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In 1949, Sir Harold Ridley implanted the first artificial intraocular lens (IOL) to reduce refractive error following cataract extraction.1 Numerous designs of IOL implants have followed and a variety of materials have been used in their manufacture, including poly(methyl methacrylate) (PMMA), silicone, acrylic, and hydrogel based materials. Important requirements of IOL implant material are to not excite an inflammatory response and the ability to remain transparent within the eye for an extended period of time. In recent years, there have been reports of opacification of IOL implants such as calcification on the optical surface of the Hydroview lens2; “glistenings” of fluid filled vacuoles in the optic of the AcrySof IOL3,4; and “snowflake” crystalline opacification of three piece rigid PMMA lenses.5
In particular, late postoperative opacification of a particular hydrophilic acrylic IOL, the SC60B-OUV, has been reported6 and analysis of these explanted IOLs have shown the presence of granular deposits within the optic.7 We report examination, using electron microscopy, of a similar explanted IOL removed following late postoperative opacification, which appears to have different surface morphology from those reported previously.
An 82 year old female patient with Fuchs’ endothelial dystrophy underwent uneventful phacoemulsification and foldable lens implantation into the capsular bag of the left eye. Two weeks later, the best corrected visual acuity was 6/9. Fifteen months later, she underwent a similar procedure with a different foldable lens in the right eye leading to a visual outcome of 6/9. At that time, the left visual acuity had dropped to 6/18 and red reflex assessment of the dilated eye with a direct ophthalmoscope was very similar to that of a senile nuclear cataract. On slit lamp examination, the intraocular lens optic was found to have become uniformly cloudy (Fig 1). The patient was offered a lens exchange procedure and this was carried out 6 months later. Extensive capsular fibrosis and capsular dehiscence meant that the lens could not be explanted in one piece. The haptics were left in situ and the optic was transected before explantation. Anterior vitrectomy and peripheral iridectomy were carried out and an anterior chamber implant was inserted. Five months postoperatively, her vision had recovered to 6/9.
The explanted lens underwent detailed examination at the School of Pharmacy and Biomolecular Sciences, University of Brighton. The surface and the interior portion of the explanted (test) lens were examined and compared to an identical unused SC60B-OUV (control) lens. Fourier Transformed infrared (FT-IR) spectroscopy was performed using a diamond attenuated reflectance unit on a Perkin-Elmer 1620 spectrophotometer under control pressure. For analysis by scanning electron microscopy (SEM), both the control and test lens were cut to produce cross sections to enable the visualisation of the interior and exterior surfaces. All sections were then sputter coated with palladium and photographed at ×20, ×2000, and ×7000 magnification using a Joel JSM 6310 scanning electron microscope.
The opaque lens was a 12.5 mm SC60B-OUV (manufactured and distributed by Medical Developmental Research Inc, USA). The lens is hydrophilic in nature and is a composite of poly(2-hydroxyethyl methacrylate) (HEMA) and PMMA with a polymerisable ultraviolet absorber. The source of the polymer was Vista Optics, UK.
The FT-IR spectra showed identical typical hydroxyl and carbonyl stretching adsorption bands for both test and control lenses. Examination of the control lens by SEM at ×20 and ×2000 magnification showed smooth, unblemished inner and outer surfaces. The inner and outer surfaces of the test lens did not appear different from the control lens when viewed at ×20 magnification. At ×2000 the outer (opaque) surface of the test lens was markedly different from the interior portion. A 5 μm thick section of the outer surface appeared to have degraded giving a sponge-like morphology (Fig 2).
The dimensions of this degraded portion only occurred within the visibly opaque section of the explanted lens and the degradation did not extend across the transected surface.
The FT-IR spectroscopy indicated that there were no significant differences in the surface chemistry of the original and explanted lens. From the SEM results it can be concluded that the opacity observed on the lens removed from the patient, corresponds to a 5 μm thick interfacial layer. The structure observed is typical of high water component, swollen hydrogel systems such as poly(HEMA) polymerised in 80% water. Such damage may therefore have been caused by slow degradation of the polymer matrix or dissolution of unpolymerised monomer/oligomers and swelling of incompletely polymerised material in the core of the optic.
These findings are different to those previously reported by Werner et al7 who found granular deposits in a region beneath the anterior and posterior surfaces with intact surface structure. The time frame for the appearance of the opacification and clinical description appears to be equivalent in both studies. The reason for the difference in SEM findings is unclear. If our findings represented an earlier phase of the same degenerative process then one would expect some residual surface degeneration in their study. Conversely, if ours is a later phase then one might expect the presence of granular deposits in the substance of the optic.
Although our lens showed the same clinical appearance of postoperative opacification before explantation as other studies, the EM results suggest that our findings may represent a different degenerative process. The nine explanted lenses examined by Werner et al7 came from the same surgeon in Turkey, and the type of opacification may be due to a “batch” effect as well as a polymer effect. In conclusion our findings may represent a different degeneration in IOL structure to that previously described.
The manufacturer has withdrawn all SC60B-OUV IOLs made from materials obtained from Vista Optics, UK and these IOLs are now being manufactured by polymer from a new source (Benz Research, USA). Out of 12 patients who received this IOL at our institution, seven experienced significant clouding, three have corrected vision of 6/12 or better, and two have died. Of the seven patients with significant clouding, two have undergone exchange, two await exchange, two are considering exchange, and one declined exchange. Figures from the Medical Devices Agency (MDA) state that of 3200 lenses distributed in the United Kingdom, only 27 reports of clouding have been received. There may be under-reporting of cases and we encourage reporting of all cases to the MDA. Vigilance is clearly necessary with this IOL to ensure that the change in polymer manufacture has resolved the problem.