[Lens refilling]. / Lens Refilling.

Cataract surgery has developed into a very safe and highly reproducible procedure but the ultimate goal to also restore physiological accommodation has not yet been achieved. A variety of accommodative intraocular lenses (IOLs) and surgical techniques have been suggested to cure presbyopia but all showed only poor accommodative effects by objective measurements. Complete lens refilling with flexible polymers might be an interesting alternative. Recent investigations on accommodation and presbyopia have given support to the lens refilling method. After development of suitable surgical techniques and filling materials only secondary cataract formation and the unsolved intraoperative control of refraction restrict the clinical use of this technique.

[Cataract surgery in childhood uveitis]. / Kataraktchirurgie bei Uveitis im Kindesalter.

The development of cataract is the most frequent vision-threatening complication of uveitis in children. In such cases cataract surgery is associated with a particular risk of intra- and postoperative complications and requires an intensive perioperative immunosuppression, an essentially atraumatic operation in a quiscient eye, and aggressive amblyopia treatment. When these factors are taken into consideration, a timely cataract operation can result in a sustained visual rehabilitation even for children with uveitis.

[Scanning electron microscopy studies of the human lens capsule after capsulorhexis]. / Rasterelektronenmikroskopische Untersuchungen der menschlichen Linsenkapsel nach Kapsulorhexis.

BACKGROUND: In order to better understand the mechanism of tearing of the human lens capsule during circular capsulorhexis, scanning electron microscopic (SEM) examinations were made particularly of the rhexis edge. MATERIALS AND METHODS: Anterior segments from cornea donor eyes, as well as capsular pieces extracted during cataract surgery, were studied after fixation in glutaraldehyde, critical point drying, and sputtering with gold. RESULTS: The edges of the capsulorhexis were found to be very regular even in the area of zonular attachment. Neither the surface of the lens capsule nor the edge of the rhexis itself indicated any morphological influence on the direction of tearing. CONCLUSION: From the results we conclude that the rhexis of the lens capsule is only directed by the forces applied and not by particular morphological structures. To avoid radial tears, a deep anterior chamber, resulting in a relief of the anterior zonular portion seems most important. This minimizes radial forces on the anterior lens capsule, which provides the best condition for a safe rhexis.

[Scanning electron microscopy studies of human lenses]. / Rasterelektronenmikroskopische Untersuchungen der menschlichen Linsen.

BACKGROUND: In order to better understand the mechanism of tearing of the human lens capsule during circular capsulorhexis, scanning electron microscopic (SEM) examinations were made particularly of the rhexis edge. MATERIALS AND METHODS: Anterior segments from cornea donor eyes, as well as capsular pieces extracted during cataract surgery, were studied after fixation in glutaraldehyde, critical point drying, and sputtering with gold. RESULTS: The edges of the capsulorhexis were found to be very regular even in the area of zonular attachment. Neither the surface of the lens capsule nor the edge of the rhexis itself indicated any morphological influence on the direction of tearing. CONCLUSION: From the results we conclude that the rhexis of the lens capsule is only directed by the forces applied and not by particular morphological structures. To avoid radial tears, a deep anterior chamber, resulting in a relief of the anterior zonular portion seems most important. This minimizes radial forces on the anterior lens capsule, which provides the best condition for a safe rhexis.

[Experimental experiences with balloon-shaped capsular sac implantation with reference to accommodation outcome in intraocular lenses]. / Experimentelle Erfahrungen mit ballonförmigen Kapselsack-implantaten im Hinblick auf einen akkommodationsfähigen Linsenersatz.

Implantation of a balloon into the capsular bag theoretically allows the injection of fluid materials for lens replacement, thus enabling accommodation. Leakage of the fluid can be avoided in this way, and a large variety of potential materials can be tested without taking into account their effect on ocular tissue. We tested ellipsoid balloons made of polydimethylsiloxane. The balloons had a maximum diameter of 11.0 mm and a wall thickness of 0.15 mm. After capsulorhexis of 2.5 mm and phacoemulsification, the balloons were implanted in enucleated pig eyes and filled with 2% methylcellulose or silicone oil through little tubes on the anterior side. Implantation of the balloons into the capsular sac was much more difficult than normal IOL implantation into the posterior chamber. We had to enlarge the tunnel incision to 4.5 mm, and it was technically difficult to leave the relatively strong capsule of the pig intact during implantation. Due to the additional surfaces we found increased reflection. Because of the difficulties described we cannot see any advantages over other refilling techniques.

