EyeWorld Asia-Pacific December 2012 Issue

24 EWAP CATARACT/IOL December 2012 Is cataract - from page 23 enrollment. Additionally, the IOP reduction in the control arm of the iStent trial represents a medicated IOP value. Indeed, the efficacy of the iStent in the trial was based on the fact that less medication was needed in the iStent arm of the trial as compared to cataract surgery alone. Not all data in agreement At the annual meeting of the American Glaucoma Society in New York, Ta Chen Peter Chang, MD , Bascom Palmer Eye Institute, University of Miami, Miami, Fla., USA, presented the results of a retrospective study to evaluate cataract surgery’s effect on IOP, using the phakic fellow eye as a control. “We identified 29 patients with either ocular hypertension or open-angle glaucoma who had previously undergone unilateral phacoemulsification with the fellow eye remaining phakic for at least 3 years postoperatively,” he said. Some patients were using IOP- lowering medications, he said. Mean IOP before unilateral surgery was comparable between groups, he said, and there was no statistically significant difference in the mean IOP of the groups at 1, 2, or 3 years post-op. “There was also no significant difference in the number of IOP- lowering medications needed postoperatively,” he said. While this study was strengthened by the use of the fellow eye as a control, its retrospective nature makes it difficult to draw conclusions that can be implemented into clinical practice. What did OHTS find? To more closely examine the effect of cataract surgery on IOP, Dr. Mansberger presented a post hoc analysis of data from the Ocular Hypertension Treatment Study (OHTS). While the OHTS was not designed specifically to answer this question, the prospective nature of the study coupled with its well- designed protocol lent weight to its findings. “We identified 63 eyes of 42 patients in the observation arm of the OHTS that underwent cataract surgery,” Dr. Mansberger said. Another 743 eyes in the same observation arm that did not undergo cataract surgery served as a control group. The mean of three IOP measurements before surgery and three more after surgery represented the change in IOP in the active group. This was compared to three corresponding IOP measurements in the control group, he explained. “Mean IOP was similar in the two groups before surgery, and there was a larger drop in IOP in eyes undergoing cataract surgery compared to controls,” he reported. The average drop in IOP was 16.5%, from a mean baseline of 23.9 mmHg to 19.8 mmHg, a 4.1 mmHg reduction, he said. “The mean IOP of the group was still below baseline at 36 months, and 40% of operated eyes enjoyed an IOP reduction of 20% or more,” he added. Possible mechanisms How might cataract surgery lower IOP? It likely is related to changes in anterior chamber depth and angle configuration. Murray Johnstone, MD , Seattle, Wash., USA, explained. “As the crystalline lens shifts forward with age, the ciliary body does, too, and this shallows the angle,” he said. “After cataract surgery the ciliary body shifts backward, a behavior known to open the intertrabecular spaces and Schlemm’s canal. This backward movement of the ciliary body provides a mechanism to explain improvement in aqueous outflow following cataract surgery alone,” Dr. Johnstone said. “This is why eyes with narrow angles seem to have greater IOP reductions after surgery,” Dr. Mansberger said. “The capsular tension created by the capsular bag ‘shrink-wrapping’ around the intraocular lens implant may pull the meshwork open as well,” Dr. Mansberger said. He added that another explanation may be biologic with increased outflow from mechanisms similar to trabeculoplasty or administration of a prostaglandin analogue. “These are the mechanisms that explain and account for the IOP reduction seen after cataract surgery alone,” Dr. Johnstone said. Clinical implications Not every glaucoma patient undergoing cataract surgery benefits, and there are risks to cataract surgery for eyes with glaucoma. “There is a 2.4-fold higher risk of a post-operative IOP spike in glaucomatous eyes compared to normal,” Dr. Coleman said. Dr. Mansberger pointed out that significant IOP reductions in the range of 20% or greater only occurred in about 40% of OHTS participants. “We should consider who is most likely to benefit,” said Dr. Samuelson. “If we could identify those patients most likely to show improved IOP with cataract surgery alone, we can limit their exposure to move invasive and riskier operations. Virtually all of the ancillary effects of cataract surgery are favorable, such as improved refractive error, deeper anterior chamber, and for many, lower IOP.” Dr. Mansberger agreed. “The next step is to predict the glaucoma patients who will have enough IOP lowering from cataract surgery alone.” EWAP Editors’ note: Drs. Chang, Coleman, and Johnstone have no financial interests related to this article. Dr. Samuelson has financial interests with Glaukos, Ivantis (Irvine, Calif., USA), AqueSys (Aliso Viejo, Calif., USA), Endo Optiks (Little Silver, NJ, USA), Alcon (Fort Worth, Texas, USA/Hünenberg, Switzerland), and Abbott Medical Optics (Santa Ana, Calif., USA). Contact information Chang: t.chang@med.miami.edu Coleman: doctor_coleman@yahoo.com Johnstone: johnstone.murray@gmail.com Mansberger: smansberger@deverseye.org Samuelson: twsamuelson@mneye.com An eye post-DSAEK. With the advent of the surgery (pictured here), the corneal endothelium has received significant attention. Source: Mark Gorovoy, MD