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Biomedical subjects

F Grehn

Publications and source records attributed to F Grehn.

83 records · Page 5Linked to original sources
PubMed1984

Effect of short-term intraocular pressure increase on cat retinal ganglion cell activity.

By means of microelectrode recordings receptive field properties and flicker responses of cat retinal ganglion cells were studied during elevated intraocular pressure (IOP). At moderate IOP elevation (perfusion pressure, PP, approx. 50 mm Hg), a slight increase in the maintained activity and the neuronal activation obtained from the receptive field (RF)-center or RF-periphery occurred in some of the neurons. At critical perfusion pressure (PP 30-10 mm Hg), the RF-periphery mechanisms were less sensitive to ischemia than the RF-center mechanisms. The spontaneous activity was completely suppressed at an average PP of 36.6 +/- 9.0 mm Hg, the flicker-evoked responses at 17.7 +/- 9.6 mm Hg. At critical perfusion pressures, the stimulus-response latency increased by 20 ms at stimulation frequencies of 10-20 Hz. The critical flicker frequency was already slightly reduced at a PP of 50 mm Hg and decreased further with a further decrease in PP. The threshold values of the intensity function shifted to higher luminance levels when PP was reduced to less than 40 mm Hg, but the slope remained constant. A close interneuronal correlation was found in simultaneous recordings of pairs of ganglion cells during different levels of increased IOP. This finding indicates that the interneuronal response variability to IOP increase appearing in successively recorded neurons was predominantly caused by experimental factors. The main impairment in retinal neuronal function during increased IOP seems to occur proximal to the receptors but distal to the retinal ganglion cell somata.

Animals↗
PubMed1984

[Neuroretinitis].

Eight patients presenting with the characteristic clinical picture of neuroretinitis are described. The decrease in visual acuity was caused by a papillitis, whereas the macular star developed later in the course of the disease when the visual acuity had already recovered. Five of our 8 cases were adults, a fact which demonstrates that neuroretinitis is not only confined to childhood. Three of the 8 cases were bilateral, two of them children. Two patients presented with neuroretinitis and additional inflammatory processes of other ocular segments (one with chorioretinitis and vasculitis; one with scleritis and uveitis), suggesting that a general vascular inflammation may be present in neuroretinitis. The macular star is produced by lipid-rich exudate in Henle's nerve fiber layer, thus giving the picture of stellate retinopathy. The exudate probably leaks from the disk due to a defect in the blood-tissue barrier or a loosening of the border tissue at the disk margin. The etiology of neuroretinitis remains an enigma. Serologic and cultural tests for preceding viral infections have so far been inconclusive.

Adolescent↗
PubMed1983

Function of retinal nerve fibers depends on perfusion pressure: neurophysiologic investigations during acute intraocular pressure elevation.

Field potentials of the ganglion cell axons were recorded in the cat from the retinal surface during electrical stimulation of the optic tract. Using this technique during intraocular pressure (IOP) elevation, the impulse conduction was investigated independent of the neuronal input to the retinal ganglion cells. By infusing Na-Nitroprusside intravenously, the mean arterial blood pressure (BPm) of the animal was adjusted to levels between 50 and 130 mmHg. Thus, by setting the perfusion pressure (PP) to values between +30 and -20 mmHg, a large range of IOPs was tested. A PP of +20 mmHg or more left the axonal impulse conduction unimpaired, independent of whether the absolute IOP was 40 or 135 mmHg. Interruption of impulse conduction occurred first at a PP of +10 mmHg. At a PP of 0 mmHg or less, the impulse conduction ceased after a constant time interval (80-120 sec, when 20 Hz electrical stimulation was used). Recovery of the field potentials after restoring normal IOP was independent of the preceding IOP or PP. This data demonstrates that in short-term IOP elevation the electrical function of the ganglion cell axon depends on the PP and not on the absolute height of the IOP.

Animals↗
PubMed1982

[Riegers' anomaly with signs of hydrophthalmia and spontaneous pressure regulation].

Several members of two families with Rieger's anomaly were found to have signs of hydrophthalmia (enlarged corneas, Descemet ruptures, optic disc damage). Two of them revealed normal intraocular pressures during later life without medical or operative treatment. Obviously a spontaneous pressure regulation had occurred. A delayed differentiation of the trabecular meshwork is possibly the cause of self-regulation in these two cases of Rieger's anomaly as in case with congenital glaucoma.

Adolescent↗
PubMed1981

Glaucomatouslike visual field defects in chronic papilledema.

In 19 patients, 31 eyes with chronic papilledema were found to have visual field defects other than enlarged blind spots. In this series, the inferior nasal quadrant was most frequently involved. Dense paracentral scotomata were found in the Bjerrum area, some of which later progressed to form ring scotomata. Visual acuity usually deteriorated late in the course of the disease. The similarities of visual field defects in papilledema and glaucoma suggest common pathogenetic mechanisms of nerve fiber atrophy in both diseases.

Brain Diseases↗