BACKGROUND:Foldable intraocular lenses (IOLs) are established in ophthalmic surgery and increasingly more complex geometries are available. This study investigates different designs of the optics of the IOL as well as the imaging quality of these optics utilizing electron microscopic photographs and mathematical approximations.METHOD:Included in this study were two different lens powers of common IOLs (+ 13 D and + 26 D). All studied IOLs were processed depending upon their water content: Aqueous IOLs with up to 25 % water content were fixed with 2.5 % glutaraldehyde in 0.1 M phosphate buffer (mPP), and then contrasted with 2 % OsO (4) and processed in an alcohol series of 30 - 100 % propanol. Subsequently, the IOLs were transferred into EPON (epoxy resin) and polymerization took place at 60 degrees C. After hardening, the samples were cut out with a leaves saw and divided into halves. Afterwards these were polished with glass and diamond knifes at the ultramicrotom (Ultracut, Rückert-Jung). After coal vaporization measurement took place in the scanning electron microscope (DSM 962, Zeiss). In the case of dry stored IOLs, the samples were sputtered with Au-Pd 20 nm and afterwards measurement was performed as described above. The measurement of the optical imaging quality was performed with correctly and inversely oriented IOLs according to the standard EN ISO 11979 -- 2 by means of a measuring system which works on the basis of the point spread function (PSF) and/or the modulation transfer function (MTF). From this the Strehl ratio was computed in each case.RESULTS:Utilizing a correlation of the electron microscopic investigation of the optics of different IOLs with their imaging quality (Strehl ratio), we were able to show that the optical design of the IOL has substantial influence on the imaging quality of an intraocular lens. In particular, with non-symmetrical designs of the optics (e. g., AR40 e; AMO) the orientation of an IOL in the eye is crucial; i. e., the Strehl ratio increased thereby from 0.68 to 0.87.CONCLUSIONS:The design of asymmetrical optics is crucial and much attention should be paid to the fact that the imaging quality can substantially be affected. A correct orientation of the lens within the eye is very important with these asymmetrical optics.

Purpose: Today, for the preparation of donor and recipient cornea during keratoplasty either single-use or reusable metal trephines are commonly used although excimer and femtosecond laser systems are available. Due to the surgical techniques as well as the configuration of metal trephine's cutting edge irregular corneal surfaces may be induced. These will result in a postoperative astigmatism. Contemporary manufacturing processes do allow for the production of minimal cutting edge diameters (400 nm - 1 mu m), however, this is related with a reduced mechanical stability of such delicate cutting edges. It has been observed that the cutting edge of metal blades is immediately bent with the first exposure to tissue. As a result, the cutting forces are increasing and the wound configuration is negatively effected. Due to the complex geometry of trephine cutting edges, no diamond trephines are currently available. We are investigating the cutting performance of conventional trephines that were modified using nanotechnology.Method: Different metal trephines were characterised using a scanning electron microscope (SEM). The diameter of the cutting edge was measured. Pig cornea were studied histologically after trepanation. Selected trephines were ion-forged in a modified PVD (physical vapour deposition) reactor using highly accelerated ions which are concentrated by magnetic fields at low temperature. The consecutive processing steps were controlled by SEM analysis of the cutting edge diameters. Randomly chosen areas of treated trephines were analysed. After processing the trephines, pig cornea were cut and analysed by histological and SEM examination. Additionally, the relevant mechanical cutting parameters of untreated as well as treated trephines were measured when penetrating into a PU (polyurethane) foil.Results: Preliminary microscopic analysis already reveals differences in the quality of the cutting edges. The nanotechnological modification of the cutting edges does not result in larger diameters. Compared with the initial cutting edges, the optical analysis of the modified trephine cutting edges reveals subjectively smoother surfaces. The force measurements prove a reduction of cutting forces for the treated trephines compared to the untreated ones. The SEM analysis show for the cornea treated with the modified trephines a subjectively smoother surface. Histology reveals that the surfaces of the treated cornea do not exhibit a smooth and unidirectional structure. This divergence became larger when untreated trephines were used. The mechanical characterisation of the treated trephines resulted in harder and longer-lasting surfaces.Discussion: The newly developed ion-forging of trephines in combination with nanostructured carbon coatings yield complex cutting edges of higher stability with diamond-like properties. This study shows that the performance of laser trepanation cannot be reached; however, the use of nanotechnology can further improve manual trephine techniques.

PURPOSE:Today, for the preparation of donor and recipient cornea during keratoplasty either single-use or reusable metal trephines are commonly used although excimer and femtosecond laser systems are available. Due to the surgical techniques as well as the configuration of metal trephine's cutting edge irregular corneal surfaces may be induced. These will result in a postoperative astigmatism. Contemporary manufacturing processes do allow for the production of minimal cutting edge diameters (400 nm -- 1 microm), however, this is related with a reduced mechanical stability of such delicate cutting edges. It has been observed that the cutting edge of metal blades is immediately bent with the first exposure to tissue. As a result, the cutting forces are increasing and the wound configuration is negatively effected. Due to the complex geometry of trephine cutting edges, no diamond trephines are currently available. We are investigating the cutting performance of conventional trephines that were modified using nanotechnology. METHOD:Different metal trephines were characterised using a scanning electron microscope (SEM). The diameter of the cutting edge was measured. Pig cornea were studied histologically after trepanation. Selected trephines were ion-forged in a modified PVD (physical vapour deposition) reactor using highly accelerated ions which are concentrated by magnetic fields at low temperature. The consecutive processing steps were controlled by SEM analysis of the cutting edge diameters. Randomly chosen areas of treated trephines were analysed. After processing the trephines, pig cornea were cut and analysed by histological and SEM examination. Additionally, the relevant mechanical cutting parameters of untreated as well as treated trephines were measured when penetrating into a PU (polyurethane) foil. RESULTS:Preliminary microscopic analysis already reveals differences in the quality of the cutting edges. The nanotechnological modification of the cutting edges does not result in larger diameters. Compared with the initial cutting edges, the optical analysis of the modified trephine cutting edges reveals subjectively smoother surfaces. The force measurements prove a reduction of cutting forces for the treated trephines compared to the untreated ones. The SEM analysis show for the cornea treated with the modified trephines a subjectively smoother surface. Histology reveals that the surfaces of the treated cornea do not exhibit a smooth and unidirectional structure. This divergence became larger when untreated trephines were used. The mechanical characterisation of the treated trephines resulted in harder and longer-lasting surfaces. DISCUSSION:The newly developed ion-forging of trephines in combination with nanostructured carbon coatings yield complex cutting edges of higher stability with diamond-like properties. This study shows that the performance of laser trepanation cannot be reached; however, the use of nanotechnology can further improve manual trephine techniques.