[Nuclear spin tomography of the human eye].
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Eye Diseases↗
Biomedical subjects
T Seiler
Publications and source records attributed to T Seiler.
The distinction of corneal water in free and bound fractions.
The corneal water is studied by NMR measurements. There are two fractions of water, one more strongly bound to relaxation centres of proteoglycanes and the other almost freely diffusible as liquid bulk water. A quantitative analysis shows that the bound fraction makes up a very small part (less than 1%) of the total water. So nearly all the water is available for the nutrition of the cornea by diffusion.
Collagen↗
Excimer laser photorefractive keratectomy.
Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.
Animals↗
Dependence of wave front refraction on pupil size due to the presence of higher order aberrations.
PURPOSE: Propagation of light through the optical pathway within the eye can lead to a deformation of the wave front that might affect objective but also subjective refraction depending on pupil size. The aim of this study was to investigate the change in wave front refraction that is calculated on the basis of second order Zernike polynomials when varying the pupil size from 6 mm to 3 mm. The change was correlated with the amount of fourth and sixth order spherical aberration and fourth and sixth order astigmatism. METHODS: Wave front aberrations were measured in 130 eyes by means of a Tscherning wave front sensor at a pupil size of 6 mm. Wave front aberrations in terms of Zernike coefficients up to sixth order were approximated for 6 mm and 3 mm pupil size. The wave front refraction was calculated based on the second order Zernike coefficients for both pupil diameters. Resulting differences in wave front refraction (sphere or cylinder) due to the change in pupil size were correlated with the initial higher order aberrations determined for the 6.0 mm pupil by means of a linear regression (Spearman rank correlation coefficient). RESULTS: The correlation between the change in sphere and cylinder on one hand and the spherical aberration and higher order astigmatism on the other hand was found to be highly significant (p<0.001), with a correlation coefficient of R = 0.96 for sphere and R = 0.85 for cylinder. CONCLUSIONS: Calculating the wave front refraction on the basis of second order Zernike polynomials is plagued with the influence of the higher order aberration preexisting in the individual eye. This is one reason why this method does not represent precisely enough subjective refraction. Other methods that calculate the refraction based on wave front measurement independent from the pupil size should be established in the ophthalmic community.
Adolescent↗
Corneal iron line associated with steep central islands after photorefractive keratectomy.
PURPOSE: To report a new corneal iron deposit after excimer laser photorefractive keratectomy (PRK). METHODS: Two patients with symptomatic persistent steep central islands were noted to have a corneal iron ring at 6 months to 1 year after surgery. This is different from the central iron spot noted in most patients at 1 year. RESULTS: One patient had repeated PRK with improvement of his symptoms and resolution of the iron ring. CONCLUSIONS: A corneal iron ring after excimer laser PRK suggests the presence of a persistent steep central island of stromal origin. Since corneal iron deposition signifies chronicity, symptomatic patients should be retreated as resolution of the steep central island is not likely to occur.
Adult↗
Iatrogenic keratectasia after laser in situ keratomileusis.
BACKGROUND: Lamellar refractive surgery reduces the biomechanical strength of the cornea which may lead to mechanical instability and keratectasia. METHODS: Three eyes had laser in situ keratomileusis (LASIK) for myopia from -10.00 to -13.50 D. The procedures were performed with two different wide-field excimer lasers and two different microkeratomes. The patients were followed up to 1 year after surgery. RESULTS: Central steep areas developed between 1 and 8 months after surgery. In contrast to conventional central steep islands, these showed rapid progression and were interpreted as keratectasia. CONCLUSION: Iatrogenic keratectasia represents a complication after LASIK that may limit the range of myopia correction. Based on biomechanical considerations we recommend a residual corneal thickness of the stromal bed of at least 250 microm.
Adult↗
Clear lens extraction in the 19th century--an early demonstration of premature dissemination.
Clear lens extraction for correction of high myopia is a concept known since at least 1800, but was performed only occasionally because of the hazards of cataract operation in general in the era before aseptic surgery. After the invention of sterilization, in 1889 a rush for myopia correction by clear lens extraction was started by Fukala in Austria/Germany and Vacher in France. It took 10 years until a retrospective comparison of operated and non-operated eyes revealed the high complication rate after clear lens extraction. After 1900, the "myopia operation" was increasingly abandoned and eventually disappeared.
Austria↗
Diametral ablation--a technique to manage decentered photorefractive keratectomy for myopia.
PURPOSE: Decentered ablation after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) is an intraoperative complication that may significantly influence the visual outcome. Currently, there is no accepted technique available to manage this problem. METHODS: A technique of reoperation for eccentric ablation after PRK called diametral ablation is presented that uses a transepithelial phototherapeutic keratectomy (PTK) that leaves epithelium over the area of primary PRK. This residual epithelium acts as a shield for the previously treated stroma during a second PRK located opposite to the primary PRK with reference to the pupil center. The results of six such retreatments (6 eyes of 6 patients) are presented. RESULTS: In all eyes, a significant improvement regarding centration and subjective complaints was achieved. The eccentricity was reduced from 1.43+/-0.66 mm to 0.36+/-0.15 mm (P = .003). CONCLUSION: Diametral ablation is a promising alternative treatment of eccentric ablation.
