Clinical results of hydrogel lens implantation

Delayed surface opacification of a hydroview intraocular lens

The insertion of an intraocular lens during cataract surgery is routine but delayed opacification of hydrophilic foldable intraocular lenses (IOLs) has been increasingly noticed as a late post-operative complication. Such opacification may present with reduced visual acuity and can be diagnosed with slitlamp biomicroscopy. Lens explantation may be required. We report an 89-year-old female presenting with opacification of a Hydroview IOL and correlate the clinical findings of the lens in situ with the light microscopy of the explanted lens, as well as transmission electron microscopy (TEM), scanning electron microscopy (SEM) and elemental analysis. Pathological analysis of an explanted IOL may assist in a better understanding of the condition and may become relevant in medico-legal proceedings.

A Hydrophobically Modified Bioadhesive Polymeric Carrier for Controlled Drug Delivery to Mucosal Surfaces

We have synthesized and studied a new type of polymeric drugcarrier based on hydrophobically modified bioadhesive graft copolymers. Two different hydrophobic oligomers, an oligo(methyl methacrylate) (oMMA) and a random co-oligomer of MMA with hydroxyethyl methacrylate (HEMA) were separately grafted to a polyacrylic acid (PAAc) backbone. This system forms a physical hydrogel network containing hydrophobic domains. The in vitro release of hydrophilic drugs such as theophylline and a model protein drug, lysozyme, and moderately hydrophobic drugs such as propranolol hydrochloride has been investigated. The results suggest the existence of a macroporous structure at higher levels of oMMA grafting. The introduction of HEMA into the graft chain slowed the release of propranolol hydrochloride, which suggests that the release rate of a moderately hydrophobic drug could be controlled by adjusting the hydrophobicity of the grafted chain. In the case of release of lysozyme, a cationic protein used as a model protein drug, the graft copolymers of oMMA retained increasing amounts of the protein as the graft level increased. This supported the concept of formation of a macroporous structure at higher MMA graft levels, with a cationic protein such as lysozyme being attracted to and bound by the hydrophobic domain interfacial regions. The introduction of as little as 10 mol% of HEAIA into the graft chain gave rise to rapid and complete release of lysozyme.

A synthetic fibrin cross-linking polymer for modulating clot properties and inducing hemostasis

Clotting factor replacement is the standard management of acute bleeding in congenital and acquired bleeding disorders. We present a synthetic approach to hemostasis using an engineered hemostatic polymer (PolySTAT) that circulates innocuously in the blood, identifies sites of vascular injury, and promotes clot formation to stop bleeding. PolySTAT induces hemostasis by cross-linking the fibrin matrix within clots, mimicking the function of the transglutaminase factor XIII. Furthermore, synthetic PolySTAT binds specifically to fibrin monomers and is uniformly integrated into fibrin fibers during fibrin polymerization, resulting in a fortified, hybrid polymer network with enhanced resistance to enzymatic degradation. In vivo hemostatic activity was confirmed in a rat model of trauma and fluid resuscitation in which intravenous administration of PolySTAT improved survival by reducing blood loss and resuscitation fluid requirements. PolySTAT-induced fibrin cross-linking is a novel approach to hemostasis using synthetic polymers for noninvasive modulation of clot architecture with potentially wide-ranging therapeutic applications.

Synthesis and Postpolymerization Modification of Thermoresponsive Coatings Based on Pentaerythritol Monomethacrylate: Surface Analysis, Wettability, and Protein Adsorption

Properties of novel temperature-responsive hydroxyl-containing poly(pentaerythritol monomethacrylate) (PPM) coatings, polymerized from oligoperoxide grafted to glass surface premodified with (3-aminopropyl)triethoxysilane, are presented. Molecular composition, chemical state, thickness, and wettability are examined with time of flight-secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), ellipsometry, and contact angle measurements, respectively. Temperature-induced changes in hydrophobicity of grafted PPM brushes are revealed by water contact angle and ellipsometric measurements. Partial postpolymerization modification of hydroxyl groups (maximum a few percent), performed with acetyl chloride or pyromellitic acid chloride, is demonstrated to preserve thermal response of coatings. Adsorption of bovine serum albumin to PPM brushes, observed with fluorescence microscopy, is higher than on glass in contrast to similar hydroxyl-containing layers reported as nonfouling. Enhanced and temperature-controlled protein adsorption is obtained after postpolymerization modification with pyromellitic acid chloride.

