Biomedical subjects

J Bühren

Publications and source records attributed to J Bühren.

13 recordsLinked to original sources

PubMed2006

[Optical quality after refractive corneal surgery].

Correction of myopia, hyperopia and astigmatism within its indicated margin by means of refractive corneal surgical procedures such as LASIK and surface ablation (e.g. PRK) is one of the standard procedures in ophthalmology. Now that advances in the fields of surgical techniques and the technical devices employed have further progressed in terms of safety and predictability, research also focuses on optical quality. "Optical quality" is not a clearly defined parameter, but can be captured indirectly by means of directly measured data. One has to start with the anatomical properties of the eye, which determine the optical images on the retinal level. The quality of the retinal image influences the eye's function, i.e. acuity and contrast perception. Finally, there is the subjective perception of the image we receive. "Optical quality" as such is reflected by the patient's evaluation of this image perception. Three phenomena are especially responsible for deterioration of the quality of the retinal image: diffraction, aberrations and dispersion. Some of the methods for measuring optical quality are subjective questionnaires, functional testing procedures for measuring visual acuity and contrast sensitivity, optical measuring procedures for the determination of optical quality, as well as biomicroscopy, aberrometry and corneal topography for assessing anatomical changes.

Cornea↗

PubMed2006

[Wavefront analysis for the diagnosis of subclinical keratoconus].

BACKGROUND: The entity of subclinical keratoconus (SKC) has not been defined sufficiently yet. The aim of the study was to describe ocular wavefront aberrations of clinically inconspicuous fellow eyes in patients with early keratoconus (KC) as a model of SKC and to assess the feasibility of higher-order wavefront analysis to discriminate eyes with SKC from normal eyes. METHODS: This prospective study included eight clinically inconspicuous fellow eyes of eight patients with newly detected KC in the contralateral eye and a paracentral inferior-superior difference (PISD) <1.4 D. In total, 15 eyes of 12 patients with newly diagnosed KC and a PISD >1.4 D were included as positive controls and 71 healthy eyes of 40 patients served as negative controls. The wavefront error was measured in all eyes with a Hartmann-Shack sensor. Discriminant analysis was performed with input from ocular HOA data and PISD. Receiver operating characteristic (ROC) curves were plotted for PISD, single Zernike coefficients, and for the output values of the discriminant functions to investigate their usefulness for discrimination between SKC eyes, early KC eyes, and healthy controls. RESULTS: There were significant differences between inconspicuous fellow eyes (group 2) and controls (group 3) for PISD, for the coefficients Z3(-3), Z3(-1), Z4(0) and Z5(-1), and for the output values of the discriminant functions. The latter discriminated between groups 2 and 3 with maximum sensitivity and specificity (A(z) ROC=1), whereas discriminative ability was considerably lower for single Zernike coefficients. CONCLUSION: Single Zernike coefficients did not appear to be useful for the detection of SKC. Using discriminant analysis, from PISD and higher-order Zernike coefficients a metric with very high discriminative ability between normal and SKC eyes could be constructed.

Adult↗

PubMed2005

[Intraindividual comparison of higher order aberrations after implantation of aspherical and spherical IOLs depending on pupil diameter].

BACKGROUND: The implantation of aspherical IOLs with negative spherical aberration should equalize the positive spherical aberration of the cornea. The aim of our study was the intraindividual comparison of higher order aberrations (HOA) after implantation of an aspherical and spherical IOL. PATIENTS AND METHODS: In ten patients we randomly implanted an aspherical IOL in one eye and a spherical IOL in the other. After 3 months, we used a Hartmann-Shack sensor to measure total HOA, 3rd to 5th order as well as spherical aberration Z4.0, in mydriasis. We compared all aberrations intraindividually for pupil diameters of 3.5-6 mm. RESULTS: For both IOLs, all aberrations rose with increasing pupil diameter. However, after implantation of the aspherical IOL total HOA, 4th order and spherical aberration Z4.0 were lower, for 4th order aberration and Z4.0 even significantly. For 3rd and 5th order aberrations, there was no difference between both IOLs. CONCLUSIONS: With implantation of aspherical IOLs, total HOA, 4th order and spherical aberration Z4.0 could be reduced compared to spherical IOLs.

Aged↗

PubMed2005

[Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS). A new test to determine contrast sensitivity under variable ambient and glare luminance levels].