[Experimental studies of the risks of endocapsular polymerization of injectable intraocular lenses]. / Experimentelle Untersuchungen zu Risiken einer endokapsulären Polymerisation injizierbarer Intraokularlinsen.

Various experimental lens refilling procedures have been proposed. One of these methods uses endocapsular polymerization of the injected material by light exposure. In this study we wanted to characterize the potential risks of this procedure due to light and temperature hazards. We performed in vitro experiments on enucleated pig eyes and an in vivo study on 15 rabbits. During the polymerization process the highest temperature recorded (45.1 degrees C) was measured at the posterior lens capsule for a few seconds. The measured irradiance (0.065 W/cm2) and the risk of photochemical damage to the retina during 20 s of polymerization was comparable to that caused by 1.5 min of standard coaxial illumination with our operating microscope. In vivo we found no serious inflammatory reactions except for four cases where surgical problems had occurred. No direct retinal damage could be detected histopathologically. In conclusion, we think that lens refilling and endocapsular polymerization are promising techniques. However, refilling materials with better physical properties than those available so far need to be developed.

Lens refilling and endocapsular polymerization of an injectable intraocular lens: in vitro and in vivo study of potential risks and benefits.

Endocapsular cataract removal and injection of a liquid artificial lens has several advantages, including restitution of accommodation, small corneoscleral incision, a more physiological position of the intraocular lens, and a reduced rate of secondary opacification. Our technique consists of bimanual phacofragmentation followed by injection of a fluid monomeric material that can be polymerized inside the capsular bag by short light exposure. Our study assessed the potential risks of the technique (e.g., heat damage to ocular tissue, light damage to the retina) and investigated the technique in vivo. We performed in vitro experiments on porcine cadaver eyes and an in vivo study on 15 rabbits. After a clinical follow-up of at least 12 weeks, the eyes were investigated histopathologically. During the polymerization process, the highest temperature measured at the posterior lens capsule was 45.1 degrees Celsius for a few seconds. The measured irradiance (0.065 watts per cm2) and the risk of photochemical damage to the retina during 20 seconds of polymerization were comparable to that caused by 1.5 minutes of standard coaxial illumination with the operating microscope. In vivo there were no serious inflammatory reactions except in four cases in which there had been intraoperative problems. The rate of secondary opacification appeared less than in conventional intraocular lens implantation in rabbits, especially when the capsule refilled completely. Retinal damage could not be detected histopathologically. In conclusion, refilling techniques may be successful once appropriate refilling materials become available.

In vitro and in vivo evaluation of a hydrophilized silicone intraocular lens.

The surface of a silicone-disc intraocular lens (IOL) was hydrophilized by plasma etching (oxygen plasma) and compared to an untreated but otherwise identical IOL. Various methods of surface analysis were used to characterize the modification (e.g., X-ray photoelectron spectroscopy, contact angle estimation). A cytotoxic effect of the modified surface was excluded by cell culture experiments evaluating cell spreading, cell morphology, DNA and protein synthesis. In vivo experiments on rabbits indicated that the postoperative foreign-body reaction was not significantly affected by the hydrophilization of the IOL surface. Throughout the entire follow-up (12 weeks) we found less induced posterior synechias in the eyes with hydrophilized lenses than in those with untreated lenses (P = .009). While the IOL dislocations out of the capsular bag and the posterior capsular opacification rate did not differ significantly between the two groups of eyes, we did see special patterns of posterior capsular opacification on the posterior capsules of eyes with the hydrophilized IOL.

A method of lens extraction for the injection of liquid intraocular lenses.

