An Ocular Grid-Planimeter Method for Enumerating Nerve Fibers

The estimation of numbers of nerve fibers in cross sections of peripheral nerves containing both fine and large fiber components can be accomplished by using an ocular grid and selectively counting a known area. With the use of a projecting apparatus and planimeter, the total cross section area is determined.

The following proportion expresses the principle involved:

total number of fibers in the nerve area of ass section of entire nerve number counted in the sample area area of sample

I f the planimeter calibration and the magnification of the tracing remain the same, a constant factor may be used for successive estimates. This factor is equal to the value of the planimeter reading of 1.000 divided by the area of the grid times the magnification squared. The final calculations are made by multiplying the number of fibers counted times the planimeter reading times the constant and dividing by the number of grid squares counted.

Counts of some nerves, using high magnification in enumerating the sample areas, can be finished in less than an hour after the preparation of slides. In comparing numbers obtained by complete counts with estimated numbers, the error was determined to be approximately ± 5%