Biomedical subjects

Jesper Ø Hjortdal

Publications and source records attributed to Jesper Ø Hjortdal.

5 recordsLinked to original sources

PubMed2005

[Efficacy and safety of laser-assisted in situ keratomileusis for myopia].

INTRODUCTION: The aim of this study was to assess the efficacy, frequency of re-operation and type and frequency of complications after laser-assisted in situ keratomileusis (LASIK) treatment for moderate to high levels of myopia. MATERIALS AND METHODS: 357 eyes from 190 patients were reviewed. The mean of the preoperative correction was -8.38 D (-1.75; -16 D) sph. (spherical), -1.00 D (0; 4.5 D) astigmatism. 15% (55 eyes) were re-treated. The mean of the correction before re-treatment was -2.78 D (+2.25; -11.00 D) sph., -0.43 D (0; -2.00 D) astigmatism. RESULTS: The three-month follow-up rate was 96% for primarily treated eyes and 99% for re-treated eyes. Where full correction was intended, 53% of the primarily treated and 93% of the re-treated eyes achieved an uncorrected visual acuity of > or =0.5. The refractive error for myopia less than -8 D was -0.80 D +/- 0.83 D and -1.37 D +/- 1.33 D for myopia -8 D and above after one treatment and -0.47 +/- 0.66 D after re-treatment. 1.2% (4) of the primarily treated and 3.9% (2) of the retreated eyes lost more than two lines in best spectacle-corrected visual acuity (BCVA). CONCLUSION: LASIK treatment for moderate to high levels of myopia leads in all cases to a reduced degree of myopia. There is a significant degree of unreliability on the accuracy of the treatment with a tendency to under correction. Postoperatively, many patients still have to use correction for distance vision. Significant loss of visual acuity occurs infrequently.

Adult↗

PubMed2005

Corneal power, thickness, and stiffness: results of a prospective randomized controlled trial of PRK and LASIK for myopia.

PURPOSE: To compare the short-, medium-, and long-term changes in corneal optical power and corneal aberrations, central corneal thickness, and corneal "stiffness" assessed by pneumotonometry readings in patients having laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) for myopia. SETTING: Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark. METHODS: One eye of each of 45 patients with myopia ranging from -6.00 to -8.00 diopters (D) (spherical equivalent spectacle refraction [SER]) was randomized to LASIK (n=25; mean SER -7.12 D +/- 0.57 [SD]) or PRK (n=20; mean SER -6.91 +/- 0.57 D). Data were collected prospectively before and 1, 3, 6, 12, and 36 months after surgery. Measurements included corneal topography (TMS-1, Tomey), corneal thickness (ultrasound pachymetry), and apparent intraocular pressure (IOP) (pneumotonometry). Retreatments were not performed during the first year, and retreated eyes were excluded from the 3-year follow-up. Changes in corneal power and aberrations, thickness, and apparent IOP were calculated in a pair-wise manner for 3 time periods: short term (preoperative to 1 month after surgery), medium term (1 to 12 months after surgery), and long term (1 to 3 years after surgery). RESULTS: In the short term, corneal power decreased equally in LASIK and PRK eyes. Spherical aberrations and coma-like aberrations increased equally, while corneal thickness decreased significantly less in LASIK eyes than in PRK eyes. The apparent IOP decreased more in LASIK eyes than in PRK eyes. In the medium term, corneal power increased significantly in both groups. Spherical aberrations decreased significantly in PRK eyes but not in LASIK eyes. From 1 to 12 months, corneal thickness increased more in PRK eyes than in LASIK eyes. During this period, the apparent IOP increased significantly in LASIK eyes. In the long term, corneal power and corneal aberrations did not change significantly in either group. Corneal thickness increased slightly but significantly in both groups. The apparent IOP increased significantly more in PRK eyes. CONCLUSIONS: Differences between LASIK and PRK related to time-dependent events affecting corneal shape and structural integrity were present. Peripheral changes in flap hydration in LASIK eyes and epithelial and/or stromal thickening in PRK eyes appeared to be the most important factors in optical power changes in the first year after treatment. The changes in apparent IOP suggest that some interlamellar healing occurred during the first year after LASIK. After LASIK and PRK, corneal bending stiffness seemed permanently decreased, although some restiffening may occur in PRK eyes in the long term.

Adult↗

PubMed2004

Plastic particles at the LASIK interface.

PURPOSE: To investigate the origin, composition, and persistence of the interface particles that frequently are observed after LASIK. DESIGN: Small case series and experimental animal study. METHODS: Four patients received LASIK using a Schwind Supratome (Schwind, Kleinostheim, Germany) and a MEL 70 G-Scan excimer laser (Asclepion, Jena, Germany) and were examined over the course of 1 year using slit-lamp and in vivo confocal microscopy. Four rabbits received a monocular microkeratome incision and were examined immediately after surgery without lifting the flap. After monthly evaluation for 4 months using in vivo confocal microscopy, 2 corneas were processed for histologic analysis and were sectioned serially. To measure the iron content, atomic absorption spectrometry was performed on 2 operated and 2 unoperated rabbit corneas. The chemical composition of the metal and plastic parts of the microkeratome blade was identified using energy dispersive x-ray fluorescence (metal part), and Raman and infrared spectroscopy (plastic part). Before and after oscillation in air, the microkeratome blade and motor-head were examined using light and fluorescence microscopy. In serial sections, interface particles were identified by fluorescence microscopy and their chemical composition was determined using Coherent Antistokes Raman Scattering microscopy. RESULTS: In LASIK patients, thousands of brightly reflecting particles (up to 30 micro m) were observed throughout the interface. The highest particle density was detected where the microkeratome blade had first entered the cornea. Both in the center and at the flap edge, the morphologic features, distribution, and density of these particles remained unaltered throughout the 1-year observation period. In rabbit corneas, interface particles were observed immediately after the microkeratome incision, even though the flap had not been lifted. These particles were similar to those observed in humans and persisted unaltered throughout the study. The operated and unoperated rabbit corneas had comparable iron content, demonstrating that the particles were not fragments of the uncoated steel blade. Only a few particles were observed on the unused microkeratome motor head and blade, whereas numerous fluorescent particles were detected after oscillation in air, the amount of particles increasing with oscillation time. Interestingly, the only fluorescent part of the microkeratome was the plastic segment of the blade. This plastic (polyetherimide) emitted fluorescence identical to that of the observed particles, whereas all metal parts of the microkeratome blade and motor head were nonfluorescent. In serial sections, interface particles showed fluorescent properties equivalent to polyetherimide and exhibited molecular resonance at 1780 and 3100 cm(-1), in accordance with the Raman spectrum of polyetherimide. CONCLUSIONS: Numerous plastic particles are generated during microkeratome oscillation and are deposited at the interface during LASIK. The particles persist unaltered for at least 1 year.

Animals↗

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↗