Corneal Power, Astigmatism, and Aberration Changes After LASIK

Observational Study of Corneal Power, Astigmatism, and Aberration Changes After LASIK

The primary goal of the study is to determine if Optical Coherence Tomography (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.

Study Overview

• Status: Completed
• Conditions: Measurements of Patients Using OCT Before and After LASIK

Detailed Description

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.

• Study Type: Observational
• Enrollment (Actual): 22

Contacts and Locations

Study Locations

• United States
  • Oregon
    • Portland, Oregon, United States, 97239
      • Oregon Health & Science University

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

Subjects undergoing routine LASIK for the correction of myopia or hyperopia with or without astigmatism

Description

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

Study Plan

How is the study designed?

Design Details

• Observational Models: Case-Only
• Time Perspectives: Prospective

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort
LASIK; Subjects undergoing routine LASIK for the correction of myopia or hyperopia.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
OCT measurement of corneal power and astigmatism vs Placido-ring	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	5 year

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
An evaluation of 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.	5 year
OCT measurements repeatability	An assessment of the repeatability of OCT measurements	5 year
The Development of a method of estimating the focusing power, astigmatism, and HOA of the crystalline lens	The Development of 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.	5 year

Collaborators and Investigators

• Sponsor: Oregon Health and Science University
• Collaborators: National Eye Institute (NEI)
• Investigators: Principal Investigator: David Huang, MD, PhD, Oregon Health & Science Universtiy

Study record dates

Study Major Dates

• Study Start: January 1, 2011
• Primary Completion (Actual): August 31, 2017
• Study Completion (Actual): August 31, 2017

Study Registration Dates

• First Submitted: July 2, 2013
• First Submitted That Met QC Criteria: July 2, 2013
• First Posted (Estimate): July 9, 2013

Study Record Updates

• Last Update Posted (Actual): April 5, 2018
• Last Update Submitted That Met QC Criteria: April 4, 2018
• Last Verified: April 1, 2018

More Information

Terms related to this study

• Keywords: LASIK; corneal power; astigmatism; HOA; Optical Coherence Tomography
• Additional Relevant MeSH Terms: Eye Diseases; Refractive Errors; Astigmatism
• Other Study ID Numbers: OHSU IRB#6612; R01EY018184 (U.S. NIH Grant/Contract)

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No