[Explantation of Multifocal Intraoular Lenses - Frequency, Causes and Course]. / Häufigkeit, Ursachen und Verlauf von Explantationen multifokaler Intraokularlinsen.

PURPOSE: Multifocal intraocular lenses (MF-IOL) are implanted for visual rehabilitation after cataract operation and refractive lens exchange (RLE). In this retrospective study, the frequency, causes and course of MF-IOL explantation are investigated. SETTING: Private eye clinic, Cologne, Germany. METHODS: Between 2009 and 2014, a total of 1438 eyes were supplied with a hydrophobic, aspherical, diffractive, multifocal posterior chamber lens (PCL) of type: Acrysof ReSTOR and ReSTOR toric, with near additions of + 2.5, + 3.0 and + 4.0 (Alcon, Fort Worth, USA). 78 % (n = 1116 eyes) were indicated because of a cataract and 22 % (n = 322 eyes) as RLE. All procedures were either performed by OK or GG, as ultrasound phacoemulsification under topical anaesthesia. Since 2013, a femtosecond laser (LensX, Alcon, Fort Worth the USA) has been used in some cases. Data analysis was performed with the help of the digital patient's recordings. RESULTS: In a total of 12 cases, the MF-IOL needed to be explanted. Causes for the explantation were strong deviations from the expected target refraction (4 eyes), epiretinal gliosis accompanied by surgically membrane peeling (2 eyes), optical discomfort (waxy vision, 4 eyes), unstable toric lens due to a vast zonulolysis (1 eye), and 5 years post-implantation glistening (1 eye). The overall frequency of MF-IOL explantationen was 0.83 %. The frequency of explantations due to specific optical side effects and discomfort was 0.28 %. In all cases, 12 months post MF-IOL explantation recovery was achieved to full visual acuity. CONCLUSIONS: Diffractive MF-IOL of the type Alcon Acrysof ReSTOR are generall very well accepted. In only 0.28 % of all cases, was an explantation performed on grounds of optical discomfort. In the other cases, the causes for explantation were not related to the optical geometry of the MF-IOL.

[Real-time monitoring of a femtosecond laser in Sub-Bowman Keratomileusis on human donor eyes using OCT]. / Echtzeitsteuerung einer Femtosekundenlaser Sub-Bowman-Keratomileusis an humanen Spenderaugen mittels optischer Kohärenztomografie.

PURPOSE: In LASIK (laser in situ keratomileusis) the thickness of the corneal flap is important since it is the residual corneal bed that determines corneal stability. The introduction of real-time OCT visualisation of the corneal layers during the fs-laser cut should enable the surgeon to control and monitor the position of the plane of laser-tissue-interaction during operation. To prove that optical coherence tomography (OCT) can be useful to guide femtosecond (fs)-laser in Sub-Bowman-Keratomileusis (SBK) an in-vitro experimental study was performed on human autopsy eyes in a research laboratory set-up. METHODS: Five human autopsy eyes, unsuitable for transplantation, received fs-laser keratomileusis (flap) cuts. The laser procedure was controlled in real-time with an OCT system (Thorlabs HL AG, Lübeck, Germany) to ensure that the cut was placed just underneath Bowman's layer. As a control all eyes were dissected histologically (H & E staining) and examined under the light microscope (LM). RESULTS: Videomonitoring of the laser process supported the feasibility of the concept to online monitor the fs-laser cutting process via OCT. A clear distinction of the corneal epithelium was possible in all eyes. Bowman's membrane was not identified in all autopsy eyes at the given resolution of the OCT used in this study. Still, LM sections confirmed that the online monitoring assured a positioning of the cutting plane at minimum distance underneath Bowman's membrane. CONCLUSION: It was proven that real-time OCT monitoring of fs-laser SBK on human eyes is in principle possible.

[In vitro and in vivo investigations on the treatment of presbyopia using femtosecond lasers]. / In-vitro- und In-vivo-Untersuchungen zur Presbyopiebehandlung mit Femtosekundenlasern.

