[Review of the past year--"cornea"].
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Animals↗
Biomedical subjects
B Jean
Publications and source records attributed to B Jean.
[Moist ablation of the corneal surface with the Er:YAG laser. Results of optimizing ablation].
The Er:YAG laser, emitting light at 2.94 microns, may be an alternative to the 193 nm excimer laser for photorefractive keratectomy. Compared to the excimer laser, the ablation rate is very high. Surface roughness is also more pronounced than for the excimer laser. Using a precorneal liquid film, these two factors can be reduced, as shown in ablation experiments performed on porcine corneas. Thermal damage of the remaining corneal tissue is another side effect. There is no significant decrease in the amount of thermal damage with this new technique,--not even when the pulse length is reduced.
Animals↗
[Effect of pulse duration of the Er:YAG laser on photoablation in ocular tissue (cornea and sclera)].
After photoablation in corneal and scleral tissue with the Er:YAG laser, two zones of thermal damage can be detected: The first zone (about 3 microns thick) consists of thermally denatured debris. The second zone (about 30 microns thick) shows a slightly more intense staining (H&E) compared to the non-influenced tissue. Variation of laser pulse duration between 100 microseconds and 1300 microseconds does not influence the extension of these two thermal damage zones. Furthermore, ablation rate and ablation volume remain nearly constant within this range of pulse durations. These data were obtained by histology (H&E staining) and with a recently published silicon cast replica method. All experiments have been performed on corneas and sclera of pig eyes.
Animals↗
Silicone replica technique and automatic confocal topometry for determination of corneal surface roughness.
No method for the objective measurement of corneal surface roughness has thus far been available for experimental and clinical investigations. The surface roughness of photoablated porcine corneas was investigated with the silicone-cast method and automatic confocal topometry. Photoablation was performed with the 193-nm excimer laser. Surface roughness was determined as a function of the repetition rate (2-60 Hz; fluence, 180 mJ/cm2; beam diameter, 2 mm; 300 laser pulses/experiment). Immediately after photoablation, a silicone replica of the ablated surface was made and analyzed later using confocal topometry. The surface roughness for excimer laser ablation was found to be frequency-dependent: 0.4-0.6 +/- 0.08 micron (2-30 Hz) and 1.2 +/- 0.12 micron (60 Hz). The silicone cast of the cornea of a healthy eye gave an exact image of the profile and curvature: the difference between radius measurements of the cornea (Zeiss ophthalmometer) and of the silicone cast (laser topometer) was about 0.5%. As the silicone-cast method can also be used for in vivo animal experiments, the correlation between surface roughness and laser repetition rate can be studied with regard to photorefractive keratectomy.
Animals↗
Noncontact photoacoustic spectroscopy during photoablation with a 193-nm excimer laser.
Photoablation with the 193-nm excimer laser in organic and inorganic material generates an audible sound wave; in a clinical context, this helps to determine when effective photoablation is taking place. We investigated whether the acoustic phenomenon would qualify as a quantitative parameter of photoablation during non-contact photoacoustic spectroscopy (NCPAS). Photoablation was performed with a 193-nm excimer laser at a fluence of 80-330 mJ/cm2 and ablation-zone diameters ranging between 1.2 and 5.13 mm. A capacitor microphone (Broel & Kjaer) emitted a time signal that was processed for Fourier transformation (FT, spectrum of frequency). The following elements of the FT-signal were studied: the integral, the amplitude, the half-value, and the location of the center frequency. The integral and the amplitude were correlated linearly with the fluence. Variation of the ablation-zone diameter between 1.2 and 5.13 mm was found to produce a squared increase of the integral and the amplitude (fluence, 180 mJ/cm2). The half-value and the center of frequency of the FT signal were constant for the same target material but varied between materials. NCPAS may qualify for the future control of various photoablation and laser parameters such as incision depth, ablation-zone diameter, fluence, and target-material identification and discrimination. Its advantage over competing optical methods is its independence from optical target properties (e.g., fluorescence, surface roughness, reflectivity).
Acoustics↗
[Silicone impression procedure. Principles for determining ablation and healing parameters in vitro and in vivo].
