FEB 2014

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

Issue link: https://digital.eyeworld.org/i/274531

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Page 50 of 114

48 P a tient satisfaction and visual outcomes after cataract surgery are largely dependent on accurate in- traocular lens (IOL) power calculations before surgery. This is especially true when using toric IOLs to correct pre-existing corneal astig- matism. Although several methods e xist for toric IOL power calculation, this aspect of cataract surgery can still be challenging, especially in cases of concurrent morbidities, such as keratoconus, and/or a prior history of surgeries that change the shape of the cornea, such as corneal transplantation. In treating most cataract pa- tients who don't have any other history of ocular comorbidities, I use standard partial coherence interfer- ometry (PCI) biometry to determine the patient's keratometry readings and calculate the lens power. Al- though this is a reasonable starting point in most patients, in cases where there are concurrent corneal morbidities, biometry is usually not sufficiently accurate. In such situa- tions, I prefer to use a dedicated to- pographer to determine the shape of the patient's cornea. A recent case of a cataract patient I treated who was keratoconic with a history of penetrating keratoplasty and high corneal astigmatism serves as an in- structive example of the importance of using corneal topography when implanting toric IOLs in compli- cated eyes. The excellent outcome achieved in this case also demon- strates the efficacy of the T-flex Aspheric IOL (Rayner Intraocular Lenses, Hove, U.K.) in correcting high degrees of corneal astigmatism. Case report The patient was a 27-year-old male with a history of keratoconus, pene- trating keratoplasty (PKP), and an ocular hypertensive response to steroid treatment. He presented to me with a dense posterior subcapsu- lar cataract. His visual acuity (VA) was hand movements that improved to only 6/60 with pinhole correc- tion. The preoperative examination revealed high corneal astigmatism. Based on the standard biometry exam (IOLMaster, Carl Zeiss Meditec, Germany), he had K1 = 38.79 D × 76 degrees and K2 = 47.87 D × 166 degrees. However, keeping in mind the patient's ocular history, I chose to also use the Orbscan II corneal topographer (Bausch + Lomb, Rochester, N.Y.) to obtain a more accurate keratometry reading. Indeed, the Orbscan values, K1 = 43.00 D × 72 degrees and K2 = 51.50 D × 162 degrees, differed from those of the IOLMaster. In order to treat the astigmatism in this case, I decided to implant the T-flex Aspheric IOL. This toric IOL is extremely versatile in that it can correct a very large range of kerato- metric astigmatism. The lens can be ordered in spherical powers as high as +35.0 D and cylindrical powers as high as +11.0 D, which was neces- sary in this case. In my opinion, the lens is also easy to load and inject and shows good rotational stability, which is essential for a toric IOL. To calculate the IOL power, I entered both the biometry and topography keratometry readings separately into Rayner's proprietary online IOL power calculator, Raytrace (www.raytrace.rayner.com). The discordant K readings gave rise to widely varying T-flex IOL recom- mendations. Based on the Orbscan II k eratometry values, the Raytrace software recommended an IOL of +11.00 D sphere and +11.00 D cylin- der placed at 162 degrees. Based on the IOLMaster values, the recom- mended lens power was +15.50 D sphere and +11.00 D cylinder placed at 166 degrees. Indeed, such varying recommendations pose a dilemma f or the surgeon as to which values to use. If we used the IOLMaster values and they were incorrect the patient would end up being myopic. In the opposite situation, if we used the topography readings and they were wrong, we would risk leaving the patient hyperopic. Although at face value the inclination would be to use the IOLMaster readings, I de- cided instead to use the topographer readings in light of the patient's corneal history. Indeed, by using the IOL power based on the Orbscan II readings, the patient achieved an unaided visual acuity of 6/12 within two days postop, which improved to 6/4 with pinhole correction. His postoperative refraction at four months was +0.50/+2.75 x 13. The patient was understandably thrilled with his visual results. Biometry vs. topography Biometry and topography both give useful information regarding the astigmatic status of a cataract pa- tient. However, it is not uncommon for the keratometry values provided by the two instruments to differ in eyes that have abnormal corneal topologies, and in such cases the ophthalmologist needs to make a decision about which value to consider while calculating IOL power. Understanding why such discordance occurs can help make this decision. The primary reason for the difference between keratometry readings obtained through biometry and topography is the method by which the measurements are made. The keratometry mode of the IOLMaster measures the curvature of only the anterior surface of the cornea by using only six data points at a diameter of 2.5 mm centered on EW REFRACTIVE SURGERY 4 8 February 2014 by Mohammed Muhtaseb, FRCOphth Toric IOLs in complicated eyes: Improving outcomes with corneal topography " Corneal topographers use 7,000 to 10,000 data points from the entire surface of the cornea, while centering the acquisition on the corneal apex, to calculate curvature. Depending on the type of topographer being used, one can also measure the power of the posterior surface, giving a more accurate measure of astigmatism. " Probability of blindness from glaucoma nearly halved A recent study published in Ophthalmology indicated that the probability of blindness from glaucoma has decreased by about half since 1980, according to a press release about the study. Advancements and improvements in diagnosis and therapy have likely contributed to this decrease. The study was conducted by a team based at the Mayo Clinic, and it was the first to assess long-term changes in the risk of progres- sion to blindness and the population incidence of glaucoma-related blindness. The researchers involved in the study reviewed every incident case (857 cases total) of open-angle glaucoma (OAG) diagnosed from 1965 to 2009 in Olmsted County, Minn., which is one of the few places in the world where long-term population-based studies are conducted. Results indicated that the 20-year probability and the population incidence of blindness due to OAG in at least one eye had decreased from 25.8% for subjects diagnosed between 1965 and 1980 to 13.5% for those diagnosed between 1981 and 2000. The population incidence of blindness within 10 years of diagnosis also decreased from 8.7 per 100,000 to 5.5 per 100,000 for those groups, respectively. However, 15% of the patients diagnosed in the more recent timeframe still progressed to blindness. 46-49 Refractive_EW February 2014-DL2_Layout 1 1/30/14 10:26 AM Page 48

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