The Effect of Hinge Position and Hinge Width on Corneal Sensation and Dry Eye After IntraLase LASIK Procedure

Study Overview
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Brief Summary
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Corneal sensation is known to play a role in tear secretion. Decreased sensation leads to decreased tear production; and when bilateral, leads to a decreased blink rate as well. Dry eyes are a common side effect of LASIK. Incidence rates vary widely, but have been reported in as many as 59% of patients. And almost all patients have some transient dry eye symptoms immediately following LASIK. Previous studies have looked at the effect of hinge position (superior vs. nasal) and hinge width on corneal sensation and dry eye after LASIK performed with a mechanical microkeratome. Corneal sensation was decreased and dry eye signs and symptoms increased immediately following LASIK in all eyes. These parameters then improved at all time periods between 1 week and 6 months post-operative. Loss of corneal sensation and dry eye signs and symptoms were greater in eyes with superior-hinge flap than nasal-hinge flap, and in eyes with narrower hinge flap rather than wider hinge flap IntraLase LASIK, using the IntraLase femtosecond laser rather than a mechanical microkeratome to cut the corneal flap, has become an increasingly popular procedure. It provides several advantages over mechanical microkeratomes, including reduced surgical complications, more predictable flap thickness, better astigmatic neutrality, decreased epithelial injury, and an ability to operate on a wider range of patients. The investigators propose this study to evaluate the effect of flap hinge size and flap thickness in corneal flaps created with the IntraLase laser. The investigators would like to determine if there is a difference from the previously discussed results found when using the mechanical microkeratome. Also, with the increased ease of programming alternate hinge width or flap thickness with IntraLase, if the investigators find a significant difference with an alternate flap configuration, it might translate to a feasible change in clinical practice.

Detailed Description
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Corneal innervation/sensation is supplied by the long ciliary nerves which branch from the trigeminal nerve. The nerves enter the cornea in the mid-stroma at the nasal and temporal limbus. They then branch and turn anterior to form a dense plexus sub-Bowman's layer. The nerves finally terminate in the wing cell layer from where they enervate the epithelium. Corneal sensation has been shown to be decreased after all corneal surgeries, including LASIK. Corneal sensation is known to play a role in tear secretion. Decreased sensation leads to decreased tear production; and when bilateral, leads to a decreased blink rate as well. Dry eyes are a common side effect of LASIK. Incidence rates vary widely, but have been reported in as many as 59% of patients. And almost all patients have some transient dry eye symptoms immediately following LASIK. Previous studies have looked at the effect of hinge position (superior vs. nasal) and hinge width on corneal sensation and dry eye after LASIK performed with a mechanical microkeratome.1,2 Corneal sensation was decreased and dry eye signs and symptoms increased immediately following LASIK in all eyes. These parameters then improved at all time periods between 1 week and 6 months post-operative. Loss of corneal sensation and dry eye signs and symptoms were greater in eyes with superior-hinge flap than nasal-hinge flap, and in eyes with narrower hinge flap rather than wider hinge flap IntraLase LASIK, using the IntraLase femtosecond laser rather than a mechanical microkeratome to cut the corneal flap, has become an increasingly popular procedure. It provides several advantages over mechanical microkeratomes, including reduced surgical complications, more predictable flap thickness, better astigmatic neutrality, decreased epithelial injury,3 and an ability to operate on a wider range of patients. We propose this study to evaluate the effect of flap hinge position and size in corneal flaps created with the IntraLase laser. We would like to determine if there is a difference from the previously discussed results found when using the mechanical microkeratome. Also, with the increased ease of programming alternate hinge position and width with IntraLase, if we find a significant difference with an alternate flap configuration, it might translate to a feasible change in clinical practice. Specific Aims: To evaluate the effect of hinge position (superior vs. temporal) , hinge width (45 vs. 90 degrees), and flap thickness on corneal sensation and dry eye after IntraLase LASIK.

Official Title
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The Effect of Hinge Position and Hinge Width on Corneal Sensation and Dry Eye After IntraLase LASIK Procedure

Conditions
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Myopia

Intervention / Treatment
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* Procedure: LASIK


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Refractive error: Myopia < 12 D, with astigmatism < 3 D, Age > 20 y/o Regular corneal curvature, sufficient corneal thickness, appropriate pupil size, normal slit lamp examination Informed consent to permit us to use their records for this study without using name, medical record number, or date of surgery. Exclusion Criteria: Pregnant/nursing Systemic collagen vascular disease Autoimmune disease Severe dry eyes

Ages Eligible for Study
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Minimum Age: 20 Years
Maximum Age: 70 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: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Hinge position<br>superior vs. temporal | Procedure: LASIK<br> <br> |
| Active Comparator: Hinge width<br>45 vs 90 degrees | Procedure: LASIK<br> <br> |
| Active Comparator: Flap Thickness<br>110 vs 130 microns | Procedure: LASIK<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| To evaluate the effect of hinge position (superior vs. temporal) , hinge width (45 vs. 90 degrees), and flap thickness on corneal sensation and dry eye after IntraLase LASIK. |  | pre operative and 1 day, 1 week, 1 month, 3 months, 6 months, and 12 months post-operative | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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IntraLase LASIK for primary myopia