BACKGROUND: Ultrashort (femtosecond) laser pulses can generate precise cuts in biological tissue without damaging the surface. The application of femtosecond laser technology at the lens was evaluated with respect to a possible treatment of presbyopia. MATERIALS AND METHODS: Femtosecond laser lentotomy was performed on 150 pig lenses in vitro. Cutting geometry and laser settings were optimized to generate smooth cuts with a minimum of produced gas bubbles. Four rabbit lenses were treated afterwards in vivo and were controlled for 3 months post-treatment. The lenses were then extracted and evaluated. RESULTS: With suitable laser settings, light scattering due to residual gas bubbles could be almost completely avoided in pig lenses. A pulse energy of less than 1.2 microJ and a cutting geometry with spot separations of more than 5 microm are important. The rabbit lenses stayed macroscopically clear for 3 months in vivo. Only the cell structures directly adjacent to the laser focus were cut; structures 5-10 microm away appeared to be intact. No cataract formation occurred during this time. CONCLUSION: Femtosecond laser application allows precise and smooth cuts inside pig and rabbit lenses without damage to adjacent tissue.

[Excimer laser treatment in deep lamellar keratoplasty 100 micrometer over Descemet's membrane]. / Excimerlaserbehandlung bei tiefer lamellärer Keratoplastik (TLKP) 100 micrometer über der Descemet.

BACKGROUND: Possible improvements of best corrected visual acuity (BCVA) and the stability of the endothelium in deep lamellar keratoplasty (DLKP) assisted by Excimer laser polishing were evaluated. PATIENTS AND METHODS: A 59-year-old male patient was treated 1 year after DLKP with the intention of improving is BCVA. Excimer laser treatment was performed on the deep layers of the graft and on the posterior lamellae of the recipient's cornea 100 micrometer over the endothelium. RESULTS: BCVA improved from 20/100 to 20/22 within 9 months. Refraction remained identical pre- and post-laser treatment at +1.25 sph=-2.0 cyl/17 degrees The endothelium remained unchanged with regard to its cell count of 2,100 cells/mm(2) and the normal morphology. CONCLUSION: Smoothing of the interface by Excimer scanning laser treatment may be recommended in such cases of DLKP in which postoperatively the resulting visual acuity does not correspond to the retinal resolution. Use of scanning or flying-spot lasers are the prerequisite for the maintenance of the endothelium.

A scanning and rotating slit arF excimer laser delivery system for refractive surgery.

PURPOSE: This study was designed to investigate the quality of a scanning and rotating slit delivery system of an ArF excimer laser (Nidek EC-5000). METHODS: The ablation patterns on polymethylmethacrylate (PMMA) wafers were examined by scanning electron microscopy. The influence of inhomogeneities in the beam profile was simulated on a computer and compared with a conventional large-area ablation system. The impairment of the ablation rate by radiation absorption of the ablation plume was measured as a function of the repetition rate and the application of a fixation ring. RESULTS: The scanning and rotating slit delivery system is tolerant of small-beam non-homogeneities. The ablation rate is sensitive to the dynamics of the ablation plume. CONCLUSIONS: Although the operating procedure takes less time with a large-area ablation system, a scanning and rotating delivery system has the advantage of reliable and homogeneous removal of corneal tissue.

[Principle and mechanism of action of an ArF excimer laser system with a scanning and rotating slit aperture]. / Prinzip und Wirkungsweise eines ArF-Excimerlasersystems mit scannender und rotierender Schlitzblende.

