Influence of the type of illumination on the measurement of the modulation transfer function in the living human eye:: a theoretical study

Applications such as refractive surgery demand an objective appraisal of the retinal image quality. The modulation transfer function (MTF) provides that information when measured directly. Moreover, the MTF obtained using a simple and objective method such as that described in this paper allows the neural contrast sensitivity function (CSF) to be obtained from the global CSF and the MTF. When calculating the MTF it must be borne in mind whether the applicable theory is coherent or incoherent. In the literature, the developed theory presents some approximations and incongruities. Also, it is interesting to note that the method of recording the MTF ( short or long time of integration, sum of images, etc.) and the: source used (laser or others) can essentially change the nature of the problem. This theory is not directly applicable to any experiment. This work comprises a thorough theoretical study of the possible cases according to the experimental method and therefore as a function of the coherence degree. Two different solutions are found: the MTF calculated as the square root of the Fourier Transform (FT) of the recorded intensity for any light source or the MTF calculated as the FT square root of the image.