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Biomedical subjects

J O Hjortdal

Publications and source records attributed to J O Hjortdal.

At least 37 records · Page 2Linked to original sources
PubMed1996

The effect of 193 nm excimer laser radiation on the human corneal endothelial cell density.

The effect of 193 nm excimer laser radiation on human corneal endothelial cell density was examined. Fifty-five eyes from 35 patients underwent photorefractive keratectomy for myopia. Photomicrographs of the endothelium were taken a short time before the operation and on an average of 7 months postoperatively with a specular microscope. The average endothelial cell densities were preoperatively 3375 +/- 266 cell/mm2 (mean +/- SD) and postoperatively 3348 +/- 287 cells/mm2, corresponding to a fall of 27 cells/mm2 (N = 55). This fall in endothelial cell density was not statistically significant. A significant correlation between the change in cell density and age of the patient was found, with older patients losing more cells (N = 35, 2p < 0.05). The magnification of the specular microscope was found to change with corneal thickness. The importance of correcting the endothelial cell densities for corneal thickness is discussed.

Adolescent↗
PubMed1995

In vitro measurement of corneal strain, thickness, and curvature using digital image processing.

A video camera, a microscope, and a PC-based digital image processing board were assembled for in vitro studies of corneal biomechanics. Central tangential corneal strain was determined by placing pairs of tiny mercury droplets on the epithelial surface and on the endothelial surface of the cornea. A distance of 3.2 mm could be determined with a standard deviation of 1.2 micron. Central corneal radius of curvature was measured from digital traces of the corneal surface contour. The standard deviation on estimating the radius of an 8 mm steel sphere was 15 microns. Corneal thickness was measured by digital optical pachometry. The standard deviation on measuring a thickness of 1 mm was 4.6 microns. The corneal extensibility was investigated in a total of 10 enucleated human eyes with increased corneal hydration. Tension was applied by varying the intraocular pressure from 2 to 100 mmHg with a column of isotonic saline. The epithelial side corneal strain and the increase in corneal curvature were approximately 1% for a change in intraocular pressure from 2 to 100 mmHg. When a high intraocular pressure was kept constant for 2 h the corneal thickness, radius of curvature, and the epithelial side strain gradually decreased, whereas the endothelial side strain increased. The elastic and visco-elastic behaviour of the human cornea was found to be closely related to changes in corneal hydration. We found digital image processing useful for in vitro biomechanical studies of the cornea.

Aged↗
PubMed1995

Extensibility of the normo-hydrated human cornea.

The extensibility of 10 human corneas was evaluated in vitro by measuring central epithelial side and endothelial side tangential strain induced by intraocular pressure loads ranging from 2 to 100 mmHg. Corneal normo-hydration was attempted by immersing and perfusing the eyes with 8% Dextran 500 in isotonic saline. The relationship between corneal strain and intraocular pressure was found to be non-linear, showing a typical stress-stiffening behaviour. Strain changes were approximately 10% higher on the endothelial side compared with the epithelial side. This difference could be fully explained by pressure induced changes in corneal volume. Compared to previous experiments performed on swollen corneas, the stiffness of the normo-hydrated human cornea was found to be higher. Young's modulus of elasticity for the corneal stroma was estimated to 3, 9, and 20 MPa for intraocular pressure intervals of 2-10, 10-25, and 25-100 mmHg, respectively.

Aged↗
PubMed1995

Effect of excimer laser keratectomy on the mechanical performance of the human cornea.

Enucleated human eye globes were set-up for measurements of pressure (2-100 mmHg) induced tangential epithelial and endothelial side corneal strain, and for measurements of central corneal thickness and central radius of curvature. In one experimental group (N = 6), a shallow ablation (15-20 microns deep) removing Bowman's layer was performed in the central 7 mm diameter zone of the cornea. The fellow eye served as control (N = 6). In another experimental group (N = 6) a 70% deep keratectomy was performed in the central 7 mm diameter zone. The pressure induced central corneal strain was 5-10% higher in corneas without Bowman's layer compared with intact corneas. The epithelial side tangential corneal strain in eyes with a 70% deep keratectomy increased to twice as much as that of intact corneas, but the endothelial side strain was similar. In all groups of eyes Young's modulus of elasticity increased rapidly with the corneal stress level up to testing loads of 25 mmHg. At higher loads the degree of stress-stiffening was smaller. The differences in average corneal strain between the 3 groups could be explained by the induced changes in central corneal thickness, as there were no statistically significant differences in stress-normalized Young's modula of elasticity between the 3 groups. The central radius of curvature did not change significantly with increasing pressure in intact eyes or in eyes without Bowman's layer. In deep keratectomized corneas the corneal radius of curvature decreased approximately 1% when the intraocular pressure was increased from 2 to 100 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Fourier analysis of video-keratographic data. A tool for separation of spherical, regular astigmatic and irregular astigmatic corneal power components.

