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

• Sponsor: Tabriz University (Other)
• Overall Status: Completed
• CT.gov ID: NCT00663923
• Collaborator: (none)
• Enrollment: 50
• Location: 1
• Arms: 2
• Duration (Months): 25
• Patients Per Site Per Month: 2

Study Details

Study Description

Brief Summary

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

Condition or Disease	Intervention/Treatment	Phase
Astigmatism	Procedure: photorefractive keratectomy (PRK)	Phase 3

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 Design

• Study Type: Interventional
• Actual Enrollment: 50 participants
• Allocation: Randomized
• Intervention Model: Parallel Assignment
• Masking: Single (Participant)
• Primary Purpose: Treatment
• Official Title: Comparison of Cross-cylinder and Conventional PRK for Laser Correction of Astigmatism: A Randomized Clinical Trial.
• Study Start Date: Nov 1, 2007
• Actual Primary Completion Date: Jun 1, 2009
• Actual Study Completion Date: Dec 1, 2009

Arms and Interventions

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

Outcome Measures

Primary Outcome Measures

1. Correction of Astigmatism [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 Outcome Measures

1. Higher Order Aberrations [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) [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) [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 [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

Eligibility Criteria

Criteria

• Ages Eligible for Study: 20 Years and Older
• Sexes Eligible for Study: All
• Accepts Healthy Volunteers: Yes

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

Locations

	Site	City	State	Country	Postal Code
1	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

Study Documents (Full-Text)

None provided.

More Information

Publications

None provided.

• Responsible Party: Tabriz University
• ClinicalTrials.gov Identifier: NCT00663923
• Other Study ID Numbers: 86-43
• First Posted: Apr 22, 2008
• Last Update Posted: Mar 13, 2012
• Last Verified: Mar 1, 2012

• Keywords provided by Tabriz University: Excimer Laser; photorefractive keratectomy; astigmatism
• Additional relevant MeSH terms: Astigmatism

Study Results

Participant Flow

Recruitment Details	Both eyes of Fifty patients with medium-high compound myopic astigmatism(1.5- 5 D) were enrolled in a prospective randomized study between sep 2007 and sep 2008 at Nikookari eye hospital and Mehr eye center
Pre-assignment Detail	All enrolled patients having inclusion criteria accepted both available techniques for correction of astigmatism.

Arm/Group Title	Photorefractivekeratectomy(PRK)
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 100 eyes of 50 participants)to undergo PRK by cross-cylinder or conventional(single) approach using Excimer laser.In cross-cylinder method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .in single method,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Period Title: Overall Study
STARTED	50
COMPLETED	48
NOT COMPLETED	2

Baseline Characteristics

Arm/Group Title	Photorefractive Keratectomy( PRK)
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to100 eyes of 50 participants)to undergo PRK by cross-cylinder or conventional(single) approach using Excimer laser.In cross-cylinder method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .In single method the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Overall Participants	50
Age (Count of Participants)
<=18 years	0 0%
Between 18 and 65 years	50 100%
>=65 years	0 0%
Age (years) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [years]	28.46 (7.05)
Sex: Female, Male (Count of Participants)
Female	39 78%
Male	11 22%
Region of Enrollment (participants) [Number]
Iran, Islamic Republic of	50 100%
Target induced astigmatism(TIA) (Diopter) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [Diopter]	1.86 (0.60)
astigmatism (diopter) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [diopter]	-2.49 (0.83)
corrected distance visual acuity (logMAR) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [logMAR]	0.06 (0.11)
high order aberration (micron) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [micron]	0.36 (0.10)
Spherical equivalent (Diopter) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [Diopter]	-5.19 (2.47)
uncorrected distance visual acuity (log MAR) [Mean (Standard Deviation) ]
Mean (Standard Deviation) [log MAR]	1.11 (0.36)

Outcome Measures

1. Primary Outcome

Title	Correction of Astigmatism
Description	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

Outcome Measure Data

Analysis Population Description

The sample size was determined by the one proportion formula where power = 0.8, d=0.02 , p= 0.5(primary outcome) and type I error probability associated with this test of null hypothesis is 0.05. The analysis was per protocol