Preparation of well-defined poly(2-hydroxyethyl methacrylate) macromonomers via atom transfer radical polymerization

A series of six near-monodisperse methacrylic macromonomers is prepared via atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate using a tertiary amine-functionalized initiator at 50 °C, followed by quaternization with excess 4-vinylbenzyl chloride at 20 °C. GPC analyses indicate polydispersities of around 1.20 and their mean degrees of polymerization (DP) range from 20 to 70, as judged by both (1) H NMR and UV spectroscopy. The former technique is more convenient but the latter proved more accurate for the higher DP values, provided that an appropriate model compound is utilized for calibration. Finally, these new macromonomers are used to prepare sterically stabilized polystyrene latexes with relatively narrow size distributions via alcoholic dispersion polymerization.

PHEMA hydrogels modified through the grafting of phosphate groups by ATRP support the attachment and growth of human corneal epithelial cells

Converting the surface of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel into a cell-adhesive surface has been successfully achieved through a method based on atom transfer radical polymerization (ATRP) grafting. Following activation of the surface hydroxyl groups of PHEMA by bromination, surface-initiated ATRP of mono(2-methacryloyloxyethyl) phosphate (MMEP) was conducted in a methanol-water system with Cu(I)Br as catalyst at room temperature. The conversion of PHEMA hydroxyl groups to brominated isobutyryl groups and the occurrence of grafting of PMMEP were confirmed by infrared and X-ray photoelectron spectroscopies. Cell attachment experiments were conducted by culturing human corneal limbal epithelial cells on the PMMEP-grafted PHEMA, and on unmodified PHEMA and tissue culture plastic for comparison. The results showed that the grafted PMMEP was homogeneously distributed, and the phosphate groups appeared to significantly promote the attachment, spreading and growth of cells, at a level comparable to the tissue culture plastic.

Analysis of aqueous humor calcium and phosphate from cataract eyes with and without diabetes mellitus

Purpose

To compare the levels of calcium and phosphorus in the aqueous humor and serum of diabetics and non-diabetics.

Methods

We divided patients into two groups: seventy-six non-diabetic cataract patients and fifty-two diabetic cataract patients. The diabetic group was divided again into three subgroups: twenty-six patients with no diabetic retinopathy, thirteen patients with non-proliferative diabetic retinopathy, and thirteen patients with proliferative diabetic retinopathy. The authors compared the levels of calcium and phosphorus in the serum and aqueous humor of cataract patients. Statistic analysis was performed to form two comparisons: 1) a comparison between non-diabetics and diabetics and 2) a comparison among non-diabetics and the three subgroups of diabetics.

Results

In serum, calcium levels did not statistically differ between non-diabetics and diabetics. The phosphorus level was also not significantly different. In the aqueous humor, however, while calcium levels did not differ significantly, the phosphorus levels in diabetics were considerably higher than those in non-diabetics. When non-diabetics were compared to the three diabetic subgroups, calcium levels did not differ in serum or aqueous humor, but the phosphorus levels in diabetics with proliferative diabetic retinopathy were significantly higher than those in non-diabetics, diabetics without diabetic retinopathy, and diabetics with non-proliferative diabetic retinopathy.

Conclusions

The level of phosphorus in the aqueous humor and serum of diabetics was significantly increased, especially in diabetics with proliferative diabetic retinopathy. This result may be related to hydrophilic acrylic IOL opacification. Future studies regarding the pathogenic role of a high concentration of aqueous humor and serum phosphorus are required.

Comparison of the Long-term Clinical Results of Hydrophilic and Hydrophobic Acrylic Intraocular Lenses

This study was performed to compare the incidence of posterior capsular opacity (PCO) and refractive errors between hydrophilic (ACR6D, Corneal) and hydrophobic (MA60BM, AcrySof) acrylic intraocular lenses (IOLs) over a 3-year follow-up after phacoemulsification surgery. The patients with AcrySof implanted in one eye and Corneal in the other eye were categorized as Group 1 (n=28), while those with one or both eyes implanted with IOLs of the same kind were categorized as Group 2 (AcrySof, n=90; Corneal, n=95). Refractive errors were evaluated at 3 months and 3 years postoperatively. The incidence of visually significant PCO was investigated 3 years postoperatively. Postoperative refractive values at 3 months were not significantly different between the two groups. However, refractive values at 3 years were significantly different between two IOLs in both groups [AcrySof -0.37+/-0.43D, Corneal -0.62+/-0.58D in Group 1 (p=0.04); AcrySof -0.38+/-0.52, Corneal -0.68+/-0.54 in Group 2 (p<0.01)]. The incidence of visually significant PCO was 14% and 32% in Group 1, and 13% and 28% in Group 2, for the AcrySof and Corneal implants, respectively. The incidence of visually significant PCO of hydrophilic acrylic IOLs was higher than that of hydrophobic acrylic IOLs in the 3-year follow-up. The postoperative 3-year refractive value of Corneal showed myopic shift.

