Author: Juan F. Zapata-Díaz, University of Manchester

Depth-of-focus is a characteristic of any optical system that allows sharp images to be formed at certain distances out of focus of the system. The human eye also counts on with this characteristic.

In last years, great interest has been taken into this property of the human eye due to the aid that it could represent to improve approaches to correct presbyopia. Contact lenses or intraocular lenses with an extended depth-of-focus may be able to simulate partially the accommodation mechanism of the eye (which is progressively lost with the development of presbyopia). This is the reason why researches have been trying to achieve these new approaches.

But human vision does not only depend on the optical part of the eye, since neural factors are also involved in vision and depth-of-focus of the human eye. This creates the need to separate both, optical and neural factors in order to study depth-of-focus objectively.

One of the partners of the Ageye Consortium, the Biomedical and Signal Processing Group (Wroclaw University of Technology, Poland), directed by Dr. Robert Iskander, has wide experience in developing methods to study depth-of-focus objectively through image quality metrics. One of these methods comprises the use of objective measurements of the imperfections of the eye (optical aberrations) and pupil size to calculate image quality at focus and at certain distances out of focus (through-focus analysis). With this technique, estimation of objective depth-of-focus can be achieved following objective criteria and avoiding the influence of neural factors.

Figure 1. Example of through-focus analysis of image quality.