Role of silicon contamination on calcification of hydrophilic acrylic intraocular lenses

Qualitative and quantitative analysis of an explanted opacified hydrophilic IOL after over two years from cataract surgery

Opacification of hydrophilic intraocular lenses (IOLs) is an uncommon complication, that can appear after uneventful cataract surgery. We report a case of opacified Hydroview® IOL in a 76-year-old woman, with a previous history of pars plana vitrectomy with silicon oil tamponade in her right eye for a proliferative diabetic retinopathy, who developed an opacification of the IOL after over two years from a silicon oil/BSS exchange in combination with an uneventful phacoemulsification. The patient complained about a progressive decrease in her visual acuity. The slit-lamp examination confirmed the opacification of the IOL. Therefore, because of blurred vision, a combined procedure of explant and exchange of the IOL was performed in the same eye. Qualitative (Optic microscope, X-Ray powder Diffraction (XRD), Scanning Electron Microscopy (SEM)) and quantitative (Instrumental Neutron Activation Analysis (INAA)) analysis of the IOL material were performed. Here, our aim is to report the acquired data of the explanted Hydroview® H60M IOL.

Stainability of Acrylic Intraocular Lens With Brilliant Blue G: An In Vitro Study

PURPOSE

To evaluate the stainability of several acrylic intraocular lens (IOLs) with Brilliant Blue G (BBG) in vitro.

DESIGN

Clinically relevant, laboratory, experimental study.

METHODS

LS313MF15 as a hydrophilic acrylic IOL and X-70, W60R, CP2.2R, YP2.2R, XC1, and XY1 as hydrophobic acrylic IOLs were included in this study. Prepared acrylic IOLs were evaluated for staining via immersion for different periods in BBG solution with adjusted concentrations. In cases where IOLs were stained blue, the sustained release of BBG and IOL cross-sectional images were evaluated, as well as changes in the optical properties of the IOLs via spectrophotometry.

RESULTS

All acrylic IOLs were stained with BBG in a BBG concentration- and staining time-dependent manner, with almost no sustained release of BBG observed. Lenses with a higher water content exhibited more pronounced staining, and BBG penetrated into the IOLs. A decrease in light transmittance with a peak wavelength of 610 to 620 nm was observed in blue-stained IOLs. LS313MF15 was markedly blue stained even with a short period of staining.

CONCLUSIONS

Any acrylic IOL can be stained with BBG, but hydrophilic IOLs are particularly susceptible to blue staining. Precautions should be taken in surgeries requiring the use of BBG staining, and efforts should be made to ensure that BBG components are sufficiently washed out intraoperatively.

New exploration of ions and fatty acids in hydrophilic acrylic intraocular lens calcification

PURPOSE

To conduct a new exploration and analysis of the ion and fatty acid levels of a medium in which calcified hydrophilic intraocular lenses (IOLs) are present.

SETTING

Qingdao Eye Hospital of Shandong First Medical University, Qingdao, China.

DESIGN

Retrospective, laboratory observational case series.

METHODS

11 patients (11 eyes) who had implantation of foldable hydrophilic acrylic posterior IOLs were found to have opacification of the IOLs. In vivo and in vitro analyses included the evaluation of patients' clinical characteristics, microscopy, histological staining, energy dispersive X-ray spectroscopy (EDS), the ion level of the aqueous humor (AH) and preserving fluid (PF), and the fatty acid content of AH.

RESULTS

10 of 11 cases were female with unilateral opacification, and 7 cases had both-eye cataract surgery, including 1 first eye and 6 second eyes with IOL opacification. 4 types of similar serial numbers were counted. The analysis of AH showed that the concentrations of phosphorus and silicon were elevated but that of calcium decreased, and an increased level of silicon was detected in 3 random PFs. The palmitic (C16:0) and stearic (C18:0) fatty acids were higher than the others in the AH. The EDS confirmed that the IOL surface deposits were composed of calcium, phosphate, and a small amount of silicon.

CONCLUSIONS

More silicon and higher C16:0 and C18:0 were found in the AH of patients with IOL opacification. New ideas and avenues have been proposed in the study of IOL opacification.

Recent Advances of Intraocular Lens Materials and Surface Modification in Cataract Surgery

Advances in cataract surgery have increased the demand for intraocular lens (IOL) materials. At present, the progress of IOL materials mainly contains further improving biocompatibility, providing better visual quality and adjustable ability, reducing surgical incision, as well as dealing with complications such as posterior capsular opacification (PCO) and ophthalmitis. The purpose of this review is to describe the research progress of relevant IOL materials classified according to different clinical purposes. The innovation of IOL materials is often based on the common IOL materials on the market, such as silicon and acrylate. Special properties and functions are obtained by adding extra polymers or surface modification. Most of these studies have not yet been commercialized, which requires a large number of clinical trials. But they provide valuable thoughts for the optimization of the IOL function.