Topometry and measurement of photoablation patterns are key questions for keratorefractive photoablation. So far, ablation rates have been determined either by tissue perforation or histological micrometry. A cast of irradiated cornea was made by using a 2-component silicon that polymerizes within minutes, thus preserving the corneal topography immediately after photoablation. The silicon surface is extremely smooth and the accuracy of the cast better than 1 micron. Reproducibility and long-term stability were proven for casts of photoablated PMMA. Thus ablation rates and profile, volumetry and topometry can be determined at any time. The method was applied for 193 nm excimer and 2.94 microns Er:YAG laser in vitro irradiation of the human cornea. Ablation rates in Bowman's layer and stroma were observed for various radiant energies and distinct pulse numbers. The average ablation rates are in agreement with published data. It could be demonstrated that there was an incubation effect for the first pulses. The method feasibility for in vivo measurement was also proven in an animal model. After excimer photoablation in rabbit eyes (beam diameter 3.5 mm, radiant energy 185 mJ/cm3, ablation rate 0.3 micron/pulse), wound healing was recorded: for the right eye silicon casts were molded at three different moments. For the left eye only photographs were taken. There was no difference in the time course of wound healing, so the silicon does not seem to interfere with repair mechanisms of the corneal epithelium. No side effects were observed.
Animals↗
Selective laser-induced inactivation of proteins (SLIP) by labelling with chromophores.
Coupling a fluorochrome (e.g. fluorescein-isothiocyanate, FITC) to a molecule can enhance specific laser light absorption, thus leading to alteration or even destruction of the molecule itself. Therefore antibodies were labelled with FITC (absorption maximum 480 nm) and irradiated with laser light (488 nm) under various conditions. Inactivation of antibodies could only be achieved at the absorption maximum of FITC (as measured by direct and indirect immunofluorescence). Positive linear correlation exists between the amount of destruction and both exposure time and energy. Similar destructive effects were obtained when FITC-labelled peroxidase was irradiated. In these cases, enzyme activities measured by absorption photometry also showed a positive correlation to the total amount of energy transferred. Non-labelled proteins were not affected by irradiation. So we conclude that labelling of proteins with fluorochromes provides a highly specific means of selection of target molecules to be destroyed or inactivated. The method is based upon the laws of linear optics and is different from photodynamic or photochemical actions. The destructions observed are most likely caused by thermally induced changes of the molecules' tertiary structure.
Antibodies↗
[Melanoma metastasis to the pancreas].
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Axilla↗
[Real time eye tracking--principles and quantification].
Tracking and quantification of eye movements in real time is a prerequisite for future computer assisted laser positioning for diagnostic or therapeutic purposes. Principles of TV-image processing are described: tracking of contrasts and pattern recognition tracking by object correlation; their relevance for tracking retinal targets is illustrated using authentic video material. For practical use, the pattern recognition technique qualifies better. The influence of the systems variable parameters on retinal target pursuence is described. Automatic target pursuence of authentic eye movements reached tracking success rates well above 90% thus outperforming manual tracking by one order of magnitude.
Computer Graphics↗
[Validity and reproducibility of confocal corneal measurements].
In order to verify reproducibility and validity of confocal measurements of the cornea we examined a well known biological model: Increasing corneal thickness under hypoxic conditions during contact lens wear. The method verified increasing thickness with high significance. In addition, reproducibility was determined within a range of 5 mu. As a result, confocal measurements proof to be a powerful tool for topographical reconstruction of corneal shape.
Algorithms↗
[Image of the cornea with the scanning laser ophthalmoscope].
With a scanning laser ophthalmoscope (SLO), a hexagonal reflex phenomenon can be observed, which originates from the tear film and corneal tissue layers. Time motion analysis verifies that it is possible to discriminate between the cornea and tear film.
Cornea↗
[The simultaneous video fluoangioscope].
The present paper describes the video simultaneous fluoangioscope. It is based on the Rodenstock simultaneous fluoangioscope, an accessory for use with the laser slit-lamp. It has been proving its clinical usefulness since 1984. Hitherto, its optical superimposition of the corresponding fluorescein angiograph onto the actual fundus view was based on angiographic film as an information carrier. Digital fluorescein angiography (videoangiography) has meanwhile made film superfluous while at the same time opening up new possibilities. The video simultaneous angioscope superimposes a selected video half-frame onto the fundus, thus transferring angiographic data and facilitating safe and easy coagulation. The advantages and new possibilities arising from them are discussed and the system peripherals are described. An illustration shows the superimposition of the images when looking through the slit-lamp.
Equipment Design↗
[Examinations of the cornea and anterior chamber angle region with a laser tomographic scanner (LTS)].
