Improving retinal imaging by corneal refractive index matching.

Imaging the retina at high resolution requires a dilated pupil, which in turn exposes more corneal irregularities. We diminish the optical errors of the cornea by refractive index matching. Lens-fitted goggles were used for corneal immersion, to reduce its aberrations, while keeping the ocular power. An additional aspheric plate reduced the residual ocular spherical aberration. A comparison of the index-matching-based retinal images with those acquired directly shows resolution improvement for subjects with normal extent of ocular aberrations. A simulation of the point spread function, obtained from an averaged ocular and corneal wavefront error, also reveals substantial improvement when using corneal index matching. The demonstrated improvement using index matching may enable further improvement of current retinal imaging techniques or relaxing requirements for active ocular aberration correction.

Estimation of the ocular point spread function by retina modeling.

Retinal imaging often suffers from blurring aberrations. With knowledge of the blurring point spread function (PSF), better images can be reconstructed by deconvolution techniques. We demonstrate a method to enhance the contrast of retinal cells by estimating the ocular PSF. This is done by finding the cells' positions and their intensity distributions and using these as a model for the image. The feasibility of this method is demonstrated by Wiener deconvolution both for adaptively and nonadaptively corrected images.