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Completed

NCT Number: NCT00663923

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

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

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Key information

Conditions

Astigmatism Eye Diseases Refractive Errors

Age range

20 year and older

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 3

Primary location

Nikookari eye hospital

Tabriz, East Azerbaijan Province, 5154645395, Iran

About this study

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.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

Photorefractive keratectomy (PRK)

Procedure

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

Primary outcomes

  1. 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.

Secondary outcomes

  1. 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 .

  2. 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.

  3. 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.

  4. 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

Sponsors and collaborators

Lead sponsor

Tabriz University

Other

Registry information

Official study title

Comparison of Cross-cylinder and Conventional PRK for Laser Correction of Astigmatism: A Randomized Clinical Trial.

Acronym: PRK

Important dates

Study start
2007
Primary completion
2009
Study completion
2009
First posted
Apr 22, 2008
Registry last updated
Mar 13, 2012

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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