[ABSTRACT]
PURPOSE: To investigate photoreceptor dysfunction caused by digoxin
toxicity.
METHODS: First, a patient who experienced toxic side effects from digoxin
was studied acutely by serial electroretinography and later during convalescence.
Second, the light responses of isolated photoreceptors exposed to varying
amounts of digoxin were studied in vitro.
RESULTS: Electroretinographic amplitudes were reduced and implicit
times were delayed when digoxin levels were elevated and recovered slowly
after return to normal digoxin levels. Isolated photoreceptors exhibited
concentration-dependent reductions in the magnitude of the light response
during digoxin exposure, suggesting reduction in the dark current due to
blockade of the sodium-potassium-adenosine triphosphatase pump. Cones were
about 50-fold more sensitive than rods.
CONCLUSIONS: Reversible rod and cone dysfunction occur during exposure
to toxic levels of digoxin. Photoreceptor dysfunction is probably due to
the diminution of the dark current in response to the sodium-potassium-adenosine
triphosphatase blockade.