Safety and efficacy of poly(methyl methacrylate), hydrophobic acrylic and hydrophilic acrylic intraocular lenses: A comparative clinical investigation

INTRODUCTION

Cataracts, which involve the clouding of the eye’s natural lens, lead to substantial visual impairment and often require surgical treatment. Cataract surgery entails the replacement of the clouded lens with an intraocular lens (IOL), thereby restoring vision and enhancing the patient’s quality of life. Choosing the optimal IOL material is vital for achieving successful outcomes, considering factors such as biocompatibility, intraoperative safety and long-term visual function.^[1-3]

Modern cataract surgery typically employs phacoemulsification and the implantation of an IOL into the capsular bag. Surgeons have access to a range of IOL types, including monofocal, multifocal, accommodating and toric lenses. Efforts are focussed on minimising potential post-surgical complications such as posterior capsule opacification (PCO), lens dislocation, cystoid macular oedema, and endophthalmitis to address the growing demands of an ageing population.^[3-6]

At present, various IOL materials and designs are available, including hydrophobic acrylic, hydrophilic acrylic, silicone and poly(methyl methacrylate) (PMMA). These IOLs can have aspheric or non-aspheric designs and can be positioned in either the anterior or posterior chamber. They can also be one-piece or three-piece designs and can be placed either in the capsular bag or fixed in the sulcus. Hydrophobic acrylic IOLs are designed to prevent hydration from affecting the lens post-implantation and are the most widely used material. Their stability within the eye is attributed to this hydration resistance. Early concerns about calcification and opacification limited the acceptance of hydrophilic acrylic IOLs. Silicone IOLs are known for their resistance to PCO but have a three-fold higher risk of serious infection compared to acrylic IOLs.^[6] In addition, they are not recommended for high myopia due to an increased risk of vitreoretinal pathology and the potential need for silicone oil.^[2,3,5,7,8]

PCO is the most prevalent complication of cataract surgery and can impair vision. IOLs with sharp-edged designs have a lower incidence, with continuous 360° square edges being more effective than square edges interrupted at the optic-haptic junction. PMMA IOLs exhibit higher rates compared to acrylic or silicone IOLs.^[1,8,9]

MATERIALS AND METHODS

RESULTS

Table 1 depicts the number of eyes that were studied under each group for their safety and efficacy.

DISCUSSION

Cataracts are the leading cause of blindness globally., affecting a significant number of individuals. The IOL material has the greatest impact on adverse events such as PCO, anterior capsule opacification, and glistening formation following cataract surgery.^[2,5,10,11]

IOLs have advanced over time, and the gold standard for an ideal lens is defined by its biocompatibility, compatibility with surgical techniques and freedom from optical defects. Modern IOLs have made advancements in terms of material chemistry and design, leading to improved performance and outcomes.^[3,5]

PCO is a frequent complication following cataract extraction, occurring in up to 50% of cases. The study by Mudhol et al. aimed to compare the effectiveness of square-edge and conventional round-edge IOLs in preventing PCO and enhancing visual outcomes in MSICS. While the incidence of PCO was similar between the two groups, incomplete cortical cleanup was linked to a higher rate of severe PCO. However, the square-edge IOL group demonstrated better visual outcomes, with a greater percentage of patients achieving good visual acuity.^[12] None of the subjects had a PCO in this study in the follow-up period.

The study by Cochener et al. assessed the progressive contraction of the anterior capsule opening following inthe-bag implantation of two types of IOLs – PMMA and silicone. Both silicone and PMMA IOLs exhibited capsule contraction, but the contraction rate was statistically higher in the silicone group. The study found no significant difference in fibrosis or cellular response between the two groups. It underscores the need to evaluate factors such as biomaterial, size, IOL design and biocompatibility in comparative studies of single-piece IOLs to understand their impact on capsule contraction better. The findings provide valuable insights for clinicians in selecting the appropriate IOLs and surgical techniques to minimise the risk of anterior capsule contraction and PCO.^[13]

Snowflake degeneration refers to the gradual opacification of PMMA IOLs, which can develop a decade or more after implantation. This condition involves the central aggregation of deposits composed of IOL material. Al-Otaibi case report details a patient with late-onset optical opacification of a PMMA IOL, which was successfully diagnosed and treated, leading to improved best-corrected vision.^[14] No case of such degeneration was evident in the present study.

The study by Kim and Shyn included 137 cataractous eyes from 108 patients who underwent phacoemulsification and IOL implantation. The eyes were randomly assigned to three groups based on IOL type: PMMA, silicone and soft acrylic. Biometric analysis and best corrected visual acuity (BCVA) measurements were conducted at 1, 3 and 6 months post-surgery. There are no statistically significant differences in BCVA amongst the three IOL types. In addition, there was no significant decentration or tilt of the IOLs, and anterior chamber depth (ACD) did not differ significantly amongst the IOL types. The study concluded that a well-constructed CCC and precise IOL implantation in normal capsular bags resulted in comparable ACD changes, IOL decentration and tilt and BCVA across silicone, PMMA and soft acrylic IOLs.^[15]

The study by Hayashi et al. compared decentration and tilt between one-piece and three-piece PMMA IOLs implanted in the capsular bag after CCC. The one-piece IOL group exhibited significantly less decentration than the three-piece IOL group at 1 week, 1 month, 3 months and 6 months postoperatively. However, there was no significant difference in tilt between the two IOL types throughout the observation periods.^[16] None of the eyes with the IOLs demonstrated any IOL decentration or tilt in the current study.

