According to a recent survey, foldable intraocular lenses (IOLs) are the preferred choice of ophthalmic surgeons for replacing the human crystalline lens. 1–16 Some advantages of foldable IOLs, including low induced astigmatism and invasiveness, better wound stability, and faster visual rehabilitation, are achieved by a marked reduction in incision size as compared to that required for rigid IOLs made of polymethyl methacrylate (PMMA). 11 Acrylic PMMA, 17 silicone, and hydrogel are among the materials used to fabricate foldable IOLs. Although their efficacy in small-incision cataract surgery has been well documented, no quantitative studies of the postoperative inflammation or blood-aqueous barrier breakdown caused by the different foldable IOL materials have been done. Despite the increasing interest in small-incision cataract surgery using foldable IOLs, we do not know which new IOL material is more advantageous than another in lessening the degree of postoperative inflammation or quickening the process of blood-aqueous barrier reestablishment. We undertook the current study to assess the clinical course after bilateral cataract surgery using different IOLs for either eye.
Subjects and Methods
Forty-five patients with cataracts were enrolled in this prospective, nonrandomized clinical study. To be eligible for the study, patients were required to have bilateral cataracts. Patients with any preoperative pathological process or those with a very hard and brunescent cataract that would confound the results were excluded prior to initiating the study. Informed consent was obtained preoperatively from all patients. All surgery was performed by two experienced surgeons (the author and a colleague) using a standardized technique of sutureless, scleral incisional phacoemulsification. Initial eyes received silicone IOL implantation, and fellow eyes received acrylic PMMA IOLs. The IOLs made of silicone or acrylic PMMA were implanted with either an injector device or implantation forceps. There were no surgical complications. The mean interval between operations was 7 days.
Patients received the same routine preoperative and postoperative medications. Preoperative papillary dilation was accomplished using topical 5% phenylephrine, 0.5% tropicamide, and 0.1% sodium dichlorphenac, each given three times with a 30-minute interval between applications. Postoperative medications included topical 0.1% betamethasone and 0.3% ofloxacin three times daily for 2 months. An antiprostaglandin agent also was instilled twice daily for 1 week and once daily thereafter for up to 2 months.
Flare intensity in the aqueous humor was measured with the laser flare-cell meter. 18 Measurements were taken preoperatively (baseline) and 1 day, 1 week, and 1, 3, and 6 months postoperatively. Each measurement was made 30 to 60 minutes after topical application of 0.5% phenylephrine and 0.5% tropicamide. To evaluate the difference of the flare intensity between right eye and left eye, rate of flare intensity (flare rate) was calculated using the following equation:EQUATION
where F.S. is the flare intensity in the eye with a silicone IOL and F.A. is the flare intensity in the eye with an acrylic PMMA IOL at the same observation period.
Best corrected visual acuity was measured before and 1 day, 1 week, and 1, 3, and 6 months after surgery, and specular microscopical examination of the corneal endothelium was performed preoperatively and 6 months postoperatively. Intraoperative and postoperative complications were recorded throughout the study period. Statistical significance was analyzed with the Wilcoxon rank-sum test. Statistical significance was defined as p < .05.
A total of 45 patients and 90 eyes were included in this study. All patients received 6 months' follow-up. The mean age of the patients was 74.0 years (standard deviation [SD], 9.6). There were 31 women and 14 men. All the surgeries were performed without any intraoperative complication.
Figure 1 compares preoperative and postoperative flare intensity in each group. Preoperative flare values were 6.2 ± 3.5 (mean ± SD) photon count per millisecond for silicone lens eyes and 6.3 ± 3.7 photon count per millisecond for acrylic PMMA eyes. In the immediate postoperative period, the silicone IOL eyes had the higher flare intensity, as compared to the acrylic PMMA eyes. Flare intensity in both groups decreased to a similar level 1 week postoperatively. However, flare intensity in the silicone lens group displayed slight rebound, and the value was significantly higher than that of the acrylic PMMA group at 1 and 3 months postoperatively (p < .05). At the 6-month postoperative examinations, this difference was not statistically apparent.
Preoperative and postoperative flare rates also were compared (Fig 2). The average preoperative flare rate was 1.1 ± 0.6, and the values increased significantly higher than this rate until 3 months postoperatively.
Postoperative best corrected visual acuity and corneal endothelium loss rate were not different among the two groups (table). In both the silicone and acrylic PMMA IOL groups, 90% of the patients had a visual acuity of 0.7 or better at 6 months postoperatively. The rate of corneal endothelial cell loss averaged 9.1 ± 11.8 in the silicone IOL group at 6 months and 10.7 ± 14.7 in the acrylic PMMA IOL group at 6 months postoperatively. The difference was not statistically significant. Neodymium–yttrium aluminum garnet (Nd:YAG) laser posterior capsulotomy was performed when posterior capsule opacification was judged to cause either a visual acuity decline of more than 2 Snellen lines or unwanted optical images. One eye that received a silicone IOL had YAG laser capsulotomy because of visual decline. There were no other postoperative complications.
With an increasing number of cataract extractions being performed by phacoemulsification, interest has increasingly been directed toward foldable IOLs that can be inserted through small incisions rather than conventional PMMA IOLs. Although the efficacy of such IOLs in small-incision cataract surgery has been well documented, few reports described a quantitative comparison of different kind of foldable IOLs. 9,11,19 Furthermore, fellow-eye comparison studies and prospective trials on this subject are scarce in the literature. The current study compared the degree of intraocular inflammation, visual acuity, and rate of corneal endothelial cell loss in fellow eyes of the same patients, the only variation being the IOL material.
Results of the present study demonstrate that immediate postoperative inflammation was significantly greater in the silicone IOL group than in the acrylic PMMA IOL group. Statistically significant differences were observed at 1 day, 1 month, and 3 months postoperatively. There was no notable difference in the efficacy of cataract and IOL surgery on the basis of IOL material with regard to postoperative visual acuity, the rate of corneal endothelial loss, and the rate of YAG posterior capsulotomy. Nonetheless, by prospectively comparing fellow eyes of the same patient, we were able to elucidate the effect of a solo variable—the IOL material—on the postoperative inflammation.
By fellow-eye examination, we found that that the eyes that received acrylic PMMA IOLs had significantly lower aqueous flare values than did the eyes that received silicone IOLs, until 3 months postoperatively. Possible explanations for this difference are as follows: first, the high refractive index of acrylic PMMA material makes the optic of this lens very thin, leaving less space between the anterior and posterior capsule (the site of migration and proliferation of the lens epithelial cells. 20) Second, unlike silicone IOLs, acrylic PMMA IOLs are believed to adhere to the lens capsule, resulting in the encapsulation of lens epithelial cells from the immunologically active postoperative aqueous humor. Because postoperative lens epithelial cells are known to produce several chemical mediators—including interleukins, basic fibroblast growth factor, and prostaglandin E 221,22 —these two mechanisms could reduce the postoperative inflammation.
At 6 months postoperatively, no significant differences were noted in aqueous flare intensity. This suggests that there is no clinically apparent difference in long-term influence on the blood-aqueous barrier function between the IOL materials used. We were interested in the finding that flare intensity in both IOL groups remained higher than the preoperative baseline measurement until 6 months postoperatively, even in the small-incision cataract surgeries. This result, which agrees with previous fluorophotometric studies, indicates that blood-aqueous barrier function is not completely reestablished for a long period after surgery.
Our clinical data and experience indicate that phacoemulsification with implantation of an acrylic PMMA IOL provoked a lesser degree of blood-aqueous barrier breakdown, thereby helping to retain the postsurgical physiological environment within the eye.
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