Central Optic Opacification of a Polymethyl Methacrylate Intraocular Lens Consistent with Snowflake Degeneration
Title: Central Optic Opacification of a Polymethyl Methacrylate Intraocular Lens Consistent with Snowflake Degeneration
Author: Bryan Masino, BS
Photographer: David Chang, MD, Liliana Werner, MD, PhD
Keywords/Main Subjects: Intraocular Lens (IOL), Snowflake Degeneration, Polymethyl Methacrylate (PMMA)
Diagnosis: Three-piece PMMA IOL with clinically significant optic opacity due to snowflake degeneration.
Description of Case: The Polymethyl Methacrylate (PMMA) intraocular lens (IOL) was implanted in the left eye of a 53-year-old female patient in 1985. The lens exhibited slow, yet progressive optic opacification that eventually led to decreased visual acuity. It was therefore explanted on October 13, 2009 (Figure 1), nearly 25 years after the implantation date, by Dr. David Chang from Los Altos, CA. The explanted lens was sent to the Intermountain Ocular Research Center (Mamalis/Werner Laboratory) for further analysis.
Gross examination in the dry state revealed that the optic displayed a prominent white discoloration located within the central 3 mm (Figure 2). Microscopic examination of the dry lens showed multiple lesions with an aspect characteristic of snowflake degeneration (Figure 3).1-3 These lesions were found where the central optic opacity was seen during clinical and gross examinations, and were distributed within the optic substance at different depths. The lesions had the appearance of small spherical “crystals” that were bounded by an outer pseudocapsule suggestively composed of compressed and degenerated PMMA.
The explanted lens was evaluated under anterior segment optical coherent tomography (AS-OCT),4 which showed the abnormal lesions within the optic substance (Figure 4).
As to mimic the environment in which the lens resided while inside of the patients eye, the explanted PMMA IOL was hydrated in balanced salt solution (BSS) and once again analyzed under gross and light microscopy, as well as under the AS-OCT. Upon gross examination the severity of the lens opacification was markedly increased and the diameter thereof nearly doubled to that of approximately 5mm (Figure 5). AS-OCT revealed a much denser and widespread area of snowflake lesions.
The hydrated explant was also evaluated under Scheimpflug photography with densitometry analysis to assess back light scattering.5 This revealed a very high light scattering with a density of 225 CCT at the level of the intraoptical lesions (Figure 7).
Light transmittance was also assessed using a spectrophotometer,5 showing decreased light transmittance through the explanted lens when compared to a control (Figure 8).
The microscopic appearance of the intraoptical lesions is consistent with snowflake degeneration of PMMA material. This is a slowly progressive opacification of PMMA lenses, occurring sometimes 10 years or more after implantation. Snowflake degeneration has been observed in three-piece PMMA lenses implanted between the early 1980’s and the mid 1990’s, which were generally manufactured by injection molding. It has been hypothesized that this degeneration is a result of long-term ultraviolet (UV) exposure. The explanted lenses analyzed in our laboratory had spherical lesions, which were interpreted as foci of degenerated PMMA material clustered in the central zone and midperipheral portion of the optic. This led to the hypothesis that the central optic was exposed to UV light over an extended period, whereas the peripheral optic may be protected by the iris. Therefore, snowflake lesions are generally not observed in the optic periphery. Although the snowflake lesions are dry, it has been observed that an unusual amount of water is collected within the affected optic area upon hydration of explanted PMMA lenses with this condition, leading to more significant optic opacification. Consequently, the clinical significance of snowflake degeneration may depend on the amount of water collected within the IOL optic.3 In vitro studies on three-piece PMMA lenses explanted because of this condition showed that they are associated with a considerable increase in forward light scatter, as well as with a decline of optical quality/performance indicators.6 This can give rise to a variety of subjective complaints, including glare in various illuminating conditions, halos around bright lights, color and contrast loss, as well as hazy vision. These symptoms may prompt IOL explantation even in the absence of significant decrease in visual acuity. It is important to point out that today industry has far greater control over the production of the PMMA material/lenses. Modern PMMA lenses are mostly produced by lathing; therefore, we do not expect to see development of snowflake degeneration in association with them.
Summary of the Case: The patient experienced a decrease in visual acuity due to slow-onset progressive opacification of a PMMA IOL that was implanted over 20 years ago. After the necessary explantation surgery, the lens was examined and exhibited marked snowflake degeneration, which has been observed with three-piece PMMA IOLs that were manufactured during the early 1980’s and the mid 1990’s.
- Werner L. Causes of intraocular lens opacification or discoloration. J Cataract Refract Surg 2007; 33:713-26.
- Apple DJ, Peng Q, Arthur SN, et al. Snowflake degeneration of polymethyl methacrylate posterior chamber intraocular lens optic material: a newly described clinical condition caused by unexpected late opacification of polymethyl methacrylate. Ophthalmology 2002; 109:1666-75.
- Dahle N, Werner L, Fry L, Mamalis N. Localized, central optic snowflake degeneration of a PMMA intraocular lens: Clinical report with pathological correlation. Arch Ophthalmol 2006; 124:1350-3.
- Werner L, Michelson J, Ollerton A, Leishman L, Bodnar Z. Anterior segment optical coherence tomography in the assessment of postoperative intraocular lens optic changes. J Cataract Refract Surg 2012; 38:1077-85.
- Michelson J, Werner L, Ollerton A, Leishman L, Bodnar Z. Light scattering and light transmittance in intraocular lenses explanted because of optic opacification. J Cataract Refract Surg 2012; 38:1476-85.
- Werner L, Stover JC, Schwiegerling J, Das KK. Effects of intraocular lens opacification on light scatter, stray light, and overall optical quality/performance. Invest Ophthalmol Vis Sci 2016; 57(7):3239-47.
Faculty Approval by: Liliana Werner, MD, PhD, and Nick Mamalis, MD.
Disclosure (Financial or other): The author does not have any financial interest in the material and methods mentioned.