This study was designed to investigate the quality of a scanning and rotating slit delivery system of an ArF-Excimer laser (Nidek EC 5000). The ablation patterns on PMMA samples were examined by REM. The influence of inhomogeneities in the beam profile was simulated on a computer and compared with a conventional large-area ablation system. The impairment of the ablation rate by radiation absorption of the ablation plume was measured as a function of the repetition rate and the application of a fixation ring. The scanning and rotating slit delivery system creates extremely smooth ablation patterns. The delivery system is very tolerant of small-beam inhomogeneities. The ablation rate is very sensitive to the dynamics of the ablation plume. Although the operating procedure takes less time with a large-area ablation system, a scanning and rotating delivery system has the advantage of reliable and homogeneous removal of corneal tissue.

ArF-excimer laser-induced secondary radiation in photoablation of biological tissue.

Secondary radiation, emitted during and after the irradiation of corneal, dermal, and dental tissue by an ArF-excimer laser (193 nm), was qualitatively and quantitatively characterized. Emission of secondary radiation was found in the range of 200-800 nm. The intensity of secondary radiation in the range of 200-315 nm (UVC and UVB) is approximately 20% of the total intensity at high laser fluences (> 2 J/cm2), and approximately 50% at moderate laser fluences (< 500 mJ/cm2); 10 muJ/cm2 in the UVC and UVB were measured at the sample surface, at fluences (< 1J/cm2) which are of relevance for clinical procedures on soft tissues. In dental tissue processing, very high fluences (> 5 J/cm2) are required. As a consequence, laser-induced plasma formation can be observed. Secondary radiation can be used as a visible guide for selective removal of carious altered tissue. The data we have found might be of assistance in estimating potential hazards for future mutagenic studies in the field.

Internal ablative sinostomy using a fiber delivered Q-switched CTE: YAG laser (2.69 microns).

Current trends of laser technology towards low-thermal photoablative pulsed mid-infrared lasers open new, more adequate approaches to experimental surgical procedures which have already been evaluated in the past. Transcorneal laser ablation of the trabecular meshwork (internal sinostomy) in human autopsy eyes was performed with a Q-switched CTE:YAG laser (wavelength: 2.69 microns, pulse width: 1 microsecond). Beam delivery was achieved with conventional optical quartz fibers (Low-hydroxy-fused-silica: 0.3 ppm, 50 cm length, 200 microns diameter). Light- and scanning-electron-microscopy were used for histological examination and micromorphological analysis. By applying two laser pulses (6 J/cm2) to the functional trabecular meshwork, a round sinostomy with a diameter corresponding to the diameter of the fiber-tip was achieved. It was possible to set several internal sinostomies into the chamber angle opposite to the entering paracentesis of the laser fiber-tip. Collateral thermal tissue alteration reached up to 50 microns, and since fiber-tip contact was maintained during laser application, thermal tissue alteration was also found around the opposite wall of Schlemm's canal. At higher energy fluences mechanical (disruptive vaporization) effects were significantly enhanced. It can be concluded, that low-thermal pulsed mid-infrared lasers are adequate instruments to perform transcorneal trabecular ablation (abinterno sinostomy). The laser used in this study (CTE:YAG) bears the advantage that its radiation can easily be delivered in conventional optical quartz fibers.

Q-switched CTE:YAG laser sclerostomies on human autopsy eyes.

Experimental laser sclerostomies were performed on human eye-bank eyes with a new mid-infrared solid-state laser that is characterized by adequate optic-fiber transmission and low-thermal tissue interaction. The laser presented herein works with a chromium thulium erbium-doped (CTE): YAG crystal as the active medium, emitting radiation at a wavelength of 2.69 microns. In the Q-switch mode, the pulse duration is tunable from 0.5 to 2.5 microseconds. The maximal energy is 50 mJ/pulse (1-10 Hz). Attenuation of energy transmission in quartz (0.3 ppm) optic fibers is < 8 dB/m (diameter, 200 microns). Absorption depths of 2.69 microns radiation in water is 12.5 microns. In vitro procedures performed were ab-interno and ab-externo full-thickness sclerostomies. Histological and micro-morphological examination was performed by light microscopy and scanning electron microscopy. Collateral tissue damage in processed sclerostomies did not exceed 50(+/- 10) microns at typical fluences (10 J/cm2). In contact guidance, 10-15 laser pulses were required in the full-thickness ab-externo procedure, whereas up to 50 pulses were required in the ab-interno procedure. The number of laser pulses applied corresponded to the length of the filtration canals created. The canal was significantly longer (2.5 +/- 1 mm) in the ab-interno approach than in the ab-externo approach (1 +/- 0.2 mm). The intraocular ostium of the filtration canal in the ab-externo procedure showed enhanced signs of mechanical deterioration. It is concluded that both the wavelength (2.69 microns) and the pulse duration (0.5-2.5 microseconds) of the CTE: YAG laser are appropriate for laser sclerostomy.(ABSTRACT TRUNCATED AT 250 WORDS)