Topographic analysis of the cornea and computation of changes in corneal topography is difficult because of the lack of a standardized concept for analysing topographic information. We have used Fourier series harmonic analysis to decompose the often very complex information given in topographic images (TMS-1 video-keratograph). The polar data values arising from each mire were separated into spherical (average power), regular astigmatic (2' harmonic) and non-regular astigmatic components. The non-regular astigmatic components were further divided into a decentration component (1' harmonic) and a higher order irregular refractive component (root mean square (r.m.s.) of the residual between original data and the sum of spherical, 1' and 2' order components). Algorithms for utilizing the Fourier analysis technique on subjective refractive and on keratometric changes in regular astigmatism were also derived. Averages of the separate refractive components were calculated for groups of normal (right and left eye of 25 patients), keratoconic (13 eyes), and transplanted eyes (20 eyes), and average topographic maps were reconstructed and imaged. Changes in the separate topographic refractive components were compared with subjective refractive changes in eyes that had undergone combined myopic-astigmatic excimer laser ablation (8 eyes). Fourier series analysis was found superior to conventional keratometry in predicting spherical and regular astigmatic changes in subjective refraction. Fourier series analysis seems to be a powerful tool to decompose the information of complex topographic corneal images into rational optical components.

Algorithms↗
PubMed1994

Histopathological findings in failed human epikeratophakia lenticules.

Six human epikeratophakia lenticules were removed 1 to 23 months after refractive keratoplasty for aphakia (n = 2) and myopia (n = 4). The myopic group included one epi-lenticule treated with ArF-excimer laser for hyperopia. Reasons for removal were epithelial defect (n = 4), edema of host cornea (n = 1), and overcorrection (n = 1). The epi-lenticule stroma showed centrally a regular fibrillar structure with a low keratocyte density. Electron microscopy (n = 1) revealed preserved cytoplasmic organelles and nuclear appearance. Mononuclear cells were absent. Polysaccharide was demonstrated in the stroma. Bowman's layer was normal without breaks. The epithelium had variable thickness. In the peripheral wound region stromal and epithelial irregularities were evident.

Adult↗
PubMed1993

Cell kinetics of normal and healing rat corneal epithelium during organ culture.

Local epithelial proliferation in corneal, limbal, and conjunctival rat epithelium was investigated during organ culture of corneo-scleral shells, by relating the number of tritium labelled cells to the total number of cells (labelling index). The changes in labelling index after a mechanically induced central corneal abrasion were also studied. Local labelling indices were measured 2 h, 1, 2, 4 and 7 days after incubation. The average labelling index increased in un-abraded specimens 4-fold after 4 days of incubation, while the total number of cells only decreased 30-50%. In eyes with a central corneal abrasion the labelling index increased 10-fold in the surrounding epithelial cells after 1 day. The labelling index of the limbal and conjunctival epithelial cells increased to the same extent after 2 days of incubation. The finding of a reduced total number of cells and an increased cell proliferation in un-abraded eyes may be explained by increased loss of mature cells normally producing growth-inhibitory substances (chalones). Alternatively, the culture medium may contain an excess of growth-stimulatory substances. The results also suggest that the proliferative response spreads in a centrifugal direction during in vitro healing of a central corneal abrasion.

Animals↗
PubMed1992

Three-dimensional visualization of velocity profiles in the porcine abdominal aortic trifurcation.

To study the local distribution of blood velocities in the abdominal aorta and trifurcation, hot-film anemometry was used for point blood velocity measurements in the entire cross-sectional area in the abdominal aorta and abdominal aortic trifurcation in pigs weighing 90 kg. The geometry was visualized by use of a casting procedure. General hemodynamic and geometric parameters in the abdominal aorta were comparable to values found in humans. The porcine trifurcation differed somewhat from the human bifurcation. The velocity measurements in the abdominal aorta showed consistently skewed velocity profiles with the highest velocities at the anterior vessel wall. No signs of developed turbulence were found. Velocity measurements in the external iliac vessels showed high velocities at the flow divider, and low velocities with signs of retrograde flow during part of diastole at the lateral vessel wall.

Animals↗
PubMed1992

Excimer laser refractive keratectomy for high myopia. 6-month follow-up of patients treated bilaterally.

