Eyes with zonular instability (ZI) usually manifests itself as phacodonesis at slit-lamp biomicroscopy, but a large lens held in a limited space between iris and vitreous body may obscure this sign. Out of fear of exacerbating pupillary block with high intraocular pressure following pharmacological mydriasis in eyes with a history of acute angle closure (AAC), displacement or tilt of the lens indicating the presence of ZI could be missed preoperatively.
The authors are to be commended for conducting this retrospective case-control study which first reports preoperative factors associated with ZI in AAC eyes, including less hyperopic spherical equivalent, longer axial length, and higher lens volt as detected with AS-OCT. Of note is that among the 10 eyes with ZI, the diseased eyes had significantly shallower anterior chamber (AC) and higher lens volt than their fellow eyes. Although the difference did not reach statistical significance after Bonferroni correction, probably due to small sample size, these findings support the conventional teaching that asymmetric AC depth between the two eyes of one subject indicates the presence of zonular weakness.
It is regretful that cases with lens subluxation not detected at the clinic but noted in the surgical theater after pupil dilation were excluded from this study. This group of eyes are those very likely to benefit from the study findings as surgeons can prepare well preoperatively for them. In addition, being a retrospective study, possibly involving more than one surgeon, which defined cases with or without ZI based on medical records (whether singlepiece IOL was placed in-the-bag or capsule tension ring was inserted, etc.), the possibility of listing some cases with iatrogenic zonular damage which occurred during operation in the ZI (+) group and misclassifying cases with mild zonular weakness in the ZI (-) group could not be ruled out.