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Niels Ehlers

Publications and source records attributed to Niels Ehlers.

5 recordsLinked to original sources
PubMed2003

Identification of differentially expressed genes in keratoconus epithelium analyzed on microarrays.

PURPOSE: The present study was conducted to investigate differential gene expression in individual samples derived from fresh-frozen human keratoconus and normal corneal epithelium, using gene microarrays. METHODS: Total RNA was extracted (11 keratoconus and 8 normal samples), labeled, and hybridized to microarrays (GeneChip; Affymetrix, Inc., Santa Clara, CA). GeneChip data were validated by verifying the expression profiles of 10 genes by real-time PCR and by recalculation using dChip software (Wong Laboratory, Department of Biostatistics, Harvard School of Public Health, Boston, MA). Furthermore, 3 of the 10 encoded proteins were stained by immunohistochemistry. RESULTS: In comparison with normal cornea, the expression of 471 of the 5600 genes on the microarrays was changed in the keratoconus samples. This number was reduced to 47 with increased expression and 9 with decreased expression when more stringent selection parameters were applied. These genes are believed to be involved in keratoconus. Two of the candidate genes, lysyl oxidase and tissue inhibitor of metalloproteinase 3, are known to be involved in other eye diseases. Expression profiles were reproduced with the software dChip (Wong Laboratory) and real-time PCR. Increases in keratin 6 and 13 were also detected at the protein level. CONCLUSIONS: Keratoconus epithelium appears to be characterized by massive changes of the cytoskeleton, reduced extracellular matrix remodeling, altered transmembrane signaling, and modified cell-to-cell and cell-to-matrix interactions. Validation of gene expression with dChip analysis and real-time PCR indicates GeneChip to be a valid technique for investigation of epithelium from single dissected corneal samples. Association between alterations at RNA and protein levels was observed for some of the tested candidates.

Adult↗
PubMed2002

[Supervision].

Within the past year, the idea of supervision has been introduced and promoted in the media by the manufacturers of wavefront-guided excimer lasers for refractive surgery. The concept is related to the ability of obtaining supernormal visual acuity and contrast sensitivity by correction of higher order aberrations in the biological optics of the human eye. However, the ocular aberrations fluctuate continuously and dynamically over time with the functional state of several of the individual optical components, including: thickness of the tear film, size of the pupil, and the degree of lens accommodation. These temporal variations represent major obstacles for achieving aberration-free images. In addition, the central perception of ideal aberration-free images may be hindered by neuronal limitations in the retina and brain. So far, only a few patients have experienced an increase in best corrected visual acuity following wavefront-guided refractive surgery. Also in the first prospective clinical trials with myopic individuals, only modest differences in visual performance have been detected between wavefront-guided and conventional treatment. Thus, immediate expectations from the new technology should be tuned down; supervision is not waiting around the corner.

Computer Simulation↗
PubMedDate not supplied

Prospective randomized study of corneal aberrations 1 year after radial keratotomy or photorefractive keratectomy.

PURPOSE: To evaluate the optical properties of the cornea 1 year after either radial keratotomy (RK) or photorefractive keratectomy (PRK) in a randomized group of patients with low myopia. METHODS: Ninety-six patients with myopia between -0.75 and -5.00 D were randomized to either radial keratotomy (n = 46) or photorefractive keratectomy (n = 50). Topography maps were obtained 1 year after surgery and analyzed by computation of total corneal wavefront aberration and Zernike polynomial coefficients for pupil sizes of 2, 4, and 6 mm. The 4-mm pupil size was used for optimization of the model. RESULTS: The total corneal wavefront aberrations after RK and PRK were similar and not statistically different. Wavefront aberrations arising from astigmatism or defocus accounted for approximately 70% of the total wavefront error at all pupil sizes in both groups. All types of aberrations, and in particular spherical aberration, increased significantly with increasing pupil size. Higher-order wavefront aberrations were almost twice as high after RK than after PRK at pupil sizes of 4 and 6 mm. Spherical aberration and coma were slightly higher after PRK than after RK. CONCLUSIONS: Pupil size had a major effect on corneal aberrations after RK and PRK. The most important aberrations were sphero-cylindrical, in which eyes became significantly more myopic with increasing pupil size. The image forming properties of the cornea are better after PRK compared with RK due to the lesser amount of higher-order aberrations.

Adult↗