The Effect of Prior Trabeculectomy on Refractive Outcomes of Cataract Surgery

We read with interest the recent article concerning the refractive outcomes after cataract surgery in patients who had a filtering bleb.

We highlight that there is significant uncertainty in regard to refractive outcomes; despite intense research, we still are unable to point out those factors that are responsible for suboptimal refractive results in the modern era of cataract surgery. In fact, partial coherence interferometry is now available to determine precise axial length (AL) measurements. The corneal power is precisely calculated, and we use small-incision phacoemulsification cataract surgery and implant high-quality intraocular lenses (IOL), and yet we can observe postoperative refractive “surprises.”

We certainly agree with Zhang and associates about the limited accuracy of the contact ultrasonography for AL measurements that was used in their study, and we would certainly encourage all surgeons to use optical biometry, given its well-recognized advantages.

We also fear that the study might have several other biases. The IOL formula used might be incorrect in some of the cases (surely the SRK II is obsolete nowadays), and the authors might be willing to perform a back-calculation of the refractive error with an appropriate IOL power-prediction formula to correct for this methodologic error. It has also been suggested that a corneal astigmatism superior to 1 diopter or high corneal powers might lead to inaccurate prediction of the postoperative error. We wonder whether the authors might have found a different distribution of these variables among the eyes they investigated.

It is also our experience that in eyes that have undergone previous intraocular surgery, particularly in shorter eyes, the zonules might appear to be abnormal during surgery, and we argue that abnormal zonules might lead to abnormal and unexpected capsule contraction phenomena, hence acting on the effective lens position and the final postoperative refraction.

Finally, we are skeptical that a marginal rise in intraocular pressure (on average 2 mm Hg in this study) could have led to a change in AL, as hypothesized by the authors. However, a future study with optical AL measurement at 3 timepoints (prior to trabeculectomy, prior to cataract surgery, and a few months after cataract surgery) might provide definitive evidence.

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Jan 9, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on The Effect of Prior Trabeculectomy on Refractive Outcomes of Cataract Surgery
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