Toxic and hypoxic damage of foveolar photoreceptors by subretinal hemorrhage can be prevented by early and minimal invasive fibrinolytic therapy. After localization of choroidal neovascularizations, treatment by focal laser coagulation is possible in some cases.

The retina of the Royal College of Surgeons (RCS) strain of rat, which is being used as an animal model for human retinal degenerations, has been employed in the study of the function of second order neurons. By about the 33rd postnatal day the dendritic branching of isolated bipolar cells is more sparse than in bipolar cells of the normal rat retina, but their GABA channels are as in the normal rat retina. The normally occurring light-induced distal potassium increase has been used as the indicator of the functional competence of second order neurons in the isolated RCS rat retina. These are dependent upon the integrity of ionotropic and metabotropic synapses. At about the 22nd postnatal day MgCl₂ enlarges the light-induced distal potassium increase in the young RCS rat retina as in the normal rat retina. It seems that MgCl₂ does not block the metabotropic synapses of on-bipolar cells. At about postnatal day 33, at which time the photoreceptors of the RCS rat retina had become severely damaged, the size of this light-induced distal potassium increase was not changed, but it was abolished by MgCl₂. This indicates that bipolar cells are still active but that the synaptic function of on-bipolar cells has become vulnerable to MgCl₂. The conclusion is that at a time when photoreceptor degeneration is already severe bipolar cells are still active, but that on-bipolars, mainly rod bipolar cells, have some functional deficit.

No abstract

A c-wave-like cornea-positive potential in the isolated rabbit retina has been described. In this study, frog retinas were investigated to see if the neural retina contributes a slow cornea-positive component to the c-wave of the electroretinogram. The eye cups of both Rana esculenta and Rana temporaria exhibited a normal electroretinogram with c-wave, a larger proximal light-induced extracellular potassium increase, a small distal extracellular potassium increase and an extracellular potassium decrease around photoreceptors. Isolated frog retinas kept receptor side-upward in a moist chamber without perfusion showed the well-known slow PIII generated by the potassium decrease around receptors. If the isolated retinas were well perfused, the slow PIII was not seen, but a cornea-positive d.c. potential sometimes appeared after the b-wave. The different slow potentials seemed to relate to different light-induced potassium changes in the proximal retina. There was a long-lasting proximal potassium increase in the superfused retinas but a quick return of the proximal potassium increase to the baseline in the retinas lacking oxygen at the vitreal side. The lasting proximal potassium increase in adequately maintained retinas may counteract the potassium decrease around receptors and cancel slow PIII.

No abstract