Hydrophobic Acrylic IOLs: A Primer - Aaren Scientific

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COVER STORYcontact inhibition of migrating LECs at the capsular bendcreated by the edge, 8 the higher pressures exerted byIOLs with a square-edged optic profile on the posteriorcapsule, 9 or combinations of these factors.Current hydrophobic acrylic IOLs generally have asquare optic edge. However, not all square edges are thesame. In an experimental study including 19 hydrophobicacrylic lenses, the area above the posterior-lateral edge ofeach IOL was measured to determine the deviation froma perfect square. 10 Variation was found not only amongthe IOL designs but also among different powers of thesame IOL. This type of evaluation can help manufacturersoptimize their IOLs’ optic edges. For example, HoyaCorp. (Tokyo) modified the edge profile of several AF-1models after results of a single-surgeon prospective felloweyecomparison showed that the PCO rate was significantlyhigher with the AF-1 YA-60BB IOL than with theAcrySof SN60AT. 11 The study was based on results in 36patients who were followed for 24 months. The result isnot surprising, considering the differences in edge designbetween these lenses in the amount of area deviatingfrom a perfect square (AF-1, 329.7 µm 2 ; SN60AT [20.00D], 97.2 µm 2 ). 10 Hoya made several manufacturingchanges, including variations in polishing process, anddifferent prototypes were sent for evaluation. 12 The areadeviating from a perfect square in the current Hoya AF-1family now measures 39.1 µm 2 . Such quantification of thearea deviating from a perfect square—and thereforeassessment of the sharpness of the posterior opticedge—is not available for many new models ofhydrophobic acrylic lenses.Another design trend observed in hydrophobic acrylicIOL manufacturing is the availability of new IOLs in a onepieceplatform. Most prospective, randomized studieshave shown no statistically significant differences betweenone- and three-piece hydrophobic acrylic IOLs in terms ofPCO rate; 13 however, it has been shown that, wheneverPCO occurs with one-piece designs, it has the tendencyto start at the level of the optic-haptic junction. 7Several manufacturers have modified the optic-hapticjunctions of their IOLs to obtain a continuous 360ºsquare edge. In one study, patients were implanted with aTAKE-HOME MESSAGE• Lens materials must be both uveal and capsularbiocompatible.• Most hydrophobic acrylic IOLs have a square edge;however, the deviation from a perfect square can varydepending on IOL design and IOL power.• The tendency for glistenings varies depending on the IOLmaterial, manufacturing technique, and packaging process.one-piece hydrophobic acrylic IOL with an interruptedoptic edge (AcrySof) in one eye and a newer one-piecehydrophobic acrylic IOL with a continuous optic edge(Tecnis 1-Piece; Abbott Medical Optics Inc.) in theother. 14 Two years after surgery, the extent and density ofPCO were significantly greater in eyes with the AcrySofIOL that those with the Tecnis IOL.BLUE-LIGHT FILTERING CHROMOPHORESSome hydrophobic acrylic lenses incorporate blue-lightfiltering chromophores, as it has been suggested thatblue-light–filtering IOLs protect lipofuscin-containingretinal pigment epithelial cells from blue-light damage. 15There is indirect evidence suggesting that blue-light filtersmay result in a reduced risk of development or progressionof macular degeneration, but the value of these yellowchromophore–containinglenses is not fully understood.Potential side effects of constantly filtering blue light mayinclude negative impacts on color vision, night vision, andsleep and circadian rhythms. 16One photochromic lens (Matrix Aurium; Medennium,Irvine, California) turns yellow when exposed to ultraviolet(UV) light because the blue light is absorbed. The lensbehaves as a standard UV-absorbing IOL in an indoorenvironment; the optic remains colorless, and there is nofiltering of blue light. This innovative concept theoreticallyeliminates the potential side effects of yellow IOLs andprovides patients with the potential for improved nightvision after cataract surgery, additional protection of themacula against blue light in daylight conditions, andimproved contrast sensitivity (as demonstrated in clinicalstudies with yellow lenses). 17In a rabbit study conducted in our laboratory, thelong-term biocompatibility and photochromic stabilityof the photochromic IOL were evaluated under extendedUV light exposure (simulating 20 years of exposure). 17The photochromic change was found to be reversible (ie,the optic returned to its colorless state after discontinuationof UV light projection) and reproducible (ie, thephotochromic change was observed at different timepoints in the clinical follow-up). Additionally, the photochromicproperty of the optic material remained stableand was present and unchanged 12 months after implantation.The rabbit eyes exhibited clinical and histopathologicchanges that are normally expected in this model,and there was no difference between study and controleyes in terms of biocompatibility.GLISTENINGSGlistenings are fluid-filled microvacuoles that formwithin an IOL optic when the lens is in an aqueous environment.3 They can be observed with any type of IOL,40 CATARACT & REFRACTIVE SURGERY TODAY EUROPE MARCH 2011
