EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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December 2013 EW MEETING REPORTER 63 Symposium of Ophthalmology He also detailed the somewhat controversial procedure of posterior assisted levitation. Although it is generally considered beyond the scope of anterior segment surgeons to perform such a procedure, Dr. Lam said that it can be considered as long as the surgeon is aware of the risks as well as the technique. Finally, he enumerated possible techniques for IOL implantation with a PCR. In-the-bag implantation is still the best if at all possible, though it may require fixing the rhexis, while sulcus implantation or anterior capture and anterior chamber IOLs are also viable options. In some circumstances, however, the surgeon may decide to forego implanting an IOL. November 10, 2013 Screen and SMILE The first refractive surgery symposium of the 9th ISO's scientific program provided "Updates and latest developments in laser and refractive surgery," beginning with the first problem a surgeon with a typical practice in the field generally faces: how to get the right candidate for surgery. Typically, that means screening keratoconus risk. "The real hallmark is to look at topography and tomography preop," said Ronald R. Krueger, MD, U.S. "Find that tip of the iceberg to find the risk for keratoconus." First, Dr. Krueger rules out contact lens warpage and ocular surface abnormalities caused by conditions like dry eye—he recommends having patients stop using soft contacts for three days, rigid contacts for three weeks, or even, when in doubt, one week for every decade of contact lens use before taking corneal measurements. He then calculates the difference between the inferior and superior powers (the I-S ratio, >1.5 D is abnormal), looks for skewed radial axes (SRA, >30 degrees is abnormal), determines the steepest K, looks for topographic changes over time, and where available recommends using advanced imaging techniques. This information is plugged into the quantitative risk assessment of the Randleman criteria, which looks at various parameters of risk, but bear in mind that topographic pattern is the most significant, most robust parameter for identifying risk: For instance, if topographic pattern is the major contributor for a score of 3 that generally only recommends caution, Dr. Krueger would recommend against going ahead with surgery. When the topographic picture isn't obviously abnormal, posterior surface tomography can provide a little more information. Posterior surface elevation maps highlight early asymmetry potentially indicative of subclinical keratoconus. However, astigmatism and asphericity of the back surface can obscure irregularities when looking at the best fit sphere. Instead, Dr. Krueger recently published a paper looking at the best fit toric aspheric (BFTA), which turns out, he said, to be the most sensitive and specific single index for screening. Looking at BFTA to determine asphericity asymmetry index, he said, values greater than 21.5 indicates abnormality. Even confined to the right candidates, LASIK is associated with its own set of complications, including flap-related complications, slow recovery of corneal sensation, and changes in corneal biomechanics. Small incision lenticule extraction (SMILE) has been proposed as an alternative. The technique eliminates the need for a flap, but how does it compare clinically? Quan Liu, MD, China, and colleagues looked at their results in 2,500 cases, focusing on three questions to make the com- parison: How is the visual quality? Is recovery of corneal sensation better? Are changes in corneal biomechanics better? The group, said Chenyi Le, MD, China, presenting for Dr. Liu, followed patients up at one week, one month, three months, and six months after surgery. They found that safety and predictability in terms of best corrected visual acuity and spherical equivalent, respectively, were comparable between LASIK and SMILE; patients who underwent SMILE recovered corneal sensation faster (recovering preop levels at one week) than those who underwent LASIK (recovering preop levels at three months); and while both procedures induced changes in corneal hysteresis and corneal resistance factor, the changes were less with SMILE. Advancing surface ablation There's no doubt that LASIK remains the mainstay of international refractive surgery, said Dennis Lam, MD, China. But what can refractive surgeons do when LASIK is not possible, such as when the cornea is too thin for the procedure? Advanced surface ablation (ASA) provides an alternative; in fact, said Dr. Lam, in some select cases, ASA is the only option. The technique, he said, achieves comparable outcomes in terms of uncorrected visual acuity and best corrected visual acuity, while providing better outcomes in terms of higher-order aberrations— without the interface problems and risk of ectasia that attend LASIK. The problem with ASA is that it causes significant haze—in some cases, up to three months postop. The prophylactic administration of mitomycin-C (MMC) intraop may provide the solution. However, Dr. Lam cautioned, MMC is "not a magic drop"—its effects, he said, are dose dependent and need to be titrated. At the standard concentration of 0.02%, exposure time to MMC increases with the degree of myopia correction. For instance, 30 seconds of 0.02% MMC is adequate for <3.0 D of myopia; 60 seconds is necessary to prevent haze at 3-6 D. Basically, higher degrees of correction require longer exposure to MMC. Surgeons may also consider transPRK—a relatively new form of ASA, said Dr. Lam. David Kang, MD, South Korea, comparing manual and transPRK in 272 patients, found that pain in the immediate 48 hours postop was much less in the transPRK group. There was also less haze, equating to less time for steroid tapering. Both the safety and efficacy indices were statistically better in the transPRK group, said Dr. Kang; he said that while final visual outcomes were similar to those achieved by alcohol and brush PRK, final VA was achieved significantly faster—within a week postop—with transPRK. CMV rising Cytomegalovirus (CMV) infection is an unusual cause of infectious keratitis, but an increasingly important one, particularly in the context of corneal transplantation. The clinical features of corneal CMV infection include endotheliitis and nodular lesions associated with keratic precipitates. In non-grafted eyes, said Donald Tan, MD, Singapore, CMV cases need to be differentiated from other forms of corneal decompensation, which may lead to unnecessary grafts. The consequences are even more troubling in eyes that have already received corneal transplants. In these cases, CMV infection may be confused with graft rejection; ramping up steroids in response to this misdiagnosis will inevitably lead continued on page 64