Computerized calculation scheme for retinal image size after implantation of toric intraocular lenses

To describe a paraxial computing scheme for tracing an axial pencil of rays through the 'optical system eye' containing astigmatic surfaces with their axes at random.

Two rays (-10 prism diopters from vertical and horizontal) are traced through the uncorrected and corrected eye. In the uncorrected eye one specific ray is selected from the pencil of rays, which passes through the pupil center. In the corrected eye any ray can be traced through the eye. From the slope angle, the intersection of the ray with the refractive surface and the refraction the slope angle of the exiting ray is determined and the ray is traced to the subsequent surface. From both rays traced through the eye an ellipse is fitted to the image to characterize the image distortion of an circular object.

Assumptions: target refraction -0.5-1.0D/A = 90 degrees at 14 mm, corneal refraction 42.5 + 3.5D/A = 15 degrees, axial length 23.6 mm, IOL position 4.6 mm, central lens thickness 0.8 mm, refractive index 1.42, front/back surface of the toric IOL 10.0 D/7.14 + 6.47D/A = 101.8 degrees. The vertical incident ray was imaged to (x, y) = (0.0055 mm, -1.6470 mm)/(0.0067 mm, -1.6531 mm) in the uncorrected/corrected eye. The horizontal incident ray was imaged to (x, y) = (1.6266 mm, -0.0055 mm)/(1.6001 mm, -0.0067 mm) in the uncorrected/corrected eye. The ellipse (semi-major/semi-minor meridian) fitted to the conjugate image of a circle sized 1.648 mm/1.625 mm in an orientation 14.2 degrees in the uncorrected and 1.654 mm/1.599 mm in an orientation 7.1 degrees in the corrected eye.

This concept may be relevant for the assessment of aniseikonia after implantation of toric intraocular lenses for correction of high corneal astigmatism.