A Novel Approach for Assessing Visual Impairment Caused by Intraocular Lens Opacification: High-Resolution Optical Coherence Tomography

PURPOSE

To quantify in vitro straylight induced by intraocular lens (IOL) localized opacification using an anterior segment optical coherence tomography (OCT) device.

DESIGN

Laboratory investigation.

METHODS

We obtained high-resolution OCT cross-section images of 44 explanted IOLs using a new in vitro application for an anterior segment OCT device, the Anterion (Heidelberg Engineering, Heidelberg, Germany). In 24 cases, the reason for IOL explantation was a centrally localized opacification, the sequela of a secondary ocular surgery. As a control, we used 20 IOLs removed after an IOL (sub-)luxation. Using image analysis, we found a threshold area value representing a metric for the amount of opacification in a region of interest in the IOL's central optic. We used a modified C-Quant straylight meter (Oculus, Wetzlar, Germany) to quantify light scattering. We derived a linear regression from calculating the correlation between the amount of opacification and straylight.

RESULTS

We visualized different amounts of IOL opacification using the OCT device. The opacified lenses showed a mean threshold area of 6.7% ± 3.3% and mean straylight was 95.1 ± 75.6 deg²/sr. The clear group's mean threshold area was 2.0% ± 0.8% and 5.0 ± 3.4 deg²/sr mean straylight. Straylight correlated statistically significantly with the threshold area, with a correlation coefficient of R² = 0.80, P < .001.

CONCLUSIONS

This high-resolution OCT imaging technique can be used to visualize IOL opacities. The amount of opacification correlated well with the straylight induced by the lens. Anterior segment OCT imaging might be used in the future as a tool for predicting the extent of visual impairment and aid clinicians to quantify patients' complaints.

Localized calcification of hydrophilic acrylic intraocular lenses after posterior segment procedures

PURPOSE

To describe the clinical and laboratory findings in a series of cases of hydrophilic acrylic intraocular lens (IOL) opacification after posterior segment procedures.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, USA.

DESIGN

Experimental study.

METHODS

Thirty hydrophilic acrylic IOLs were explanted after various posterior segment procedures (pars plana vitrectomy, intravitreal anti-vascular endothelial growth factor injections) because of localized central anterior surface and subsurface optic opacification associated with decreased visual function. Once received by the laboratory in the dry state or in fixative by the explanting surgeons, microscopic, histochemical (alizarin red), and surface analysis (scanning electron microscopy [SEM], energy-dispersive X-ray spectroscopy [EDS]) evaluations were performed on the IOLs. The surgeons were sent a questionnaire to obtain information pertinent to each case.

RESULTS

Of the 30 explanted IOLs, 9 hydrophilic acrylic designs from 7 different manufacturers were identified. Gross microscopy and light microscopy showed granular deposits in a dense round pattern of distribution within the margins of the capsulorhexis or pupil on the anterior surface/subsurface of the IOLs. The granules stained positive for calcium with alizarin red. On SEM coupled with EDS, the granular deposits were found to comprise calcium and phosphate.

CONCLUSIONS

A localized pattern of anterior surface/subsurface calcification was seen on hydrophilic acrylic IOLs from various manufacturers. The calcification resembled the pattern seen on calcified IOLs after anterior segment procedures using intracameral injections of air or gas. This calcification of hydrophilic acrylic IOLs is likely the result of blood-aqueous barrier breakdown from repeated intraocular procedures.

A review of late intraocular lens opacifications

PURPOSE OF REVIEW

Phacoemulsification cataract surgery is one of the most commonly performed surgical procedure worldwide. In the majority of cases, intraocular lenses (IOLs) are implanted. Due to the increasing life expectancy and the fact that cataract surgery is performed in earlier stages, the anticipated IOL duration in the eye has increased over the last decades. The aim of this study was to review the types and describe the characteristics of late intraocular lens opacifications.

RECENT FINDINGS

Calcification was the most commonly reported type of opacification in hydrophilic IOLs; it usually negatively impacted the visual function and required IOL explantation. Glistening manifested in hydrophobic acrylic lenses and was frequent in some IOL models. In most cases glistening and subsurface nanoglistenigs do not lead to a decline in visual acuity or require IOL exchange. Current studies indicate that fluid-related phenomena may induce straylight, leading to a decrease of comfort and quality of vision.

