Issue: December 2007
Correcting Aberrations with
Part 2 of our look at the current and future
realities of correcting aberrations with contact
By Pete S. Kollbaum, OD, PhD, FAAO, & Arthur Bradley, PhD
Dr. Kollbaum is a research associate at Indiana University. He can be
reached at email@example.com.
Arthur Bradley is a professor of Optometry and Vision Science at Indiana
University. He can be reached at firstname.lastname@example.org.
In Part 1 of this two-part series we examined some of the
theoretical challenges anticipated for correcting higher-order
aberrations (HOAs) with contact lenses. In this article, we'll
examine the current status of aberration-controlling contact
lenses and consider the pros and cons associated with
different strategies for correcting aberrations.
How It Works
One way to describe how we need to alter a contact lens to correct aberration is to think of refractive error in terms of
optical path lengths (OPL). The OPL is the "optical distance" each ray of light must travel from one point (object) to
Figure 1 graphically demonstrates the computation of the change in OPL produced by a uniform slab of material that has a
different refractive index than the surrounding medium. In air, the OPL between points A and B is simply the physical
distance between the two points multiplied by the refractive index that the two points are in (n=1). However, a uniform
slab of material placed into this path will introduce a net change in OPL equal to the product of the physical thickness of
the slab and the change in refractive index (delta n).
Figure 2a shows the wavefront aberration function for simple myopic defocus. Wherever the aberrated wavefront lags
behind the reference plane wave (dashed line), we refer to that part of the wavefront as "retarded" and wherever the
wavefront is in front of the reference, we refer to the wavefront as "advanced."
Contact Lens Spectrum