[Photoablation of the cornea with pulsed 2790 nm ErCr:YSGG laser irradiation. Basic studies]. / Zur Photoablation der Hornhaut mit gepulster 2790 nm ErCr:YSGG-Laserstrahlung. Grundlegende Untersuchungen.

The potential of 3 microns solid-state lasers as an alternative to excimer lasers for photoablative corneal surgery was investigated. A Q-switched ErCr:YSGG laser (2790 nm, 200 ns) was used for irradiation of porcine corneas and agar-agar samples. Mechanical tissue effects (stroma, endothelium) were documented by micromorphology. Laser-induced shock-waves were analyzed by piezo-electric transducers. No sharp ablation threshold, as in excimer laser photoablation, could be determined. Energy fluences < 2 J/cm2 led to dehydration of the irradiated samples. Higher fluences are necessary for the evaporation of tissue water to be so vigorous that the tissue matrix is expelled along with the organic matrix. At high fluences, the ablation rate exceeds the absorption depth of the laser radiation (up to 25 microns/pulse). At fluences between 2.5 and 28 J/cm2 the thermal necrosis zone adjacent to the crater was 7 +/- 3 microns. The intensity of the laser-induced acoustic shock waves can peak to some hundred bar. Small gas bubbles up to 1 mm were found in the surrounding area of the ablation crater. Apparently, they were pressed between the collagen lamellas by the explosive force of the ablative process. In deep excisions (> 75%) endothelial defects underneath the beam axis could be documented. Large-area tissue ablation, with a resolution in the range of 1 micron, as necessary in myopia correction, will not be possible with the present generation of ErCr:YSGG lasers. Its high ablation rate makes this laser suitable as a cutting (astigmatism, keratoplasty, vitreous surgery) and drilling (glaucoma) device.

Q-switched CTE:YAG (2.69 microns) laser ablation: basic investigations on soft (corneal) and hard (dental) tissues.

Ablative infrared lasers either show poor transmission in optical fibers (Er:YAG: 2.94 microns; ErCr:YSGG: 2.79 microns or are characterized by potential relevant thermal side effects (Ho:YAG: 2.1 microns). The CTE:YAG laser (Cr,Tm, Er doted YAG) emits radiation at a wavelength of 2.69 microns. Efficiently high optical fiber transmission is accomplished (attenuation: < 8db/m for Low-Hydroxy-Fused-Silica (LHFS): 0.3 ppm). Since the laser can easily be run in the Q-switch mode (pulse duration: 0.5-2.5 microseconds) thermal side effects of tissue interaction were expected to be low. Laser tissue interaction was studied on soft (porcine and human cornea), as well as on hard (human dental) tissue. Histological and micromorphological examinations were performed by light microscopy and scanning electron microscopy. It was found that ablation rates in corneal tissue increased from 5 to 90 microns/pulse with increasing laser fluences (5.5-20 J/cm2). Collateral thermal damage reached as far as 20 +/- 5 microns, and was higher (up to 50 microns) when craters where processed in the contact mode using LHFS-optical fibers. In comparison to soft tissue ablation, hard dental tissue ablation showed very little increase of ablation rate (1-3 microns/pulse) when higher fluences were applied. In dental tissue processing, the ablative effect was accompanied by a luminescence, indicating the presence of plasma. We conclude that the presented CTE:YAG laser can be considered as an effective tool for a variety of laser surgical applications where high power optical fiber delivery is required and where strong thermal side effects are not desired.