Adult↗
Techniques for stiffening the cornea.
In keratoconus, corneal stiffness is decreased. The purposes of this study were to search for techniques to stiffen the cornea and to determine a dose-response relation. The stiffness of collagenous tissues can be increased by cross-linking. Cross-linking techniques--riboflavin and ultraviolet irradiation (365 nm, 2 mW/cm2, 45 min), glutaraldehyde of low concentration, and several aldehyde sugars--were tested on corneas of enucleated porcine eyes. The stress-strain relation was measured and compared to untreated corneas. Aldehyde sugars produced cross-links by nonenzymatic glycation only after a prolonged time (realized in diabetics). Riboflavin and UV seems to be a promising technique to stabilize the cornea by artificial cross-linking.
Aldehydes↗
Limitations of erbium:YAG laser photorefractive keratectomy.
PURPOSE: The erbium:YAG laser (lambda = 2.94 microm) has been considered promising as an alternative to the ArF excimer laser in photorefractive keratectomy (PRK). However, corneal application of this mid-infrared solid state laser is still plagued with various disadvantages compared to that of the ArF excimer laser (lambda = 193 nm). We discuss the limitations of PRK with the erbium:YAG laser. METHODS: Measurements of ablation threshold, ablation efficiency, and thermal damage were done to compare the process of erbium:YAG laser photoevaporization to the ArF excimer laser. PRK procedures were performed on fresh enucleated pig corneas to investigate the morphology and surface roughness of the cornea after scanning-spot and fundamental mode photoablation. Surface roughness was measured by using a tactile surface reprofiling system. RESULTS: The ablation threshold and the ablation efficiencies for the erbium:YAG laser are significantly higher compared to the ArF excimer laser. Collateral thermal damage decreases with a reduction of laser pulse duration to a minimum of approximately 5 microm. Scanning electron microscopy and surface roughness measurements of the corneal surface after erbium:YAG laser treatment demonstrated higher surface roughness compared to ArF excimer laser treatments. CONCLUSIONS: The erbium:YAG laser is not at present an alternative to the ArF excimer laser for photorefractive keratectomy.
Animals↗
Wavefront-guided laser in situ keratomileusis: early results in three eyes.
PURPOSE: Wavefront optical aberrations induced by refractive corneal surgery correction of myopia are probably the reason for deterioration of visual performance in some eyes after surgery. Customized photoablation of the cornea to correct both the sphero-cylindrical refractive error as well as individual optical aberrations may improve postoperative visual acuity and visual performance. METHODS: In 3 eyes of 3 patients the wavefront deviations were measured by means of an aberrometer of the Tscherning-type. Based on these measurements an ablation pattern was determined and applied during a LASIK procedure using a Wavelight Allegretto scanning spot excimer laser with a spot size of 1 mm and a laser repetition rate of 200 Hz. The 3 eyes are part of a prospective study on wavefront-guided LASIK started in July 1999. RESULTS: At 1 month after LASIK, all 3 eyes had gained up to 2 lines of best spectacle-corrected visual acuity. Best spectacle-corrected visual acuity improved to 20/10 in all 3 eyes, uncorrected visual acuity was 20/10 in two eyes, and 20/12.5 in 1 eye 1 month postoperatively. The wavefront deviations were reduced by 27% on average. At 3 months, best spectacle-corrected visual acuity was 20/10 in 2 eyes and 20/12.5 in 1 eye. CONCLUSION: Wavefront-guided LASIK is a feasible approach in refractive corneal surgery. Optimized ablation patterns may further improve the visual results.
Adult↗
Principles of Tscherning aberrometry.
Higher-order optical errors of the human eye are often responsible for reduced visual acuity in spite of an optimal spherical or cylindrical refraction. These optical aberrations are of natural origin or can result from operations on the eye involving optical structures. The presented wavefront analyzer is based on Tscherning's aberroscope. A collimated laser beam illuminates a mask with regular matrix pin holes which forms a bundle of thin parallel rays. These rays form a retinal spot pattern on the retina that is more or less distorted according to the optical errors of the eye. This retinal spot pattern is imaged onto the sensor of a low-light CCD camera by indirect ophthalmoscopy. The deviations of all spots from their ideal regular positions are measured by means of a personal computer, and from these values the optical aberrations are computed in the form of Zernike polynomials up to the 8th order.
Diagnostic Techniques, Ophthalmological↗
Clinical experience with the Tscherning aberrometer.