SUMMARY

Several reports on late IOL opacifications have been published in recent years. In some cases, particularly in glistening, the development of the opacifications might be related to IOL aging. The influence of the fluid-related microvacuoles on the quality of vision requires further research.

Physicochemical Analysis of Sediments Formed on the Surface of Hydrophilic Intraocular Lens after Descemet's Stripping Endothelial Keratoplasty

An intraocular lens (IOL) is a synthetic, artificial lens placed inside the eye that replaces a natural lens that is surgically removed, usually as part of cataract surgery. The opacification of the artificial lens can be related to the formation of the sediments on its surface and could seriously impair vision. The physicochemical analysis was performed on an explanted hydrophilic IOL and compared to the unused one, considered as a reference IOL. The studies were carried out using surface sensitive techniques, which can contribute to a better understanding of the sedimentation process on hydrophilic IOLs’ surfaces. The microscopic studies allowed us to determine the morphology of sediments observed on explanted IOL. The photoelectron spectroscopy measurements revealed the presence of organic and inorganic compounds at the lens surface. Mass spectroscopy measurements confirmed the chemical composition of deposits and allowed for chemical imaging of the IOL surface. Applied techniques allowed to obtain a new set of information approximating the origin of the sediments’ formation on the surface of the hydrophilic IOLs after Descemet’s stripping endothelial keratoplasty.

Glistening formation in a new hydrophobic acrylic intraocular lens

Background

The formation of fluid-filled microvacuoles, termed glistenings, is a common complication of intraocular lenses (IOLs) made from hydrophobic acrylate. Using our well-established in-vitro laboratory method, we evaluated a new IOL material’s resistance to glistening formation.

Methods

An in-vitro stress test for glistening induction was performed on 20 samples of hydrophobic acrylic IOLs: ten of the new Eyecryl ASHFY600 (Biotech Vision Care, Ahmedabad, India) compared with ten samples of AcrySof IQ SN60WF (Alcon, Fort Worth, USA). The number of microvacuoles per square millimetre (MV/mm²) was evaluated in five sections of each IOL. The results for each model were compared and rated on a modified Miyata Scale for grading glistening severity.

Results

In all cases, glistening number was higher in the central section of the IOL optic than in the periphery. Mean number of MV/mm² was highest in the central part of the AcrySof IQ SN60WF, with 41.84 (±27.67) MVs/mm². The lowest number of glistenings was found in the five sections of the Eyecryl ASHFY600 with 0.52 (±0.24) MVs/mm². Mean value of the Eyecryl ASHFY600 IOL, using the Miyata Scale, was Zero.

Conclusion

In this in-vitro laboratory study, the new hydrophobic acrylic IOL showed a high resistance to microvacuole formation. Results from this in-vitro study suggest that glistening numbers will be low in clinical use in the Eyecryl ASHFY600.

Clinical and material degradations of intraocular lenses: A review

PURPOSE

To review the published scientific literature concerning clinical and material degradations of intraocular lenses after implantation in cataract surgery.

METHODS

A search was undertaken using the following databases: CENTRAL (including Cochrane Eyes and Vision Trials Register; The Cochrane Library: Issue 2 of 12 February 2019), Ovid MEDLINE (R) without Revisions (1996 to February week 2, 2019), Ovid MEDLINE (R) (1946 to February week 2, 2019), Ovid MEDLINE (R) Daily Update 19 February 2019, MEDLINE and MEDLINE non-indexed items, Embase (1980-2019, week 7), Embase (1974-2019, 19 February), Ovid MEDLINE (R) and Epub Ahead of Print, in-Process & Other Non-Indexed Citations and Daily (1946 to 19 February 2019), Web of Science (all years), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrial.gov) and the WHO International Clinical Trials Registry Platform (www.who.int/ictrp/search/en). Only published articles in English were selected. Search terms/keywords included 'IOL' or 'intraocular lens', combined with 'opacification', degradation, glistenings, nanoglistenings, whitening, transmittance, light scatter, discolouration/discoloration, performance, quality, material, biocompatibility, calcification, explantation and ultraviolet/UV radiation. Relevant in-article references not returned in our searches were also considered.

RESULTS

After review of the available articles, the authors included 122 publications in this review, based on the quality of their methodology and their originality. The studies included in this review were randomized controlled trials, cohort studies, case-controlled studies, case series, case reports, laboratory studies and review papers. Differing material degradations of intraocular lenses have been described and their associated pathophysiology studied. Reported anomalies include photochemical alterations, water vacuoles, internal and surface calcific deposits, surface coatings and discolouration. The nature of such changes has been shown to depend on the type of intraocular lenses material used and/or manufacturing processes and storage conditions employed. Changes in the intraocular lens can also be influenced by surgical technique, coexisting ocular pathologies and topical and systemic medications. The clinical significance of these degradations is variable, with some resulting in significant visual disturbance and the need for intraocular lens explantation and others producing only minimal visual impairments. Failure to recognize the precise nature of the problem may lead to unnecessary laser capsulotomy procedures.