Both eyes of twenty patients were treated for myopia with refractive keratectomy using an excimer laser (193 nm), and followed for six months. The 40 eyes were divided into Group I (22 eyes) with an attempted refraction change of 5-8 diopters; and Group I (18 eyes) with 9-12 diopters of attempted refraction change. In Group I the corrected visual acuity improved or was unchanged in 16/22 eyes. Two eyes with high preoperative corrected visual acuity had experienced a significant loss in corrected visual acuity after 6 months. In Group II, the corrected visual acuity decreased in 10/18 eyes, in 4 eyes significantly. Among the 40 eyes, 39 had a refraction change less than intended after 6 months. Overcorrection was seen in only 1 eye. In Group I, 20/22 eyes were corrected up to 2.5 diopters less than attempted. In Group II, 9/18 eyes were more than 2.5 diopters from the attempted correction. All eyes developed subepithelial opacification ('haze'), which, in spite of steroid treatment, was still present after 6 months. The haze was more severe in eyes treated with 9-12 diopters of attempted refraction change. The achieved refraction change in the two eyes of the same patient was found to be correlated, possibly due to an individual factor in corneal wound healing.

Adolescent↗
PubMed1991

The relationship between Apgar score, umbilical artery pH and operative delivery for fetal distress in 2778 infants born at term.

A total of 2778 infants born at term were studied to determine the relationship between Apgar scores after 1 min, umbilical artery pH values, mode of delivery, a diagnosis of fetal distress leading to operative delivery, and sex. Eighty-three percent of the population had normal Apgar scores (greater than or equal to 8) and normal pH values (greater than 7.15) in which 10% were operatively delivered for fetal distress (ODFD). Sixty-one percent of the children with low Apgar scores (less than or equal to 7) had normal pH values, and 74% of the infants with acidosis (pH less than or equal to 7.15) had normal Apgar score. Twenty-four percent of the infants with a low Apgar score and/or acidosis were ODFD (sensitivity). Ninety percent of the infants who had Apgar scores and pH values were not ODFD (specificity). The predictive value (a low Apgar score and/or acidosis) of ODFD was 33%, and the negative predictive value (normal Apgar score and a normal pH) of ODFD was 85%. A significantly higher incidence of ODFD and acidosis was found in boys.

Acidosis↗
PubMed1991

Velocity field studies at surgically imposed arterial stenoses on the abdominal aorta in pigs.

In order to describe velocity profiles and the size of deterministic and non-deterministic velocity disturbances at arterial stenoses, symmetrical and asymmetrical stenoses with intended area reductions of 50% ('moderate') and 85% ('severe') were applied on the abdominal aorta in six pigs. Blood velocities were registered by hot-film anemometry in 21 measuring points distributed across the vessel cross-sectional area in one pre-stenotic and three post-stenotic positions. Signal analysis included ensemble averaging, the high-pass filtering technique, and three-dimensional visualization. None of the stenoses affected the pre-stenotic velocity field. Downstream moderate stenoses flow separation and vortex formation were present. Moderate asymmetric stenoses induced turbulence in the post-stenotic velocity field. Immediately downstream of severe stenoses a prominent post-stenotic jet was present. Farther downstream, a multitude of coherent vortices and turbulence dominated the flow field. The transverse distribution of turbulence intensity paralleled with the peak systolic velocity profile, whereas transverse profiles of the relative turbulence intensity (turbulence intensity/mean velocity) revealed peak values in flow field locations with high velocity gradients. Velocity parameters for symmetric and asymmetric severe stenoses were highly comparable. However, the exact degree of stenosis was significantly higher for symmetrical (85%) than for asymmetrical (76%) stenoses. Therefore, recalling that stenosis severity strongly influences the development of velocity disturbances, this indicates that asymmetry of a stenosis is a predictor for blood velocity disturbances.

Animals↗
PubMed1991

Epikeratophakia for high myopia.

A cryo-technique for production of corneal epi-lenses has been developed. During the manufacturing procedure the anterior surface of the tissue is moulded and the posterior surface cut with a microtome. After cutting, the epi-lenses are stored for days to weeks in an organ culture medium. Twelve eyes in 10 patients have been treated with epikeratophakia for high myopia (greater than -7 D). In all eyes, epithelialization was complete within one week, and at follow-up 3-18 months after the operation all epi-lenses were clear. The average refractive change in spherical equivalents was 9.7 +/- 4.4 D. All eyes obtained better uncorrected visual acuity, and no eyes lost more than one line of the best corrected visual acuity. At the time of follow-up, the patients' native cornea had regained normal hydration, whereas the epi-lenses did not thin as much as expected.

Adult↗
PubMed1991

A clinical comparison of optical and ultrasonic pachometry.