Calcification postopératoire des lentilles intraoculaires acryliques hydrophiles : aspects cliniques et pathologiques

PURPOSE

The aim of this study was to evaluate the clinical aspects of ten eyes with calcified hydrophilic acrylic intraocular lenses and pathological data obtained from seven explanted lenses.

MATERIAL AND METHODS

Forty-seven eyes of 40 patients received the same implant in the first 6-month period of 2001. Ten eyes showed intraocular lens opacification detected 6-18 months after the operation: seven lenses were explanted and three were left in place because they were not causing a decrease in visual acuity or glare at light. Five of ten eyes were diabetic. The explanted lenses were examined under the light microscope and the electron microscope. The elemental analysis of the lens surfaces was made by energy dispersive spectrometry.

RESULTS

The light microscopy showed an irregular surface covered by a gray-white opacity. The electron microscopy detected multiple granulations on the front and back surfaces of the lenses including some portions of the haptics. The size and density of these granulations were smaller on the back surface. The energy dispersive spectrometry showed the presence of calcium and phosphate on both surfaces. The spikes of calcium and phosphate were smaller for the back surface of the lenses.

DISCUSSION

Calcification was predominantly seen on the surfaces that were in contact with aqueous not covered with anterior capsule. Half (5/10) of the cases were diabetic even though 18% of all patients receiving this lens were diabetic. The presence of diabetes is very common in other series. These data suggest the role of a metabolic factor influencing the milieu of the lens in this calcification process.

CONCLUSION

Calcification of the hydrophilic acrylic lenses is a relatively serious complication, but the conditions leading to its appearance and the physiopathology have not yet been fully elucidated. The surgeon should be very careful in the choice of the intraocular lens to implant, and even more so if the patient is diabetic.

Anterior capsule contraction and intraocular lens decentration and tilt after hydrogel lens implantation

AIM

To prospectively investigate changes in the area of the anterior capsule opening, and intraocular lens (IOL) decentration and tilt after implantation of a hydrogel IOL.

METHODS

100 patients underwent implantation of a hydrogel IOL in one eye and an acrylic IOL implantation in the opposite eye. The area of the anterior capsule opening, and the degree of IOL decentration and tilt were measured using the Scheimpflug videophotography system at 3 days, and at 1, 3, and 6 months postoperatively.

RESULTS

The mean anterior capsule opening area decreased significantly in both groups. At 6 months postoperatively, the area in the hydrogel group was significantly smaller than that in the acrylic group. The mean percentage of the area reduction in the hydrogel group was also significantly greater than that in the acrylic group, being 16.9% in the hydrogel group and 8.8% in the acrylic group. In contrast, IOL decentration and tilt did not progress in either group. No significant differences were found in the degree of IOL decentration and tilt throughout the follow up period.

CONCLUSIONS

Contraction of the anterior capsule opening was more extensive with the hydrogel IOL than with the acrylic IOL, but the degree of IOL decentration and tilt were similar for the two types of lenses studied.

Visually significant calcification of hydrogel intraocular lenses necessitating explantation

PURPOSE

To report two cases of HydroviewR (Storz H60M) hydrogel intraocular lens (IOL) opacification necessitating explantation. To analyse the explanted lenses and compare them with a new lens in order to determine the cause of opacification.

METHODS

Two cases are presented. Both patients complained of subjective decreases in vision approximately 1 year following uneventful cataract extraction and implantation of hydrogel lenses by the same experienced surgeon in the same institution. The reduced contrast sensitivity was thought to be due to failure of the hydrogel lenses which appeared opacified at the slit-lamp. They were then exchanged for acrylic lenses. Pre- and postoperative contrast sensitivity testing was performed using the VectorvisionR CSV-1000E instrument. A detailed comparative analysis of the opacified explanted lenses and a new lens was undertaken. This included surface microscopy, infrared spectral analysis, X-ray elemental analysis, scanning electron microscopy, and electron microscopy of lens slices.

RESULTS

Lens exchange resulted in an improvement in subjective visual acuity (VA) and in objective contrast sensitivity testing. Analysis revealed deposits of calcium phosphate (hydroxyapatite) on the explanted lens' surfaces.

CONCLUSIONS

The surface of the HydroviewR H60M intraocular lens is subject to opacification as a result of calcium phosphate (hydroxyapatite) deposition, thereby limiting the patient's visual outcome, and in some cases necessitating explantation. The reason for surface calcification requires further study.

12 year results of a prospective trial comparing poly(methyl methacrylate) and poly(hydroxyethyl methacrylate) intraocular lenses

PURPOSE

To compare long-term biocompatibility of single-piece poly(methyl methacrylate) (PMMA) and poly(hydroxyethyl methacrylate) (P-HEMA) intraocular lenses (IOLs).

