EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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EW RESIDENTS 58 November 2014 by Alison Huggins, MD, Jinali Patel, MD, Marta Melnyk, MD, Priya Sharma, MD, Brenton Finklea, MD, Nathan Cutler, MD, Michelle Wilson, MD, Faheem Ahmed, MD, and Murtaza Adam, MD M anual phacoemulsifi- cation cataract surgery (PCS) uses ultrasound energy to emulsify the crystalline lens and in some cases is associated with devel- opment of corneal edema related to corneal endothelial cell loss. 1 The most significant surgical risk factors for postoperative corneal edema include the total duration of ultrasound time, or effective phacoemulsification time (EPT), and the amount of energy used. 2–4 Femtosecond laser-assisted cataract surgery (FLACS) is now being ex- plored as an alternative to tradition- al PCS and is gaining momentum due to the creation of automated (laser-performed) incisions, precise capsulorhexis creation, and laser- assisted nuclear fragmentation. Pretreatment with the femtosecond laser has been found to significantly decrease effective phacoemulsi- fication time and, in some cases, completely eliminate the need for phacoemulsification energy during cataract extraction. 2,4 By reducing the amount of ultrasound energy delivered to the anterior chamber, there is less biomechanical disrup- tion and thermal energy delivery to ocular tissues and subsequent damage to the corneal endothelium. Current reports of reduced corneal endothelial cell loss and early post- operative corneal edema associated with FLACS have been promising, 2,4,5 but more studies exploring the long- term effects of FLACS on corneal parameters are needed. 6 In the November issue of the Journal of Cataract & Refractive Surgery, Abell and colleagues report- ed their experience using FLACS and observed effects on the corneal endothelium in comparison to PCS. In this non-randomized, prospec- tive cohort study of 620 eyes, a single surgeon performed either phacoemulsification after FLACS or conventional PCS. 7 The majority of eyes undergoing FLACS had manu- ally created corneal incisions (287 eyes) while the remainder (118 eyes) had automated incisions. Although selection criteria for method of cataract extraction were not explic- itly described, preoperative baseline demographics were similar between groups. General exclusion criteria, including a history of ocular trauma or inflammation, were applied to both patient arms. Additional exclusion criteria including corneal scarring and pupil dilation less than 5 mm were applied exclusively to patients undergoing FLACS. Patient dropout from the study was not disclosed. Metrics to determine effects on endothelial function included cen- tral corneal thickness (CCT), central 3.0 mm corneal volume, endothelial cell density, and a volume stress index (VSI). VSI is a novel metric of endothelial cell function calcu- lated by dividing the postoperative volume increase within the central 3.0 mm of the cornea by the central endothelial cell density. 8 The validi- ty of VSI as a measure of endothelial function has not been established. Measurements were obtained pre- operatively and were subsequently repeated at day 1, 3 weeks, and 6 months postop. A sub-analysis was performed to compare patients who underwent FLACS with manually created and automated incisions. In this study, Abell and col- leagues demonstrate that FLACS affords a short-term, small but statistically significant reduction in the corneal endothelial cell loss at 3 weeks as compared to PCS (4.2% vs. 5.8%). While there was also a small difference in corneal edema at 1 day, this difference resolved by 3 weeks. The authors infer that the transient reduction in postoperative corneal edema and endothelial cell loss in FLACS is related to the observed reduction in phacoemulsification time. Differences in corneal metrics after FLACS and PCS were transient, and no significant difference was found in central corneal volume, central corneal thickness and endo- thelial cell density at postoperative month 6. The clinical significance of transiently decreased corneal sequelae with FLACS over PCS is accordingly in question. While cat- aract surgeons are most concerned with serious complications such as pseudophakic bullous keratopathy, the importance of quick visual reha- bilitation should not be understated. Just as patients may select LASIK over PRK when undergoing refrac- tive surgery, some patients might prefer FLACS to PCS if perceived differences in visual rehabilitation are demonstrably proven. The current study does not address pa- tient satisfaction and/or other visual metrics at each study time point to parse out potential differences in subjective patient perceptions of visual recovery. Of note, when analyzing all cases of FLACS with zero EPT, those with manual incisions exhibited 50% reduction in endothelial cell loss at 6 months, compared to those with automated incisions. How- ever, the number of FLACS cases with zero EPT is not reported. It is also important to note that exact incision placement relative to the corneoscleral limbus and incision size were not standardized. The au- thors suggest that direct delivery of laser energy to the cornea, alteration of endothelial cell surface tension by microbubbles created by corneal photodisruption, and laser-mediated lens fragmentation may account for this difference. Other factors also could be responsible for this Review of "Effect of femtosecond laser-assisted cataract surgery on the corneal endothelium" Effect of femtosecond laser-assisted cataract surgery on the corneal endothelium Robin G. Abell, MBBS, Nathan M. Kerr, MBChB, Allister R. Howie, Mohd A.A. Mustaffa Kamal, MBBS, Penelope L. Allen, PhD, Brendan J. Vote, FRANZCO J Cataract Refract Surg (Nov.) 2014;40:1777–1783 Purpose: To investigate the effect of femtosecond laser-assisted cataract surgery (LCS) on the corneal endothelium compared to conventional manual phacoemulsification cataract surgery (PCS). Setting: Launceston Eye Institute, Launceston, Tasmania, Australia. Design: Prospective, interventional, masked, comparative cohort study. Methods: Six hundred and twenty eyes of 490 patients underwent either phacoemulsification after LCS (n=405) or conventional phacoemulsification (n=215). Central corneal thickness (CCT), central 3-mm corneal volume, volume stress index (VSI), and central endothelial cell density were measured pre- and postoperatively at day 1, 3 weeks, and 6 months. Results: Postoperative corneal edema was significantly less after LCS at day 1 and week 3. However, this difference was not appreciable at month 6. The LCS group demonstrated a significant reduction in endothelial cell loss compared to PCS at week 3, but this difference was not present at 6 months (–149±233 cells/mm 2 versus –150±244 cells/ mm 2 ). Eyes treated with laser automated corneal incisions had greater endothelial cell loss at 6 months than both PCS and LCS performed with manual corneal incisions (P<0.0001). Eyes in the LCS group with zero effective phacoemulsification time and manually created corneal incisions had statistically significant reduced endothelial cell loss at 6 months compared to all groups (P<0.0001). Conclusions: Femtosecond laser pretreatment to cataract surgery is associated with a significant reduction in early postoperative corneal edema and endothelial cell loss compared to conventional phacoemulsification, however the difference diminishes with time. Laser automated corneal incisions seem to adversely affect corneal endothelial cells. Tara Uhler, MD, director of resident education, Wills Eye Hospital One proposed benefit of femto laser- assisted cataract surgery might be reduced endothelial cell loss. I asked the Wills residents to review this sizable study evaluating this hypothesis in the November issue of JCRS. –David F. Chang, MD, chief medical editor continued on page 60 EyeWorld journal club