Since the introduction of intraocular lens (IOL) implantation at the end of the 18th century, permanent and rapid advancements have been made in surgical technique and lens material. Starting with the glass implants of Tadini and Casamatas1 and the large-surface, rigid poly(methyl methacrylate) (PMMA) lenses used by Ridley,2 we now have a nearly unlimited range of modern, highly refractive, and foldable IOLs of different materials and various forms. The first aim of these developments is to provide surgical techniques that are as nontraumatic and safe as possible (ie, small incision).3,4 The second purpose is to achieve maximum biocompatibility of the implanted lens.
Amon5 was the first to make a distinction between uveal and capsular biocompatibility. This distinction now permits ophthalmologists to evaluate different IOLs in terms of early and late foreign-body reaction (inflammatory cell ongrowth) on the one hand and lens epithelial cell (LEC) complications (anterior capsule opacification [ACO], posterior capsule opacification [PCO], LEC ongrowth on the IOL's anterior surface) on the other hand. Posterior capsule opacification continues to be the main complication after cataract surgery.6–11
Over the past years, several methods have been shown to reduce the development of PCO.12–16 So far, no technique has been found to sufficiently inhibit capsule opacification. However, intensive research has delineated important factors that markedly reduce this complication. These factors include the selection of lens material,17–20 a central capsulorhexis that completely covers the anterior surface of the IOL,21,22 and, especially in recent years, a sharp-edged lens design.23–25
This study evaluated for the first time the uveal and capsular biocompatibility of 2 foldable square-edged IOLs of different materials 3 years after surgery.
Patients and methods
Fifty eyes scheduled for cataract surgery were enrolled in this comparative study. Exclusion criteria were proliferative diabetic retinopathy, uncontrolled glaucoma, corneal pathology, and previous intraocular surgery. Patients with a history of uveitis or antiinflammatory medication within 14 days before surgery were also excluded.
All surgery was performed by 1 experienced surgeon (M.A.) using peribulbar anesthesia. The standardized surgical technique included a temporal 3-plane clear corneal incision performed with a 3.2 mm steel blade, a continuous curvilinear capsulorhexis created under sodium hyaluronate 1% (Healon®), hydrodissection and hydrodelineation with fortified balanced salt solution (BSS Plus®), and phacoemulsification using the bimanual divide-and-conquer technique. Cortical remnants were carefully removed by manual irrigation/aspiration.
After the anterior chamber and capsular bag were refilled, an IOL was implanted in the capsular bag. Twenty-five patients received an AcrySof® IOL (Alcon), an acrylic (2-phenylethyl acrylate/2-phenylethyl methacrylate) lens with PMMA haptics, and 25 received a CeeOn® 911A® IOL (Pharmacia), a silicone (dimethyldiphenylsiloxane) lens with PVDF (polyvinylidene fluoride) haptics. Both lenses have square-edged optics and an optic diameter of 6.0 mm. The overall size of the AcrySof is 13.0 mm and of the CeeOn 911A, 12.0 mm. Both IOLs have hydrophobic surfaces with a water content less than 1%. After IOL implantation, the viscoelastic material was carefully removed using manual irrigation and the anterior chamber was refilled with balanced salt solution (BSS®).
Postoperatively, all patients received betamethasone/neomycin ointment (Betnesol N®) the night after surgery and betamethasone 0.1%/neomycin 0.5% eyedrops (Betnesol N) and diclofenac 1% eyedrops (Voltaren Ophtha®) 4 times daily for 4 weeks.
At the 3-year follow-up visit, 21 patients in the AcrySof group and 20 in the CeeOn 911A group had a thorough examination in accordance with a standardized protocol. Two patients died before this examination, and 7 patients were in poor physical condition or lost to follow-up. The protocol included an examination of the aqueous humor (flare and cells), a semiquantitative evaluation of inflammation cells and LECs, an assessment of ACO and PCO, evaluation of IOL decentration, and a semiquantitative evaluation of intralenticular glistening.
Aqueous flare and cells were measured using the Kowa FC-1000 laser flare-cell meter after the pupil was dilated with tropicamide 0.5% (Mydriaticum Agepha®) and phenylephrine 2.5%. Measurements with a difference between entry and exit signals of more than 8% were excluded. The mean values of 5 measurements were used for calculation.
Biomicroscopic examinations were performed using a Haag Streit slitlamp.
The anterior surface of the IOL was examined by specular microscopy to measure inflammatory cells such as small round cells or spindle-shaped cells as well as epithelioid cells and foreign-body giant cells. A semiquantitative grading system (0 = none; 1 = fewer than 10; 2 = 10 to 25; 3 = more than 25) was used to evaluate the quantity of the different cell types.
For evaluation of ACO, the anterior capsular leaf was divided into 3 parts: a capsulorhexis rim area, a capsule/optic area, and a capsule/capsule area. The posterior leaf of the capsule behind the IOL optic was divided into a central portion (3.0 mm in diameter) and a periphery. Capsule opacification was subjectively graded as follows: 0 = absent; 1 = very mild; 2 = moderate; 3 = dense white.
To evaluate LEC ongrowth, all lenses with persistent LECs on the anterior IOL surface were counted and the percentage was calculated.
