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Accommodation & Presbyopia

  1. Presbyopia: a loss of accommodation with age
  2. Presbyopic Correction

1. Presbyopia: a loss of accommodation with age

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)

2. Presbyopic Correction—Increasing the Depth of Focus

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).

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 primary and secondary spherical aberrations (SA) with defocus. The graph below compares the depth of focus and image quality at best focus for different magnitudes of primary and secondary SA.


Figure 3: Depth of focus, in diopters, calculated for a 4mm pupil, with various amounts of primary and secondary spherical aberration.

In this figure, the closed circles represent the largest vsOTF (image quality) values. This is overlaid with the variable depth of focus (solid black – primary SA, solid gray – secondary SA). This illustrates the trade off between extended depth of focus and reduction of the overall image quality. We are further testing this concept to evaluate the optimal magnitudes and higher spherical aberration orders to correct for presbyopic eyes.

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