Clinical trial NCT01893671: Corneal Power, Astigmatism, and Aberration Changes After LASIK
Official title: Observational Study of Corneal Power, Astigmatism, and Aberration Changes After LASIK
Study type: OBSERVATIONAL
Overall status: COMPLETED
Conditions: Measurements of Patients Using OCT Before and After LASIK
Keywords: LASIK
corneal power
astigmatism
HOA
Optical Coherence Tomography
Lead sponsor: Oregon Health and Science University
Sponsor class: OTHER
Collaborators: name: National Eye Institute (NEI)
First posted: 2013-07-09
Enrollment: 22
Sex: ALL
Minimum age (years): 18
Standard ages: ADULT
OLDER_ADULT
Accepts healthy volunteers: no
Observational model: CASE_ONLY
Time perspective: PROSPECTIVE
Sampling method: NON_PROBABILITY_SAMPLE
Study population: Subjects undergoing routine LASIK for the correction of myopia or hyperopia with or without astigmatism

Brief summary: 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.

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.

Eligibility criteria: 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

Primary outcomes:
measure: OCT measurement of corneal power and astigmatism vs Placido-ring
timeFrame: 5 year
Secondary outcomes:
measure: An evaluation of OCT-based epithelial thickness mapping
timeFrame: 5 year
measure: OCT measurements repeatability
timeFrame: 5 year
measure: The Development of a method of estimating the focusing power, astigmatism, and HOA of the crystalline lens
timeFrame: 5 year
Other outcomes:
Locations:
city: Portland
country: United States
facility: Oregon Health & Science University
state: Oregon
Study officials:
affiliation: Oregon Health & Science Universtiy
name: David Huang, MD, PhD
role: PRINCIPAL_INVESTIGATOR
References: