Year : 2006 | Volume
: 54 | Issue : 2 | Page : 105--109
Comparison of acrylic and polymethyl methacrylate lenses in a pediatric population
Murali K Aasuri, Merle Fernandes, Padmaja Preetam Pathan
Cornea Service, L. V. Prasad Eye Institute, Hyderabad, India
L. V. Prasad Eye Institute, L. V. Prasad Marg, Banjara Hills, Hyderabad - 500034
Purpose: To compare the intra-patient incidence of posterior capsular opacification (PCO) and their post operative course, in children with bilateral cataract, following implantation of acrylic (Group 1) and polymethyl methacrylate (PMMA) (Group 2) intraocular lenses (IOLs).
Materials and Methods: This was a prospective, interventional intra-patient case series. Twenty-five children with bilateral cataract, 5 years and older, underwent cataract surgery and implantation of an acrylic (AcrySof MA30BA, Alcon, Fortworth, TX) in one eye and PMMA (Indo Am IAB 203, Ocular Vision, Inc.) IOL in the other eye of each patient. They were followed up for an average of 11.1 ± 9.5 months to assess the incidence of clinically significant PCO and occurrence of postoperative complications.
Results: Twenty-three children (46 eyes), were included in this study. Post-operatively, 22(95.6%) patients with acrylic IOLs and 20 (86.9%) patients with PMMA IOLs, either maintained or improved their vision. In the acrylic and PMMA IOL groups respectively, the incidence of clinically significant PCO was 21% (4) and 75% (12) ( P =0.002), with a median onset at 2.9 months and 0.7 months. Other complications included pupillary capture in 2 (8.7%) eyes and uveal prolapse in 1 (4.3%) eye in the acrylic group and increased uveal inflammation in 6 (26.1%) eyes and presumed noninfectious endophthalmitis in 2 (8.7%) eyes in the PMMA group.
Conclusion: Incidence of PCO and post operative uveal inflammation is significantly less with acrylic lenses and were safe to use in pediatric eyes.
|How to cite this article:|
Aasuri MK, Fernandes M, Pathan PP. Comparison of acrylic and polymethyl methacrylate lenses in a pediatric population.Indian J Ophthalmol 2006;54:105-109
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Aasuri MK, Fernandes M, Pathan PP. Comparison of acrylic and polymethyl methacrylate lenses in a pediatric population. Indian J Ophthalmol [serial online] 2006 [cited 2022 Aug 14 ];54:105-109
Available from: https://www.ijo.in/text.asp?2006/54/2/105/25831
The incidence of posterior capsular opacification (PCO) in children, 2 years after surgery, almost equals 100%. This obscures the visual axis and is a significant cause of amblyopia. Several surgical techniques are currently used to prevent PCO. These include posterior capsular continuous curvilinear capsulorrhexis (PCCC), with or without anterior vitrectomy (AV), with or without optic capture of the intraocular lens (IOL) through the PCCC.,,,, Most of these studies had a population less than 5 years of age and it is still unclear whether AV should be done routinely in older children or not. Other methods (some of which are experimental), include posterior capsule polishing or the use of pharmacological agents to reduce the number of lens epithelial cells left at the end of surgery, to inhibit their proliferation or cause their destruction. There is increasing evidence of PCO reduction with newer IOL designs and materials.,,,14],,, The formation of PCO is significantly less with acrylic lenses, compared to PMMA or silicone lenses. Since the incidence of PCO is very high in pediatric patients and the long-term effect of AV and Nd:YAG capsulotomy in this group is not known, use of an IOL to inhibit PCO formation is highly desirable. In this study, we evaluated the performance of PMMA and acrylic IOLs on the development of PCO and on the post-operative course in a group of pediatric patients.
Materials and Methods
This was a prospective, interventional intra-patient case series, comprising of 46 eyes of 23 patients whose age ranged from 60 to 180 months (mean 88.9 ± 26.8 months).
Inclusion criteria included parents willing to give consent and patients with bilateral congenital or developmental cataract. One-eyed patients, presence of associated ocular disease (microophthalmos, microcornea, glaucoma, uveitis, traumatic or complicated cataract, posterior lenticonus, coloboma) and systemic disease were excluded. The occurrence of intraoperative complications such as zonulodialysis, posterior capsular dehiscence or inability to implant the IOL in the bag or the presence of a pre-existing posterior capsular plaque, were also excluded from the study. The study period was between 25th October 1997 and 14th April 2001 and patients were followed up for a minimum of 1.4 to 35 months (mean 11.1±9.5 months).
All patients were subjected to a detailed preoperative evaluation. The visual acuity was recorded with Snellen's visual acuity charts or the illiterate 'E' chart. Fixation patterns were noted in uncooperative patients. Special mention was made of the presence of nystagmus, amblyopia or strabismus. Nystagmus was defined as a rhythmic, involuntary oscillation of one or both eyes. Amblyopia referred to poor vision caused by abnormal visual development, secondary to abnormal visual stimulation, with at least 2 Snellen's lines' difference in visual acuity. Strabismus was defined as an ocular misalignment or a tendency towards misalignment, measured with the alternate cover prism test.
Slit-lamp biomicroscope examination was done and if deemed necessary, an evaluation under anesthesia was carried out. Intraocular pressure (IOP) was measured in most patients with either the Goldmann applanation tonometer or the Perkins hand-held tonometer. Preoperative keratometry was done wherever it was possible and otherwise determined intraoperatively, under general anesthesia using the hand-held keratometer. After determining the axial length, the SRK IIÔ formula was used for IOL power calculation. The IOL power was selected to ensure post-operative emmetropia.
Preoperatively, the pupils were dilated with 1% Cyclopentolate eye drops and 2.5% Phenylephrine eye drops. Surgery was performed under general anesthesia. One eye of the patient received an all PMMA (Indo Am IAB 203, Ocular Vision, Inc.) IOL and the other received an acrylic foldable (AcrySof MA30BA, Alcon, Fort Worth,TX) I0L. The two eyes were not operated on simultaneously and the decision on the type of IOL implanted into the first eye was made arbitrarily by the operating surgeon. A single surgeon (MKA) operated all patients. Under all aseptic precautions, a fornix-based conjunctival flap was raised, 0.5 mm from the limbus. A 3.2 mm or 5.0 mm wide sclero-corneal tunnel for acrylic foldable IOL (Group 1) and PMMA IOL (Group 2) respectively, was made. Through a paracentesis, 0.9% Sodium hyaluronate (Proviscβ, Alcon) was injected into the anterior chamber. A 4.5-5.0 mm anterior capsular continuous curvilinear capsulorrhexis was initiated with a 26G needle cystotome and completed with a rhexis forceps. The lens matter was aspirated with the automated irrigation-aspiration handpiece, taking care not to leave any lens matter behind. The posterior capsule was left intact. The capsular bag was filled with 0.9% Sodium hyaluronate and either a 5.5 mm foldable acrylic IOL (MA30BA) or after extending the tunnel, a 5 mm all PMMA IOL (IAB203), was implanted in the bag. The viscoelastic was aspirated. The main valve incision was sutured with a single, box 10-0 nylon suture if there was pouting of the anterior and or posterior lip of the scleral tunnel, at the end of surgery.
Postoperatively, all patients received a standard regime of 1% Prednisolone acetate eye drops every 4 hours, tapered weekly over a month and 0.3% Gentamicin sulfate eye drops, every 6 hours for a week. Patients were examined on the first post-operative day and subsequently at 1 week, 1 month, 6 months and 1 year. At each visit, the best-corrected visual acuity (BCVA) and IOP were recorded. Slit-lamp biomicroscope examination was done by an independent observer (PP), who was unaware of the type of IOL implanted. Indirect ophthalmoscopy with mydriatics was done at the 1-month follow up. The PCO was graded as shown in [Table 1]. Grade 0-2 was considered as clinically insignificant, while Grades 3 and 4 were taken as clinically significant.
Statistical analysis was done using Fisher's exact test. Kaplan Meier cumulative survival analysis was used to assess the development of PCO in the two groups. P P =1.000, Yate's corrected chi square test). [Figure 1] depicts the comparison of pre- and post-operative BCVA in both groups. While 22 (95.6%) eyes in the first group either maintained or improved their vision post-operatively, this was seen in 20 (86.9%) of eyes in the second group. In both groups, the 4 eyes that worsened were amblyopic and the patients were non-compliant for amblyopia therapy. One eye (group 1) had iris prolapse and increased uveal inflammation.
