Intraocular silicone lenses in silicone oil: an experimental study

The Postvitrectomy Cataract

To review the recent literature regarding risk factors for cataract formation after vitrectomy, the challenges and management strategies for anterior segment surgeons when facing post-vitrectomy cataract surgery, and the visual outcomes of patients undergoing post-vitrectomy cataract surgery. Cataract surgery after vitrectomy can be safely performed to significantly improve the visual outcome in most post-vitrectomy patients, although final visual acuity is primarily limited by the patient’s underlying vitreoretinal pathology.

Silicone Oil Adhesion to Hydrophobic Acrylic Intraocular Lenses: A Comparative Laboratory Study of a New versus an Established Hydrophobic Acrylic Intraocular Lens Material

Background

In vitro assessment of silicone oil adhesion to a new hydrophobic acrylic intraocular lens (IOL) material, the Clareon model CNA0T0, compared with the established AcrySof model SN60WF was carried out.

Methods

Silicone oil adhesion was assessed for two types of IOLs, Clareon CNA0T0 (n = 10) and AcrySof SN60WF (n = 10). Lenses were immersed in an aqueous sodium chloride solution for 12 hours and then incubated at room temperature in silicone oil for 12 hours. The lenses were washed with distilled water and photographed at 25x magnification using a microscope. The percent coverage was calculated by dividing the area of oil coverage by the total surface area of the lens.

Results

Silicone oil adhesion to the surface of the CNA0T0 lens ranged from 4% to 22%, with a mean ± SD coverage of 8% ± 4%. Silicone oil adhesion to the surface of the SN60WF lens ranged from 1% to 17%, with a mean coverage of 9% ± 4%. The silicone oil adhesion of CNA0T0 was equivalent to that of SN60WF (P > 0.05).

Conclusions

The new Clareon model CNA0T0 IOL has silicone oil adhesion and interaction that are equivalent to the established AcrySof IOL.

Removal of Silicone Oil From Intraocular Lens Using Novel Surgical Materials

PURPOSE

To design, fabricate, and evaluate novel materials to remove silicone oil (SiO) droplets from intraocular lenses (IOL) during vitreoretinal surgery.

METHODS

Three different designs were fabricated using soft lithography of polydimethylsiloxane (PDMS), three-dimensional (3D) inverse PDMS fabrication using water dissolvable particles, and atomic layer deposition (ALD) of alumina (Al₂O₃) on surgical cellulose fibers. Laboratory tests included static and dynamic contact angle (CA) measurements with water and SiO, nondestructive x-ray microcomputer tomography (micro-CT), and microscopy. SiO removal was performed in vitro and ex vivo using implantable IOLs and explanted porcine eyes.

RESULTS

All designs exhibited enhanced hydrophobicity and oleophilicity. Static CA measurements with water ranged from 131° to 160° and with SiO CA approximately 0° in 120 seconds following exposure. Nondestructive x-ray analysis of the 3D PDMS showed presence of interconnected polydispersed porosity of 100 to 300 μm in diameter. SiO removal from IOLs was achieved in vitro and ex vivo using standard 20-G vitrectomy instrumentation.

CONCLUSION

Removal of SiO from IOLs can be achieved using materials with lower surface energy than that of the IOLs. This can be achieved using appropriate surface chemistry and surface topography. Three designs, with enhanced hydrophobic properties, were fabricated and tested in vitro and ex vivo. All materials remove SiO within an aqueous environment. Preliminary ex vivo results were very promising, opening new possibilities for SiO removal in vitreoretinal surgeries.

TRANSLATIONAL RELEVANCE

This is the first report of an instrument that can lead to successful removal of SiO from the surface of IOL. In addition to the use of this instrument/material in medicine it can also be used in the industry, for example, retrieval of oil spills from bodies of water.

Removal of silicone oil droplet adhering to a silicone intraocular lens using 25-gauge instrumentation

A 36-year-old man with proliferative diabetic retinopathy who had had silicone oil tamponade and removal, silicone intraocular lens (IOL) implantation, and neodymium:YAG capsulotomy presented with blurred vision. Slitlamp examination revealed a silicone oil droplet on the posterior surface of the silicone IOL. Pars plana vitrectomy using 25-gauge instruments was performed, and the droplet was easily aspirated with the 25-gauge vitreous cutter.

Noninvasive identification of different intraocular lenses using Raman spectroscopy in porcine eyes

PURPOSE

To develop a noninvasive technique for identifying the specific type of intraocular lens (IOL) implanted in porcine eyes.