BACKGROUND: The purpose of the present study was to evaluate a computerized test for measurement of contrast sensitivity thresholds under variable ambient and glare luminance levels. METHODS: A total of 40 eyes of 40 healthy subjects were examined with the FF-CATS and the Functional Acuity Contrast Test (FACT) at 0.167 cd/m(-2) (mesopic) and 167 cd/m(-2) (photopic). Measurements were performed twice with and without glare in a randomized fashion. Tests were evaluated according to three criteria: (1) repeatability, (2) discriminative ability, and (3) validity. RESULTS: The FF-CATS showed a higher discriminative ability between the two groups compared to the FACT charts. Under photopic conditions, the COR value was 0.39 for the FF-CATS and 0.26 for the FACT charts; under mesopic illumination, the COR value for the FF-CATS was 0.46 and 0.36 for the FACT charts. CONCLUSION: The FF-CATS is a reliable, sensitive, valid, and flexible test system for the determination of visual acuity and contrast sensitivity thresholds under variable ambient and glare luminance conditions.

Adult↗

PubMed2004

[Current state of wavefront guided corneal surgery to correct refraction disorders].

The present review describes the current status of wavefront-guided corneal surgery and up-to-date results. Wavefront-guided LASIK procedures performed to date achieved uncorrected vision of i.o or better in a larger number of patients than with conventional LASIK surgery, but the "eagle eye" has remained the exception. In part of the patients reductions of higher order aberrations could be obtained, but in the majority of ca-ses an increase was observed. This increase was however less than with conventional LASIK surgery. Correction of higher order aberrations has not yet been perfected since the predictability of corrections appears to be deserving of improvement on the one hand and aberrations are still induced by the technique on the other hand.

Humans↗

PubMed2004

[Higher order aberrations after implantation of an iris claw pIOL (Ophtec Artisan) in the phakic eye].

BACKGROUND: The purpose of the present study is to demonstrate the change of higher order wavefront aberrations (HOA) after implantation of an iris claw pIOL. METHODS: Thirteen eyes of seven patients were examined preoperatively and 1 month after implantation of an Artisan lens. The mean preoperative spherical equivalent was -10.69+/-1.92 D (-7.63 to -14.88 D). The diameter of the IOL optic was 6 mm and the lens was inserted though a tunnel incision at 12 o'clock. The root mean square (RMS) wavefront error was computed for all aberrations of the third to fifth order for pupil diameters of 3.5 and 6 mm. RESULTS: On average, HOA RMS changed for a 3.5 mm pupil by 0.037+/-0.089 microm (6 mm pupil: 0.405+/-0.245 microm). Third-order aberrations changed by 0.031+/-0.098 microm (0.320+/-0.269 microm). For both pupil diameters, a notable increase of Z 3,-3 of 0.117+/-0.085 microm (0.596+/-0.350 microm) could be observed depending on the distance between the limbus and incision. Fourth-order aberrations changed on average by 0.018+/-0.037 microm (0.280+/-0.143 microm), namely Z 4,0 increased by 0.025+/-0.034 microm (0.296+/-0.164 microm). CONCLUSION: After implantation of the Artisan lens HOA increased slightly. Particularly induction of Z 3,-3 and Z 4,0 contribute to the increase of HOA. The induction of trefoil ( Z 3,-3) is a result of the incision, whereas the increase of spherical aberration is due to the implant.

Adult↗

PubMed2003

[Laser in situ keratomileusis for correction of hyperopia and hyperopic astigmatism using a scanning spot excimer laser. Results of a prospective clinical study after 1 year].

PURPOSE: The purpose of this investigation was to evaluate the safety, efficacy, predictability, stability and complications of LASIK for the treatment of hyperopia and hyperopic astigmatism using a scanning spot excimer laser. PATIENTS AND METHODS: A total of 64 consecutive LASIK operations (37 patients, mean age 41 years, range 22-68 years) have been evaluated. The Hansatome microkeratome producing a superior hinge (flap diameter 9.5 mm) and a scanning spot excimer laser with an optical zone of 6.0 mm were used. Examinations were performed preoperatively, after 1 day, 7 days, 1 month, 4 and 12 months. RESULTS: One year after the primary procedure only 1 eye lost 2 or more lines of best-corrected visual acuity, 91% were within +/-1 line and 4 eyes gained 2 lines. Of these eyes 50 (86%) reached an uncorrected visual acuity of > or=0.5, 32 (55%) > or=0.8, 16 (28%) > or=1.0, 24 eyes (41%) needed a refractive correction of +/-0.5 D, 44 eyes (76%) of +/-1.0 D and 55 eyes (95%) of +/-2.0 D. The mean spherical equivalent after 1 year was +0.17+/-0.85 D. CONCLUSIONS: LASIK is suitable for the correction of hyperopia (up to a maximum of +5 D) and for hyperopic astigmatism (up to a maximum of -5 D). However, results were better in lower hyperopia (up to +3 D) than in the moderate hyperopia. The refractive results showed overall a good stability during the 12-month study period, but higher regression occurred in a few cases.

Adult↗

PubMed2002

[Diffuse lamellar keratitis after laser in situ keratomileusis. Clinical and confocal microscopy findings].

