Corneal Power, Astigmatism, and Aberration Changes After LASIK

A prospective observational study on refraction and HOA changes after LASIK will be conducted
at OHSU and Baylor. We will enroll 50 subjects undergoing routine LASIK for the correction of
myopia or hyperopia. The Optovue anterior segment OCT prototype will be used to measure
corneal power, astigmatism, HOA, and epithelial thickness map. The ultrahigh-speed MIT OCT
prototypes will also be used when they become available. A comprehensive eye examination will
be performed preoperatively. OCT scan, manifest refraction, visual acuity, Placido-ring
corneal topography, slit scanning/Scheimpflug camera, and wavefront measurements will be
acquired preoperatively and 3-6 months after the surgery. The LASIK-induced refraction and
wavefront HOA changes will be used as the reference standard to evaluate the accuracy of
OCT-measured corneal power, astigmatism, and HOA changes. The primary goal of the study is to
determine if OCT measurement of corneal power and astigmatism is more accurate than
conventional Placido-ring corneal topography. A second goal is to evaluate OCT-based
epithelial thickness mapping. The postoperative epithelial thickness variation will be used
to calculate refractive effects and calibrate the smoothing parameter in the mathematical
model relating corneal mean curvature and epithelial thickness. A third goal is to assess the
repeatability of OCT measurements. A fourth goal is to develop a method of estimating the
focusing power, astigmatism, and HOA of the crystalline lens based on measurements of the
lens' anterior and posterior capsular topographies and positions with the ultrahigh-speed MIT
OCT prototype. The reference standard for lens focusing power and astigmatism will be based
on a Gaussian optics model that takes as inputs manifest refraction, crystalline lens
position, axial eye length, and OCT corneal power and astigmatism measurements. The reference
standard for lens HOA will be the difference between wavefront HOA and corneal HOA. For each
eye, the best-fit effective index of the lens will be found so that OCT measurements will
match the reference data. Although the lens index is likely to be higher centrally than
peripherally, this secondary perturbation will be accounted for by a posterior shift of the
posterior lens capsule in OCT images, due to the fact that apparent distances in OCT images
is a product of physical distance and optical group index. Thus HOA due to index variation in
the lens would translate to unevenness in the posterior capsule surface that could be
measured with OCT.

Inclusion Criteria:

1. Patients who qualify for primary LASIK for either myopia or hyperopia, with or without
astigmatism.

Exclusion Criteria:

1. Inability to give informed consent.

2. Inability to maintain stable fixation for OCT imaging.

3. Inability to commit to required visits to complete the study.

4. Eyes with concurrent cataract, retinal diseases, glaucoma, or other eye conditions
that may limit the visual outcome after surgery