PURPOSE: With the aberrometer based on Tscherning's principle, measurements of wavefront aberrations of human eyes with high accuracy and reproducibility are available for standard diagnostic investigations. METHODS: During investigational and clinical trials, wavefront-aberrations of about 300 human eyes were measured and evaluated within the last few years. RESULTS: measurements are presented in terms of Zernike coefficients and as height maps that can be converted directly to ablation profiles for wavefront-guided laser treatments. CONCLUSION: The Tscherning aberrometer is a simple optical device with high accuracy appropriate for routine clinical investigations on optical aberrations of the human eye.
Adolescent↗
Operative correction of ocular aberrations to improve visual acuity.
PURPOSE: Optical aberrations of the human eye degrade the quality of the retinal image and may, therefore, represent a major limit of visual acuity. METHODS: In 15 eyes, ocular aberrations were corrected in addition to myopia and astigmatism by means of wavefront-guided laser in situ keratomileusis (LASIK). RESULTS: At 1 month after surgery, a supernormal visual acuity of 20/10 and better was obtained in 4 eyes (27%). The increase in root mean square wavefront error ranged from 0.6 to 2.3 and was significantly correlated with the increase in visual acuity (R2 = 0.79; P = .03). CONCLUSION: Although the correction of aberrations was not yet optimal, these results show that ocular optical aberrations limit visual acuity in humans and supernormal visual acuity can be achieved by operative correction.
Adult↗
Influence of corneal curvature on calculation of ablation patterns used in photorefractive laser surgery.
PURPOSE: The aim of this work was to clarify the influence of the effective illumination area and possible reflection losses that occur during laser-tissue interaction on the modeling of profiles for customized corneal ablation, such as wavefront-guided treatments. METHODS: The changes of the ablation depth per laser pulse due to the projection of a laser spot onto the corneal front surface and reflection losses at the air-tissue interface were calculated. RESULTS: Moving with a scanning-spot from the center of the cornea toward the limbus resulted in an increase of the effective illumination area and reflection losses, which led to a decrease in the ablation depth per laser pulse. The decrease of the ablation depth was strongly related to the initial radiant exposure and the corneal curvature radius. CONCLUSIONS: The corneal front surface must be taken into consideration for ablation profile calculations, especially in customized treatments, due to the strong dependence of the ablation depth on the corneal curvature.
Computer Simulation↗
Quantification by competitive quantitative RT-PCR of VEGF121 and VEGF165 in renal cell carcinoma.
The field of angiogenesis and its mediators in tumour tissue is gaining more and more interest because of their therapeutic implications to arrest progressive growth and metastasis. We examined the expression status of the proangiogenic vascular endothelial growth factor (VEGF) in tumour tissue and adjacent tumour-free tissue from renal cell carcinoma (RCC) as well as in cell cultures deriving from tumour tissue. Quantification of both secreted isoforms ot VEGF by competitive RT-PCR revealed a marked increase of VEGF message in tumours and especially in cell cultures from RCC. We found a significant correlation of VEGF expression and microvessel density which was investigated immunohistochemically. As further compared to other urological neoplasms we investigated for VEGF mediated vascularization, RCC is the most promising candidate for anti-angiogenic therapies.
Carcinoma, Renal Cell↗
Report on psychosocial findings and satisfaction among patients 1 year after excimer laser photorefractive keratectomy.
BACKGROUND: The first 26 patients who underwent photorefractive keratectomy with an excimer laser in our clinic with a 1-year follow up voluntarily answered a questionnaire. METHODS: It was intended to get information about their social status, motivation, expectations, and satisfaction with myopic excimer laser photorefractive keratectomy. RESULTS: All patients wore corrective lenses before surgery; 74% wore no optical correction after the photorefractive keratectomy. "To improve general vision" was the highest ranked motivation while "looking better" was only of minor importance. Seventy-two percent reported that their subjective vision became better; 28% felt that it didn't change, but none reported deterioration of subjective vision. Seventy-five percent of the patients reported improvement of their lifestyle after surgery, whereas 21% reported no change and one patient stated that his lifestyle got worse. On a scale ranging from 1 to 5, early postoperative course was painful with a mean score of 2.25; the treatment itself was considered as professional (1.42 +/- 0.8) and well done (1.54 +/- 0.8). Eighty-four percent of the patients reported that they were satisfied with the overall results. CONCLUSIONS: All patients would decide again to have photorefractive keratectomy for myopic correction.
Adult↗
Phototherapeutic keratectomy with excimer laser for Reis-Bückler's corneal dystrophy.
Two patients with decreased visual acuity and recurrent epithelial erosions due to Reis-Bückler's corneal dystrophy underwent phototherapeutic keratectomy with the 193-nanometer excimer laser. Because the epithelial surface was relatively smooth prior to surgery, ablations were performed through an intact epithelium. Postoperatively, visual acuity was improved and symptoms of erosion decreased in both patients. Although no refractive shift was intended with the phototherapeutic procedure, both patients were hyperopic following surgery. Superficial keratectomy with the 193-nanometer excimer laser thus provides an alternative to conventional surgical keratectomy.
Adult↗