Optical aberrations are of the most important factors which degrade the quality of image in any optical system. Human eye, as an optical system, may suffer from optical aberration and in particular, from higher order optical aberrations. Evaluation of the effects of optical aberrations on degrading the retinal image has been assessed so far, but most of researches have aimed the visual acuity as an image quality metric. In this paper an approach for objective evaluation of ocular aberration effects on the retinal image contrast has been introduced.

We have used the Zernike polynomials to represent optical aberrations of the eye up to 5th order. The RMS (Root Mean Square) of each aberration has been assumed form 0.25 to 8 microns (0.25, 0.50, 1, 2, 4 and 8 microns) and 3 different pupil sizes has been simulated (2mm, 4mm and 6mm diameter). Furthermore, Matlab software has been used to create the corresponding pupil functions and PSFs (Point Spread Function) of each one of optical aberrations. These PSFs have been used to simulate the image that is formed on the patient's retina. Besides, a Michelson contrast definition and a test pattern have been implemented to evaluate retinal image contrast, both objectively and subjectively.

The simulated results using Matlab software have been revealed that increasing of optical aberration from 0.25 micron to 8 microns will decrease the Michelson contrast by 59% from 0.97 to 0.57 for a 4mm pupil. Moreover, if pupil constricts from 4mm to 2mm, the contrast will decrease dramatically from 0.97 to 0.24, and if the pupil dilates form 4mm to 6mm, the contrast will increase from 0.97 to 2.24. However, image quality is declined since the RMS of aberrations in the 6mm pupils has increased significantly.

We have simulated and demonstrated an objective image quality measure using Michelson contrast to evaluate the effects of each ocular optical aberration, up to 5th order of Zernike polynomials, on the contrast of retinal image. Furthermore, Simulated contrasts using a test pattern conforms to the visual subjective evaluations.