SETTING

Department of Ophthalmology, University of Ulsan College of Medicine, Asan Medical Center, and Department of Chemistry Education, Seoul National University, Seoul, Korea.

METHODS

A confocal Raman spectroscopy system was used to identify various acrylic (AcrySof SA60AT [Alcon], Sensar AR40e [Advanced Medical Optics], I-Flex [I-Medical Intraocular Lenses]) and silicone (ClariFlex, [Advanced Medical Optics]) IOLs implanted in enucleated pig eyes. Confocal Raman spectra of IOLs were obtained by photoexcitation using the 514.5 nm line from an argon-ion laser, with a power of 1 mW at the sample and an acquisition time of 10 to 100 seconds.

RESULTS

All IOLs, including those composed of acrylic optic material from different manufacturers, exhibited distinct spectral peaks before and after implantation in pig eyes.

CONCLUSION

Confocal Raman spectroscopy may represent a novel method for obtaining specific information about implanted IOLs through direct and noninvasive confocal observation of spectral characteristics.

Effect of heparin surface modification in reducing silicone oil adherence to various intraocular lenses

PURPOSE

To evaluate surface properties of various intraocular lenses (IOLs), including a newly fabricated heparin-surface-modified (HSM) silicone IOL, with special reference to their efficiency in reducing potential silicone oil adherence to the IOL optics.

SETTING

Center for Research on Ocular Therapeutics and Biodevices, Department of Ophthalmology, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

Five groups of rigid and foldable IOLs were analyzed in an in vitro test for the percentage of silicone oil adherence: a single-piece foldable hydrophilic-acrylic IOL (n = 9); a single-piece rigid poly(methyl methacrylate) (PMMA) IOL with HSM coating of the lens optic (n = 9); a 3-piece foldable silicone optic IOL with HSM coating of the optic (n = 10); a single-piece standard rigid PMMA IOL (n = 7); and a standard 3-piece foldable silicone optic IOL (n = 9). After the IOLs were immersed in water and then in silicone oil, gross photographs taken. Image analysis was performed to evaluate the percentage of silicone oil coverage of the anterior and posterior surfaces of each IOL optic.

RESULTS

The mean silicone oil coverage of the hydrophilic-acrylic IOLs was 5.6% +/- 2.5% (SD); of the HSM PMMA IOLs, 6.2% +/- 4.3%; of the HSM silicone optic IOLs, 6.7% +/- 3.2%; and of the standard PMMA IOLs, 20.3% +/- 13.3%. The mean silicone oil coverage was greatest on the standard silicone optic IOLs, 98.2% +/- 3.1%.

CONCLUSIONS

Intraocular lenses with a hydrophilic optic have less tendency toward adherence to silicone oil than more hydrophobic designs. A foldable silicone IOL with heparin surface modification can significantly reduce potential silicone oil adherence, comparable to the level achievable with the rigid HSM PMMA designs. Two new foldable IOL styles, the HSM silicone IOL and IOLs in the general class of hydrophilic-acrylic, were highly efficacious in reducing silicone oil adherence. There is now a real choice of foldable lenses for patients with actual or potential vitreoretinal diseases.

Silicone oil-intraocular lens interaction: which lens to use?

AIM

To determine a suitable intraocular lens for implantation in patients at high risk of lens exposure to silicone oil in their lifetime.

METHODS

PMMA, AcrySof, AR40, AQUA-Sense, and Raysoft lenses were examined. Each lens was immersed for 5 minute intervals in balanced salt solution (BSS), in stained silicone oil, and again in BSS before being photographed in air and in BSS. Percentage silicone oil coverage of the lens optic was determined.

RESULTS

The mean percentage coating (MPC) for the lens biomaterials ranged from 5.2% to 21.5%. The Raysoft lens had significantly less oil coverage when statistically compared with the other lens types (p < 0.001).

CONCLUSION

A Raysoft (Rayner) lens is a suitable lens for implantation in patients who are at risk of severe vitreoretinal disease.

Solvent for removing silicone oil from intraocular lenses: experimental study comparing various biomaterials

PURPOSE

To evaluate the effectiveness of a perfluorocarbon-perfluorohexyloctane (PFHO)-in removing silicone oil from different intraocular lenses (IOLs) and determine whether any removal technique enhances the removal of silicone oil.