[193 nm Excimer laser photoablation of the cornea. Spectrum and transmission behavior of secondary irradiation]. / 193 nm Excimer-laserphotoablation der Hornhaut. Spektrum und Transmissionsverhalten von Sekundärstrahlung.

In order to estimate the photomutagenic and phototoxic potential involved we analyzed the spectrum and intensity of secondary radiation induced with a 193 nm excimer laser in photoablation of corneal tissue. The spectrum of secondary radiation was analyzed by an optical multichannel analyzer. A pyroelectrical detector was used to evaluate the energy of the secondary radiation. We found the secondary radiation to be in the range of ultraviolet to infrared. The spectrum has a relatively high quantity (20%) of radiation between 240 and 280 nm. The intensity of the secondary radiation depends on the energy fluence of the primary laser pulse and can reach a quantum yield of up to 10(-3) (at 800 mJ/cm2). At a fluence of 230 mJ/cm2 (193 nm), the secondary radiation in the range of 240-280 nm is approximately 5 microJ/cm2. Radiation below 300 nm was not transmitted through the cornea. Since the high genetic activity of UV radiation in the range from 240-280 nm is well known, evaluation of the potential mutagenicity of 193 nm excimer laser radiation should take into consideration the presence of secondary radiation in this problematic spectral range. However, there is no incidence known for specific UV-induced corneal cancers, which supports the argument that the potential mutgenic risk of clinical excimer laser application can be considered to be low. Because of the full corneal absorption of radiation below 300 nm, there is no risk known for pigmented intraocular structures.

Contact cw-Nd:YAG laser cyclophotocoagulation for treatment of refractory glaucoma.

Contact cw-Nd:YAG laser transscleral cyclophotocoagulation was performed on 42 patients (44 eyes) with glaucoma who were not responding to medical treatment or had failure of prior surgical procedures. No selection was made as to the type of glaucoma (congenital, primary, secondary due to trauma or inflammation). We applied between 16 and 60 exposures 0.5-2 mm posterior to the limbus. Prior to cyclophotocoagulation the mean intraocular pressure (IOP) was 40.4 mm Hg (+/- 8.0). As a result of the treatment, the mean IOP was lowered to 21.1 mm Hg (+/- 5.2). In eyes with congenital, neovascular, and inflammatory glaucoma, a therapeutic effect could only be achieved by repeated coagulations. The patients were followed for a mean of 4.8 months (3-7 months). One eye developed a transient choroidal detachment. In two eyes, iris hemorrhages were noted. Contact cyclophotocoagulation is generally well tolerated. Randomized studies are to be carried out to confirm whether cyclophotocoagulation is an effective tool in the treatment of glaucoma. Until then, cyclophotocoagulation should be restricted to cases not responding to conventional therapy.

[Structure and dynamics of photo-acoustic shock-waves in 193 nm excimer laser photo-ablation of the cornea]. / Struktur und Dynamik photoakustischer Schockwellen bei der 193 nm Excimerlaserphotoablation der Hornhaut.

The structure and dynamics of acoustic shock waves generated with a 193-nm ArF-excimer laser pulse (20 ns) in corneal photoablation were investigated using piezoelectric transducers (PVDF foily). The shock waves passed through the cornea at the speed of sound (1630 +/- 120 m/s). The duration of the acoustic half-value thickness was approximately 60 ns. At clinically relevant laser energy densities (200 mJ/cm2) the amplitude of the shock-waves was 80 bar. At higher energy densities (500 mJ/cm2) the amplitude reaches 150 bar. When laser pulses were applied with a spot size of 100 microns the amplitude of the acoustic transient decreased inversely with the distance to the interaction zone. At large beam diameters (4 mm), however, even at a distance of 3 mm from the interaction zone no significant decrease of the shock-wave amplitude could be found. It is assumed that the mechanical stress involved in laser-induced acoustic shock-waves may be the cause of cellular alterations and the structural damage to adjacent collagen layers leading to the onset of postoperative scar formation.

