Recall from Section 4.4 that the human eye lens can change its optical power through the process of accommodation. For young adults, the amount of change is around $ 10$D (diopters), but it decreases to less than $ 1$D for adults over $ 50$ years old. The ciliary muscles control the lens and their tension level is reported to the brain through efference copies of the motor control signal. This is the first depth cue that does not depend on signals generated by the photoreceptors.

Steven M LaValle 2020-01-06