CONCLUSION

Clinical degradations of intraocular lenses are uncommon but have been reported following the implantation of intraocular lenses made of differing biomaterials. Their correct identification and thorough investigation to determine the underlying cause is necessary for optimal patient management and the prevention of such problems. Choosing a lens made of a particular material may be important in patients with certain ocular conditions.

Opacification of Akreos Hydrophilic Acrylic Lens After Retinal Detachment Repair with Silicone Oil Tamponade: A Case Report

We report localized opacification of a sclera-fixated Akreos^® hydrophilic acrylic intraocular lens after successful repair of rhegmatogenous retinal detachment with silicone oil tamponade in a nondiabetic patient. No intraoperative lens opacification during air-fluid exchange or lens dislocation was encountered. Granular opacities within the optic were noted at 5 months after surgery, and did not relent to scrubbing with a vitrector during oil removal. Akreos lens opacification under silicone oil is not well documented in the literature. Surgeons must be aware of this potential complication, which is known to occur with various types of hydrophilic acrylic lenses after exposure to air or gas.

Serial intraocular lens opacifications of different designs from the same manufacturer: Clinical and light microscopic results of 71 explant cases

PURPOSE

To report clinical findings and light microscopic results of 71 opacified hydrophilic acrylic intraocular lenses (IOLs).

SETTING

Vivantes Klinikum Neukoelln, Ophthalmology Department, Berlin, Germany.

DESIGN

Retrospective case series.

METHODS

Sixty-three patients (71 eyes) were referred to the clinic because of vision-impairing IOL opacification between December 2012 and September 2016 after routine cataract surgery elsewhere. The explanted IOLs were analyzed with light microscopy at the John A. Moran Eye Center (University of Utah, Salt Lake City, Utah, USA). Medical records were reviewed for visual acuity, comorbidities, and complications. Clinical follow up was 6 months.

RESULTS

Seventy-one opacified 1-piece or 3-piece hydrophilic acrylic IOLs (Lentis) of different designs from 2009 to 2012 (LS-502-1, LS-402-1Y, LS 312-1Y, LS-313-1Y, L-402, L-312) were found. Morphological findings were surface, subsurface, or deep calcifications of the IOL material. Explantation was performed 4 years ± 1.2 (SD) after initial phacoemulsification. The mean patient age was 78.6 ± 8.2 years. Ocular and systemic comorbidities were found without statistical correlation: the most frequent were diabetes, uveitis, and glaucoma. The preoperative mean corrected distance visual acuity changed from 0.63 ± 0.47 logarithm of the minimum angle of resolution (logMAR) to 0.20 ± 0.28 logMAR postoperatively (P < .001).

CONCLUSIONS

Different designs of IOLs by the same manufacturer, implanted between 2009 and 2012, developed late calcification with significant visual loss after routine cataract surgery. No medical, surgical, or ophthalmologic trigger could be determined. A manufacture issue might be the reason for the opacification.

Material Analysis and Optical Quality Assessment of Opacified Hydrophilic Acrylic Intraocular Lenses After Pars Plana Vitrectomy

PURPOSE

Explanted hydrophilic intraocular lenses (IOLs) with clinically significant opacification after pars plana vitrectomy (PPV) were assessed for material change and optical quality, in an in vitro laboratory study.

DESIGN

Retrospective observational case series.

METHODS

Ten opacified IOLs after PPV with intraocular gas injection were analyzed in a laboratory setting. Analyses included evaluation of patients' medical history, optical quality assessment, light microscopy, histologic staining, scanning electron microscopy, and energy dispersive x-ray spectroscopy.

RESULTS

In all 10 IOLs a thin layer of calcium phosphate that had accumulated underneath either the anterior or posterior optical surface in a central circular area of the IOL optic caused the opacification. The calcifications lead to deterioration of the modulation transfer function (MTF) across all spatial frequencies.

CONCLUSION

PPV with instillation of gas into a pseudophakic eye with an acrylic hydrophilic lens seems to increase the risk for secondary calcification irrespective of the manufacturer. In these cases, IOL exchange is the only treatment option available. Since IOL exchange is associated with a high intraoperative complication rate, our results suggest to consider the risk of IOL calcification when implanting hydrophilic acrylic IOLs.