Arm/Group Title	Cross-cylinder PRK	Single PRK
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by cross-cylinder approach using Excimer laser.In this method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by single approach using Excimer laser.In this method ,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Measure Participants	48	48
Measure eyes	48	48
Mean (Standard Deviation) [diopter]	-0.54 (0.43)	-0.59 (0.33)

Statistical Analysis 1

Statistical Analysis Overview	Comparison Group Selection	Cross-cylinder PRK, Single PRK
	Comments
	Type of Statistical Test	Superiority or Other
	Comments
Statistical Test of Hypothesis	p-Value	<0.05
	Comments	two - tailed p value <0.05 were considered statistically significant.
	Method	t-test, 2 sided
	Comments	in this study degrees of freedom is sample size - 1
Method of Estimation	Estimation Parameter	Mean Difference (Final Values)
	Estimated Value	-0.05
	Confidence Interval	(2-Sided) 95%; -.62 to -.001
	Parameter Dispersion	Type: Standard Deviation; Value: .10
	Estimation Comments

2. Secondary Outcome

Title	Higher Order Aberrations
Description	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

Outcome Measure Data

Analysis Population Description

the analysis was per protocol.

Arm/Group Title	Cross-cylinder PRK	Single PRK
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by cross-cylinder approach using Excimer laser.In this method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by single approach using Excimer laser.In this method ,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Measure Participants	42	42
Measure eyes	42	42
Mean (Standard Deviation) [micron]	0.51 (0.21)	0.51 (0.20)

3. Secondary Outcome

Title	Corrected Distance Visual Acuity(CDVA)
Description	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

Outcome Measure Data

Analysis Population Description

the analysis was per protocol

Arm/Group Title	Cross-cylinder PRK	Single PRK
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by cross-cylinder approach using Excimer laser.In this method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by single approach using Excimer laser.In this method ,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Measure Participants	48	48
Measure eyes	48	48
Mean (Standard Deviation) [LogMAR]	0.02 (0.02)	0.03 (0.03)

4. Secondary Outcome

Title	Uncorrected Distance Visual Acuity (UCDVA)
Description	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

Outcome Measure Data

Analysis Population Description

the analysis was per protocol

Arm/Group Title	Cross-cylinder PRK	Single PRK
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by cross-cylinder approach using Excimer laser.In this method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by single approach using Excimer laser.In this method ,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Measure Participants	48	48
Measure eyes	48	48
Mean (Standard Deviation) [LogMAR]	0.08 (0.15)	0.10 (0.16)

5. Secondary Outcome

Title	Surgically Induced Astigmatism
Description	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
Time Frame	six months after surgery

Outcome Measure Data

Analysis Population Description

[Not Specified]

Arm/Group Title	Cross-cylinder PRK	Single PRK
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by cross-cylinder approach using Excimer laser.In this method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by single approach using Excimer laser.In this method ,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
Measure Participants	48	48
Mean (Standard Deviation) [Diopter]	1.98 (0.57)	1.51 (0.43)

Adverse Events

Arm/Group Title	Cross-cylinder PRK		Single PRK
Arm/Group Description	Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by cross-cylinder approach using Excimer laser.In this method , half of the cylinder is treated along the steepest meridian and the other half is ablated along the flattest meridian .		Right or left eye of 50 patients was randomly enrolled(data provided in this module refer to 50 eyes of 50 participants)to undergo PRK by single approach using Excimer laser.In this method ,the steepest meridian is treated by elliptical ablation to match the flattest meridian.
All Cause Mortality
	Cross-cylinder PRK		Single PRK
	Affected / at Risk (%)	# Events	Affected / at Risk (%)	# Events
Total	/ (NaN)		/ (NaN)
Serious Adverse Events
	Cross-cylinder PRK		Single PRK
	Affected / at Risk (%)	# Events	Affected / at Risk (%)	# Events
Total	0/48 (0%)		0/48 (0%)
Other (Not Including Serious) Adverse Events
	Cross-cylinder PRK		Single PRK
	Affected / at Risk (%)	# Events	Affected / at Risk (%)	# Events
Total	0/48 (0%)		0/48 (0%)

Limitations/Caveats

[Not Specified]

More Information

Certain Agreements

All Principal Investigators ARE employed by the organization sponsoring the study.

There is NOT an agreement between Principal Investigators and the Sponsor (or its agents) that restricts the PI's rights to discuss or publish trial results after the trial is completed.