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

This study has been completed.
Sponsor:
Information provided by (Responsible Party):
Tabriz University
ClinicalTrials.gov Identifier:
NCT00663923
First received: April 18, 2008
Last updated: March 10, 2012
Last verified: March 2012
  Purpose

The purpose of this study is to determine whether cross-cylinder approach is more effective than routine method in laser correction of astigmatism.


Condition Intervention Phase
Astigmatism
Procedure: photorefractive keratectomy (PRK)
Phase 3

Study Type: Interventional
Study Design: Allocation: Randomized
Endpoint Classification: Safety/Efficacy Study
Intervention Model: Parallel Assignment
Masking: Single Blind (Subject)
Primary Purpose: Treatment
Official Title: Comparison of Cross-cylinder and Conventional PRK for Laser Correction of Astigmatism: A Randomized Clinical Trial.

Further study details as provided by Tabriz University:

Primary Outcome Measures:
  • Correction of Astigmatism [ Time Frame: six months after surgery ] [ Designated as safety issue: No ]
    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.


Secondary Outcome Measures:
  • Higher Order Aberrations [ Time Frame: six months postoperative ] [ Designated as safety issue: No ]
    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 ] [ Designated as safety issue: Yes ]
    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 ] [ Designated as safety issue: No ]
    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 ] [ Designated as safety issue: No ]

    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



Enrollment: 50
Study Start Date: November 2007
Study Completion Date: December 2009
Primary Completion Date: June 2009 (Final data collection date for primary outcome measure)
Arms Assigned Interventions
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
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
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.
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

Detailed Description:

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.

  Eligibility

Ages Eligible for Study:   20 Years and older
Genders Eligible for Study:   Both
Accepts Healthy Volunteers:   Yes
Criteria

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
  Contacts and Locations
Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study. To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below. For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT00663923

Locations
Iran, Islamic Republic of
Nikookari eye hospital
Tabriz, East Azarbaijan, Iran, Islamic Republic of, 5154645395
Sponsors and Collaborators
Tabriz University
Investigators
Study Director: Mohammad R Sedghipoor, MD Ophthalmology Department, Tabriz University of medical Sciences
  More Information

No publications provided

Responsible Party: Tabriz University
ClinicalTrials.gov Identifier: NCT00663923     History of Changes
Other Study ID Numbers: 86-43
Study First Received: April 18, 2008
Results First Received: December 30, 2009
Last Updated: March 10, 2012
Health Authority: Iran: Ethics Committee

Keywords provided by Tabriz University:
Excimer Laser
photorefractive keratectomy
astigmatism

Additional relevant MeSH terms:
Astigmatism
Refractive Errors
Eye Diseases

ClinicalTrials.gov processed this record on July 20, 2014