Optical and material analysis of opacified hydrophilic intraocular lenses after explantation: a laboratory study

Background

The opacification of hydrophilic intraocular lenses (IOLs) is a very rare complication in terms of absolute numbers. We report on the analyses of opacified Euromaxx ALI313Y and ALI313 IOLs (Argonoptics, Germany) using light and scanning electron microscopy, X-ray spectroscopy and optical bench analysis.

Methods

Opacified Euromaxx ALI313Y and ALI313 IOLs were explanted after patients presented with a decrease in visual acuity. The explants were sent to our laboratory and examined using light and scanning electron microscopy. The composition of the deposits was analysed using X-ray spectroscopy. The optical quality of the intraocular lens (IOL) was assessed using the OptiSpheric IOL PRO optical bench (Trioptics GmbH Wedel, Germany). Modulation transfer function (MTF) was measured at all spatial frequencies and United States Air Force (USAF) 1951 resolution target pictures were documented.

Results

Macroscopically, the entire optic was opacified in all IOLs. Light and scanning electron microscopy revealed numerous fine, granular, crystalline-like deposits, which were always distributed in a line parallel to the anterior and posterior surfaces of the IOLs. X-ray spectroscopy could prove the deposits consisted of Calcium and Phosphate. Measurements in the optical bench showed deterioration of MTF values at all spatial frequencies and the USAF target pictures demonstrated a significant reduction of brightness as well as resolution with the opacified IOLs.

Conclusions

The calcification of hydrophilic IOLs only occurs rarely. The exact chemical composition of the deposits can be assessed by means of X-ray spectroscopy. Optical quality analysis of the explanted Euromaxx ALI313Y and ALI313 IOLs showed significant reduction of MTF values, which was confirmed by USAF target pictures.

Determination of scattering in intraocular lenses by spectrophotometric measurements

This study presents a method for measuring scattering in explanted intraocular lenses (IOLs). Currently, determining scattering in IOLs is usually performed by Scheimpflug cameras and the results are expressed in the units used by this apparatus. The method we propose uses a spectrophotometer and this makes it possible to measure the total transmission of the IOL by using an integrating sphere; the direct transmission is determined by the double-beam mode. The difference between these two transmissions gives a value of the scattering in percentage values of light lost. In addition, by obtaining the spectral transmission curve, information about the most scattered wavelengths is also obtained. The IOL power introduces errors when directly measured, particularly with high powers. This problem can be overcome if a tailor-made cuvette is used that shortens the distance between the IOL and the condensing lens of the spectrophotometer when the IOL powers are below 24 diopters. We checked the effectiveness of this method by measuring the scattering of three explanted IOLs from cornea donors. This method, however, does not make it possible to ascertain whether the scattering measured is caused by surface light scattering or internal light scattering.

Light scattering and light transmittance in a series of calcified single-piece hydrophilic acrylic intraocular lenses of the same design

PURPOSE

To evaluate light scattering and light transmittance of Ioflex hydrophilic acrylic intraocular lenses (IOLs) explanted because of clinically significant opacification secondary to calcification.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Seven explanted and 8 control Ioflex IOLs were studied. Gross and light microscopy of all the IOLs were performed. Light scattering was measured with a Scheimpflug camera, and light transmittance was assessed with a spectrophotometer. Analyses were performed at room temperature in the hydrated state, and findings of the explanted and control IOLs were compared.

RESULTS

Light scattering was 219.71 computer compatible tape (CCT) ± 2.62 (SD) for explanted IOLs and 4.75 ± 2.50 CCT for controls. The mean light transmittance in the visible light spectrum was 75.94% to 87.25% for explanted IOLs and 97.54% to 98.97% for controls. The most striking finding was variable degrees of light transmittance between 290 nm and 350 nm (ultraviolet-A and B radiation) in the explanted and control IOLs with expiration dates in 2009/2010 but 0% transmittance in this region in all controls with expiration dates in 2011/2012.

CONCLUSIONS

Light scattering was extremely high and transmittance was significantly reduced in calcified IOLs. Differences in transmittance observed in the 290 to 350 nm region between IOLs with different expiration dates were related to use of different hydrophilic acrylic raw material suppliers in the manufacture of the IOLs, highlighting the complexity of IOL calcification investigations.

Akreos Adapt AO Intraocular Lens Opacification: A Case Report

A 79-year-old hyperglycemic patient was referred to the 'Santa Maria delle Croci' Hospital, Ravenna, Italy. He presented with visual impairment in the right eye. Four years ago, he had had an uneventful cataract surgery in the right eye. We observed an opacification of the intraocular lens (IOL) causing significant visual disturbance. The IOL was exchanged. Unfortunately, pathologic analysis was not performed. Patient-related factors such as hyperglycemia and hypertension might have been responsible for the opacification. To our knowledge, there is only one previous report of opacification of the Akreos Adapt AO IOL.