The postoperative complications are listed in [Table 3]. The increased uveal inflammation noted in 6 (26.1%) eyes, subsided with an increased frequency of instillation of 1% Prednisolone acetate eyedrops and a mydriatic-cycloplegic (1% Atropine sulphate eyedrops). All these eyes had PMMA IOLs implanted. Thus a significantly ( P =0.0001, Chi square test for proportions) greater number of patients with these IOLs had increased postoperative inflammation, compared to those who received acrylic IOLs.
Two patients in group 2 had presumed non-infectious endophthalmitis, seen in the first postoperative week. One patient underwent vitreous biopsy and an intraocular injection of Vancomycin hydrochloride 0.1 mg/0.1 ml and Amikacin sulphate 400 mg/0.1ml. The cultures were sterile and on treating with 1% Prednisolone acetate and systemic steroids, the reaction resolved with a BCVA of 20/30, at the last follow up. The other patient also improved with similar medical treatment. At the last visit, the BCVA of this patient was 20/25p.
Iris prolapse without antecedent trauma occurred in one patient with an acrylic IOL, 10 days post-operatively and was accompanied with increased uveal inflammation. Following iris abscission and anterior chamber lavage, the BCVA at last follow up was 20/200. This patient had amblyopia and was non-compliant with occlusion therapy.
The onset of clinically significant PCO was found to vary from 0.03 to 6.4 months (mean 3.0 ± 3.0 months, median 2.9 months) and 0.03 to 8.9 months (mean 2.3 ± 2.7 months, median 0.7 months) from the date of surgery, in groups 1 and 2, respectively. The number of patients developing PCO was 19 (82.6%) in group 1 and 16 (69.6%) in group 2 [Table 4]. There was no statistically significant ( P =0.491, Fisher's exact test) difference between these groups. We analyzed the number of eyes with clinically significant PCO, as per the criteria previously described. A significantly ( P =0.002, Fisher's exact test) larger number of eyes with clinically significant PCO was noted in group 2 than group 1. Fifty percent of eyes (6 of 12 eyes) with a PMMA IOL and clinically significant PCO also had increased uveal inflammation. This association however was not statistically significant ( P =0.069, Fisher's exact test). All 4 eyes with clinically significant PCO in group 1 and 7 (58.3%) in group 2 underwent a Nd:YAG laser capsulotomy. The age of these patients at the time of Nd:YAG capsulotomy ranged from 60-96 months (mean ± SD, 73.7 ± 15.5 months). They were all compliant for the procedure. Nystagmus was present in one case and 3 eyes were exotropic. The remaining patients with visually impairing PCO did not undergo the scheduled procedure due to financial constraints (2 patients) and 3 patients were lost to follow up. [Figure 2] depicts the Kaplan - Meier curves of the cumulative survival probability of both groups, with respect to development of PCO. The mean survival time of eyes with acrylic IOLs was 24.4 ± 2.8 months and for PMMA IOLs was 11.9 ± 4.1 months, which was statistically significant. ( P =0.005, Log Rank test)
The management of PCO in a child is difficult. The efficacy of Nd: YAG laser capsulotomy in the pediatric population, largely depends upon the density of the membrane and the cooperation of the child. Atkinson and Hiles advocate a Nd: YAG laser capsulotomy at 3 weeks after surgery. Complications like retinal detachment, cystoid macular edema and glaucoma, are known to occur in adults. A longer follow up of pseudophakic children who have undergone Nd:YAG laser capsulotomy is required to evaluate the long term effects. Also, recurrence of opacification of visual axis has been noted following Nd:YAG capsulotomy in young children.
Thus prevention of PCO is desirable. In children, modifications in the surgical technique have been described. These involve creating an opening in the PC and a limited AV or optic capture. PCCC with AV is associated with IOL dislocation (3-20%), and cystoid macular edema. There is always a risk of retinal detachment if vitreous is incarcerated in the wound. A pars plana membranectomy may be needed, if the visual axis is occluded by secondary membranes. Optic capture provides better IOL centration, but tends to predispose to an increased uveal inflammatory response and is technically more demanding. Opacification of the visual axis has been reported following optic capture without AV.
