Brief Title
Simultaneous TransPRK and Corneal Collagen Cross-Linking
Official Title
A Prospective Trial of Simultaneous Combined Transepithelial Photorefractive Keratectomy and Corneal Collagen Cross-linking for Keratoconus
Brief Summary
Young patients with keratoconus face two problems: disease progression and corneal shape
irregularity leading to poor vision even in spectacles.
Corneal collagen cross-linking (CXL) is a new treatment designed to halt disease progression
in keratoconus. The aim is to stiffen the cornea thereby preventing further shape
deterioration.
Topography or wavefront guided transepithelial photorefractive keratectomy (transPRK) uses
the excimer laser (the laser used to correct sight in 'laser eye surgery') to reduce corneal
shape irregularity in early stage keratoconus, reducing dependence on contact lenses.
In transPRK, the corneal skin layer is removed in a well controlled, no touch procedure,
preparing the cornea for CXL. Performing both treatments simultaneously (combining both
procedures in one operation) may offer several advantages over performing CXL first then
waiting for corneal shape to stabilise before performing transPRK. In particular, visual
rehabilitation may be faster. This study aims to evaluate visual recovery after simultaneous
CXL and transPRK in progressive early stage keratoconus. Visual recovery in these patients
will be compared with results for a similar group of patients with early stage keratoconus
who have already been treated with CXL alone.
Detailed Description
Features which distinguish this trial from previous trials of combined photorefractive
keratectomy (PRK) and corneal collagen cross-linking (CXL) are: a rapid, pulsed light, CXL
protocol; and a treatment programming algorithm for PRK designed to target higher order
aberrations only with no compensatory additional laser corneal tissue removal.
Excimer laser treatment will be performed with the Schwind Amaris 750S laser
(www.eye-tech-solutions.com). Unique features of this system utilised here include:
- Pre-programmed transepithelial ablation - laser removal of the minimum area of corneal
epithelium required for PRK promoting more rapid recovery than conventional methods (20%
alcohol application and manual epithelial removal). An 8mm diameter ablation zone will
be applied throughout.
- Enhanced algorithms for minimal laser tissue removal - in this trial, the investigators
are targeting higher order aberrations only (coma in particular) with the aim of
improving spectacle corrected visual acuity without regard to the predicted
spherocylindrical outcome. Unlike other current excimer laser platforms, Schwind Amaris
treatment programming software allows treatment for irregular astigmatism without
additional compensatory laser tissue removal to correct the spherocylindrical change
induced by treatment of higher order aberrations. Higher order aberrations can also be
treated selectively. The investigators will use an algorithm step that targets only
aberrations (up to 6th order Zernike polynomials) with a value greater than 2 standard
deviations from the population mean in normative data. These treatment planning steps
allow the laser to create a large diameter treatment with minimal treatment depth.
Laser epithelial removal alone (transPTK at depth 55µm) removes a maximum 65µm of tissue in
the corneal periphery. For patients with 390µm at the thinnest point, transPTK will therefore
leave above 325µm residual stromal thickness prior to CXL. This is in line with
recommendations for minimum stromal thickness after epithelial removal in the CXL protocol
used here. Limited stromal reshaping is achieved in this simple embodiment of transPRK for
keratoconus by taking advantage of the masking effect of the corneal epithelium, which tends
to be thinnest over the cone apex. Where the thinnest point is greater than 390µm, further
reductions in corneal shape irregularity can be produced by adding either wavefront or
topography guided additional stromal ablation using custom programming on the Schwind Amaris
laser. Ocular wavefront (aberrometry) guided smoothing will be used for patients with a 5.5mm
or larger pupil at scanning and a consistent scan sequence (3 scans within 0.5 dioptre (D)
spherical equivalent refraction). Corneal wavefront (topography) guided smoothing will be
used for patients with ocular wavefront scans which do not meet these criteria. In all cases,
a minimum corneal stromal thickness prior to CXL of 325µm will be preserved.
Immediately after PRK, corneal collagen cross-linking will be performed using the following
protocol
Riboflavin soak: 10 minutes total soak time; application of 0.1% riboflavin preparation
(VibeX Rapid - www.avedro.com) each 2 minutes with gentle balanced salt solution irrigation
to remove excess riboflavin prior to UV light exposure.
UV light exposure: Total treatment time 8 minutes (370nm wavelength; 30mW/cm2 irradiance; 4
minutes total UV exposure time, pulsed 1.5 seconds on 1.5 seconds off; Avedro KXL I light
source)
Mitomycin C will not be used. A bandage contact lens will be applied at the end of treatment
and a standard post photorefractive keratectomy topical and systemic drug treatment regimen
will be used in every case with initial clinical review 1 week after surgery.
Study Type
Interventional
Primary Outcome
Change in LogMAR Corrected Distance Visual Acuity (CDVA)
Secondary Outcome
Clinically Significant Visual Gain
Condition
Keratoconus
Intervention
Transepithelial Photorefractive Keratectomy (TransPRK)
Study Arms / Comparison Groups
TransPRKCXL
Description: Simultaneous combined transepithelial photorefractive keratectomy (TransPRK) and corneal collagen cross-linking (CXL)
Publications
* Includes publications given by the data provider as well as publications identified by National Clinical Trials Identifier (NCT ID) in Medline.
Recruitment Information
Recruitment Status
Procedure
Estimated Enrollment
55
Start Date
August 2014
Completion Date
July 2017
Primary Completion Date
July 2016
Eligibility Criteria
Inclusion Criteria:
- Patients with progressive stage II or III keratoconus
- CDVA < 0.00 logMAR or subjective problems with spectacle corrected visual quality
(ghost images or light scatter symptoms)
Exclusion Criteria:
- Active ocular surface disease
- Minimum corneal thickness <390µm (leaving 325µm residual stromal thickness after
transPTK - in line with minimum thickness recommendations for the study CXL protocol)
- Vulnerable groups (patients whose capacity for giving informed consent to participate
in the trial may be impaired)
Gender
All
Ages
18 Years - 35 Years
Accepts Healthy Volunteers
No
Contacts
Bruce D Allan, MD FRCOphth, ,
Location Countries
United Kingdom
Location Countries
United Kingdom
Administrative Informations
NCT ID
NCT02208089
Organization ID
ALLB1018
Responsible Party
Sponsor-Investigator
Study Sponsor
Bruce Allan
Collaborators
Moorfields Eye Hospital NHS Foundation Trust
Study Sponsor
Bruce D Allan, MD FRCOphth, Principal Investigator, Moorfields Eye Hospital NHS Foundation Trust
Verification Date
September 2018