Author: Juan F. Zapata-Díaz (The University of Manchester)

In last decade, the depth-of-focus (DoF) of the human eye has become an important issue to address due to the hypothetical improvement that could represent on the new approaches to correct presbyopia. Nevertheless, DoF of the human eye has been widely studied in last century.

Some of the findings achieved by researchers were the factors that may influence DoF of the human eye. These factors could be categorized as internal and external factors. External factors refer to the characteristics of the environment where the subject is placed while internal factors are the optical and neural characteristics of the subject’s visual system that influence DoF.

External factors are: luminance of the test field; and contrast, spatial frequency and target detail. Internal factors are: pupil size; optical aberrations; refractive state; retinal eccentricity; and age.

Apart from these factors, DoF has been found to be influenced by a neural factor associated to subjects’ blur sensitivity and that could be responsible for the large differences between objectively and subjectively measured DoF, and for the wide variability among subjects.