METHODS

Six IOL materials were analyzed: standard poly(methyl methacrylate) (PMMA), heparin-surface-modified (HSM) PMMA, AcrySof, 2 polyHEMAs with different water contents, and a second-generation SLM-2 silicone. One or 2 microL of a highly viscous silicone oil (5700 cs) was applied to the center of each IOL optic. Perfluorohexyloctane (2 mL) was then used to remove the silicone oil by 1 of 3 techniques: immersion of the IOL in PFHO; irrigation of the silicone oil with a small, blunt cannula; mechanical wiping with a PFHO-saturated Merocel swab (used only when irrigation failed). Next, each IOL was examined by light and scanning electron microscopy. The expanse of silicone oil residue remaining on the IOLs was objectively quantified using an integrated computerized analysis system combined with energy-dispersive spectrometry.

RESULTS

After application of 1 microL silicone oil, immersion in PFHO did not remove silicone oil from any IOL material. Irrigation with PFHO removed the silicone oil from the HSM PMMA and polyHEMA IOLs, but oil remained on the other lens materials. Mechanical wiping was necessary to remove the oil from the PMMA, AcrySof, and silicone IOLs. Attempts to remove 2 microL of silicone oil produced similar results. Although mechanical wiping of the AcrySof IOL removed all silicone oil, a slight residue remained on the PMMA and silicone IOLs. The PFHO irrigation removed significantly more silicone oil from the HSM PMMA than the unmodified PMMA IOL (P =.001). More silicone oil was removed from polyHEMA IOLs than from the AcrySof or silicone IOLs (P =.05).

CONCLUSION

Although PFHO can remove silicone oil, it is of limited usefulness. The effectiveness of PFHO depends on the removal technique, IOL material, and amount of silicone oil present. Based on these results, we recommend PFHO irrigation followed by mechanical wiping with a PFHO-saturated swab.

Vitreoretinal surgery through multifocal intraocular lenses compared with monofocal intraocular lenses in fluid-filled and air-filled rabbit eyes

PURPOSE

To compare vitrectomy procedures and visualization of posterior segment structures through multifocal silicone intraocular lenses (IOLs) with the same procedures through monofocal silicone IOLs in rabbit eyes.

DESIGN

Experimental study.

PARTICIPANTS

Twelve eyes of six rabbits.

METHODS

Each rabbit eye underwent phacoemulsification of the lens and posterior chamber implantation of a silicone multifocal or silicone monofocal IOL. The type of IOL (monofocal vs. multifocal) implanted in the first eye of each rabbit was randomly decided. The fellow eye then received the other IOL type. Vitrectomy procedures were performed through the IOLs by using a flat contact lens (part 1) or wide-angled contact lens (part 2) for visualization through fluid-filled (parts 1 and 2) and air-filled (part 2) eyes.

MAIN OUTCOME MEASURES

Image quality, stereopsis, and contrast were subjectively graded on a scale of 0 (none) to 4 (excellent) for each eye by each surgeon.

RESULTS

In part 1, image quality averaged 4 for the monofocal IOL and 3.6 for the multifocal IOL. Stereopsis averaged 4 for the monofocal IOL and 4 for the multifocal IOL. Contrast averaged 4 for the monofocal IOL and 3.9 for the multifocal IOL. Vitrectomy with retinal surface maneuvers was successfully performed in both pigmented and nonpigmented rabbit eyes through both IOL types. In part 2, image quality, stereopsis, and contrast were rated as 4 for both multifocal and monofocal silicone IOLs. Air-fluid exchange was performed without difficulty. Image quality, stereopsis, and contrast were rated as 4 for air-filled eyes.

CONCLUSIONS

Visualization of posterior segment structures through multifocal silicone IOLs was sufficient for retinal surface maneuvers during vitrectomy procedures in both fluid-filled and air-filled rabbit eyes.

Identification of intraocular lens materials using confocal Raman spectroscopy

PURPOSE

To develop and test a noninvasive method to identify intraocular lens (IOL) materials in vitro.

SETTING

Center for Biomedical Engineering and the Department of Ophthalmology, University of Texas Medical Branch, Galveston, Texas, USA.

METHODS

A laser confocal Raman spectroscopy system (Conforam) was used for the noninvasive assessment of Raman spectra in the lower and the higher spectral regions (299.1 to 1833.7 cm-1 and 2633.8 to 3819.6 cm-1, respectively) of 4 IOL materials: silicone, poly(methyl methacrylate) (PMMA), acrylic, and hydrogel.

RESULTS

Each lens material showed a distinctive spectrum in both the higher and the lower spectral regions. Most materials had unique peaks and a distinct profile using 1 mW of laser power and a 1 second exposure time. All materials still had a unique spectrum in both the higher and the lower region that allowed 1 material to be distinguished from the others.