SETTING

District General Hospital, United Kingdom.

METHODS

In a prospective trial of 250 eyes that had uncomplicated extracapsular cataract extraction, 2 groups of 125 eyes each were matched for age and sex. One group received single-piece looped PMMA IOLs and the other, single-piece solid-haptic P-HEMA IOLs. In all eyes, the IOLs were implanted in the capsular bag at the time of surgery using the envelope technique.

RESULTS

Twelve years after surgery, 75 eyes were available for examination. In the PMMA group (40 eyes), 50% had a visual acuity of 20/20 and 50% had intact capsules, many of them with a degree of fibrosis. In the P-HEMA group (35 eyes), 71% had an acuity of 20/20 and 80% had intact capsules (P = .0085).

CONCLUSION

In the long term, biocompatibility was better in the P-HEMA group than in the PMMA group.

A systematic overview of the incidence of posterior capsule opacification

OBJECTIVE

Reported rates of posterior capsule opacification (PCO) vary widely and are based on various definitions of PCO, varying lengths and intervals of follow-up, and the use of different surgical techniques, intraocular lens (i.o.l.) designs, and methods of IOL implantation. This study was designed to obtain a more precise overall estimate of the incidence of PCO and to explore factors that might influence the rate of PCO development.

DESIGN

A meta-analysis.

METHODS

Published articles were selected for study based on a computerized MEDLINE search of the literature and a manual search of the bibliographies of relevant articles. Articles meeting selected inclusion criteria were reviewed systematically, and the reported data were abstracted and synthesized using the statistical techniques of meta-analysis.

MAIN OUTCOME MEASURE

Pooled estimates of the proportion of eyes developing PCO at three postoperative timepoints--1 year, 3 years, and 5 years--were measured.

RESULTS

There is significant heterogeneity among published rates of PCO. The overall pooled estimates (95% confidence limits) of the incidence of PCO were 11.8% (9.3%-14.3%) at 1 year, 20.7% (16.6%-24.9%) at 3 years, and 28.4% (18.4%-38.4%) at 5 years after surgery. There is no evidence of a significant decline in PCO incidence during the study period.

CONCLUSIONS

Visually significant PCO develops in more than 25% of patients undergoing standard extracapsular cataract extraction or phacoemulsification with posterior chamber intraocular lens implantation over the first 5 years after surgery. Patient characteristics, surgical techniques, and differences in research design and reporting may account for some of the variability in reported rates. However, no specific factors were identified in the authors' analysis. More precise estimates of incidence and identification of risk factors for PCO will depend on the development of a standardized measurement of PCO and wider adoption of more rigorous study methodology.

Posterior capsule opacification and capsulotomy rates with taco-style hydrogel intraocular lenses

PURPOSE

To evaluate posterior capsule opacification (PCO) formation and neodymium: YAG (Nd:YAG) laser capsulotomy results in eyes with an logel intraocular lens (IOL).

SETTING

First University Hospital, Vienna, Austria.

METHODS

A retrospective study was done of 108 eyes with one of three types of an logel IOL that had decreased vision from PCO and required posterior capsule discission.

RESULTS

In general, in eyes with sulcus-placed IOLs, a Soemmering's ring formed and the capsulorhexis rim tightly adhered to the posterior capsule, sealing the capsular bag periphery. Elschnig pearls had broken the barrier, invading the retrolental space. In eyes with bag-placed IOLs, there was a gap between the IOL and posterior capsule in which Elschnig pearls had accumulated. This gap frequently extended beneath the flanges to the periphery of the capsular bag, allowing residual lens epithelial cells to proliferate and migrate centrally.

CONCLUSION

The logel lenses led to a high incidence of regeneratory PCO within the gap between the lens and capsule that might be the result of the properties of the lens' hydrogel material rather than its design.

Correlation between intraocular lens hydrophilicity and anterior capsule opacification and aqueous flare

PURPOSE

To study the correlation between a basic parameter of intraocular lens biocompatibility, hydrophilicity, and two clinical parameters, postoperative inflammation and anterior capsule opacification.

SETTING

Miyake Eye Hospital, Nagoya, Japan.

METHODS

Three combinations of IOLs that were identical in shape but had distinct contact angles of water were used in this prospective double-masked study: (1) experimental comparison of collagen type IV and poly(methyl methacrylate) (PMMA) IOLs in rabbit eyes; (2) clinical comparison of heparin-surface-modified and PMMA IOLs; (3) clinical comparison of three foldable IOLs, silicone, acrylic, and memory. One of the two IOLs being compared in each situation was randomly assigned to both eyes of each animal or patient. At 1 and 3 months postoperatively, the degree of anterior capsule opacification and the amount of flare in the anterior chamber were determined.

