Yoon Lab: Presbyopia

Presbyopia and Accommodation

Presbyopia originating from the Greek word presbyteros, meaning "elder", is the loss of accommodation of the human eye due to the natural aging of the lens. In the eye the natural lens grows throughout life, and recent studies suggest that the enlarging of this lens with age is the cause of its reduced pliability resulting in the inability of the lens to change shape when one looks from far to near objects. This loss of accommodative ability requires corrective optics such as glasses, contacts, refractive surgery or intraocular lenses (IOL).

Figure 1: Maximal and minimal accommodative amplitudes as a function of age measured in 1500 subjects using a "push up" technique (Duane 1912)

In the Yoon lab we are focusing on the design of new innovative IOLs for presbyopic corrections. We are using the concept of aberration interaction to design lenses that will give people depth of focus with good retinal image quality. Meaning, people will have the ability to once again see objects over a range of distances from far to near without compromising, too much, the clarity of the image that the eye sees. Below is an example of depth of focus illustrated here with a letter E. The top line shows how a person without the ability to accommodate would see this letter at different distances, and the bottom line is an example of how aberration interaction can improve not only the range that can be clearly seen, but also the clarity that can be produced.

Figure 2: A letter E as seen with out any correction (top line), and with the addition of negative spherical aberration (bottom line).

Increasing Depth of Focus

We are currently testing our designs using an optical test bench equipped with a liquid-crystal spatial light modulator (SLM). This system can generate different wavefront patterns replicating an IOLs aberrations so that preliminary tests such as visual acuity and contrast sensitivity can be done in order to predict the feasibility of the IOL design. Recently we have been looking into the interaction of negative spherical aberration with defocus and have tested 3 subjects with our system to see what improvements negative spherical aberration can produce.

Figure 3: Contrast changes with (green dots) and without (blue dots) negative spherical aberration as a function of defocus. Higher contrast with spherical aberration can be seen for defocus larger than 0.75D.

The above graph shows the average subject data (dots) compared to theoretical calculations for the contrast of rectangular gratings set to a 20/40 letter size. The blue dots and lines represent the subjects’, and the theoretical contrast with out any aberrations induced, respectively (1 being highest contrast). The green dots and line represent the subjects’ and the theoretical contrast sensitivity when negative spherical aberration has been generated in the system. The negative spherical aberration was calculated to maximize the image quality at 2D. For both the theoretical and subject tested cases, the contrast increased with the addition of negative spherical aberration. This shows a promising result which we are further testing to evaluate the optimal magnitudes and higher spherical aberration orders to correct for presbyopic eyes.

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