CONCLUSIONS

A Conforam differentiated silicone, PMMA, acrylic, and hydrogel lenses in vitro. Raman spectroscopy using the Conforam may provide a fast, safe, and reliable noninvasive method to gain information about the material of an implanted IOL and the stability of lens materials and their coatings.

Intraocular lens changes after short- and long-term exposure to intraocular silicone oil. An in vivo study

OBJECTIVE

Silicone oil frequently is used as a vitreous substitute after complex vitreoretinal procedures. The authors sought to study the effect of short- and long-term exposure to silicone oil on polymethyl methacrylate (PMMA, MC60BM; Alcon, Ft. Worth, TX), silicone (SI-30NB; AMO, Irvine, CA), and soft acrylic (MA60BM; Alcon) intraocular lenses (IOLs).

DESIGN

An experimental animal study.

INTERVENTION

Forty-one New Zealand white rabbits underwent lensectomy, vitrectomy, capsulotomy, and placement of one of the three types of IOLs into the ciliary sulcus. All lenses were weighed before implantation and 24 hours after explanation. In the short-term study, an fluid-air exchange was performed followed by the use of silicone oil (1000 centistokes) to coat the posterior lens surface. Immediately thereafter, an air-fluid exchange was performed and the remaining silicone on the posterior lens surface was aspirated or wiped or both for 1 minute using a soft-tipped extrusion cannula for 1 minute. In the long-term study, the posterior segment was filled with 1000 centistokes silicone oil after fluid-air exchange. Animals were observed by slit-lamp biomicroscopy and photographed at 1 week, 1 month, and 3 months after surgery. At 3 months, all animals underwent silicone-fluid exchange, an attempt to manually remove any remaining silicone oil, and lens explanation.

RESULTS

In the short-term study, no silicone oil remained after manual wiping and/or aspiration in any of the four rabbits implanted with PMMA or acrylic IOLs. In the animals with silicone IOLs, a significant amount of silicone oil remained on the posterior lens surface of all lenses (P < 0.01 for silicone vs. acrylic and silicone vs. PMMA). No statistically significant difference was found when comparing the lens weights in each group before and after implantation. In the long-term study, aqueous droplet formation was found on the posterior lens surface of six of nine PMMA IOLs and ten of ten silicone IOLs at 3 months. No opacities were observed in the group with acrylic IOLs (P < 0.001 for acrylic vs. silicone, P = 0.0018 for acrylic vs. PMMA, and P = 0.047 for PMMA vs. silicone). Adherent silicone oil remained on two of nine PMMA IOLs and on none of ten acrylic IOLs. In contrast, a significant amount of silicone oil remained on the posterior lens surface of ten of ten silicone IOLs (P < 0.001 for silicone vs. acrylic and silicone vs. PMMA). Furthermore, there was a statistically significant increase in lens weights before and after implantation in the silicone IOL group but not in the PMMA or acrylic group (P < 0.01).

CONCLUSIONS

It is extremely difficult or impossible to remove remaining silicone oil from the posterior surface of a silicone IOL after short- or long-term exposure to silicone oil. This oil may interfere with the surgeon's view of the retina and may diminish the patient's visual acuity. In contrast, oil is readily removed from the posterior surface of an acrylic IOL. The authors therefore recommend the use of a soft acrylic or PMMA IOL over a silicone IOL when choosing a lens for implantation in patients who may require vitreoretinal procedures with silicone oil tamponade.

Low-vacuum, low-voltage scanning electron microscopy of poly(methyl methacrylate) intraocular lenses

PURPOSE

To evaluate the usefulness of low-vacuum, low-voltage scanning electron microscopy (LVSEM) in examining the surfaces of intraocular lenses (IOLs) without preparation.

SETTING

In vitro laboratory experiment.

METHODS

Six commercially available IOLs made of poly(methyl methacrylate) (PMMA) and one explanted PMMA IOL were evaluated with LVSEM without sputter coating. Sham surgical maneuvers were performed on some IOLs and the surface changes observed.

RESULTS

Smooth surfaces of IOL optics and haptics, relatively sharp edges of optic holes, and irregularities at the optic/haptic junction were clearly observed. Crystalline deposits were seen on the surfaces after the IOLs were dipped and dried in saline solution. Scratches and marks were observed after they were grasped with a forceps.

CONCLUSIONS

Low-vacuum, low-voltage scanning electron microscopy is a time-saving procedure that can be used by inexperienced investigators. The resolution under relatively low magnification appeared to be satisfactory for evaluating the IOL surface.