Anterior segment optical coherence tomography in the assessment of postoperative intraocular lens optic changes

PURPOSE

To evaluate the use of anterior segment optical coherence tomography (AS-OCT) to assess postoperative intraocular lens (IOL) optic changes.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

DESIGN

Experimental study.

METHODS

Intraocular lenses explanted because of various complications were used, including poly(methyl methacrylate) (PMMA) IOLs with snowflake degeneration, hydrophilic acrylic IOLs with calcification, a silicone IOL with calcification from an eye with asteroid hyalosis, and hydrophobic acrylic IOLs explanted because of decentration, subluxation, or uveitis-glaucoma-hyphema syndrome. After gross and light microscopy, the IOLs were examined in the dry and hydrated states using AS-OCT. Selected hydrophilic acrylic IOLs were stained for calcium. In-the-bag IOLs in pseudophakic cadaver eyes were also evaluated by AS-OCT before and after explantation to confirm correspondence with the clinical situation.

RESULTS

Intraoptic changes, such as snowflake lesions in PMMA IOLs, calcification in hydrophilic acrylic IOLs, and glistenings in hydrophobic acrylic IOLs, could be imaged by AS-OCT. The method was also helpful in analyzing the location and density. However, in cases of more superficial changes, unless the lesions/deposits were present on the optic surface with an extension to the optic substance of at least 0.1 mm, they could not be clearly differentiated from the overall outline of the IOL surface.

CONCLUSIONS

Anterior segment OCT may be helpful in assessing the presence, location, and density of intraoptic changes, avoiding a misdiagnosis of IOL opacification and the performance of unnecessary procedures, such as posterior capsulotomy or vitrectomy.

Magnesium deficiency: does it have a role to play in cataractogenesis?

Magnesium is one of the most important regulatory cation involved in several biological processes. It is important for maintaining the structural and functional integrity of vital ocular tissues such as lens. Presence of high magnesium content especially in the peripheral part of lens as compared to aqueous and vitreous humor has been observed. Magnesium plays significant role as a cofactor for more than 350 enzymes in the body especially those utilizing ATP. Membrane associated ATPase functions that are crucial in regulating the intracellular ionic environment, are magnesium-dependent. Moreover, the enzymes involved in ATP production and hydrolysis are also magnesium-dependent. Magnesium deficiency by interfering with ATPase functions causes increased intracellular calcium and sodium and decreases intracellular potassium concentration. Furthermore, magnesium deficiency is associated with increased oxidative stress secondary to increased expression of inducible nitric oxide synthase and increased production of nitric oxide. Thus the alterations in lenticular redox status and ionic imbalances form the basis of the association of magnesium deficiency with cataract. In this paper we review the mechanisms involved in magnesium homeostasis and the role of magnesium deficiency in the pathogenesis of cataract.

Experimental investigation on mechanism of hydrophilic acrylic intraocular lens calcification

PURPOSE

To construct a model simulating intraocular lens (IOL) opacification attributable to the formation of calcium phosphate deposits and to investigate the kinetics of deposit formation.

DESIGN

Prospective laboratory investigation.

METHODS

SETTING

Department of Ophthalmology, Medical School and Department of Chemical Engineering, Laboratory of Inorganic and Analytical Chemistry, University of Patras, Greece.

STUDY POPULATION

Three hydrophilic acrylic IOLs (26% water content) were placed inside a 10-mL double-walled thermostated reactor simulating the anterior chamber. Simulated aqueous humor was injected continuously into the reactor using a pump with variable speed.

OBSERVATION PROCEDURES

The observation of IOLs was carried out in situ daily by optical microscopy. Scanning electron microscopy and energy-dispersive radiographic spectroscopy were used for the identification of the morphologic features and the composition of the deposits.

RESULTS

The lenses were removed and inspected 5, 9, and 12 months after the initiation of the experiment. Investigation showed deposits of calcium phosphate crystallites in the interior of opacified IOLs. However, these deposits were not observed on the surface of the IOLs.

CONCLUSIONS

In agreement with earlier reports by our group and in the literature, IOL opacification is the result of calcification. It is suggested that the surface hydroxyl groups of the polyacrylic polymeric components of the IOLs are capable of inducing surface nucleation and crystal growth of calcium phosphates. However, most important is the finding that the calcification of IOLs is initiated from their interior through the development of sufficiently high local supersaturation, realized through the diffusion of calcium and phosphate ions.

