EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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28 EW NEWS & OPINION June 2012 ASCRS Best papers of session At the ASCRS•ASOA Symposium & Congress, the Best Paper of Session is selected by the moderator and panel for each free paper symposium. In the next several issues of EyeWorld, the medical editors will be highlighting some of these best papers by inviting the authors to submit a brief summary or abstract. David F. Chang, M.D., chief medical editor Single or paired intrastromal corneal ring segments combined with crosslinking in keratoconus Judy Y. Ku, M.B.Ch.B., F.R.A.N.Z.C.O., Sonia N. Yeung, M.D., Ph.D., F.R.C.S.C., Stephanie A. Low, B.H.Sc., David S. Rootman, M.D., F.R.C.S.C. This retrospective review evaluated the outcomes of implantation of femtosecond laser-enabled (IntraLase FS, Abbott Medical Optics, Santa Ana, Calif.) placement of sin- Using continued from page 27 operative spectral-domain OCT may be of benefit before such corneal clouding occurs," he added. Dr. Mehta also recommends using either a spectral-domain or Fourier-domain OCT in lieu of time- domain OCT, as the former two pro- vide "increased speed and resolution that are essential in determining accurate changes in thickness and anatomy," he said. C-scan images can identify "even the most subtle macular puck- ering," Dr. Mehta said, "as well as [provide] the ability to evaluate the macula for subtle atrophy of the choroid and RPE, as seen in macular degeneration." As soon as corneal transparency has been re-established, cataract sur- geons should take an OCT image if visual acuity "is far below the ex- pected," he said. Although it doesn't occur often, upon occasion post-op OCT will discover an impending macular hole (Figure 2). "Sometimes thin epiretinal membranes may be present but not discovered until the media transparency has been restored," he said. OCT is "no longer an esoteric piece of equipment," Dr. Safran said, but should be an integral part of any anterior segment surgeon's pre- op/post-op evaluations. "In my opinion, no retina can be defined as 'normal' without an OCT evaluation," Dr. Bellucci said. EW References 1. Chen JC, Lee LR. Clinical spectrum of lamellar macular defects including pseudo- holes and pseudocysts defined by optical coherence tomography. Br J Ophthalmol. 2008;92(10):1342-6. 2. Spaide RF. Age-related choroidal atrophy. Am J Ophthalmol 2009;147(5):801-10. 3. Mirshahi A, Hoehn F, Lorenz K, Hattenbach LO. Incidence of posterior vitreous detachment after cataract surgery. J Cataract Refract Surg. 2009;35(6):987-91. Editors' note: Dr. Bellucci has financial interests with Bausch + Lomb (Rochester, N.Y.). Dr. Safran has financial interests with Heidelberg (Ger- many). Drs. Boyer and Mehta have no financial interests related to this article. Contact information Bellucci: +39 045 812 3035, roberto.bellucci@ospedaleuniverona.it Boyer: 213-483-8810 Mehta: 303-893-5183, fovea1@comcast.net Safran: 215-962 5177, safran12@comcast.net gle (38 eyes of 34 patients) or paired (47 eyes of 40 patients) intrastromal corneal ring segments (regular and SK Intacs, Addition Technology, Sunnyvale, Calif.) combined with collagen crosslinking (CXL) in kera- toconus. At 1 year, both groups showed significant improvement in uncorrected visual acuities, spherical equivalent, cylindrical errors, steep and mean keratometry compared to baseline. When comparing the pre- to post-op changes at 1 year between the two groups, there was no signifi- cant difference in all outcome meas- ures apart from greater reduction in spherical equivalent in the singles group. It was concluded that im- plantation of both single and double intrastromal corneal ring segments combined with CXL is effective in the treatment of selective kerato- conus patients. Accuracy of automated endothelial cell counts Marianne O. Price, Ph.D., Francis W. Price Jr., M.D. Fully automated endothelial cell count software is improving, but some versions are still significantly less accurate than a trained techni- cian at correctly identifying endothelial cells, especially in non- normal corneas. In this study, man- ual cell density measurements of specular and confocal microscopy images agreed well in a cohort of normal eyes, as well as a cohort of Descemet's stripping endothelial keratoplasty (DSEK) eyes. Fully auto- mated software was evaluated on three imaging devices. Only one produced readings that agreed with the manual readings in both the normal and DSEK cohorts. Further- more, the fully automated software erroneously returned readings within the normal range in Fuchs' dystrophy eyes with dense guttae. Therefore, fully automated software should be used with cau- tion, and both the technician and physician should carefully evaluate the results to assess whether the cells were correctly identified. The inaccuracy of the SRK/T formula Thomas Olsen, M.D. The author has recently described an improved method to predict the IOL position after IOL implantation using Lenstar LS 900 biometry (Haag-Streit USA, Mason, Ohio) of the pre-op anterior chamber depth and lens thickness. The method is based on the newly developed con- cept of the "C-constant" describing the IOL position as a fraction of capsular bag thickness so that IOLcenter=ACDpre+C*LTpre, where IOLcenter=post-op position of the IOL, ACDpre=pre-op anterior cham- ber depth, LTpre=pre-op lens thick- ness ("bag thickness"), and C= C-constant of the given IOL type. As compared with the SRK/T for- mula as well as other thin-lens formulas, the implementation of C-constant in the Olsen formula showed significantly higher accuracy in a consecutive series of 1,071 rou- tine IOL implantations. Based on optimized lens constants the mean absolute error (MAE) was found to be reduced 14-22% (equivalent to a 50% reduction of errors >+1 D) with significantly lower error over the en- tire range of axial lengths. In order to explain the larger error of the SRK/T formula, the error of this formula was plotted against the anterior segment size (anterior chamber depth + lens thickness) and found to have a highly significant correlation. The error of the SRK/T formula was also found to be signifi- cantly associated with age and gen- der (both factors known to influence anterior segment anatomy). The conclusion was that the SRK/T for- mula as well as other thin-lens for- mulas using only K-reading and axial length as input are blind to the variation in the anterior segment causing an error (bias) in the IOL power calculation. This error was not seen with the Olsen formula utilizing the C-constant concept. Therefore, IOL power calculation can be improved using Lenstar biometry of the anterior segment. Residents and Fellows Best Paper Crosslinking and long-term hyper- opic LASIK stability: Initial clinical findings in contralateral eye study Jonathan Kahn, M.D., A. John Kanellopoulos, M.D., Christian Song, M.D., Michelle Cho, M.D. Crosslinking is an established treat- ment for ectasia internationally. Our group previously introduced pro- phylactic crosslinking in routine myopic LASIK to stabilize higher myopic corrections and to reduce the risk of ectasia. We now present the initial clinical findings of crosslinking in routine, topography- guided, hyperopic LASIK, which is intended to stabilize hyperopic corrections and reduce hyperopic regression. Our study of 27 patients (54 eyes) demonstrates both safety and efficacy of intrastromal crosslinking in routine hyperopic LASIK. Eyes that underwent crosslinking had less corneal steep- ening and less regression than con- trol eyes. We conclude that the combination of crosslinking in rou- tine hyperopic LASIK is safe and ap- pears to significantly stabilize its long-term effects, possibly by modu- lating a hyperopic LASIK biome- chanical response. EW