Measurement Repeatability in Contemporary Aberrometry

Study Overview
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Brief Summary
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Wavefront scans are a common form of diagnostic test applied in preparing patients for laser eye surgery. An optical map of the eye is created by wavefront scanning, and information from these maps is used to program lasers used to correct focusing errors in the eye. Here the investigators are comparing how repeatable measurements are with a new wavefront scanner and one that is already in widespread use.

Detailed Description
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Aberrometers are used to measure each element of defocus (aberration) in an optical system. In LASIK, information derived from aberrometry (scans performed using aberrometers) is used to program the pattern of laser pulses delivered by an excimer laser in therapeutic reshaping of the cornea to correct defocus. To do this accurately, aberrometry findings need to be repeatable and correspond closely to manifest refraction. Here the investigators compare repeatability of measurements for a new aberrometer (Peramis) versus the aberrometer most widely used in contemporary wavefront guided laser vision correction (iDesign). The test aberrometer will be: Peramis (Schwind Eye-tech Solutions, Kleinostheim, Germany). Control aberrometer will be: iDesign (AMO, Santa Clara, CA)

Official Title
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A Comparative Study of Measurement Repeatability for Two Aberrometers

Conditions
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Refractive Errors

Intervention / Treatment
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* Device: Peramis aberrometry
* Device: iDesign aberrometry


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Myopic LASIK candidates (manifest refraction spherical equivalent range 0 to -10 diopters with up to 6 diopters cylinder) or patients attending corneal service with stage II-III keratoconus or post-keratoplasty Exclusion Criteria: Visually significant co-pathology (CDVA<6/6) other than irregular astigmatism; Patients unable to complete a sequence of 2 good scans (acquisition diameter >5mm) in one eye within 4 attempts

Ages Eligible for Study
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Minimum Age: 21 Years
Maximum Age: 60 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Diagnostic
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Myopia (Peramis)<br>Peramis aberrometry: 30 consecutive LASIK candidates with myopia and regular astigmatism who agree to participate in the study will have up to 4 aberrometry scans acquired consecutively using the Peramis (test) aberrometer. | Device: Peramis aberrometry<br>* A non-invasive photographic scan sequence acquired in under 10 seconds<br>* Other names: Wavefront scanning;|
| Active Comparator: Myopia (iDesign)<br>iDesign aberrometry: The same 30 consecutive LASIK candidates scanned in the Myopia (Peramis) arm will also have up to 4 aberrometry scans acquired consecutively using the iDesign aberrometer (control) aberrometer. The order of scans (Peramis and iDesign) will be randomised. | Device: iDesign aberrometry<br>* A non-invasive photographic scan sequence acquired in under 10 seconds<br>* Other names: Wavefront scanning;|
| Experimental: Irregular astigmatism (Peramis)<br>Peramis aberrometry: 30 consecutive cases with stage II-III keratoconus or post corneal transplantation cases with irregular astigmatism will have up to 4 aberrometry scans acquired consecutively using the Peramis (test) aberrometer | Device: Peramis aberrometry<br>* A non-invasive photographic scan sequence acquired in under 10 seconds<br>* Other names: Wavefront scanning;|
| Active Comparator: Irregular astigmatism (iDesign)<br>iDesign aberrometry: 30 consecutive cases with stage II-III keratoconus or post corneal transplantation cases with irregular astigmatism will also have up to 4 aberrometry scans acquired consecutively using the iDesign aberrometer (control) aberrometer. The order of scans (Peramis and iDesign) will be randomised. | Device: iDesign aberrometry<br>* A non-invasive photographic scan sequence acquired in under 10 seconds<br>* Other names: Wavefront scanning;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| 2nd to 4th order aberrations (5mm pupil). | M, J0, J45, Coma, Trefoil, Spherical Aberration. Different types of defocus or aberration can be defined and measured by wavefront scanning. Aberrations are classified and quantified by a mathematical treatment called Zernike analysis in which harmonic elements of the waveform of the light detected by the wavefront sensor (aberrometer) are quantified in sequence, starting with simple (lower order) waveforms such as sphere and cylinder (M, J0, J45) corrected in a normal spectacle prescription, and progressing through more complex (higher order) waveforms including, coma, trefoil and spherical aberration which may influence quality of vision. The amount of each aberration varies as a function of pupil size. So pupil size is standardised at 5mm diameter for quantification. | <10 seconds | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| % of patients with qualifying scan sequence | % of patients in whom two 5mm diameter aberrometry scans can be acquired within 4 attempts | <5 minutes |