EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/176967
74 EW RESIDENTS September 2013 EyeWorld journal club Yale residents' review of: "Corneal endothelial cell loss and corneal thickness by Daniel Greene, MD, Ting Ting Liu, MD, and David R. Shield, MD, Yale residents; Jessica H. Chow, MD, faculty advisor; and John J. Huang, MD, residency program director, Yale University, New Haven, Conn. John Huang, MD Residency program director Yale University Does femtosecond laser nuclear fragmentation decrease endothelial cell loss? This month, I invited the Yale residents to review this prospective study that appears in the September issue of JCRS. –David F. Chang, MD, chief medical editor C orneal endothelial cell loss is an inevitable complication following cataract surgery and occurs after any cataract technique.1-7 Previous studies comparing endothelial cell loss after intracapsular extraction, conventional extracapsular extraction, small-incision extracapsular extraction, and phacoemulsification (standard incision and microincision) failed to demonstrate a statistically significant difference. Furthermore, among phaco-chop, stop-and-chop, and divide-and-conquer techniques, no approach has shown an advantage over another in reducing endothelial cell loss.8,9 However, two studies conclude that torsional phacoemulsification may be superior to longitudinal phacoemulsification in limiting endothelial cell loss.10,11 Corneal endothelial cell loss and corneal thickness in conventional compared with femtosecond laser-assisted cataract surgery: Three-month follow-up Ina Conrad-Hengerer, MD, Mayss Al Juburi, MD, Tim Schultz, MD, Fritz H. Hengerer, MD, H. Burkhard Dick, MD J Cataract Refract Surg (Sept.) 2013; 39: 1308–1314 Purpose: To quantify changes in endothelial cell counts and corneal thickness measurements in patients having standard phacoemulsification compared with femtosecond laser-assisted cataract removal. Setting: Ruhr University Eye Clinic, Bochum, Germany. Design: Prospective randomized intraindividual cohort study. Methods: One eye of each patient had standard phacoemulsification (control group) and the other eye had femtosecond laser-assisted phacoemulsification (study group), both with intraocular lens implantation. Pulsed ultrasound energy was used for phacoemulsification. Noncontact endothelial cell microscopy and corneal pachymetry were performed preoperatively and one day, three to four days, seven to 10 days, 50 to 60 days, and 90 to 100 days postoperatively. Results: The mean endothelial cell loss was 7.9%±7.8% (SD) one week postoperatively and 8.1%±8.1% three months postoperatively in the study group and 12.1%±7.3% and 13.7%±8.4%, respectively, in the control group. The mean relative change in corneal thickness from the preoperative values was −0.0%±1.9% at one day, 2.8%±1.8% at one week, and 3.3%±1.7% at three months in the study group and −0.9%±2.3%, 2.4%±1.5%, and 3.2%±1.4%, respectively, in the control group. Conclusion: The femtosecond laser did not add to the endothelial damage caused by cataract surgery and might be beneficial in eyes with low preoperative endothelial cell values (e.g., cornea guttata cases). Financial disclosure: Dr. Dick is a member of the medical advisory board of OptiMedica Corp. No other author has a financial or proprietary interest in any material or method mentioned. The emergence of the femtosecond laser for cataract surgery has raised the question of whether laser pre-fragmentation can better protect the corneal endothelium during cataract surgery. The femtosecond laser technique has already been shown to reduce the total amount of phacoemulsification required for lens removal.12 In this month's issue of the Journal of Cataract & Refractive Surgery, Conrad-Hengerer et al.13 address the important question of whether femtosecond laser-assisted phacoemulsification decreases postoperative endothelial cell loss and corneal thickness in comparison with conventional phacoemulsification at three months follow-up. The authors present a prospective cohort study involving 73 patients (146 eyes) that were randomized to undergo conventional phacoemulsification in one eye (control group) and femtosecond laser-assisted phacoemulsification in the other eye (study group), both with intraocular lens implantation. Preoperative, intraoperative and postoperative data at several postoperative intervals until threemonth follow-up were collected. Differences in percentage of endothelial cell loss were statistically significant for the entire postoperative period between the two groups (study group: 7.9%±7.8% at one week, 8.1%±8.1% at three months; control group: 12.1%±7.3% at one week, 13.7%±8.4% at three months; p<0.001). Slight statistical significance was demonstrated for absolute endothelial cell count at three months (study group: 2207±264; control group: 2115±290; p=0.049). The study group achieved better corneal thickness values and corrected distance visual acuity (CDVA) than the control group in the immediate postoperative period; however, these differences were temporary as both corneal thickness and acuity were similar between the groups after one week. Minimal ultrasonic (US) energy was used in the study group (mean effective phacoemulsification time [EPT] = 0.0±0.1 seconds). The authors state that eyes with dense cataracts (mean nuclear opalescence [NO] 3.1±0.8) showed a statistically significant reduction of endothelial cell loss (41%) at three months in the study group compared with the control group. We commend the authors for designing a prospective, randomized study that investigates the impact of femtosecond laser-assisted cataract surgery on corneal thickness and the corneal endothelium. The use of the fellow eye as an intraindividual control eliminates inconsistent patient selection and minimizes other variables such as differences in anterior chamber depth and axial length, which may alter the effect of mechanical forces (instruments or nuclear fragments) on the corneal endothelium. The patients and methods were thoroughly described, demonstrating highly standardized surgical steps including incision size and site as well as chopping technique. Although consistent techniques were used, a study including additional surgeons utilizing slight variations in surgical approach would yield more broadly applicable results while minimizing bias inherent in a single surgeon performing all operations. The involvement of a single surgeon also leads us to question why the percentage of endothelial cell loss in the standard phacoemulsification group was relatively high (13.7%±8.4 at three months) compared with several recent studies that report endothelial cell loss ranging from 3–8% after phacoemulsification.9,10,11 In the box plot data analysis of postoperative percentage of endothelial cell loss, absolute endothelial cell loss, corneal thickness, and CDVA, the authors identify outliers as observations that are 1.5 times outside the interquartile (25–75%) range. While this may be a valid method of defining outliers, the authors do not provide any clinical or technical explanations that would better justify the decision to exclude these data. It would be helpful to mention, for example, any possible errors in measurements and whether patients may have had pre-existing guttae or especially low preoperative endothelial cell counts. The authors also reported measurements of EPT, total operating time and volume of irrigation solution infused into the eye. Previous studies show conflicting results on whether aspiration time and irrigation volume contribute to endothelial cell loss.14,15,16