Disector

Disector is a stereological method used to obtain unbiased estimates of the number of discrete particles within a defined volume, typically cells such as neurons or glia in histological sections. The method relies on comparing two planes in space and counting particles that are present in one plane but absent in the other, yielding an estimator of total particle number that is independent of particle size, shape, or orientation.

There are two main implementations: the physical disector and the optical disector. In the physical disector, two parallel tissue sections separated by a known distance are analyzed; a counting frame is applied to both sections and particles meeting defined criteria (for example, a nucleus present in the reference section but absent in the lookup section) are counted. In the optical disector, a thick section is used and the microscope focuses through the tissue; a defined focal interval serves as the counting volume, and particles coming into focus within that interval between focusing planes are counted. In both cases, systematic random sampling is employed. When used with the fractionator sampling scheme, the method is often referred to as the optical or physical fractionator.

Disector counts are used to estimate cell number per region or per unit volume (N/V). It is widely applied in neuroscience and pathology for quantifying neurons, glia, synapses, and other particles. Advantages include reduced bias from particle size, shape, and orientation, and compatibility with unbiased sampling schemes. Practical use requires clear counting rules, guard zones to avoid boundary effects, and appropriate randomization.

The disector principle was introduced by Sterio in 1984 and remains a core tool in quantitative histology for robust cell counting and density estimation.