Laser Correction of Astigmatism Using Vector Analysis

Study Overview
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Brief Summary
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To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis that uses 3 fundamental vectors : target induced astigmatism vector ( TIA) , surgically induced astigmatism vector , and difference vector , as described by Alpins method.

Detailed Description
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Astigmatism is a condition of the eye where the cornea (clear window in front of the eye) has 2 different curvatures (much like an American football cut in half) so that, instead of being a single focal point, there ends up being two different focal points, neither of which is in focus. As you can imagine, this makes whatever you are looking at blurred and fuzzy like a camera out of focus. Both objects up close and far away can look blurred and fuzzy with astigmatism. Many people with astigmatism also are nearsighted or farsighted. There are several different treatment options if you have astigmatism with or without nearsightedness or farsightedness. Various treatment options available from an eye specialist include: Glasses, Contact Lenses and Laser Eye Surgery Laser Eye Surgery: Laser eye surgery, or laser vision correction, involves using lasers to reshape the front surface (cornea) of your eyes so that you can focus better. It can correct short-sightedness , long-sightedness and astigmatism.There are several different laser eye surgery options that can be used to help correct vision problems caused by astigmatism.Laser eye surgery corrects the refractive error in the cornea so that, instead of there being two focal points, there will be only one focal point that is in focus post-surgery.Laser vision correction can be used if you have astigmatism with or without nearsightedness or farsightedness.However, what laser eye procedures you are an ideal candidate for will vary based on your vision correction needs LASIK( Laser ASsisted In-situ Keratomileusis ),PRK ( Photorefractive Keratectomy ) and SMILE (Small Incision Lenticule Extraction ) . Unlike glasses or contacts, which just address astigmatism so you can see clearly with assistive devices, laser eye surgery is the only treatment to potentially resolve astigmatism so you no longer need glasses or contacts. To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis that uses 3 fundamental vectors: target induced astigmatism vector (TIAT), surgically induced astigmatism vector, and difference vector, as described by the Alpins method. Alpins method : This method of astigmatism analysis enables the examination of results of astigmatism treatment by both refractive and corneal measurements. The approach uses vector analysis, which is used in this series for examining regular astigmatism. This can be further applied to irregular astigmatism by separately examining the 2 halves of the cornea by adding a second analysis between 181and 360 degrees and displaying both together on a 360 degree polar diagram as they would appear on an eye or topography map drawn between the two points . The length of this line represents the WTW ( White To White ) value [16].

Official Title
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Adjustment of Astigmatism for Laser Correction Using Vector Planning Calculator

Conditions
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Astigmatism

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: At least 18 years of age . Stable eyeglass and contact lenses prescription for at least 2 to 3 years . Stable vision over at least the past year . No history or findings of active corneal disease . No significant dry eye . Not pregnancy or nursing . Refractive cylinder more than -1D (Diopter) . Exclusion Criteria: Certain conditions make the method inadvisable : Residual , recurrent or active ocular disease such as uveitis , sever dry eyes , sever allergic eye disease , glaucoma visually significant cataract , and retinal disease . Previous corneal surgery or trauma within the corneal flap zone . Patent corneal vascularisation within 1mm of the corneal flap zone . Age less than 18 years old . Pregnancy or breast feeding . Certain medical conditions such as autoimmune diseases (eg. lupus , rheumatoid arthritis), immunodeficiency states (eg. HIV) and diabetes may prevent proper healing after a refractive procedure. Systemic medications likely to affect wound healing such as retinoic acid and steroids . Keratoconus or other active eye disease .

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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All

Study Plan
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How is the study designed?
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What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| . Post operative Visual Acuity | To determine the effectiveness of correcting astigmatism by laser refractive surgery by a vectorial astigmatism outcome analysis by : CDVA and UCDVA, pentacam , 3 month, 6 month and 1 year after surgery. 3 months postoperative : assessment of visual acuity using corrected distance visual acuity (CDVA) , and uncorrected distance visual acuity (UCDVA) and pentacam measures . 6 months postoperative : assessment of visual acuity using corrected distance visual acuity (CDVA) , and uncorrected distance visual acuity (UCDVA) and pentacam measures . One year postoperative : assessment of visual acuity using corrected distance visual acuity (CDVA) , and uncorrected distance visual acuity (UCDVA) and pentacam measures . | one year | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Postoperative Assessment | Wavefront Analysis of post operative corneal results , 3 months after surgery to assess visual acuity . wavefront analysis is that it measures the entire visual system, rather than just the corneal surface, as in corneal topography. | 3 months |