Journal of Clinical Ophthalmology and Research

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Year
: 2016  |  Volume : 4  |  Issue : 3  |  Page : 149--150

A rare case of polymethylmethacrylate intraocular lens opacity


Somen Misra1, Kunal Patil2, Neeta Misra1,  
1 Department of Ophthalmology, Pravara Institute of Medical Sciences, Loni, Maharashtra, India
2 Department of Ophthalmology, Rural Medical College, Pravara Institute of Medical Sciences, Loni, Maharashtra, India

Correspondence Address:
Kunal Patil
Rural Medical College, Pravara Institute of Medical Sciences, Loni Bk - 413 736, Maharashtra
India

Abstract

Optical transparency of the intraocular lens (IOLs) is paramount in maintaining visual improvement after cataract extraction. There have been reports of the IOL developing opacity after years of cataract surgery. IOL opacities have been reported in silicone, acrylic lens, and very rarely in polymethylmethacrylate (PMMA) IOLs. Though the exact cause is not known, long-term exposure to ultraviolet light can be one of the most probably causes, leading to disruption of PMMA and release of gaseous (nitrogen) within the PMMA substance. We report one such rare case of PMMA IOL opacity in a 75-year-old female.



How to cite this article:
Misra S, Patil K, Misra N. A rare case of polymethylmethacrylate intraocular lens opacity.J Clin Ophthalmol Res 2016;4:149-150


How to cite this URL:
Misra S, Patil K, Misra N. A rare case of polymethylmethacrylate intraocular lens opacity. J Clin Ophthalmol Res [serial online] 2016 [cited 2022 Dec 3 ];4:149-150
Available from: https://www.jcor.in/text.asp?2016/4/3/149/190783


Full Text

Optical transparency of the intraocular lens (IOLs) is paramount in maintaining visual improvement after cataract extraction. There have been reports of the IOL developing opacity after years of cataract surgery. IOL opacities have been reported in silico ne, acrylic lens, and very rarely in polymethylmethacrylate (PMMA) IOLs.[1] PMMA IOLs are still widely used in a developing country like India, millions of cataract surgeries are being performed every day, but there are no any recent reports of such opacification. This fact makes the case quite rare and important to note. We report one such case of PMMA IOL opacity.

 Case Report



A 75-year-old female presented to the outpatient department with the complaint of foggy vision in the right eye 15 years after being operated for cataract surgery with best corrected visual acuity being 20/40. The cataract surgery was uneventful with the immediate postoperative best corrected visual acuity being 20/30. Present day best corrected visual acuity in the right eye was 20/40 and in left eye was 20/80 with +10 diopter (D) since it was left aphakic after cataract surgery. The IOL (manufactured by Excelens) in the right eye was found to have developed opacification within its substance on slit-lamp examination [Figure 1] and [Figure 2]. The IOL was found to be made of PMMA, based on slit-lamp examination and old records. Rest findings on slit-lamp examination were within normal limits. Intraocular pressure in both eyes was 17.3 mm of Hg. The patient was a known asthmatic with no other systemic illness.{Figure 1}{Figure 2}

 Discussion



Extracapsular cataract extraction followed by posterior chamber IOL implantation is the standard line of management for cataract. The transparency of the IOL is very essential in maintaining a good vision. The clouding within the IOLs can be easily mistaken for posterior capsular opacification. Keen examination is needed to differentiate the former from the later.

Intraocular clouding or opacity have been reported previously in different types of lenses.[2] Several theories have been put forward to explain the late clouding of the IOL optic.[3],[4],[5],[6]

Very few cases of PMMA IOL opacification have also been reported in the literature. PMMA IOLs are still widely used in a developing country like India, millions of cataract surgeries are being performed every day, but there are no any recent reports of such opacification. This fact makes the case quite rare and important to note.

Trivedi et al. examined a total of 25 cases of which nine underwent explantation of the IOL. All of the explanted IOLs were 3-piece PC-IOLs with rigid PMMA optical components and blue polypropylene or extruded PMMA haptics.[1]

In almost all cases, opacification developed usually 8–15 years after the implantation. They noted that the clinical, light, and electron microscopic findings were almost identical, with each differing only in the degree of intensity of the lesion which could be an indicator of the severity and probably the duration of the opacification. Visual acuity was not affected in the early stages. However, in the later stages with significant opacification, patients complained of reduction in visual acuity along with the decrease of contrast sensitivity and various visual disturbances and aberrations, including glare.[1]

The 'snowflake' lesions were most commonly observed in the central and mid-peripheral portion of the IOL optics. The peripheral rim of the lens optics appeared to be free of opacification. On detailed examination of the explanted IOLs, there was no evidence of any infiltration of exogenous material.[1] It was hypothesized that the lesions may be due to the long-term solar (ultraviolet [UV]) exposure as only the central portion of the IOL was affected.[1] Moreover, supporting this is the fact that the opacities are present most commonly and intensely on the anterior one-third IOL's thickness.

Poor filtrations of the precured monomeric components, nonhomogeneous disbursement of the UV chromophore and/or thermal initiator into the polymer chain, excessive thermal energy during the curing process leaving voids in the polymer matrix, insufficient postannealing of the cured PMMA polymer could be the other probable causes of the opacification.

PMMA is a polymer of methyl methacrylate (MMA), manufactured by additional polymerization using the MMA monomer. This process is being started by an initiator substance, like azobis-isobutyryl nitrile (ABIN).[7],[8],[9] The disruption of the PMMA could be because of the residual initiator substance (ABIN) embedded in the substance of the PMMA optic. This can occur during a molding process. The two double-bonded units of the ABIN initiator may be broken by gradual UV stimulation, with a release of nitrogen gas (N2). Either heat or UV light exposure can cause such gas formation.

With a poor manufacturing process, for example, using excessive initiator more than the fractional amount required, unwanted initiator might be entrapped in the PMMA substance. With long-term exposure to UV radiation, there could be the release of gaseous N2 within the PMMA substance.

In our case, explantation and detailed investigation of the IOL would be required to find the exact cause of opacification. The patient was not willing for explantation as her vision was not grossly impaired, so we did not explant the IOL and subject it to detailed investigation.

 Conclusion



IOL opacities have been reported in silico ne and acrylic lens but are very rare in PMMA lens. Since PMMA IOLs are still used in India, it is very important to correctly diagnose such cases and explant the IOLs when visually blinding without going for unnecessary investigations.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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