Spectroscopic study of explanted opacified hydrophilic acrylic intraocular lenses

PURPOSE

To report a detailed spectroscopic analysis of explanted hydrophilic acrylic intraocular lenses (IOLs) that were removed because of postoperative opacification of the lens optic.

METHODS

Thirteen Hydroview H60M (Bausch & Lomb Surgical) IOLs were explanted from 13 different patients on average 56 months after phacoemulsification and IOL implantation. All patients had decreased visual acuity because of a fine granularity of the optical surface of the IOLs. The surface was investigated by gross, microscopic, histochemical and scanning electron microscopic analysis, and the elemental composition of the opacified IOLs was determined by X-ray fluorescence spectroscopy (XRF). The spectrograms were compared to three different originally packed and never-implanted hydrophilic acrylic IOLs.

RESULTS

Light and scanning electron microscopy of the optical surface of explanted IOLs revealed multiple fine granular deposits varying in size and shape that were positive for alizarin red. XRF confirmed that the explanted IOLs contained not only the previously reported calcium and phosphorous (calcium apatite), chlorine, silicone, sodium, aluminum and magnesium but also iron, sulfur, potassium as well as lesser amounts of iodine, zinc, strontium and yttrium.

CONCLUSION

This is the first spectroscopic analysis determining the content of more than 10 elements of explanted and originally packed never-implanted hydrophilic acrylic IOLs. The possible origin of the different elements obtained from the spectrograms and their implications are discussed.

Opacification of the optic of an Akreos Adapt intraocular lens

A 60-year-old diabetic patient transferred to our retina clinic for a regular follow-up for diabetic retinopathy. He had uneventful cataract surgery at the time of pars plana vitrectomy in the right eye due to diabetic retinopathy at a private ophthalmologic hospital. Six months after the surgery, neovascular glaucoma with hyphema developed in the right eye and an Ahmed valve was implanted at our hospital. Ten months after cataract surgery, we found opacification of the intraocular lens (IOL) which was causing significant visual disturbance. At the time, the best corrected visual acuity (BCVA) in the right eye was hand motion. The IOL was explanted 45 months after the operation. Five months after explantation, the BCVA was 0.06. Unfortunately, pathologic analysis was not performed. Patient-related factors such as an anterior chamber reaction caused by hyphema might have been responsible for the opacification. To our knowledge, there are no previous reports of opacification of the Akreos Adapt IOL.

Complications of foldable intraocular lenses requiring explantation or secondary intervention--2007 survey update

The tenth annual survey of complications associated with foldable intraocular lenses (IOLs) requiring explantation or secondary intervention was sent to members of the American Society of Cataract and Refractive Surgery and the European Society of Cataract and Refractive Surgeons. Preoperative data about visual acuity, patient signs and symptoms, and complications requiring IOL removal were evaluated. Complications were then tabulated for each of the following major foldable IOL groups: 1-piece (plate) silicone, 1-piece hydrophobic acrylic with haptics, 3-piece silicone, 3-piece hydrophobic acrylic, 3-piece hydrophilic acrylic (hydrogel), 3-piece unknown, multifocal acrylic, and multifocal silicone. One hundred forty-two surveys were returned for evaluation. Dislocation/decentration, incorrect IOL power, glare/optical aberrations, and IOL calcification were the most common reasons for removing foldable IOLs. Good surgical technique, accurate IOL power measurements, and high manufacturing standards for foldable IOL materials and designs are the most important factors in preventing complications.

Opacification of hydrophilic acrylic intraocular lens attributable to calcification: investigation on mechanism

PURPOSE

To identify the nature and to investigate the biochemical mechanisms leading to late opacification of implanted hydrophilic acrylic intraocular lenses (IOLs).

DESIGN

Retrospective laboratory investigation.

METHODS

setting: Department of Ophthalmology, Medical School, Department of Chemical Engineering, Laboratory of Inorganic and Analytical Chemistry, University of Patras and FORTH-ICEHT, Greece. study population: Thirty IOLs were explanted one to 12 years postimplantation attributable to gradual opacification of the lens material. observation procedures: Materials analysis was done using scanning electron microscopy (SEM) equipped with a microanalysis probe (EDS), confocal microscopy, x-ray diffraction (XRD), and Fourier transform infrared (FTIR) for the identification of the substances involved in the opacified lenses.

