BME MS Defense: Lana Jeanne Nagy
Higher Order Spherical Aberration Interactions to Increase Depth of Focus and Retinal Image Quality for Presbyopic Corrections
Supervised by Prof. Geun-Young Yoon
Presbyopia is a condition in which the natural aging of the eye results in a loss of accommodation. This loss in functionality is accompanied by a decrease in the compensatory mechanism between the aberrations of the cornea and lens. The result is a decrease in image quality and ability to focus on near objects.
Spherical aberrations (SA) inherently produce a depth of focus (DOF) when they exist in an optical system. Presented here is a theoretical analysis of the application of higher order SAs to the ocular optical systems of presbyopic subjects in order to provide DOF. Proposed SAs were tested in a small pre-presbyopic subject group to evaluate the effectiveness of the aberration interactions in providing enhanced through focus image quality.
Primary and secondary SAs were found to have a linear relationship with defocus in optimizing image quality. When primary SA was 1/3 the value of defocus, or secondary SA was 1/2 the value of defocus optimal image quality was measured as a peak in the visual Strehl ratio based on the optical transfer function. Adequate DOF can be achieved with varying levels of higher order SA. Combining the primary and secondary SA with in the optical system also functionally increases the DOF while allowing for a reduction in the magnitude of the SA terms used. When tested with higher order SA values chosen to optimize viewing for 50cm (2D), all four subjects reported an increase in DOF in addition to a slight decrease in visual acuity as predicted.
Other factors such as decentration, chromatic aberration and the Stiles-Crawford effect had little impact on the induced DOF achievable with SA. The image quality reduction was minimal with these factors; however the greatest impact in DOF and image quality was produced with large amounts of corneal aberrations such as astigmatism and coma.
A trade off exists between the DOF and image quality achievable, therefore SA terms must be chosen in order to minimize the negative effects of each. The analysis presented here provides a basis for further investigation and optimization of higher order aberration interactions for customized presbyopic corrections.