Biomedical subjects
Publications and source records attributed to J Röver.
Loss of the crystalline lens into the vitreous cavity can lead to corneal damage and expulsive hemorrhage. In this technique, the lens is released from adhesions by vitrectomy and then extracted from the vitreous cavity by phacoemulsification using a special tip. No protective liquids are used to cover the retina. This technique was successful in 44 patients.
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BACKGROUND: Especially in aged patients testing the visual acuity can be most time consuming. An automatic test could therefore be of great help. The recently introduced "Freiburg Visual Acuity Test' (FVT) using a forced-choice determination of Landolt orientation has proved a reliable method of automatic visual acuity testing in younger patients. PATIENTS: To learn about practicability and ease of this self-administered test, we tried this test in 87 patients (mean age 73) before and after cataract surgery. The Landolt ring was presented in 8 different positions on a monitor. A keyboard of 8 buttons, depicting the possible orientation of the Landolt C, allowed the patients to run through the test by themselves. With each patient's correct response, the size of the Landolt ring decreased accordingly. RESULTS: Although near vision of all patients was grossly impaired and accommodation power zero, handling of the keyboard for the subject's response was generally reported as easy. The reliability and reproducibility of the obtained values were good and close to acuity values obtained using projected test figures according to DIN. Prior to cataract surgery we found DIN values statistically significantly lower than FVT values. This difference did not persist after surgery. CONCLUSION: Although the tested patients were definitely no computer freaks, the procedure of the test was rapidly understood. The average testing time was 4.5 min, thus prolonged by 40% in comparison to assisted DIN testing, however consuming only 1.0 min of personnel's time. The test proved to be equally reliable in the elderly patient.
BACKGROUND: one of the most intriguing complications in phacoemulsification is the rupturing of the posterior capsule with los of the nucleus into the vitreous. As severe inflammation will follow, the removal of the nucleus is mandatory. Several methods have been described. Our approach has the advantage to minimize some of the imminent risks. PATIENTS AND METHOD: On 15 eyes phacoemulsification in the vitreous cavity following vitrectomy has been carried out. Supporting liquids like viscoelastic substances or fluordecalin were not necessary. RESULTS: There was no indication of retinal damage caused by this procedure. The early postoperative vision, however, was compromised by a longer lasting corneal edema. The long term visual prognosis was good. CONCLUSIONS: Phacoemulsification in the central vitreous cavity proved to be safe and fairly easy procedure without adverse effects on retina and sclera. It helps to reduce intraoperative risks of alternative methods, avoiding a large opening of the anterior chamber and hypotony of the eye globe.
The pattern electroretinogram was recorded in patients with initial stages of visual field defects due to open-angle glaucoma and in age-matched normal subjects. Both normal subjects and glaucoma patients had a visual acuity above 0.8. Counterphasing checkerboard patterns were used as visual stimuli with a range of check sizes from 0.8 degree to 15 degrees at 7.8 reversals/s. Whereas the amplitude in glaucoma patients was nearly normal for large check sizes, it was significantly reduced for small check sizes (p = 0.003). Possibly two separate mechanisms that generate the pattern electroretinogram for small and large checks are differentially affected; they may be related to the magnocellular and parvocellular systems. The difference between normals and glaucoma patients was even more significant when the ratios of the amplitudes at small and large check sizes were compared (p less than 0.0002). When this ratios is used, the amplitude variability can be partly overcome and the pattern electroretinogram can be a sensitive indicator of ganglion cell function.
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Along the processing chain in the visual pathway the pattern electroretinogram (PERG) is a better indicator of the peripheral function than the visual evoked potential (VEP). Therefore the PERG and the VEP will be impaired equally by disturbances before the ganglion cell layer (e.g., blurred image or retinal disease) and differently by further centrally located diseases (e.g., tumor compression of the optic nerve). Thus in patients complaining of reduced visual acuity who show disturbed VEP but a normal PERG, malingering can be definitely ruled out. Representative combinations of PERG and VEP findings are described.
The c-wave and the electrooculogram (EOG) are retinal potentials predominantly generated by the pigment epithelium. In most diseases both parameters show a parallel decrease in amplitude. However, in patients with dominant drusen, and cone dystrophies, and in clinically nonaffected members of families suffering from vitelliform macula degeneration, the EOG is close to normal whereas the c-wave shows a reduced amplitude. These findings suggest a higher sensitivity of the generators of the c-wave compared with those responsible for the EOG. Thus the direct current electroretinogram provides additional diagnostic information.
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The c-wave of the human direct current ERG may give new insights about the involvement of the retinal pigment epithelium in hereditary degenerations. In our single-sweep recordings from 236 alert patients we saw reduced c-waves not only in vitelliforme macular degenerations but also in dominantly inherited drusen, Stargardt's disease, cone dystrophies, and x-linked retinoschisis. In achromatopsia the c-wave was close to normal. The relationship of the b- and c-wave, however, was altered only in Best's disease, cone dystrophy, and x-linked retinoschisis. We postulate that the c-wave when more severely reduced than the b-wave reflects not merely the dysfunction of the pigment epithelium but more precisely whether this retinal layer is involved earlier than the photoreceptors.
A target screen stimulus takes into account the necessity of larger checkerboard patterns with rising eccentricity. The target pattern should be calculated to fit the retinocortical magnification factor. This proposition is based on the working hypothesis that for maximal visual evoked potential (VEP) amplitude the stimulus should appear on the cortex as an undistorted checkerboard pattern. We describe the cortical response elicited by four different target screen stimuli based on a similar algorithm. No significant difference to normal checkerboard was found.
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A simple electronic device is described which simulates evoked potentials with variable amounts of superimposed noise to facilitate routine checking and testing of apparatus and computer programs in an evoked potential laboratory.
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