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.