Intraocular lens complications requiring removal or exchange

Intraocular lens (IOL)-related complications are caused primarily by mechanical trauma, inflammatory or infectious complications, or optical problems. Complications may occur at the time of surgery or be the result of an ongoing postoperative process. Mechanical and inflammatory injury may produce corneal decompensation, cystoid macular edema, hyphema, uveitis, and glaucoma, causing reduced vision and in some cases chronic pain. Optical problems may be due to a wrong power of the IOL or to postoperative decentration or dislocation of the lens. Ophthalmologists should be aware of the indications for IOL removal or exchange in those patients who have ongoing IOL-induced injury or impairment. Removal or exchange of an IOL frequently involves a complex decision-making process and is often associated with immense technical challenge. Various medical and surgical treatments may be tried to correct IOL problems before the decision is made to remove or exchange the lens.

Silicone oil adhesion to intraocular lenses: an experimental study comparing various biomaterials

PURPOSE

To perform an in vitro experimental study comparing the degree of adherence of silicone oil to various rigid and foldable intraocular lens (IOL) designs and to the human lens capsule.

SETTING

Center for Research on Ocular Therapeutics and Biodevices, Department of Ophthalmology, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

Seven IOL styles comprising various biomaterials were studied: fluorine-treated (Fluorlens), heparin-surface-modified (HSM), hydrogel, Memory-Lens, Poly(methyl methacrylate) (PMMA), soft acrylic, and silicone lenses; the human crystalline lens was also studied. Each lens was immersed in silicone oil for 12 hours, than photographed, studied by scanning electron microscopy (except the crystalline lens), and subjected to computer-generated image analysis to determine the silicone oil coverage.

RESULTS

Silicone oil coverage of dry silicone lenses was 100% and of lenses immersed in normal saline, 82.5%. The least coverage was on the heparin-surface-modified lens (mean score 9.4%). Coverage of the other four lenses ranged from approximately 15.1% to 33.7%. Mean coverage of the human lens capsule was 10.9%.

CONCLUSION

Although a silicone IOL shows maximal adherence to silicone oil, other lens biomaterials are not immune to this complication. Silicone oil coverage was related to the dispersive energy component of the surface charge of the IOL biomaterial. Low dispersive energy materials had less silicone oil coverage, while those with higher dispersive energy had more oil coverage.

Condensation on polymethylmethacrylate, acrylic polymer, and silicone intraocular lenses after fluid-air exchange in rabbits

PURPOSE

Condensation occurs rapidly on silicone intraocular lenses (IOLs) after vitrectomy and fluid-air exchange in the presence of a posterior capsulotomy, severely limiting the retinal view. Foldable IOLs made of an acrylic polymer are now available. The authors compare the condensation and subsequent retinal view degradation after vitrectomy and fluid-air exchange in rabbit eyes implanted with polymethylmethacrylate (PMMA), soft acrylic polymer (ACRYSOF), and silicone IOLs.

METHODS

Thirty rabbits underwent bilateral lens removal. Twenty PMMA, 20 acrylic polymer, and 20 silicone IOLs were implanted into the capsular bag. After three-port vitrectomy, eyes were randomly assigned to undergo a posterior capsulotomy or to an intact posterior capsule. Fluid-air exchange was performed, and the amount of condensation on the IOL surface and resultant retinal view was graded. Surgical maneuvers then were performed to decrease the condensation. These maneuvers included wiping the IOL surface with a soft-tipped cannula and coating it with viscoelastic.

RESULTS

No condensation occurred on IOLs in eyes with an intact posterior capsule. Significantly more condensation occurred on IOLs in eyes with a capsulotomy, regardless of IOL type (P < 0.014). Wiping the condensation resulted in significantly less condensation and improved retinal view on the PMMA and acrylic IOLs when compared with the silicone IOLs (P < 0.024). Condensation was eliminated on all three IOL types after viscoelastic was applied. However, increased distortion of the retinal view was induced by the viscoelastic on the silicone IOL as compared with the other IOLs.

CONCLUSIONS

Condensation and subsequent retinal image degradation occurs uniformly after vitrectomy, posterior capsulotomy, and fluid-air exchange in eyes with PMMA, acrylic, and silicone IOLs. Because the condensation can be eliminated most easily on acrylic IOLs compared with silicone IOLs, when foldable IOL techniques are used it is likely that an acrylic polymer IOL would be advantageous for those patients at risk for future vitreous procedures requiring fluid-air exchange.