Retrospective study of retinal detachment following neodymium:YAG laser posterior capsulotomy.

A retrospective study of 1,000 cases that had Nd:YAG laser posterior capsulotomy after cataract surgery is presented. We analyzed the correlation of the patient's age, axial length of the eye, method of cataract surgery, and laser parameters (exposures, energy, and burst mode) with the incidence of retinal detachment (1.6% overall). The highest risk for retinal detachment (12.3%) was in patients with an axial eye length of 26.1 mm to 28.0 mm. The average age of patients with retinal detachments was 60.6 years, ten years younger than the collective average age. Laser parameters, such as energy, exposures, and burst mode, and the method of cataract surgery (extracapsular or phacoemulsification) did not correlate with the incidence of retinal detachment. After surgical treatment of the 16 retinal detachments, a good postoperative visual acuity (better than 20/40) was achieved in most cases.

[Preparation of hard tooth structure with Excimer lasers. In vitro study]. / Bearbeitung von Zahnhartgeweben mit einem Excimer-Laser. Eine In-vitro-Studie.

The present study will show, that caries removal and conditioning of tooth surfaces by an (ArF)*-Excimer-Laser is an alternative to conventional preparation methods without thermal and mechanical irritations. This promises caries removal without pain to the patient. The photoablative process leads to retentive surfaces of the treated cavities. These findings promise good results in adhesive techniques. In vitro studies show, that photoablation of dental tissue is effective enough to make clinical usage possible.

[Preparation of hard tooth structure with Excimer lasers]. / Bearbeitung von Zahnartsubstanzoberflächen mit einem 193 nm-ArF-Excimer-Laser.

In this study the possible application of photoablation with an Excimer UV laser for the creation of retentive surfaces was studied as an alternative to conventional enamel conditioning methods using acids. Surfaces of untreated enamel and of prepared cavities were irradiated with an argon fluoride Excimer laser at a wavelength of 193nm and evaluated in a scanning electron microscope. The bond strength of composites to these surfaces was measured in tear tests. "Laser conditioning" left the surfaces similarly roughened as chemical etching. The variable extension of the laser field allows a sharp delineation of the area to be conditioned. The tear tests with human tooth enamel showed bond strength values corresponding to approx. 75% of those obtained by acid etching techniques. The question if these bonds are durable is the subject of current studies.

Mass spectroscopic analysis of excimer laser ablated material from human corneal tissue.

The clinical feasibility of photorefractive keratectomy depends on the surface structure of the ablated cornea. Two factors that influence the remodeled surface are the homogeneity of the energy distribution and the properties of the laser source (energy and wavelength). Currently, the homogeneity of the beam is difficult to control. The second factor, laser source properties, was the focus of this study. We investigated the effect of laser wavelength and energy by analyzing the reaction products of photoablation. We monitored the fragments produced by UV-laser ablation of human corneas using mass spectroscopy in the range of 0 to 100 atomic mass units. At 248 nm (KrF), average photon energy was 5 mJ/cm2, increased to 90 mJ/cm2 by intervals of 5 mJ/cm2. At 193 nm (ArF), photon energy was increased by the same interval from 5 mJ/cm2 to 80 mJ/cm2. Our experiments showed that there was a fluence threshold of approximately 40 mJ/cm2 at 193 nm (ArF) and 50 mJ/cm2 at 248 nm (KrF). Exceeding this threshold led to sudden increases in the number and relative intensity of fragment peaks in mass spectroscopy. This indicates the onset of multiple-photon processes and effective photochemical breakdown. There was a significant difference between both wavelengths in the distribution of mass peaks, indicating higher ionization power at 193 nm.