RESULTS

In all three comparative situations, greater postoperative inflammation and more rapid anterior capsule opacification was seen in the eyes with hydrophobic IOLs.

CONCLUSION

There was a correlation between the hydrophilicity of an IOL and the severity of postoperative inflammation and the speed of anterior capsule opacification.

Four year follow-up of the MemoryLens

PURPOSE

To determine whether the long-term results of implantation of thermoelastic MemoryLens intraocular lenses (IOLs) are comparable to those of conventional poly(methyl methacrylate) (PMMA) IOLs.

SETTING

St. Elisabeth Hospital, Dillingen, Germany.

METHODS

This retrospective study compared visual acuity, astigmatism, lens decentration, biocompatibility, and posterior capsule opacification in 36 eyes with a MemoryLens with those in 36 eyes with a conventional PMMA IOL over 4 years. The MemoryLenses were implanted in 1991 after cataract extraction by phacoemulsification.

RESULTS

Four years postoperatively, best corrected visual acuity was 20/20 to 20/25 in 63.9% of the MemoryLens group and 55.6% of the PMMA group. Mean astigmatism was 0.84 diopters (D) in the MemoryLens group and 1.20 D in the PMMA group. No cellular precipitates, as evaluated by biomicroscopy, or lens decentration greater than 0.5 mm were found in either group. Posterior capsule opacification, which developed in 22.2% in the MemoryLens group and 38.9% in the PMMA group, was treated with a neodymium: YAG laser capsulotomy.

CONCLUSION

The MemoryLens allows small incision cataract surgery and long-term results that compare favorably with those of PMMA IOLs.

Simultaneous bilateral cataract extraction in the UK

AIMS/BACKGROUND

Simultaneous bilateral extracapsular cataract extraction (SBCE) is not routinely performed in the developed world. This study investigated the safety and efficacy of this procedure as performed in the UK.

METHODS

A review of 319 consecutive patients (638 eyes) who underwent SBCE with posterior chamber intraocular lens implantation is presented.

RESULTS

The incidence of intraoperative complications was 7.7%. These included posterior capsule rupture (0.8%) and vitreous loss (0.3%). Postoperative complications were seen in 8.7% of operated eyes and included iris prolapse (0.3%) and raised intraocular pressure (3.0%). Endophthalmitis occurred in one eye (0.15%). There were no major bilateral complications, and, in particular, no cases of bilateral endophthalmitis. Final visual acuities compared favourably with reports for unilateral surgery. Eighty two per cent achieved a final visual acuity of 6/12 or better, and 41% tested 6/6 or better.

CONCLUSION

This study illustrates that SBCE is not associated with an increased incidence of complications and that the visual results are good. Where indicated, and under strict surgical protocol, this procedure is safe.

Lens capsule opacification in aphakic and pseudophakic eyes

BACKGROUND

Posterior capsule opacification (PCO) is the most common complication of lens extraction. Although intraocular lenses (IOLs) are thought to inhibit capsule opacification, the mechanisms by which they do this are poorly understood. This study was done to determine the effects of pseudophakia on secondary cataract and PCO in experimentally lentectomized dogs.

METHODS

Twenty-four normal dogs were bilaterally lentectomized by phacoemulsification and unilaterally implanted with a plano-convex polymethylmethacrylate IOL. Secondary cataracts and capsule opacification were evaluated at weeks 1, 2, 4, 10, 14, and 20 after surgery by retrolillumination photography, light microscopy, and scanning and transmission electron microscopy.

RESULTS

The pattern of secondary cataract and PCO in dogs was found to be similar to that in other animal species. Production of new lens material was prominent in the equatorial region, and PCO resulted from fibrous metaplasia of lens epithelium and subsequent capsular fibrosis and wrinkling. The presence of an IOL did not prevent the posterior migration of epithelium, nor did it prevent fibrous metaplasia. The presence of an IOL did, however, minimize the capsule-wrinkling effects of fibroplasia and limit the space available for lentoid formation.

CONCLUSION

In pseudophakic eyes, IOLs influence secondary cataract formation by limiting the space available for lentoid formation and by maintaining a linear scaffolding for lens epithelial fibrous metaplasia.

Melanin-containing hydrogel intraocular lenses: a histopathological study in animal eyes

Poly(2-hydroxyethyl methacrylate) hydrogel intraocular lenses, containing adrenochrome-melanin, were manufactured and implanted in animal eyes in order to assess the effect of melanin upon (a) biocompatibility of implants with the eye tissues, and (b) fibrous proliferation of lens epithelium responsible for the opacification of the posterior capsular membrane. An equal number of control lenses were also implanted. The animals were followed up for durations up to two years, and a detailed histopathological examination of the eyes was performed subsequent to their enucleation. The postoperative complications were minor and probably caused by surgical trauma. The study failed to give any indication of the postulated antiproliferative activity of adrenochrome-melanin since minimal capsular opacification occurred in the operated eyes, regardless of the presence of melanin.

