The Vexing Problem of Retained Lens Fragments
The Vexing Problem of Retained Lens Fragments
Retained lens particles remain one of the most stressful and emotionally challenging adverse events in cataract surgery. This is especially true in the current age of advanced cataract surgery, because both the patient's and the surgeon's hopes for instantly improved vision may have been thwarted.
No cataract surgeon is spared from the potential for this adverse event. Yet, having an understanding of the mechanism, risk factors, management, and potential comorbid conditions associated with retained lens particles can help manage the anxiety that this event causes and aid in the development of a logical treatment plan, which can help achieve the best outcome for the patient.
Retained lens fragments occur, on average, in about 1 in 300 (0.3%) phacoemulsification cataract surgeries. The incidence correlates inversely with surgical volume of the individual surgeon. A retrospective analysis by Aasuri and colleagues found an incidence of retained lens fragments of 1 in 500 (0.2%) for experienced surgeons vs 1 in 165 (0.6%) for surgeons considered inexperienced. When they asked surgeons whether posterior capsular rupture and retained lens fragments has occurred over the past year, 6% of experienced surgeons admitted to that complication, compared with 73% of less experienced surgeons.
Rates during the early part of residency training seem to be higher: on average 1%-2%. This rate declines with experience, and the rate of complications in resident-performed cataract surgery has been found to fall by 50% after the first 40 cases. Previous use of a computer-generated simulator in ophthalmic surgery for training ophthalmologists should reduce these rates.
Lens capsule. Risk factors for retained lens fragments are the same as those for posterior capsular rupture and vitreous loss. Knowing the anatomy of the lens capsule and its support structures helps to understand these risk factors.
The posterior capsule is the thinnest and most delicate portion of the capsular bag. There is a twofold reduction in the thickness of the lens capsule from the mid-periphery of the anterior capsule to the equator of the lens, and another twofold reduction in thickness to the posterior pole of the posterior capsule. The posterior pole of the posterior capsule has a mean thickness of 3.5 μm.
Although the width of the capsule plays a role, other biochemical changes that occur with age reduce the capsule's mechanical strength. Krag and Andreassen observed a gradual decline in the extensibility (tensile strength) and thickness of the posterior capsule with age, such that the force required to break it is reduced by a factor of 5 over a person’s lifespan.
Vitreous-zonular-capsular complex. Even though the posterior capsule is delicate, the surrounding structures, including the vitreous-zonular-capsular complex, help keep the lens capsule taut, protecting it from the transmitted shear forces of cataract surgery. The vitreous-zonular-capsular complex consists of the anterior hyaloid, the zonules, and the lens capsule.
The zonules (suspensory ligament of the lens) and the ligamentum hyaloideo-capsulare (Wieger ligament) attach to the lens capsule and support it. The zonules attach not only to the lens capsule but also to the anterior hyaloid face, which is believed to add structural support to the entire complex.
The elasticity and strength of the vitreous-zonular-capsular complex are known to diminish with age. Besides aging, other ocular comorbid conditions and previous surgeries or trauma can destabilize the vitreous-zonular-capsular complex, increasing the risk for posterior capsular rupture, zonular lysis, and vitreous loss during cataract surgery.
A Challenge for Cataract Surgeons
Retained lens particles remain one of the most stressful and emotionally challenging adverse events in cataract surgery. This is especially true in the current age of advanced cataract surgery, because both the patient's and the surgeon's hopes for instantly improved vision may have been thwarted.
No cataract surgeon is spared from the potential for this adverse event. Yet, having an understanding of the mechanism, risk factors, management, and potential comorbid conditions associated with retained lens particles can help manage the anxiety that this event causes and aid in the development of a logical treatment plan, which can help achieve the best outcome for the patient.
Incidence of Retained Lens Fragments
Retained lens fragments occur, on average, in about 1 in 300 (0.3%) phacoemulsification cataract surgeries. The incidence correlates inversely with surgical volume of the individual surgeon. A retrospective analysis by Aasuri and colleagues found an incidence of retained lens fragments of 1 in 500 (0.2%) for experienced surgeons vs 1 in 165 (0.6%) for surgeons considered inexperienced. When they asked surgeons whether posterior capsular rupture and retained lens fragments has occurred over the past year, 6% of experienced surgeons admitted to that complication, compared with 73% of less experienced surgeons.
Rates during the early part of residency training seem to be higher: on average 1%-2%. This rate declines with experience, and the rate of complications in resident-performed cataract surgery has been found to fall by 50% after the first 40 cases. Previous use of a computer-generated simulator in ophthalmic surgery for training ophthalmologists should reduce these rates.
Anatomical Considerations
Lens capsule. Risk factors for retained lens fragments are the same as those for posterior capsular rupture and vitreous loss. Knowing the anatomy of the lens capsule and its support structures helps to understand these risk factors.
The posterior capsule is the thinnest and most delicate portion of the capsular bag. There is a twofold reduction in the thickness of the lens capsule from the mid-periphery of the anterior capsule to the equator of the lens, and another twofold reduction in thickness to the posterior pole of the posterior capsule. The posterior pole of the posterior capsule has a mean thickness of 3.5 μm.
Although the width of the capsule plays a role, other biochemical changes that occur with age reduce the capsule's mechanical strength. Krag and Andreassen observed a gradual decline in the extensibility (tensile strength) and thickness of the posterior capsule with age, such that the force required to break it is reduced by a factor of 5 over a person’s lifespan.
Vitreous-zonular-capsular complex. Even though the posterior capsule is delicate, the surrounding structures, including the vitreous-zonular-capsular complex, help keep the lens capsule taut, protecting it from the transmitted shear forces of cataract surgery. The vitreous-zonular-capsular complex consists of the anterior hyaloid, the zonules, and the lens capsule.
The zonules (suspensory ligament of the lens) and the ligamentum hyaloideo-capsulare (Wieger ligament) attach to the lens capsule and support it. The zonules attach not only to the lens capsule but also to the anterior hyaloid face, which is believed to add structural support to the entire complex.
The elasticity and strength of the vitreous-zonular-capsular complex are known to diminish with age. Besides aging, other ocular comorbid conditions and previous surgeries or trauma can destabilize the vitreous-zonular-capsular complex, increasing the risk for posterior capsular rupture, zonular lysis, and vitreous loss during cataract surgery.