Intraocular lens decentration was semiquantitatively graded as 0 = none; 1 = 0 to 0.25 mm; 2 = 0.25 to 0.50 mm; 3 = 0.50 to 1.00 mm; 4 = more than 1.00 mm.
For statistical analysis, differences between both groups were assessed with an unpaired t test or Wilcoxon-Mann-Whitney U test. Differences with a P value of 0.05 or less were considered significant. The SPSS statistical software system (SPSS Inc.) was used for calculation.
With respect to blood-aqueous barrier disturbances, significantly lower flare (P = .003) and cell (P = .003) values were seen in the CeeOn 911A group (Figures 1 and 2). There were no significant differences in the preoperative flare and cell values.
Regarding uveal biocompatibility, no IOL in either group had small round cells or spindle-shaped cells during the observation period. Epithelioid cells or foreign-body giant cells were observed on no silicone IOL and on 28.6% of acrylic IOLs. The difference between groups was clinically significant (P = .011) (Figure 3).
Regarding capsular biocompatibility, the only difference between groups in ACO was in fibrosis of the capsulorhexis rim. The difference was not clinically significant (P = .074). There were no between-group differences in fibrosis of the capsule/optic area (P = .165) or the capsule/capsule area (P = .957) (Figure 4). Anterior LEC outgrowth was also not significantly different. Persistent LECs were found on 9.5% of the AcrySof lenses and 0% of the CeeOn 911A lenses (P = .162).
Posterior capsule opacification was not significantly different between the 2 groups (central PCO, P = .323; peripheral PCO, P = .863) (Figure 5). Although the ratio between fibrotic PCO and Elschnig regenerates was somewhat more balanced in the silicone group, it shifted toward regeneratory secondary cataract in the acrylic group. Mixed forms of PCO were only slightly different between the 2 groups (Figure 6).
Decentration of the IOL optic was significantly more common in the CeeOn 911A group (P = .025) (Figure 7). The AcrySof lenses had a significantly higher mean vacuolar density (P = .000) (Figure 8).
Several recent studies describe 3 parameters that are considered to substantially influence the development of PCO. Ravalico et al.21 showed that PCO is significantly reduced when the capsulorhexis rim in toto is located on the anterior surface of an in-the-bag IOL. In contrast to the first parameter, the other 2 parameters are assigned a varying degree of importance and are controversially discussed.
Ursell et al.17 and Hollick and coauthors19 conclude that lens material is the main factor responsible for the development of PCO. In contrast, Nagata and Watanabe23 and subsequently Nishi and Nishi26 and Kruger et al.24 report the PCO-minimizing effect of IOLs with sharp optic edges. The results of our study, the first to compare a silicone with an acrylic IOL, both with sharp optic edges, corroborate this concept. We found no significant difference in PCO formation between the lenses 3 years postoperatively. These findings concur with those of Nishi and coauthors,27 who in an animal experiment observed no difference in PCO development 3 to 4 weeks after implantation of the same types of lenses. These recently published results permit the conclusion that it is primarily the square optic edge, not the IOL material, that inhibits PCO formation (Figure 9).
Nevertheless, the surface properties of different materials play an important role in the emergence and spread of LECs. For example, our silicone group had significantly more pronounced fibrosis of the capsulorhexis rim. However, excessive fibrosis of the entire anterior capsule, as reported in earlier studies,28,29 was not observed. Even though the degree of ACO was not significantly different between the silicone and acrylic IOL groups, we suspect that contact between silicone and the capsule causes a relatively stronger contraction of the capsule (as in other silicone lenses). This, and the more pronounced fibrosis of the capsulorhexis rim, seem to be responsible for the more frequent IOL decentration in the silicone group. This phenomenon requires further study of the nature and intensity of the influence of lens material on capsular biocompatibility.
The investigation of uveal biocompatibility also reveals partly significant differences that may be important when selecting one or the other lens type. Thus, the significantly higher flare and cell values and the colonization of AcrySof lenses by inflammatory cells even after 3 years indicate that a persistent late foreign-body reaction occurred. To the best of our knowledge, this is the first publication that describes late cellular foreign-body reactions in normal eyes 3 years after cataract surgery with foldable IOL implantation. The foreign-body reaction was mild and subclinical and thus is not perceived by the patient. Nevertheless, this observation prompted us to initiate a further study (in progress) in which we are investigating the uveal and capsular biocompatibility of these 2 lenses in patients with chronic ocular irritation such as uveitis. The issue is whether this subclinical foreign-body reaction is clinically relevant in patients with chronic inflammatory eye disease.
Intralenticular glistenings, which occur in both IOL types, have been extensively described and frequently reported. As in other IOLs, this phenomenon appears to be related to the difficulty of producing highly refractive lens material. Our results show a higher intensity of this intralenticular phenomenon in acrylic lenses. However, as reported by other authors, this observation is also not clinically relevant.
In conclusion, the IOLs we evaluated were highly biocompatible. In addition to their good uveal biocompatibility, their sharp optic-edge design makes them forerunners in terms of capsular biocompatibility. In their respective material group, they may be regarded as the reference product for further development.
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