitoring for and treating associated complications, as LAZ itself is usually asymptomatic and does not require direct intervention.
Cataract surgery considerations
Patients with LAZ undergoing cataract surgery require particular surgical strategies due to the small zonular-free zone (ZFZ). The main challenge is achieving an adequately sized capsulorhexis while ensuring intraoperative capsular stability during phacoemulsification. Some surgeons advocate creating a capsulorhexis that stays within the ZFZ, while others suggest sacrificing the anteriorly extended zonules to enable a larger capsulorhexis for safer phacoemulsification.[9]
A larger, continuous curvilinear capsulorhexis (CCC) can be created, cutting, when needed, the LAZ fibers if they interfere with capsulorhexis formation, as the sacrifice of these fibers has not shown to compromise lens stability intra or postoperatively. However, if the capsulorhexis experiences radial extension, techniques like the Little maneuver—redirecting the capsulorhexis flap centrally—can be used to correct it.[10]
Creating a small capsulorhexis within the ZFZ is another option, though it may increase the risk of intraoperative complications and postoperative capsular phimosis.
Some surgeons perform a small continuous curvilinear capsulorhexis (CCC), followed by the insertion of a capsular tension ring, after which the CCC is enlarged to achieve the desired size.
However, there is no clear evidence favoring one capsulorhexis technique over another in LAZ.
References
- ↑ Wiesen, JonathaMoshe Ornstein2, Adriano R Tonelli1, Venu Menon3 and RW, Ashton. 基因的改变NIH Public Access. Bone. 2008;23(1):1–7.
- ↑ Roberts DK, Newman TL, Roberts MF, Teitelbaum BA, Winters JE. Long anterior lens zonules and intraocular pressure. Investig Ophthalmol Vis Sci. 2018;59(5):2015–23.
- ↑ Roberts DK, Wilensky J. Long anterior lens zonules. Clin Exp Ophthalmol. 2012;40(7):764–6.
- ↑ Ayyagari R, Mandal MNA, Karoukis AJ, Chen L, McLaren NC, Lichter M, et al. Late-onset macular degeneration and long anterior lens zonules result from a CTRP5 gene mutation. Investig Ophthalmol Vis Sci. 2005;46(9):3363–71.
- ↑ 5.0 5.1 Moroi SE, Lark KK, Sieving PA, Nouri-Mahdavi K, Schlötzer-Schrehardt U, Katz GJ, et al. Long anterior zonules and pigment dispersion. Am J Ophthalmol. 2003;136(6):1176–8.
- ↑ Roberts DK, Ayyagari R, Moroi SE. Possible association between long anterior lens zonules and plateau iris configuration. J Glaucoma. 2008;17(5):393–6.
- ↑ Cao X, Qin J, Li Z, Jia P, Gao B, Feng L, et al. Long anterior lens zonules with retinal stripes: a case report. BMC Ophthalmol [Internet]. 2022;22(1):1–5. Available from: https://doi.org/10.1186/s12886-022-02496-7
- ↑ Borooah S, Collins C, Wright A, Dhillon B. Late-onset retinal macular degeneration: Clinical insights into an inherited retinal degeneration. Postgrad Med J. 2009;85(1007):495–500.
- ↑ Khurana M, Shah DD, George RJ, Vijaya L, Balekudaru S. Phacoemulsification in eyes with long anterior zonules. J Cataract Refract Surg. 2020;46(2):209–14.
- ↑ Roberts DK, Yang Y, Wilensky JT. Cataract surgery in African Americans with long anterior lens zonules. Clin Exp Ophthalmol. 2014;42(9):898–900.
