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Retinal Ganglion-cell Activity is Reduced in the Vitrectomized Cat Eye after Fluid-air Exchange

1Hesse L., 2Schanze T., 2Greve N.,
1Augenklinik der SLK-Kliniken (Marburg)
2Philipps-Universität Marburg, FB Physik, AG NeuroPhysik (Marburg)

Purpose: After vitrectomy with fluid-air exchange visual field defects were reported. We quantified retinal ganglion cell activity before and after fluid-air exchange in the vitrectomized cat eye.
Methods: In the cat a combined lensectomy and vitrectomy was performed two weeks prior to recording experiments. To measure retinal activity the tip of two microelectrodes (80Km) were inserted to a sclerotomy and placed on the surface of the retina two disc diameters above the optic nerve head using a micromanipulator. Precise positioning of the electrodes' tip were verified by ophthalmoscopy and simultaneous electrical recording. Electrical activity of the retina was continously recorded and intraocular pressure maintained constant at 29 mmHg. Fluid air exchange was performed slowly to avoid dehydration injury of the retina.
Results: Spontaneous retinal activity decreased up to 50% within 3 minutes after completing fluid air-exchange. Fifteen minutes after fluid-air exchange the flash light induced spike rate was 10-fold reduced. Even one hour after refilling the eye with BSS retinal activity did not recover completely.
Conclusions: Rapid decrease of retinal activity after fluid-air exchange is best explained by disturbance of the extracellular ion concentration. Because of the air-bubble siphoning of excess of K+ ions into the vitreous by Müller cells is blocked. From our experiments a permanent damage of ganglion cells or nerve fibres after fluid air exchange can not excluded.

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