A method for the injection of liquid intraocular lenses into the capsular bag would offer many benefits in the treatment of cataracts. The corneoscleral incision could be made even smaller, the lens diaphragm would be conserved more physiologically, and a method of therapy for presbyopia might eventually be possible. As a prerequisite, a method of endocapsular lens removal is needed. We have developed such a method for our experiments on the injection of liquid intraocular lenses in the enucleated pig eye. We use a bimanual technique through two opposing 1-mm corneoscleral incisions and two openings measuring 1 mm in diameter in the peripheral anterior capsule. By using curved needles and suction tips, we could remove the capsular contents completely. The injected material was polymerized in situ by exposure to blue light and resulted in an optically clear cast of the lens capsule of surprisingly good optical quality.

Light-induced endocapsular polymerization of injectable lens refilling materials.

The use of advanced phacoemulsification techniques enables the surgeon to remove opacified lens material while preserving a nearly complete capsular bag. For this reason, several groups are presently working on lens refilling techniques. We have developed a method for the injection of a liquid monomer into the lens capsule. The material can be polymerized by exposure to cold light (wavelength, 400-500 nm) within the capsular bag. Using cell-culture experiments, we selected an optically clear material that has cytotoxic properties when placed in direct contact with cells but does not release cytotoxic substances into the surrounding medium. We have shown that reflux of the liquid monomer into the anterior chamber can be avoided by using a material that can be polymerized within the capsule. Initial experiments in rabbits indicate that the technique can be used without inducing a significant postoperative inflammatory response or leading to morphological changes in the cornea or the retina.

Plasma-induced surface modifications on silicone intraocular lenses: chemical analysis and in vitro characterization.

In contrast to the high standard of intraocular lens implantation today, lens fixation and the occurrence of secondary opacifications are still not satisfactory. We are working on an implant that builds a stable connection to the surrounding lens-capsule. Disc-shaped lenses made of poly(dimethylsiloxane) were treated with different kinds of plasma to bring functional groups to the surface. This allows further macromolecular coating. The results of the surface modifications were characterized by electron spectroscopy for chemical analysis, scanning electron microscopy, Fourier transform infrared spectroscopy and cell culture experiments. O2 plasma induces a rapid increase of functional groups on the lens surface. CO2 plasma has to be used for longer treatment periods to achieve the same increase, but as SEM shows, did not lead to surface damage up to periods of 300 s. Using O2 plasma for longer than 60 s, a crack formation occurred. Therefore, CO2 plasma may be a more effective and sensitive tool in grafting functional groups to the surface.

[Experience with hydrophilic silicone disc intraocular lenses]. / Erfahrungen mit hydrophilisierten Silikon-Disk-Intraokularlinsen.

When oxygen plasma was used for plasma etching it was possible to hydrophilize the surface of silicone intraocular lenses (IOLs) without changing the chemical composition or the properties of deeper layers of the polymer. The modification was characterized by surface analysis. (Electron spectroscopy = XPS, contact angle estimations) and by scanning electron microscope. A cytotoxic influence of the modified surface could be excluded by cell culture experiments in which we evaluated cell spreading, cell morphology, DNA synthesis and protein synthesis. In vivo experiments on rabbits showed that the postoperative foreign body reaction was not significantly influenced by the hydrophilization of the IOL surface. Over the entire follow-up period (12 weeks), there was a reduced tendency to induce posterior synechiae in the group with hydrophilized lenses (P = 0.009). The number of dislocations and the incidence of posterior opacification did not differ significantly; on the other hand there were indications of improved adhesion to the posterior lens capsule of the hydrophilized IOL.

[Immunohistochemical studies of the human lens capsule]. / Immunohistochemische Untersuchungen der menschlichen Linsenkapsel.

In this study we made an attempt to localize components of the human lens capsule using immunohistochemical methods. Type IV collagen could be shown in all parts of the capsule in equal distribution. It could be found over the whole thickness of the lens capsule. By comparison, laminin could be detected only at the inner layer of the capsule. There was no difference concerning the contribution of these components between the anterior and the posterior capsule. No specific staining of collagen types I and III or of fibronectin could be found.