Measurements of the acuity of rod vision made by two different techniq
ues show it to vary only slightly with eccentricity. At eccentricities
beyond 15 deg acuity is well predicted from the sampling properties o
f the mosaic of the P-class of ganglion cells. With decreasing eccentr
icity acuity falls progressively below the sampling limit of P-cells,
but even at the lowest eccentricity examined (5 deg) does not reach th
e limit imposed by the sampling properties of the mosaic of M-cells. A
t an eccentricity of 5 deg rod vision could be supported by as few as
20% of P-cells.