Preliminary results with a new hydrogel intraocular lens

The merits of hydrogel as an intraocular lens material are that it is soft, foldable, hydrophilic, autoclavable and more biocompatible than polymethylmethacrylate (PMMA). Twenty eyes were implanted with a new hydrogel design after phacoemulsification. Fifty per cent achieved a corrected acuity of 6/5 and all achieved 6/9 with correction. Results confirmed an excellent biocompatibility of the material but two cases of asymptomatic decentration indicated the occasional instability within the capsular sac. For best results the hydrogel requires an intact capsulorrhexis with a diameter between 4.5 and 5.0 mm.

Assessment of the blood-aqueous barrier by fluorophotometry following poly(methyl methacrylate), silicone, and hydrogel lens implantation in rabbit eyes

Intraocular lenses of silicone, hydrogel, or acrylic materials that can be implanted through small incisions are being proposed as an alternative to conventional poly(methyl methacrylate) lenses. The potential of each of these materials to stimulate intraocular inflammation is important in their selection as an implantable material. To investigate the potential of each material, we assessed by clinical slitlamp examination, fluorophotometry, and histopathology the inflammatory response induced in the rabbit eye following phacoemulsification and implantation of hydrogel, silicone, or poly(methyl methacrylate) intraocular lenses. All lenses seemed to be equally well tolerated. In general, the degree of inflammation seen clinically decreased over the four-month study; however, anterior segment fluorophotometry showed continued mild interruption of the blood-aqueous barrier in all lens groups. Fluorophotometry is a sensitive method to assess persistent subclinical anterior segment inflammation.

Combined small incision phacoemulsification and trabeculectomy

A method of combined cataract extraction and trabeculectomy is described in which phacoemulsification is performed through a 3.5 mm incision with insertion of a foldable hydrogel lens. This procedure is suitable for most cases in which glaucoma and cataract are coincident. In an initial series of ten patients followed for nine months, all those without additional pathology achieved a corrected visual acuity of 20/40 or better. The maximum induced astigmatism was 0.5 diopters (D), with no change or a reduction in astigmatism in seven patients (70%). Astigmatic shift between week 1 and three months was minimal (average = 0.075 D), with little change thereafter. Intraocular pressures were controlled (< or = 21 mm Hg) without adjunctive medication in all but one of the patients at nine months. This combined procedure preserves the principal advantages of small incision phacoemulsification: low induced astigmatism, early refractive stabilization, and rapid visual rehabilitation. In addition, reducing the extent of tissue dissection may reduce the stimulus to wound healing and early filtration failure.

Posterior capsule opacification

A complication of extracapsular cataract extraction with or without posterior chamber intraocular lens (PC-IOL) implantation is posterior capsule opacification. This condition is usually secondary to a proliferation and migration of residual lens epithelial cells. Opacification may be reduced by atraumatic surgery and thorough cortical clean-up. Clinical, pathological and experimental studies have shown that use of hydrodissection, the continuous curvilinear capsulorhexis and specific IOL designs may help reduce the incidence of this complication. Capsular-fixated, one-piece all-polymethylmethacrylate PC-IOLs with a C-shaped loop configuration and a posterior convexity of the optic are effective. Polymethylmethacrylate loops that retain "memory" create a symmetric, radial stretch on the posterior capsule after in-the-bag placement, leading to a more complete contact between the posterior surface of the IOL optic and the taut capsule. This may help form a barrier against central migration of epithelial cells into the visual axis. Various pharmacological and immunological methods are being investigated but conclusive data on these modalities are not yet available.

A comparison of 141 polymacon (Iogel) and 140 poly(methyl methacrylate) intraocular lens implants

In a prospective controlled trial 290 consecutive patients were randomly allocated a polymacon or a poly(methyl methacrylate) (PMMA) intraocular lens. Early Treatment of Diabetic Retinopathy Study (ETDRS) acuity charts gave similar results with both lenses. However Pelli-Robson contrast sensitivity charts gave a better result with PMMA lenses. Polymacon lenses appeared to remain free of any adhesions after implantation raising the question of long term stability. Four patients experienced problems related to this, three involved total lens dislocation. Seven patients developed early 'fibrin' membranes coating the polymacon lens, of which three were florid.

