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Letter

Reply: Factors affecting stromal hydration of clear corneal incision architecture

Calladine, Daniel MB BS, MRCOphth

Journal of Cataract & Refractive Surgery: March 2010 - Volume 36 - Issue 3 - p 529
doi: 10.1016/j.jcrs.2009.12.018
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The comments of Hu et al. and Zaffar highlight some of the challenges faced when conducting similar clinical studies. While we recognize that a small amount of corneal edema at the CCI site commonly occurs as a direct result of cataract surgery, it is unlikely to occur in large amounts in routine cases. If a significant amount of edema occurs, it is easily visible at the end of surgery as a local area of white corneal opacification around the CCI; this was not seen in our study. In our study, stromal hydration was performed generously with balanced salt solution to produce a visibly significant amount of local corneal edema. While we accept this was a subjective intervention, the optical coherence tomography (OCT) images are objective and clearly demonstrate the boundary between hydrated cornea and surrounding nonhydrated cornea. In light of this, we are confident with our conclusion that stromal hydration tended to increase the local corneal thickness around the CCI, which significantly increased the measured incision length. To further support this, we reexamined some eyes in the study that had stromal hydration a month after surgery. At this time point, local corneal thickness at the CCI site had returned to normal and the incision length was shortened, in line with our study findings.

Both Hu et al. and Zaffar correctly state that central corneal thickness can effect IOP measurement. We reviewed the OCT images from all hydrated eyes in the study and found the induced corneal thickening did not extend to the central cornea. The IOP was measured using Goldmann applanation tonometry on the central cornea; therefore, it is unlikely that the increased corneal thickness around the CCI site would alter the measured IOP. The advantage of performing OCT imaging of the central cornea at the same time point is that central corneal thickness can be measured and a correction factor for IOP can be applied. However, it may be erroneous to apply a correction factor calculated from nomograms of normal eyes to the immediate postoperative period of cataract surgery.

Hu et al. refer to other factors, such as retention of OVD, that are known to affect IOP in the early postoperative period. However, it is probably too soon for this mechanism to take effect within 1 hour of surgery. We apologize for not mentioning that the cohesive OVD Provisc (sodium hyaluronate 1%) was used throughout our study and that we adopted an approach similar to that described by Hu et al. to ensure full removal of OVD from the posterior and anterior chambers at the end of surgery. We find full removal is most easily achieved by pressing down gently on the center of the optic using bimanual irrigation/aspiration handpieces. This encourages any OVD located behind the IOL to move forward around the edge of the optic to be easily aspirated.

We have shown how local detachment of Descemet membrane commonly occurs at the CCI site even in routine surgical cases.1 It is most likely caused by 1 of 3 mechanisms: the initial corneal incision, insertion of the phaco tip or IOL during surgery, or stromal hydration at the end of surgery. We agree in part with the comments by Hu et al. that local detachment of Descemet membrane is probably more likely to occur in difficult surgical cases in which a greater amount of positional manipulation is required via the phaco handpiece and second instrument. However, we think the amount of unnecessary repeated removal and reinsertion of instruments through the CCI may be more relevant to local detachment of Descemet membrane and this factor may be more common in difficult surgical cases or with junior surgeons.

REFERENCE

1. Calladine D, Packard R. Clear corneal incision architecture in the immediate postoperative period evaluated using optical coherence tomography. J Cataract Refract Surg. 2007;33:1429-1435.
© 2010 by Lippincott Williams & Wilkins, Inc.