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

Astigmatism Clinical Trial

— PRK  

Official title:

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

Clinical Trial Details — Status: Completed

Administrative data

• NCT number: NCT00663923
• Other study ID #: 86-43
• Status: Completed
• Phase: Phase 3
• First received: April 18, 2008
• Last updated: March 10, 2012
• Start date: November 2007
• Est. completion date: December 2009

Study information

• Verified date: March 2012
• Source: Tabriz University
• Contact: n/a
• Is FDA regulated: No
• Health authority: Iran: Ethics Committee
• Study type: Interventional

Clinical Trial Summary

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

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.

Recruitment information / eligibility

• Status: Completed
• Enrollment: 50
• Est. completion date: December 2009
• Est. primary completion date: June 2009
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: Both
• Age group: 20 Years and older

Eligibility

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 Design

Allocation: Randomized, Endpoint Classification: Safety/Efficacy Study, Intervention Model: Parallel Assignment, Masking: Single Blind (Subject), Primary Purpose: Treatment

Related Conditions & MeSH terms

• Astigmatism

Intervention

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

Locations

Country	Name	City	State
Iran, Islamic Republic of	Nikookari eye hospital	Tabriz	East Azarbaijan

Sponsors (1)

Lead Sponsor	Collaborator
Tabriz University

Country where clinical trial is conducted

Iran, Islamic Republic of, 

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	Correction of Astigmatism	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	No
Secondary	Higher Order Aberrations	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	No
Secondary	Corrected Distance Visual Acuity(CDVA)	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	Yes
Secondary	Uncorrected Distance Visual Acuity (UCDVA)	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	No
Secondary	Surgically Induced Astigmatism	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	No