Panahi-Bazaz et al. compared the use of hydrophilic acrylic and PMMA IOLs in paediatric cataract surgery and found that hydrophilic acrylic IOLs had comparable biocompatibility and visual outcomes to PMMA IOLs but had fewer post-operative complications.^[17]

The study by Gozum et al. compared visual functions following cataract surgery and IOL implantation using different lens materials (acrylic and PMMA) with those of age-matched subjects with clear phakic eyes. Acrylic IOLs demonstrated superior visual quality in pseudophakic eyes compared to PMMA IOLs.^[8] The present study showed similar improvements in visual quality.

The meta-analysis by Zhao et al. comparing hydrophobic and hydrophilic IOLs in preventing PCO after cataract surgery found that hydrophobic IOLs were linked to lower neodymium-doped yttrium aluminium garnet laser capsulotomy rates compared to hydrophilic lenses. In addition, hydrophobic IOLs were associated with lower subjective and estimated PCO scores.^[18]

The study by Johansson et al. assessed the visual, refractive and safety outcomes of a hydrophilic acrylic IOL in cataract patients with or without pre-existing ocular pathologies. After 12 months, 95% of eyes achieved monocular corrected distance visual acuity (CDVA) of 0.3 logMAR or better, with a mean post-operative CDVA of 0.06 ± 0.17 logMAR and a mean UNDVA of 0.31 ± 0.29 logMAR. Visual acuity outcomes significantly improved post-surgery compared to pre-operative values, and the IOL remained stable in the capsular bag.^[19] The findings are similar to the current study.

The study by Zacharopoulos et al. evaluated the safety and efficacy of a hydrophilic acrylic IOL over a 2-year follow-up period. The results demonstrated excellent optical performance, good centration and a low rate of intra- and post-operative complications. However, the incidence of PCO increased significantly over time, with 77% of eyes exhibiting some degree of PCO by the end of the 2^nd postoperative year.^[20] Although there was no follow-up for 2 years, the present study showed no intra and post-operative complications and no PCO development in the follow-up period.

The study by Van Der Linden et al. compared the outcomes of a new apodised diffractive hydrophilic multifocal IOL with a well-established apodised diffractive hydrophobic multifocal IOL. It found that the mean UNDVA was not significantly different between the two groups, but the CDVA was significantly better with the new study lens.^[21]

The study by Koshy et al. found that both hydrophilic and hydrophobic IOLs performed comparably in terms of capsular bag performance and PCO development, with no significant differences between the two groups. Both IOL types demonstrated good capsular bag performance and low PCO rates within the first 2-year post-surgery, and there was no statistically significant difference in PCO scoring between the groups. Intraoperative complications included a capsular tear in the hydrophobic IOL group and damage to the haptics of the IOL in the hydrophilic IOL group.^[22]

The PMMA design used in this study is more prone to risk compared to other designs, making it the bottom design in the PMMA product line. However, the clinical investigation conducted for the product PMMA lens spherical did not pose any risk or side effects such as vision loss, wound leakage, corneal oedema, blurred vision, inflammation, posterior capsule rent during the surgery and post-surgery in any subjects participating in this study. Even though being the bottom-design product, the PMMA lens spherical model demonstrated the expected safety and performance through the clinical investigation performed, which in turn substantiated the same outcomes for aspheric and 360° square edge designs.

Although double haptic design in hydrophilic lens offers better stability and centration, it is more prone to risk compared to other designs, making it the bottom design in the hydrophilic product line. However, the clinical investigation conducted for the product hydrophilic IOL-spherical did not pose any risk or side effects during the surgery and post-surgery in all the subjects participating in this study. Even though being the bottom-design product, hydrophilic IOL spherically demonstrated the safety and performance through the clinical investigation performed which in turn substantiate the same outcomes for aspheric and 360° square edge designs.

The design for the hydrophobic lens in this study was chosen as it is comparatively produced and sold in larger numbers compared to others. Even though being the bottom-design product, hydrophobic IOL spherically demonstrated the safety and performance through the clinical investigation performed which in turn substantiate the same outcomes for aspheric and 360° square edge designs.

The current clinical investigation undertaken demonstrates the safety and efficacy of PMMA, hydrophilic and hydrophobic IOLs in improving vision in cataract patients. The findings are consistent with established literature regarding their biocompatibility and durability. While various studies have had episodes of intra and post-operative complications, the current clinical evaluation performed has no such events recorded. There was significant improvement in the visual outcomes without any adverse events.

CONCLUSION

Modern IOLs aim to be defect-free, with materials and designs that minimise potential complications during and after surgery. The continuous evolution of IOLs has led to a wide variety of options, allowing surgeons to select lenses that are best suited to individual patient needs. This study contributes valuable data on the safety and efficacy of PMMA, hydrophilic and hydrophobic IOLs in cataract surgery. Choosing the optimal IOL material requires a comprehensive understanding of individual patient needs, preferences and risk factors. Continued research is crucial to evaluate emerging IOL materials further.

The purpose of conducting a clinical study is crucial for ensuring the safety and efficacy of medical devices in accordance with current regulations and standards. A well-executed clinical evaluation provides essential information for decision-making. Manufacturers must systematically collect, analyse and report safety and performance data from real-world use of the device in humans. In this context, the clinical investigation contributes valuable real-life data for the IOLs assessed in this study.