This question often arises when obtaining measurements with variable output values. First, regarding pupil diameter: the pupil naturally dilates in a dark room, but there is considerable individual variation in pupil diameter, and sometimes the laser beams may not pass through both paths. The latest NAVI model has been adjusted to enable measurement with a pupil diameter of 5 mm or larger.
When blood flow values tend to vary, even when attempting to establish a control by taking initial measurements without any intervention, patients may initially show lower blood flow readings due to nervousness (stress?).
For example, if values seem to vary after three consecutive measurements because the pupil diameter was borderline, using a mydriatic agent may reduce alignment errors and stabilize the values.