Modelling an artificial eye with a CCD camera: see how they see!

In September I attended the "IX Reunión Nacional de Óptica" (Spanish National Optics Meeting); one of the posters presented there by the Optics Group from Zaragoza (J. Ares, V. Collados, J. Arines and A. Sánchez-Cano) was "Adiestramiento de la refracción subjetiva con ojos simulados mediante cámaras web". In this communication, the authors reported a system based on a CCD camera to simulate an artificial eye that is used to teach optics and optometry.

Let's start by explaining how the eye works.

Figure 1: Scheme of the eye

In the image an schematic view of an eye is represented; in a very simple model, we can consider the eye as a system formed by a refractive surface, the cornea, and the lens. In a normal eye, the light is focused at the fovea and the image is well-defined. When a person suffers from myopia, light is focused before the fovea; when a person suffers from long-sight, image is formed after the fovea.

Now, how can it be modelled with a web camera? Well, basically the webcam is a CCD sensor with a lens. If we replace this lens by a 35mm focal length lens (typical value for a human eye) and a diaphragm (which will act as a pupil), we can build an artificial eye.

Once, the webcam is ready you can try how people see. Ask for example for a pair of glasses and place them immediately before the webcam. If the person who has lent you the glasses suffers from myopia, you will see a blurred image: this is how this person sees without glasses (or better said, the opposite to the way this person sees: it corresponds to the vision of a long-sighted person with the same gradation):

Figure 2: Pictures from the first row represent a near-sighted eye without (left) and with (right) glasses to correct the myopia. The second row corresponds to a normal eye (ie., the webcam) without (left) and with (right) the same lenses as used in the previous case.