BACKGROUND: Diffuse lamellar keratitis (DLK) is a sterile inflammation after lamellar corneal surgery. A clinical staging for DLK was recently set up. In this observational case series, the clinical and confocal microscopic findings of stages 1-3 are reported. METHODS: Six eyes of six patients (three eyes with DLK stage 1, two eyes with DLK stage 2, and one eye with DLK stage 3) were examined by slit lamp biomicroscopy and confocal microscopy. RESULTS: In all cases, confocal microscopy showed an infiltration of inflammatory cells into the anterior stroma and the flap interface. The number of cells varied between the eyes with DLK stage 1, and both stage 2 corneas had dense infiltrates. In the eye with stage 3 DLK, an aggregation of decayed cells, most likely granulocytes, was noticed clinically and by confocal microscopy. CONCLUSIONS: The DLK stages represent different clinical intensities of interface inflammation after LASIK. While stages 1 and 2 have a similar confocal microscopic appearance, stage 3 is a result of aggregation of a high amount of inflammatory cells.

Adult↗

PubMed2001

[LASIK with a superior hinge and scanning spot excimer laser ablation for correction of myopia and myopic astigmatism. Results of a prospective study on 100 eyes with a 1-year follow-up].

PURPOSE: Recently laser-in-situ-keratomileusis (LASIK) has been increasingly used to correct refractive errors. The purpose of this investigation was to evaluate the safety, efficacy, predictability, stability and complications using the scanning spot excimer LASIK technology. PATIENTS AND METHODS: The results of 100 consecutive LASIK operations carried out between 2/1998 and 2/1999 on 60 patients (mean age 37 years, range 20-55 years) have been evaluated. The Hansatome microkeratome with a superior hinge (flap diameter: 9.5 mm) and a scanning spot excimer laser (Technolas C-Lasik 217) were used in all cases. The mean spherical equivalent of the subjective manifest refraction was -6.96 +/- 2.87 diopters (D), the mean sphere was -6.47 +/- 2.71 D and the mean astigmatism was -0.98 +/- 0.94 D. In 6% of the eyes preoperative visual acuity was not better than 20/40. Examinations were performed preoperatively, after 1 and 7 days, after 1,4 and 12 months. Safety, efficacy, predictability, stability and complications were calculated using the datagraph software (version 1.11). RESULTS: All 100 eyes were examined after 1 day and 1 week, 96 after 1 month, 95 after 4 months and 92 after 1 year. Following 1 year none of the eyes lost 2 or more lines of best corrected visual acuity, 99% were within +/- 1 line and 1% gained 2 lines (safety index 1.03). In 92% of all eyes an uncorrected visual acuity of > or = 0.5 was reached, in 77% > or = 0.8 and in 51% > or = 1.0 (efficacy index 0.89). For 60 eyes (65.21%) a refractive correction of +/- 0.5 D was necessary, for 82 eyes (89.13%) +/- 1.0 D and for 91 eyes (98.91%) +/- 2.0 D. The mean spherical equivalent after 1 year was -0.15 +/- 1.31 D. Between 1 and 12 months a mean regression of -0.14 D occurred. On the request of the patients, 5 eyes were retreated during the study period for under- or over-correction. Complications due to the microkeratome did not occur. Corneal infections were not observed, a diffuse lamellar keratitis (DLK) was seen in 12 cases, but all cases healed with no loss of visual acuity. In 7 eyes a slight decentration of the ablation was observed using corneal topography, which in one case caused an increase in glare sensitivity. CONCLUSIONS: LASIK with superior hinge and scanning spot excimer photoablation is suitable for the correction of myopia (up to a maximum of -12 D) and for myopic astigmatism (up to a maximum of -5 D). The refractive results showed a high stability during the 12-month study period but there is still room for improvement of the predictability.

Adult↗

PubMed2001

Diffuse lamellar keratitis after laser in situ keratomileusis imaged by confocal microscopy.

OBJECTIVE: To report the confocal microscopic findings of two different cases of diffuse lamellar keratitis (DLK) after primary laser in situ keratomileusis (LASIK) and LASIK flap relifting. DESIGN: Observational case report of two cases. METHODS: Two cases of DLK with different clinical appearances after primary LASIK and LASIK flap relift were selected. A third case of uneventful LASIK was selected as control case. Examination with a white-light tandem slit-scanning confocal microscope was performed in addition to routinely applied slit-lamp biomicroscopy. RESULTS: In both cases, confocal microscopic examination showed infiltration of cells considered most likely to be mononuclear cells and granulocytes into the flap interface. Under treatment with topical steroids, the inflammation was reduced in both cases, to a minimum within 1 week, without loss of visual acuity. At this stage, only remnants of the granulocytelike cells, but not active inflammation, were imaged by confocal microscopic examination. CONCLUSIONS: Our findings confirm the clinical observation that DLK is an inflammation confined to the flap interface. Confocal in vivo microscopy could be a useful noninvasive tool to study the course of DLK in humans.

