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

March 10, 2012 updated by: Tabriz University

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.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

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.

Study Type

Interventional

Enrollment (Actual)

50

Phase

  • Phase 3

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Iran, Islamic Republic of
    • East Azarbaijan
      • Tabriz, East Azarbaijan, Iran, Islamic Republic of, 5154645395
        • Nikookari eye hospital

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

20 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

Yes

Genders Eligible for Study

All

Description

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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Single

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
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 Names:
  • 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 Names:
  • photoastigmatic keratectomy

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
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.
six months after surgery

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
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 .
six months postoperative
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.
six months
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.
six months
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
six months after surgery

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Tabriz University

Investigators

  • Study Director: Mohammad R Sedghipoor, MD, Ophthalmology Department, Tabriz University of medical Sciences

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

November 1, 2007

Primary Completion (Actual)

June 1, 2009

Study Completion (Actual)

December 1, 2009

Study Registration Dates

First Submitted

April 18, 2008

First Submitted That Met QC Criteria

April 21, 2008

First Posted (Estimate)

April 22, 2008

Study Record Updates

Last Update Posted (Estimate)

March 13, 2012

Last Update Submitted That Met QC Criteria

March 10, 2012

Last Verified

March 1, 2012

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 86-43

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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