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Comparison of Cross-cylinder and Conventional Photorefractive Keratectomy(PRK) in Correcting Medium-high Astigmatism (PRK)

This study has been completed.
Sponsor:
ClinicalTrials.gov Identifier:
NCT00663923
First Posted: April 22, 2008
Last Update Posted: March 13, 2012
The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details.
Information provided by (Responsible Party):
Tabriz University
April 18, 2008
April 22, 2008
December 30, 2009
December 30, 2011
March 13, 2012
November 2007
June 2009   (Final data collection date for primary outcome measure)
Correction of Astigmatism [ Time Frame: six months after surgery ]
It shows the result of correction of astigmatism .In compound myopic astigmatism the meridians of maximum and minimum power are both too strong.So both line images fall short of the retina.It is measured by refraction(using autorefractor).Diopter is a unit of measurement of the optical power of any refracting surface ,which is reciprocal of the focal length measured in meters.
Improvement of visual acuity (snelen chart), refraction, aberrometry [ Time Frame: six months after surgery ]
Complete list of historical versions of study NCT00663923 on ClinicalTrials.gov Archive Site
  • Higher Order Aberrations [ Time Frame: six months postoperative ]
    Although lower- order aberrations decrease after laser vision correction,higher -order aberrations may increase after conventional PRK or LASIK(Laser in situ keratomileusis).Higher-order aberration is Composed of delicate irregularities within the cornea not correctable by spectacles.It is measured using aberrometer.In this study OPD scan was used that is one of the methods of wavefront analysis .
  • Corrected Distance Visual Acuity(CDVA) [ Time Frame: six months ]
    CDVA is attained after correction of refractive errors using lenses of varying powers .the data are the LogMAR values calculated from the snellen chart using the visual acuity conversion chart(the units would be LogMAR).Any patient with better vision can see the smallest letters at 20 feet(20/20=0.00 LogMAR).Higher LogMAR values represent worse outcome.Log MAR(logarithmic minimum angle of resolution)notation ,has gained widespread use in statistical calculations.
  • Uncorrected Distance Visual Acuity (UCDVA) [ Time Frame: six months ]
    UCDVA is attained without correction of refractive errors .the data are the LogMAR values calculated from the snellen chart using the visual acuity conversion chart( the units would be LogMAR).Any patient with better vision can see the smallest letters at 20 feet(20/20=0.00 LogMAR).Higher LogMAR values represent worse outcome.Log MAR(logarithmic minimum angle of resolution)notation ,has gained widespread use in statistical calculations.
  • Surgically Induced Astigmatism [ Time Frame: six months after surgery ]

    It is the vector of the astigmatic change actually induced by the surgery.Participant population was the same as baseline participants.

    It was measured by refraction(using autorefractor) and vector analysis(using special software).Diopter is a unit of measurement of the optical power of any refracting surface ,which is reciprocal of the focal length measured in meters

aberrometry for higher order aberrations, refraction for residual and regressed astigmatism, snelen chart for visual acuity test [ Time Frame: six months postop ]
Not Provided
Not Provided
 
Comparison of Cross-cylinder and Conventional Photorefractive Keratectomy(PRK) in Correcting Medium-high Astigmatism
Comparison of Cross-cylinder and Conventional PRK for Laser Correction of Astigmatism: A Randomized Clinical Trial.
The purpose of this study is to determine whether cross-cylinder approach is more effective than routine method in laser correction of astigmatism.
Both eyes of 50 patients(100 eyes) with medium-high compound myopic astigmatism and inclusion criteria,will be treated by photorefractive keratectomy (PRK) using excimer laser.It breaks chemical bonds within corneal stroma.It's wavelength is 193 nm that is in the ultraviolets range with high energy and very low tissue penetrance. The right or left eye of every patient would be allocated randomly to one of the study groups using RandList 1.1. In spite of recent advances in excimer laser machines and surgical techniques,correction of astigmatism is not more successful compared to myopia. In this study we will compare two methods of laser correction of astigmatism regarding to visual acuity,residual error and aberrations.
Interventional
Phase 3
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single (Participant)
Primary Purpose: Treatment
Astigmatism
Procedure: photorefractive keratectomy (PRK)
comparison of PRK by cross-cylinder approach in one eye and conventional (single) method in the other eye for laser correction of astigmatism
Other Name: photoastigmatic keratectomy
  • Experimental: cross-cylinder
    In this technique the laser is programmed with the axis and amount of cylinder,so that the steepest meridian is flattened with central cylindrical ablation and the flattest meridian steepens with paracentral ablation
    Intervention: Procedure: photorefractive keratectomy (PRK)
  • Active Comparator: single
    In this technique ,cylinder is treated only on one meridian by performing an elliptical ablation to to flatten the steeper meridian to match the flatter meridian.
    Intervention: Procedure: photorefractive keratectomy (PRK)
Not Provided

*   Includes publications given by the data provider as well as publications identified by ClinicalTrials.gov Identifier (NCT Number) in Medline.
 
Completed
50
December 2009
June 2009   (Final data collection date for primary outcome measure)

Inclusion Criteria:

  • >20 years of age
  • refractive stability for at least one year
  • regular and symmetric astigmatism of >1.5 diopters

Exclusion Criteria:

  • corneal thickness<470 microns
  • keratoconus or suspected keratoconus
  • active ocular disease and systemic collagen disease
Sexes Eligible for Study: All
20 Years and older   (Adult, Senior)
Yes
Contact information is only displayed when the study is recruiting subjects
Iran, Islamic Republic of
 
 
NCT00663923
86-43
Yes
Not Provided
Not Provided
Tabriz University
Tabriz University
Not Provided
Study Director: Mohammad R Sedghipoor, MD Ophthalmology Department, Tabriz University of medical Sciences
Tabriz University
March 2012

ICMJE     Data element required by the International Committee of Medical Journal Editors and the World Health Organization ICTRP