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Low vaulting of phakic IOL associated with small white-to-white distance, older age
J Refract Surg. 2009;25(3):259-264.
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Older eyes and those with smaller white-to-white distance were more prone than other eyes to have low vaulting.
Low vaulting of an IOL over the crystalline lens poses a risk of lens opacity and cataract, the study authors said.
“It has been reported that eyes with lower vaulting … were more predisposed to the risk of secondary cataract formation, and thus vaulting is considered to be an important factor in the improvement of the safety of [IOL] implantation,” they said.
The retrospective study included 123 eyes of 68 patients who received the Implantable Collamer Lens (STAAR Surgical). The patients had a mean age of 34.6 years (range, 20 years to 59 years). Mean preoperative myopic error was –10.07 D (range, –3.25 D to –22.75 D).
Investigators used slit lamp microscopy to assess the magnitude of central vaulting at 3 months postop.
Results showed mean central vaulting of the ICL of 603.6 µm at 3 months postop. Variables most closely associated with vaulting were white-to-white distance (P = .0002) and patient age (P = .011).
No contact between ICL and crystalline lens was identified during follow-up.
Cataract development associated with ICL vaulting may be attributed to ICL-crystalline lens contact or nutrients not reaching the lens because of poor aqueous circulation. Further study is needed, the authors said.
One of the greatest risks of phakic lens implantation into the posterior chamber is anterior supcapsular cataract formation. A greater vaulting or separation of the posterior surface of the phakic IOL from the anterior lens capsule should reduce this risk of cataract formation. This study demonstrates statistically that older patients (presumably with greater protrusion of the anterior crystalline lens surface due to lens growth) and eyes with decreasing white-to-white measurements have less vaulting, thus increasing the risk of anterior supcapsular cataract formation.
The practical import of this study is a lessening of importance of the preoperative anterior chamber depth (ACD) measurement (found to be an insignificant independent variable for vaulting in this study) and an increasing importance of horizontal white-to-white measurement.
It is interesting that in this study, 3.3% of eyes developed anterior subcapsular cataracts postoperatively during a very short mean follow-up period of 3 months. None of those eyes showed physical contact of the collamer lens with the anterior crystalline lens capsule during slit lamp examination. However, these vaulting study measurements were taken during pharmacological mydriasis, which has been shown to shift the collamer lens anteriorly as the iris moves to the periphery while simultaneously the crystalline lens moves posteriorly from the iris-lens diaphragm shift. This fact calls into question the significance of these vaulting measurements in the real-life setting of a normal nondilated pupil. In the meantime, I will continue to pay very close attention to my preoperative ACD measurements.
– Richard J. Duffey, MD
OSN Refractive Surgery Board Member