Central corneal thickness (CCT) of normal and oedematous corneae was measured in a study comparing a modified Haag-Streit optical pachometer and an ultrasonic pachometer (Teknar Ophthasonic, preset velocity 1630 m/s). Sixty-eight patients were examined before and after cataract extraction with implantation of an anterior chamber lens. Mean values of CCT before operation were 531 +/- 4.9 (SEM) micron by optical pachometry and 524 +/- 4.7 microns when measured by ultrasound (not significantly different). On the first post-operative day the values were 618 +/- 8.4 and 602 +/- 7.6 microns for optical and ultrasonic measurements, respectively (significantly different, 2P less than 0.001). Correlation analysis showed a high dependence between the methods with coefficients of correlation being 0.955 before and 0.958 after the operation. Linear regression analysis revealed small, but significant differences between the techniques. The difference between the two methods increased with increasing corneal hydration, whereas it could not be ascribed to sex, age, or intraocular pressure. It is concluded that for clinical purposes optical and ultrasonic pachometry techniques are comparable.

Aged↗
PubMed1989

Exogenous, ocular, and systemic factors associated with keratitic ulceration.

Information on type and frequency of empirically observed exogenous, ocular, and systemic predisposing factors for keratitic ulceration is important for clinical identification of groups at risk and may form a basis for planning experimental studies on the pathogenesis of ulceration. Therefore a retrospective study comprising 104 patients with 25 herpetic and 79 non-herpetic corneal ulcerations was performed. Patients with herpetic ulcerations were mainly males and were younger than patients with non-herpetic corneal ulceration. Keratoplasty and steroid treatment was found as frequent co-existing predisposing factors in the herpetic group. In the non-herpetic group an exogenous factor was found in 56%, an ocular factor in 56%, and a systemic predisposing factor in 46% of the patients. In only 2.5% of these patients was there found no predisposing factor. Pathogenetic mechanisms of predisposing factors for non-herpetic corneal ulceration is discussed.

Adolescent↗
PubMed1989

Some metabolic changes during human corneal organ culture.

In order to evaluate the changes in medium composition during closed system corneal organ culture at 30 degrees C, pH, pO2, glucose and lactate was measured 1 to 7, 14 and 28 days after incubation of a total of 49 human corneas. During organ culture pO2 decreased from 17.3 kPa to 8.8 kPa at day 28. The average oxygen consumption was initially 0.16 mumole/h/cm2, but decreased rapidly to an average of 0.04 mumole/h/cm2 during the first weeks of incubation. The glucose concentration fell from 5.1 mM to 0.25 mM after 28 days, and the lactate concentration rose from 2.5 mM to 11 mM. The concentration changes were for both substances highest during the first 14 days of organ culture. The pH fell from 7.36 to 6.64 after 28 days. These findings indicate that the cultured human cornea predominantly metabolizes glucose anaerobically, and that the metabolic activity decreases during incubation. The limiting metabolic factors for prolonging the culture period seem to be development of severe acidosis and glucose depletion in the medium.

Adult↗
PubMedDate not supplied

Acute tissue deformation of the human cornea after radial keratotomy.

PURPOSE: The regional deformation pattern of the cornea after radial keratotomy, which is essential for understanding the mode of action of the procedure, has not previously been studied in detail. METHODS: Up to 90 tiny mercury droplets were placed from center to limbus on the epithelial and endothelial corneal surfaces of eight eviscerated human donor eyes with four radial keratotomies (depth 100% of central corneal thickness, 3.5-mm clear zone). From digital images obtained under pressure loads ranging from 2 to 100 mm Hg, the distances between the fixed droplets were measured with an accuracy of 1 micron. After transforming the data to polar coordinates, regional meridional and circumferential strain patterns were calculated. Regional meridional and circumferential radii of curvatures were calculated from corneal profile images obtained at different pressure loads before and after keratotomy. RESULTS: Increasing the intraocular pressure from 2 to 100 mm Hg induced: an epithelial side wound gape of 44 mm; epithelial side circumferential tissue compression between incisions; considerable epithelial side meridional tissue elongation at and between incisions; little endothelial side circumferential strain across incisions; and little endothelial side meridional strain at and between incisions. The radial keratotomy induced 2.30 diopters (D) of central corneal flattening at an intraocular pressure of 2 mm Hg. The degree of central flattening correlated linearly with the amount of wound gape. In the physiological pressure range of the central cornea flattened 0.05 D for each millimeter-of-mercury increment in intraocular pressure. Pronounced meridional steepening was induced corresponding to the middle and peripheral parts of the keratotomy incisions. CONCLUSIONS: Our study suggests that the peripheral "tissue addition" seen after radial keratotomy is a net result of wound gape and circumferential tissue compression. Local bending of intact stromal tissue below the incisions plays an important role for the generation of the wound gape at the corneal surface. These data may help verify finite-element computer models of the human cornea.

Aged↗