COMMENTARY

Capsule Tears: Manual vs Laser Cataract Surgery

William W. Culbertson, MD

Disclosures

February 13, 2015

Comparison of the Mechanical Properties of the Anterior Lens Capsule Following Manual Capsulorrhexis and Femtosecond Laser Capsulotomy

Sándor G, Kiss Z, Bocskai Z, et al
J Refract Surg. 2014;30:660-664

Seeking Answers, Finding More Questions

Femtosecond cataract lasers create perfectly round anterior capsulotomies at the diameter and position of the ophthalmic surgeon's choosing. However, scanning electron microscopy shows that the edge of the laser-created capsulotomy is notched, owing to the postage stamp-like perforations that the laser makes in order to cut the capsule. In comparison, the torn edge of a manually created anterior capsulorrhexis is smooth, without notches.

Common sense suggests that the notched laser capsulotomies would be more vulnerable to tearing when stretched, given that the resistance to tearing would only be as strong as the weakest notch. However, previous in vitro testing in porcine capsules suggested that laser capsulotomies paradoxically appeared to be stronger than manual ones, although there is no obvious explanation for this observation.[1,2] Clinical reports offer further discrepancies; for example, one shows a slightly greater frequency of radial anterior capsule tears in laser-created anterior capsulotomy compared with manual capsulorrhexis,[3] whereas another shows no difference in capsulotomy extension rates.[4]

Because the four commercially available lasers have fundamental differences in their focusing and lasing functions, it has been difficult to draw conclusions regarding a potentially clinically important predilection for radial tears. Also, the performance of an individual laser is sensitive to its tuning status at any given time, making it difficult to assess whether there is really a difference in capsular extension rates in manual vs laser cases.

Study Summary

Sándor and colleagues performed anterior capsulotomy in whole pig eyes using the LenSx® (Alcon; Dallas, Texas) cataract laser, which was set to typical clinical settings. They evaluated the morphology of the edge of the capsulotomy with scanning electron microscopy and tested the stretching and breaking under load characteristics of the capsulotomy openings. Scanning electron microscopy confirmed the notched appearance of the laser capsulotomy and the relatively smooth edge of the manual capsulorrhexis previously reported.

The study investigators stretched the capsule opening between two pins attached to a force dynamometer and measured the force at which the capsule opening breaks. They found that the average capsule rupture force was lower in the laser cases than the manual cases, although there was a comparatively wider range for the manual cases, with some rupturing at lower loads than in the weakest laser cases. They postulated that the notches in the laser capsulotomy edges constitute focal points of weakness that accounted for the lower average rupture threshold.

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