April 2008

 

CATARACT/ IOL

 

Be aware of high phaco power


by Matt Young EyeWorld Contributing Editor

   

Greater endothelial cell loss could result

High power phaco is often desirable, but a new study suggests that it may contribute to endothelial cell loss in patients with pseudoexfoliation syndrome Source: Jorge L. Alió, M.D.

Pseudoexfoliation syndrome (PEX) combined with high phaco power could lead to significantly greater endo-thelial cell loss, a recent study, published in the Annals of Ophthalmology, suggests. “In regression analysis PEX in interaction with overall phaco impact (phaco time multiplied by power) had a significant influence on endothelial cell loss,” wrote lead study author Kuldar Kaljurand, M.D., department of ophthalmology, University of Tartu, Estonia. “This indicates that PEX in cases with high phaco impact (e.g., hard nucleus) significantly increases the risk of endothelial cell loss.”

PEX alone was not found to impact endothelial cell loss. “In our study there was a significant difference between the two groups in phaco time, which could be explained by more-cautious surgical technique in PEX eyes due to insufficient mydriasis and zonular weakness,” Dr. Kaljurand noted. “We did not find a direct relationship between phaco time and ECD, but time became significant in interaction with phaco power.”

Comparing groups

PEX clearly increases the complications of cataract surgery, and ophthalmologists still search for answers on how to prevent them. Dr. Kaljurand and colleagues provided more insight into these issues by analyzing 27 consecutive patients with PEX and 26 without who underwent cataract surgery. Pre-op endothelium was not significantly different between the two groups. Mean endothelial cell loss was 18.1% in PEX patients one month post-op and 11.6% in the non-PEX group. The difference “had a statistically weak significance” (P=0.06).

“Phaco time and used BSS values were significantly higher in patients with PEX but had no significant influence on endothelial cell loss,” Dr. Kaljurand noted. Phaco power and age, meanwhile, did influence endothelial cell loss significantly. “PEX in interaction with overall phaco impact had a negative influence on endothelial cell loss,” Dr. Kaljurand reported. Corneal oedema was noticed in both groups on post-op day one, but both groups returned to normal in this aspect by the one month follow-up. “The cornea was more affected centrally as well as paracentrally in the PEX group than in the non-PEX group 1 month after the operation, but the difference between the two groups had a statistically weak significance,” Dr. Kaljurand reported. “Moreover, age but not PEX, as the most influential preoperative factor, seems to take credit for this difference.”

The most clinically relevant tip resulting from the study appears to be this: In a case of hard nucleus and PEX, take caution when turning up the phaco power, because greater endothelial cell loss could result. “An experienced surgeon using highly adhesive viscoelastic should operate in cases of presumably prolonged operation time on eyes with a hard nucleus and PEX,” Dr. Kaljurand concluded.

Investigating IOP

IOP results differed somewhat from previous research. “Although cataract surgery in the long run decreases intraocular pressure, the transient pressure peaks occurring in the early postoperative period are more common in eyes with exfoliation,” Dr. Kaljurand noted in the study introduction. But by the end of the study, the researchers made different conclusions. Although they found that IOP did tend to spike in the PEX group, it showed no significant difference in that regard compared to controls. This spike did not have any significant influence on endothelial cell damage. Unrelated to this study but also of note, pseudoexfoliation glaucoma eyes were recently found to have steeper central corneas and higher central corneal thickness than normal eyes, according to study author Ibrahim F. Hepsen, M.D., Fatih University Hospital, Eye Center, Ankara, Turkey. The study was published in the October 2007 issue of the Canadian Journal of Ophthalmology. This could be of clinical significance because overestimation of true intraocular pressure may then occur in these eyes. That’s because in eyes with steeper corneas, error in evaluating goldmann applanation tonometry (GAT) could occur. “The GAT tends to overestimate IOP in the steeper cornea,” Dr. Hepsen noted. “A steep curvature results in a false high pressure reading because more force is used to flatten the cornea. Although several authors have previously discussed the effect of [corneal thickness] on GAT, to the best of our knowledge, the corneal steepness in [pseudoexfoliation syndrome] eyes has never been demonstrated before.”

Dr. Hepsen also found that normotensive pseudoexfoliation syndrome eyes had significantly thinner central corneal thickness than hypertensive pseudoexfoliation syndrome eyes and pseudoexfoliation glaucoma eyes. It stands to reason that if IOP measurements are more easily skewed in PEX eyes, then past research suggesting transient pressure differences occurring after phacoemulsification in PEX patients compared to normal subjects could have been flawed. “However, the statistical significance of CCT or CC does not necessarily correlate with clinical significance,” Dr. Hepsen noted. “Therefore, further studies are needed to clarify the clinical importance of our findings and ascertain whether there is a correlation between CC and pseudoexfoliation.”

Editors’ note: Drs. Hepsen and Kaljurand have no financial interests related to this study.

Contact Information

Hepsen: hepsenif@hotmail.com

Kaljurand: kuldar.kaljurand@kliinikum.ee

Referece:

1. Kaljurand K and Teesalu P. Annals of Ophathalmology 2007; 39(4):327-333.

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