In vitro cytotoxicity of melanized poly(2-hydroxyethyl methacrylate) hydrogels, a novel class of ocular biomaterials

Due to their ability to absorb ultraviolet and visible radiation, we have proposed the melanized poly(2-hydroxyethyl methacrylate) hydrogels as biomaterials suitable for the manufacture of soft artificial intraocular lenses. Their biocompatibility has not been evaluated so far. In this study, poly(2-hydroxyethyl methacrylate) containing various amounts of adrenochrome-melanin were synthesized and the cytotoxicity of their aqueous extracts was assessed by using four in vitro testing techniques (trypan blue dye exclusion, inhibition of DNA synthesis, lactate dehydrogenase release, and inhibition of cell growth). Assays were based on incubation with human choroidal fibroblasts. By the first three techniques, no cytotoxicity was found in the extracts. The inhibition of cell growth test showed a slight cellular protein loss, however only in the extracts of polymers with high melanin content. The results suggest that the release of potentially toxic agents from melanized hydrogels into an aqueous medium is not significant. However, when an assay in collagen gel was carried out in the presence of specimens of melanized hydrogels, a toxic reaction was clearly revealed. This can be caused by a delayed release of toxic molecules from melanin, or by some other mechanism. The use of melanin-containing polymers as implant materials becomes questionable and further research is necessary.

One year follow-up study on polymetacrylate and hydrogen intraocular lenses

This study includes two selected groups of patients operated for cataract with implantation of either a polymetacrylate (PMMA, Sinskey J-loop, prolene haptics, Mod.102H, Pharmacia) or a soft hydrogel (IO-gel, Alcon) posterior chamber lens. There were 27 patients in the PMMA group and 32 in the hydrogel lens group. The study concludes that after 1 year of observation a comparison between the two groups disclosed no major difference concerning the visual outcome and influence on the ocular tissue. No substantial observations point towards the hydrogel lens as the more biocompatible of the two lenses.

Animal model experimentation using the expansile hydrogel intraocular lens

To determine the biocompatibility of the expansile hydrogel intraocular lens, a two-year animal study was undertaken. After phacoemulsification, hydrogel expansile intraocular lenses were implanted in four Dutch-belted rabbit eyes. Slitlamp examinations revealed minimal anterior chamber reaction and lens synechias. Gross pathology and histology demonstrated hyperplastic residual cortex, but confirmed our clinical impression that the lenses were well tolerated. Electron diffraction energy dispersive X-ray microanalysis revealed deposition of aluminum, silicon, magnesium, and calcium, but there was no evidence of matrix penetration.

Surface analysis of surface-passivated intraocular lenses

We analyzed the surfaces of six different types of poly(methyl methacrylate) intraocular lenses using electron spectroscopy for chemical analysis (ESCA), static secondary ion mass spectroscopy (SIMS), and two techniques for determining surface energies. The tested lenses were (1) Ioptex lathe-cut surface-passivated, (2) Ioptex lathe-cut, (3) another manufacturer's lathe-cut, (4) cast-molded, (5) polyfluorocarbon-coated, and (6) polyvinylpyrrolidone-grafted. The ESCA testing revealed marked differences in the chemical composition of the surfaces of the polyfluorocarbon-coated and polyvinylpyrrolidone-grafted lenses compared to the other four. Minute amounts of silicon were present on the cast-molded and surface-passivated lenses. Static SIMS testing revealed the presence of siloxane contaminants on the three lathe-cut and the cast-molded lenses; a statistically smaller amount of siloxane was present on the surface-passivated lenses. Contact angle and surface energy analysis revealed statistically lower surface energies for the polyfluorocarbon-coated materials and statistically higher surface energies for the polyvinylpyrrolidone-grafted; we found no differences in the contact angles and surface energies among the surface-passivated, lathe-cut, and cast-molded lenses.

Cytotoxic effects of residual chemicals from polymeric biomaterials for artificial soft intraocular lenses

Development of improved hydrogels for soft intraocular lenses, based on 2-hydroxyethyl methacrylate monomer, requires the use of various other monomers and polymerization additives which have potential ocular toxicity. Three monomers, 2-hydroxyethyl methacrylate, methyl methacrylate, and 2-ethoxyethyl methacrylate, as well as two common inhibitors, hydroquinone and 4-methoxyphenol, were subjected to in vitro cytotoxicity assays as aqueous solutions at different concentrations. A new polymerization initiator, 2,2'-azo-bis-(2,4-dimethyl valeronitrile), was thermally decomposed in water at different concentrations and the products were also assayed for cytotoxicity. Assays were based on incubation with human choroidal fibroblasts. Cell death was evaluated by trypan blue dye exclusion, DNA synthesis inhibition, and lactate dehydrogenase tests. While methyl methacrylate and 2-ethoxyethyl methacrylate were found nontoxic, the other chemicals displayed high cytotoxicity. However, when extracts of synthesized poly(2-hydroxyethyl methacrylate) specimens, differentially treated after polymerization, were subjected to the same assays it was found that toxicity from residual 2-hydroxyethyl methacrylate monomer was lost during steam sterilization and storage in water because of the removal of the monomer through aqueous washing. The lack of toxicity in these specimens suggests that residual contents of inhibitor and initiator are too low to cause toxic effects on choroidal fibroblasts. It is concluded that hydrogels have low cytotoxic effects in vitro.