The Laser Tomographic Scanner LTS based on laser scanning and confocal detection is a system to generate and measure optical section images. The periphery of the cornea and the anterior chamber angle region is shown in the horizontal section image with high image quality and high signal-to-noise ratio. 130 patients and 163 eyes were examined in this way. First experience shows possible applications for special clinical situations. Using horizontal optical section images, a procedure is generated to measure the anterior chamber angle without contact or local anesthesia with a reproducibility of 2 degrees. Horizontal section images clearly demonstrate changes of anterior chamber angle depth following e.c. cataract extraction and implantation of posterior chamber IOLs. Using the generated measurement procedure, these changes could be quantified.
Adult↗
[Laser-induced occlusion of corneal blood vessels with variable emission and absorption].
Laser light has repeatedly been proposed for the occlusion of corneal neovascularizations. Priority has to be given to minimize laser energy in order to limit side effects such as corneal burns. We investigate the influence of variable emission wavelength using a dye laser or dye-enhanced absorption with intravenous sodium fluorescein. Laser energy can be reduced using intravenous dyes at vessel diameters less than 50 microns. Permanent occlusion is achieved in 43% instead of 28% without dye-enhanced absorption. Vessels measuring greater than 50 microns in diameter can be occluded best at lowest laser energy levels when 575 nm laser light is used, which approximates the absorption maximum of hemoglobin.
Absorption↗
[Laser scanning in ophthalmology].
The current state of the art for the major laser scanning methods, laser scanning ophthalmoscopy (LSO) and laser tomographic scanning (LTS) is discussed and the function principles are described. Experience with a prototype of each instrument from Rodenstock (LSO) and Heidelberg Instruments (LTS) is reported. LSO imaging of the cornea, vitreous, retina, and optic disc, as well as on-line processing is demonstrated with examples (nerve fibre colour coding and histograms). Measurement of the cornea, optic disc and retinal topography with LTS is also demonstrated with examples. An example of polarization optical imaging of the cornea's assumed interferometric "tension patterns" is shown. The current status and future possibilities of laser scanning, its expanded diagnostic potential with microperimetry, IR scanning angiography and polarization optic imaging and measurement (eg. nerve fibre thickness) is discussed extensively. The safety aspects of laser light exposure of the macula are also mentioned. Laser scanners as imaging and measuring sensors of unknown accuracy open a new area of possibly revolutionary diagnostic possibilities.
Cornea↗
[Imaging the optic papilla with the laser scanning ophthalmoscope].
The laser scanning ophthalmoscope offers tissue examination and support of papillometrical evaluations as a result of different forms of illumination. Confocal, mixed, and Tyndall light are used in the differential diagnosis and identification of the scleral rim. With highpower mixed light under miotic conditions, imaging of the excavation is possible.
Glaucoma↗
[Use and technic of the CO2 laser on the external surface of the eye].
The CO2 laser, emitting at 10,600 nm in the extreme infrared wavelength has special advantages for ophthalmology: its hemostatic properties and its ability to cut, vaporize, and shrink tissue make it particularly effective on the external eye and adenexae. In particular, it can be used for layerwise removal of tissue on the conjunctiva, the sclera, and the lids. Energy and exposure time are especially important. Irradiation of sclera from enucleated globes showed that these two parameters have a direct effect on the depth of craters - the CO2 laser's typical impact - and the laser's thermal effect on tissue. Technical and practical observations and the clinical results of more than 80 cases treated with the CO2 laser are presented and discussed. The low-power CO2 laser is a useful ophthalmological tool which can partially replace conventional surgery and extend treatment indications.
Conjunctival Diseases↗
[CO2 laser vaporization of xanthelasmas].
Until now surgery was the only means of removing xanthelasmas. However, their proximity to blood vessels and consequent tendency to bleed makes visual supervision of the excision difficult. The CO2 laser's infrared wavelength permits photovaporization of tissue with excellent hemostasis. It is thus an ideal tool for removing xanthelasmas. Visual supervision is excellent, and the laser's shallow penetration depth permits layerwise removal of the yellow foam cell plaques. The resulting lesions heal without significant scarring, and deeper layers of the skin remain unharmed. The procedure is fast and easy, and postoperative care is minimal; cosmetic results and patient acceptance are excellent. A clinical case and the results of ten treatments are described. The authors conclude that surgical excision of xanthelasmas can be replaced entirely by CO2 photovaporization.
Adult↗