RESULTS

SEM investigation showed plate-like as well as prismatic nanoparticle deposits of calcium phosphate crystallites on the surface and in the interior of opacified IOLs. The plate-like deposits exhibited morphology and particle size typical for octacalcium phosphate (OCP), while the respective characteristics of the prismatic nanocrystals were typical of hydroxyapatite (HAP). EDS analysis confirmed the chemical composition of the deposits. Aqueous humor analysis showed that the humor is supersaturated with respect to both OCP and HAP, favoring the formation of the thermodynamically more stable HAP, while the formation and kinetic stabilization of other transient phases is also very likely. In vitro experiments using polyacrylic materials confirmed the clinical findings.

CONCLUSIONS

Hydrophilic acrylic IOLs' opacification may be attributed to the deposition of calcium phosphate crystallites. HAP is the predominant crystalline phase of these crystallites. Surface hydroxyl groups of the polyacrylic materials facilitate surface nucleation and growth.

Characterization of the calcification of cardiac valve bioprostheses by environmental scanning electron microscopy and vibrational spectroscopy

Bioprosthetic heart valve tissue and associated calcification were studied in their natural state, using environmental scanning electron microscopy (ESEM). Energy dispersive X-ray micro-analysis, X-ray diffraction, Fourier-transform infrared and Raman spectroscopy were used to characterize the various calcific deposits observed with ESEM. The major elements present in calcified valves were also analyzed by inductively coupled plasma-optical emission spectroscopy. To better understand the precursor formation of the calcific deposits, results from the elemental analyses were statistically correlated. ESEM revealed the presence of four broad types of calcium phosphate crystal morphology. In addition, two main patterns of organization of calcific deposits were observed associated with the collagen fibres. Energy dispersive X-ray micro-analysis identified the crystals observed by ESEM as salts containing mainly calcium and phosphate with ratios from 1.340 (possibly octacalcium phosphate, which has a Ca/P ratio of 1.336) to 2.045 (possibly hydroxyapatite with incorporation of carbonate and metal ion contaminants, such as silicon and magnesium, in the crystal lattice). Raman and fourier-transform infrared spectroscopy also identified the presence of carbonate and the analyses showed spectral features very similar to a crystalline hydroxyapatite spectrum, also refuting the presence of precursor phases such as beta-tricalcium phosphate, octacalcium phosphate and dicalcium phosphate dihydrate. The results of this study raised the possibility of the presence of precursor phases associated with the early stages of calcification.

Causes of intraocular lens opacification or discoloration

Various pathologic processes may lead to clinically significant opacification or discoloration of the optic component of intraocular lenses (IOLs) manufactured from different biomaterials and in different designs. Factors such as the patient's associated conditions, the manufacturing process, the method of IOL storage, the surgical technique and adjuvants, or a combination of these may be involved. The complication may be observed intraoperatively or postoperatively from a few hours after implantation to many years after surgery, depending on the processes involved. Based on a review of the literature as well as our own laboratory analyses, the following types of processes were identified: formation of deposits/precipitates on the IOL surface or within the IOL substance; opacification by excess influx of water in hydrophobic materials; direct discoloration by capsular dyes or medications; coating by substances such as ophthalmic ointment and silicone oil; and a slow, progressive degradation of the IOL biomaterial.

Postoperative surface deposits on intraocular lenses in children

PURPOSE

To report the clinicopathologic features of 4 intraocular lenses (IOLs) composed of 3 different hydrophilic biomaterials explanted from children who had postoperative opacification of the IOL optic.

SETTING

David J Apple, MD, Laboratories for Ophthalmic Devices Research, John A. Moran Eye Center, Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, Utah, USA.

METHODS

The IOLs were explanted 20, 11, 22, and 25 months postoperatively from children aged 10, 3, 36, and 20 months old, respectively, at IOL implantation. Clinical data were obtained to correlate the findings with possible associated risk factors. The explanted IOLs were examined by gross and light microscopy. They were further analyzed with a stain for calcium, alizarin red 1%. Scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) were also performed.

RESULTS

The primary reason for cataract surgery in Case 1 and Case 2 was persistent hyperplastic primary vitreous (PHPV); 1 patient received a B-Lens IOL (Hanita) and the other a Centerflex IOL (Rayner). The primary reason in Case 3 was familial bilateral congenital cataract and in Case 4, rubella cataract; both patients received a Hydroview IOL (Bausch & Lomb). All 4 IOLs had surface deposits on the optic, but the morphology of the deposits on the B-Lens and Centerflex IOLs was different than that in previously reported cases. The deposits in all four cases stained positive with alizarin red and consisted of calcium and phosphorus when imaged with EDS.

CONCLUSIONS

Calcified deposits on 2 Hydroview IOLs explanted from children were similar to those seen in adults with the same IOL. The deposits on the B-Lens and Centerflex IOLs were probably secondary to a breakdown of the blood-aqueous barrier caused by preexisting PHPV.