COVER STORYalthough they have mainly been described in associationwith hydrophobic acrylic lenses. Experimental and clinicalstudies suggest that different hydrophobic acryliclenses exhibit different tendencies for the occurrence ofglistenings. Factors that may influence their formationinclude IOL material composition, IOL manufacturingtechnique, IOL packaging, patient-associated conditionssuch as glaucoma or those leading to breakdown of theblood-aqueous barrier, and concurrent use by the patientof ocular medications.The exact impact of glistenings on postoperative visualfunction and an understanding of their evolution in thelate postoperative period remains a matter of controversy,partly because IOL explantation due to glistenings israrely reported. Although it is likely that each hydrophobicacrylic IOL exhibits different tendencies toward glisteningformation, no peer-reviewed articles are currentlyavailable for the IOLs listed in Table 1. Most of the peerreviewedliterature describes glistening formation, incidence,and severity in the AcrySof material; 3 a relativelysmall number of articles and presentations evaluate glisteningformation in the Acryfold VA60CA/CB (HoyaCorp.), Acrylmex (Ophthalmic Innovations International,Inc.; now Aaren Scientific, Ontario, California), SensarAR40(e), and XACT (Advanced Vision Science, Inc.,Goleta, California) IOLs. 3In one Japanese clinical study of glistenings, 18 74 eyeswere implanted with the AcrySof SA30AL (n=17), theAcryfold VA60CB (n=37), or the Sensar AR40e (n=20).Follow-up ranged from 6 to 18 months. Slit-lamp examinationshowed the presence of grade 1C glistenings(Miyata classification) in 35.3% of the AcrySof IOLs and62.1% of the Acryfold IOLs but in 0% of the Sensar IOLs.Hoya investigated the reports of glistenings (a total of 29)in its early IOL models VA60CA and VA60CB, which werenever commercially released outside of Japan and weresubsequently discontinued. Improvements were implementedin the polymerization and cleaning processes ofthe company’s lenses, and continued monitoring ofthe manufacturing processes and a low level of customercomplaints indicate that these changes havebeen effective.STORAGE MEDIA CAN CAUSE GLISTENINGSAccording to information contained in the US Foodand Drug Administration (FDA) Summary of Safety andEffectiveness Data and on IOL labeling (obtained throughthe manufacturer, Advanced Vision Science, Inc.), theXACT IOL was originally packaged in 10.0% saline. Thepresence of glistenings was reported in 40 eyes (40patients) between 1 week and 1 month after surgery,with decreased density at each visit thereafter. 3 No differencesin contrast sensitivity were observed between thestudy and control eyes, except for a clinically insignificantdifference in contrast sensitivity detected in the highestspatial frequencies at 1 month. It was postulated that,after implantation, the osmotic differential between theIOL and aqueous humor caused more water to beabsorbed into the IOL optic, resulting in the appearanceof glistenings. However, a change of hydration/storagemedia from 10.0% to 0.9% saline was implemented, andlaboratory testing demonstrated elimination of the glistenings.This was confirmed in an additional clinical trialconducted in the Dominican Republic and Germany, thedata from which were included in the FDA marketingapplication for the IOL. 19 In this study, 172 eyes (142patients) were examined at least once between 1 and 6months, and 123 eyes (101 patients) were examined atleast once between 6 months and 2 years. No glisteningswere observed at any time.The XACT IOL was approved for use in the UnitedStates in February 2009 (subsequently licensed to Bausch+ Lomb, Rochester, New York) and in Japan in 2008(trade name, Santen Eternity). This hydrophobic acrylicIOL, packaged in 0.9% saline, is also gamma sterilized.NO REPORTED GLISTENINGSOther IOLs with no reported glistenings include theAurolab lens (Aurolab, New Delhi, India), the AcrylmexIOL (three- and one-piece models EC-3 and EC-1Y,respectively), Hanita hydrophobic acrylic lenses (HanitaLenses, Kibbutz Hanita, Israel), and the Artis (Cristalens,France).Aurolab. In a study of 120 patients implanted with theAurolab lens at the Aravind Eye Hospital in Madurai,India, BCVA was 6/12 or better, and no eye had IOLinducedintraocular pressure increase (informationobtained from the manufacturer). Decentration was notsignificant, and IOL tilt, discoloration, or opacity was notreported. However, adverse events included one case ofiritis and one case of secondary surgical intervention dueto haptic damage.Acrylmex. Two European clinical studies presented atthe 2009 ASCRS meeting 20,21 showed the absence of glisteningsat 1 year after implantation of the Acrylmex IOL.The first study included at least 10 cases with a minimumfollow-up of 18 months.Hanita hydrophobic acrylic lenses. These IOLs aremanufactured with a hydrophobic acrylic materialprovided by Benz Research. The material supplierassesses a glistenings severity index for each batch ofmaterial for quality assurance. IOLs immersed in salinewere observed for 6 months; the severity index wassignificantly lower than that of the AcrySof lensesMARCH 2011 CATARACT & REFRACTIVE SURGERY TODAY EUROPE 41
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Hydrophobic Acrylic IOLs: A Primer - Aaren Scientific

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