Anterior chamber depth with sulcus and capsular bag placed IOGEL lenses

The anterior chamber depth was measured in 15 eyes with sulcus placed (Group 1) and 12 eyes with bag placed (Group 2) IOGEL PC-12 lenses, and in 11 eyes with bag placed IOGEL 1103 lenses (Group 3). The mean anterior chamber depth was 3.29 mm in Group 1, 4.17 mm in Group 2, and 4.16 mm in Group 3. The difference between the mean anterior chamber depth with sulcus and bag placed IOGEL PC-12 lenses is statistically significant (P less than .0005). One effect of the different anterior chamber depths was that the anterior surface of a sulcus placed IOGEL lens frequently touched the pupillary border, whereas this rarely occurred when it was placed in the capsular bag. Another effect of differing anterior chamber depths was a different A-constant for the SRK-formula for sulcus or bag placement. In this study it was about 1 diopter greater with bag fixation than with sulcus fixation. It is recommended that each surgeon use specific A-constants to enhance the predictability of the postoperative refraction.

Early results with the 8 mm and 9 mm HEMA disc intraocular lens

This study presents our experience with 34 HEMA disc intraocular lenses implanted in the capsular bag. Despite the small number of cases and the relatively short mean postoperative follow-up of nine months, the results show a low incidence of uveitis and capsular fibrosis and excellent biocompatibility. The following complications were observed: four luxations of the 8 mm lens and one of the 9 mm lens in the anterior chamber. A visual acuity of 20/20 to 20/40 was obtained in 32 patients (94%).

Evaluation of 150 consecutive cases of poly HEMA posterior chamber lenses implanted in the bag using a small-incision technique

We report the results of 150 capsular bag implantations of the IOGEL PC-12 hydrogel lens. Mean follow-up was seven months. Following capsulorhexis and phacoemulsification, a Faulkner folder was used to insert the lens through a 3.5 mm to 4.0 mm scleral tunnel incision. Initially, a number of surgical complications were encountered. Because of increasing experience and modified instrumentation and technique, these did not occur in the later cases. Visual results were good, all eyes gaining a best case visual acuity of 20/40 or better and 97% achieving 20/25 or better. Morphological results were satisfactory. Generally the lenses remained centered and at a distance from the iris. Retention of viscoelastic substance or debris between the lens and the posterior capsule, occasionally observed at the start of the series, has been avoided by retrolental aspiration. Persistent pigment dispersion, which was observed when the lens had been implanted in the sulcus, was not seen. Tolerance of the lens material was generally satisfactory. There were six cases (4%) of fibrinoid uveitis, which is a relatively high incidence. From our experience and results we conclude that this implantation procedure allowed controlled insertion and placement of the IOGEL lens, provided that adequate instrumentation and technique was used; visual performance was comparable to that of poly(methyl methacrylate) lenses; capsular bag fixation furnished satisfactory morphological results, provided an adequately shaped capsulorhexis was performed.

Laser-induced damage to transparent polymers: chemical effect of short-pulsed (Q-switched) Nd:YAG laser radiation on ophthalmic acrylic biomaterials. I. A review

The use of short-pulsed lasers in ophthalmic surgery inspired and called for research on the damage inflicted by the laser radiation upon the acrylic polymers from which artificial intraocular lenses are made. The possible release of toxic monomers by laser-induced depolymerization is of great concern but past investigations of this phenomenon have been very limited. The present knowledge of various types of laser-induced damage to transparent polymers is reviewed with particular emphasis on the acrylic materials and intraocular lenses.

Seventy-six consecutive cases of IOGEL intraocular lens implants

A single piece hydrogel IOGEL (poly-HEMA) intraocular lens was implanted in 76 eyes. Patients obtained a visual acuity of 20/40 or better in 86.9% of cases and a best case visual acuity of 20/40 or better in 98.5% of cases. Patients were followed an average of 12 months (four to 19 months). Two lenses were exchanged with poly(methyl methacrylate) lenses because of decentration-induced glare. Cystoid macular edema occurred in two cases, resulting in visual acuity worse than 20/40 in one case. Results of the study at one year mean follow-up indicate the safety and efficacy of the IOGEL lens as an intraocular implant.