Several factors related to the IOL design help in reducing PCO. The IOL material also plays a role. In a study by Ursell et al , 11.75% adult patients with acrylic lenses developed PCO, compared to 43.65% and 33.5% with PMMA and silicone lenses, respectively. Experimental studies have shown that there is a significantly greater adhesion of the capsule to acrylic IOLs, due to its tacky surface. The exact mechanism by which the IOL material influences the behavior of these cells, is not known. It is claimed that the acrylic IOL may have bioactive properties.
Most of the reports in literature compare the efficacy of IOLs of different materials on the reduction of PCO in adult populations and only 2 describe the outcome in children., At the end of a 3 year follow up, Hollick and coauthors demonstrated that none of the patients with acrylic IOLs needed a Nd:YAG laser capsulotomy, compared to 26% with PMMA and 14% with silicone IOLs. More extensive PCO was associated with the PMMA lens, than the acrylic or the silicone IOL.
The incidence of clinically significant PCO was 21.1% in the group with acrylic IOLs. In the group with PMMA IOLs, 12 (75%) eyes developed a PCO, which was obscuring vision. Kaplan Meier curves distinctly demonstrate that in patients with acrylic IOLs, the posterior capsule remained clearer for a greater period of time, compared to the group with PMMA IOLs. In patients over 4 years old, with more than 2 years follow up, the incidence of visually significant PCO following acrylic IOL implantation, was 50% (13 of 26 eyes). In another study comparing 2 groups with acrylic and PMMA IOLs implanted, there were less complications in the group with acrylic IOLS, though there was no difference in the incidence of PCO between groups. Our data show that in pediatric eyes with acrylic IOLs implanted, the incidence of clinically significant PCO was lesser than with PMMA lenses. This is the first study in this age group, wherein acrylic and PMMA IOLs have been compared in the same patient.
Acrylic IOLs have a higher degree of biocompatibility in the eye, as evidenced by the lesser amount of cellular reaction on the IOL surface and may have a role to play in those patients with a jeopardized blood-aqueous barrier. A significant finding amongst our patients was that, none of the eyes with an acrylic IOL experienced any postoperative uveal inflammation, unlike 26.1% of the eyes with a PMMA IOL. All of the eyes with PMMA also developed clinically significant PCO. Thus the IOL biocompatibility, associated uveal inflammation and development of PCO, are inter-related. However, the long-term effects of acrylic IOLs in children whose life expectancy is much more, are yet to be assessed. In adults, acrylic IOLs have been in use for less than a decade. They appear to induce less inflammatory reaction in the eye, compared to PMMA IOLs., Similar results have been reported earlier in children. Thus, in those patients in whom the intra-ocular inflammation is expected to be greater, particularly in younger age group, acrylic lenses may be preferred.
Following the introduction of angulated haptics and capsular bag fixation of the IOL, pupillary capture is less commonly seen, though an incidence as high as 30.8% has also been described. It is attributed to be one of the causes of suboptimal vision postoperatively. We noted partial pupillary capture as a late complication in 2 eyes with an acrylic IOL, due to a fusion of the iris to the PC, in an area where the rhexis was not overlying the optic, resulting in a mild lens tilt anteriorly. Both patients had good visual acuity post operatively and no signs of chronic uveitis or cells on the IOL surface were noted. Pupillary capture may occur due to the flexibility of the optic, the greater length of the lens and rigid low-angulated loops.
The protocol we follow for management of presumed non-infectious endophthalmitis, has been described earlier. The final visual outcome of both the patients was better than 20/40. It may be argued that the straight edge of the acrylic IOL optic may be responsible for the reduced incidence of PCO, since this is advantageous in IOLs of other materials too. A comparative study between straight and rounded edge acrylic IOLs is needed to determine the effect of a difference in the IOL design.
The major limitations of this study was the small sample size, short duration of follow up, lack of randomization and masking of the observers, which limit our ability to draw convincing conclusions from this data. However, the acrylic IOLs appear to cause less visually significant PCO and are more biocompatible compared to PMMA IOLs. This needs to be substantiated by further studies.
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