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

Tabriz University50 enrolled

Overview

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.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

SINGLE

Enrollment

Conditions

Astigmatism

Interventions

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

Eligibility

Sex: ALLMin age: 20 YearsHealthy volunteers:

Medical Language ↔ Plain English

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

Locations (1)

Nikookari eye hospital

Tabriz, East Azerbaijan Province, Iran

Outcomes

Primary Outcomes

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.

Time frame: six months after surgery

Secondary Outcomes

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 .

Time frame: six months postoperative

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.

Time frame: six months

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.

Time frame: six months

Data from ClinicalTrials.gov

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