Eyeworld

EW CORNEA 76 March 2011 N ew research has found that there's a lot more to the visual side effects of pterygium than with-the- rule astigmatism. "Pterygium and its size have sig- nificant influence on high-order aberrations of the eye especially on measured total coma and total tre- foil compared with normal fellow eye," according to study co-author Siamak Zarei-Ghanavati, M.D., Eye Research Center, department of oph- thalmology, Khatam-al-Anbia Eye Hospital, Mashhad University of Medical Sciences, Mashhad, Iran. The study was published online in Cornea in August 2010. "The larger the size of the ptery- gium, the more high order the ocu- lar aberrations," Dr. Zarei-Ghanavati reported. "The most significant in- crease in higher-order aberration be- longed to total coma and total tetrafoil according to the size of UOZ [uninvolved optical zone]." Beyond astigmatism Dr. Zarei-Ghanavati analyzed 62 eyes of 31 patients with unilateral ptery- gium. Normal fellow eyes were used as controls. "According to the size of unin- volved optical zone (UOZ), pterygia were classified into 3 groups, includ- ing 9 mm and more than 9 mm UOZ (≥9 mm UOZ group), between 7 and 9 mm UOZ (7- to 9-mm UOZ group), and between 7 and 5 mm UOZ (5- to 7-mm UOZ group)," Dr. Zarei-Ghanavati reported. "UOZ was measured with the eye in the pri- mary position and the slit beam coaxial. Patients with large ptery- gium involving 5-mm central optical zone were excluded because of insuf- ficient quality of measurements." As expected, eyes with ptery- gium experienced statistically significantly more with-the-rule astigmatism as compared to the con- trols. There was also a variety of higher-order aberrations that were more pronounced in the pterygium eyes. "The total high-order RMS in 5- mm optical zone was 1.85 +/–2.22 and 0.36 +/–0.44 mm in the affected and normal eyes, respectively," Dr. Zarei-Ghanavati reported. "The dif- ference was statistically significant between 2 groups." Pterygium eyes had more third, fourth, and fifth higher-order aberra- tions. Among these greater aberra- tions, total trefoil and total coma ranked as the most significant. There was not, however, a statis- tically significant difference in terms of spherical aberration. There were significant differ- ences within the three groups of pterygium. "There were significant differences between groups in the RMS of all aberrations except spheri- cal aberration," Dr. Zarei-Ghanavati reported. "With decreasing the UOZ (increasing the size of pterygium), all RMS of modes and orders in- creased, including RMS of higher- order aberrations." Other increases in this scenario included RMS of odd-order aberra- tions, RMS of the third-order aberra- tions, fourth-order aberrations, RMS of total coma, RMS of total trefoil, and RMS of total tetrafoil. "However, again the increasing of RMS of spherical aberration was not statistically significant," Dr. Zarei-Ghanavati reported. Another important finding of the study included the fact that the size of the cornea matters in deter- mining pterygium impact. "Although the size of UOZ is rel- evant to the size of pterygium, it is also dependent to the size of cornea," Dr. Zarei-Ghanavati noted. "For example, 2 eyes with equal pterygium size of 3 mm, with differ- ent corneal size of 11 and 13 mm, have different UOZ of 5 and 7 mm, respectively, and logically have not the same induced aberrations." Meanwhile, although some pre- vious research has attempted to elu- cidate the relationship between pterygium and higher-order aberra- tions, Dr. Zarei-Ghanavati believes this study should more accurately explain the effects. "We used the normal eyes of the same patients for comparing the high-order aberrations as control group in our study," Dr. Zarei- Ghanavati reported. "This fellow eye study can exclude the different aber- rations, which are not related to the pterygium, and determine more ex- actly the high-order aberrations in- duced by pterygium. In addition, the range of age was limited in our study (range: 31–50 years). There- fore, the measured aberrations were less influenced by the effect of aging on ocular wavefront." Dr. Zarei-Ghanavati believes these results may be useful for clini- cians. "These findings may be help- ful in deciding the time of surgery in the eyes with pterygium and may justify why the patients with ptery- gium have significant visual symp- toms despite visual axis sparing and appreciated spectacle correction," Dr. Zarei-Ghanavati concluded. Audrey R. Talley-Rostov, M.D., Northwest Eye Surgeons, Seattle, added that before performing cataract surgery or LASIK, "you want to remove the pterygium to get the cornea as normal as possible." The surgeon then has to wait several months for the cornea to heal completely before proceeding with visual correction. "It takes 6 to 12 weeks after you do anything to the cornea for it to heal," Dr. Talley- Rostov said. "After cataract surgery, you have to wait 3 months, for in- stance, to do an enhancement." After the pterygium has been excised and the cornea has healed, examine the corneal topography to see if it has stabilized, she said. Then begin to think about the second pro- cedure, considering the location and size of the pterygium. "Some patients who have giant pterygium removed have significant corneal scarring and are not going to have a normal cornea," she said. They may therefore have significant residual higher-order aberrations. EW Editors' note: Dr. Talley-Rostov has no financial interests related to her com- ments. Dr. Zarei-Ghanavati has no financial interests related to this study. Contact information Talley-Rostov: Atalley-rostov@nweyes.com Zarei-Ghanavati: zareis@mums.ac.ir by Matt Young EyeWorld Contributing Editor Study finds pterygium affects higher-order aberrations Procedure pluses Investigators saw the same thing with astigmatism. "We had pre-oper- ative mean astigmatism of 1.85 D, and this slightly increased to 2.5 D at 6 months, but then went back to baseline over the course of the next several years," Dr. Yoo said. "Maybe that is the biggest plus of this proce- dure, that there is no significant shift in either astigmatism or spherical equivalent." Another plus is the rate at which vision returned. "In terms of speed of visual recovery, 83% of our patients achieved within two lines of their best spectacle-corrected vision at 5 weeks after surgery." From a clinical perspective, Dr. Yoo sees patients as benefiting from the approach. "The clinical implica- tions are that we can use this tech- nology to aid us in anterior lamellar keratoplasty so that we can perform it without sutures in this select group of patients, with the advan- tage of quick visual recovery and lit- tle induced refractive change," she said. Going forward, Dr. Yoo envi- sions a day when the femtosecond technology will be paired with some type of liquid interface or contact lens on the surface of the eye that would allow for a smoother cut. "The key to advancing this would be to find a way to couple the fem- tosecond laser technology with some type of interface that would allow us to correct for the irregular astigmatism as well as correct for the opacity itself," she said. EW Editors' note: Dr. Yoo has financial interests with Abbott Medical Optics (Santa Ana, Calif.) and Carl Zeiss Meditec (Dublin, Calif.). Contact information Yoo: 305-326-6322, syoo@med.miami FALK continued from page 74 When removing the pterygium before cataract surgery or LASIK, examine the corneal topography before the second procedure to see if the cornea has stabilized

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