Adult↗

PubMed2001

[Scheimpflug photographic imaging following implantation of anterior and posterior chamber phakic intraocular lenses: preliminary results].

BACKGROUND: For the correction of refractive errors lenticular procedures are increasingly used in addition to corneal refractive surgery. One of those techniques is the implantation of intraocular lenses into phakic eyes (pIOL). Due to the close neighborhood of the implant to delicate intraocular structures, exact positioning and high postoperative stability are required. Scheimpflug photography has been shown to be a suitable instrument for the biometry of the anterior eye segment and the examination of IOL position. PATIENTS AND METHODS: Four anterior chamber phakic IOLs (pIOLs) (Bausch & Lomb NuVita) and 7 posterior chamber pIOLs (Staar ICL) were examined 1 week, 1 month and 3-6 months following implantation. At each examination 1 Scheimpflug slit image and 1 infrared retroillumination image were taken using the anterior eye segment analysis system EAS-1000 (Nidek Co., Gamagori, Japan). Evaluation of the images was performed with a personal computer and the software provided by the manufacturer. The distance of the pIOL to cornea and human lens was calculated and incidence and amount of pIOL rotation around the optical axis and potential crystalline lens opacification were assessed. RESULTS: The distance between the anterior chamber pIOL and the cornea 1 week after implantation was 1.61 +/- 0.10 mm. The distances between the myopic posterior chamber pIOL and the human lens were 0.34 +/- 0.11 mm and between the hyperopic posterior chamber pIOL and the human lens 0.26 and 0.29 mm, respectively. The values were constant over a period of 3-6 months. The pIOL showed no movement or change of position around the optical axis. There was no detectable cataract formation in the human lens. CONCLUSIONS: All implanted phakic anterior and posterior chamber IOLs showed a stable position in the eye within the observation period. Scheimpflug photography is proved to be a useful technique for the postoperative evaluation of the positioning of phakic IOLs.

Anterior Chamber↗

PubMed2000

Expression of the neurotrophin receptor p75NTR in medulloblastomas is correlated with distinct histological and clinical features: evidence for a medulloblastoma subtype derived from the external granule cell layer.

Medulloblastomas (MBs) are primitive neuroectodermal tumors (PNET) of the cerebellum. They represent the most frequent malignant pediatric brain tumors, but their origin still remains unresolved and controversial. MB cells correspond to different stages of neural development and differentiation as illustrated by their expression of neuronal and glial markers. In the present study, we examined the expression pattern of the common low-affinity neurotrophin receptor p75NTR in a series of 167 MBs by immunohistochemistry. While p75NTR was present in only 17% of classic MBs (CMB), we found expression of p75NTR in all desmoplastic (nodular) MBs (DMB) examined, and in 71% of those MBs with a significant desmoplastic component. Furthermore, both desmoplastic histology and p75NTR expression were present preferentially in those tumors of adolescents and adults that are frequently located laterally in the cerebellar hemispheres. In DMBs, p75NTR was expressed predominantly in the proliferative, reticulin-rich areas, which may show coexpression of GFAP. In the pale islands of DMB, p75NTR was expressed only weakly or was absent. The expression pattern showed an inverse relation to that of the synaptic vesicle protein synaptophysin that was predominant in p75NTR negative classic MBs. Since the neurotrophin receptor p75NTR is expressed in cells of the external granule cell layer (EGL) of the fetal cerebellum, our findings suggest that progenitor cells of the EGL are the cellular origin of a distinct subset of MB, namely the desmoplastic variant and MBs with a significant desmoplastic component.

Adult↗

PubMedDate not supplied

Confocal microscopic imaging of reticular folds in a laser in situ keratomileusis flap.

PURPOSE: To report the clinical and confocal microscopic characteristics of reticular folds (mudcracks) in a cornea after laser in situ keratomileusis (LASIK). METHODS: A 30-year-old male showed reticular flap folds on slit-lamp examination 1 week after LASIK. In addition to slit-lamp biomicroscopy, confocal in vivo microscopy was performed. RESULTS: Examination with a confocal white-light slit-scanning microscope revealed distinct folds of Bowman's layer and underlying microfolds throughout the flap stroma. After flap re-lifting, no changes could be determined, either clinically or by confocal microscopy. At 12 months following the procedure, best spectacle-corrected visual acuity was slightly improved, but the folds, as imaged by confocal microscopy, still persisted. CONCLUSIONS: In the present case, reticular folds after LASIK involved the entire thickness of the flap. Simple flap lifting was not sufficient for smoothing out the folds.

Adult↗