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Topography-Guided Photorefractive Keratectomy
for Irregular Astigmatism following
Penetrating Keratoplasty Johnson Tan, MBBS MRCSEd (Ophth) FRCSEd (Ophth) FAMS1,2
Simon Holland, MD FRCSC1,3
David TC Lin, MD FRCSC3
1University of British Columbia, Vancouver, Canada2National Healthcare Group Eye Institute, Singapore
3Pacific Laser Eye Centre, Vancouver, Canada
WCC, San Diego 2015
Financial InterestHolland, Simon:
Alcon Laboratories Inc: Research SupportAllergan and Bausch & Lomb: Travel Support
The other authors have no financial interests in the materials mentioned
PurposeTo evaluate the efficacy and safety of the
custom Topographic Neutralization Technique (TNT) in Topography-Guided Photorefractive Keratectomy (TG PRK) in irregular astigmatism following Penetrating Keratoplasty (PK)
MethodsRetrospective, non-randomized, consecutive, case
series
49 eyes with irregular astigmatism after PK
Topography-Guided Customized Ablation Treatment (T-CAT) planning software with ALLEGRETTO WAVE® (AW) Eye-Q Excimer laser platform (Alcon Laboratories Inc, Ft Worth, Texas)
Custom Topography Neutralization Technique (TNT) adjust for the induced refractive change of surface
regularization from topography-guided treatments
ProcedureTrans-epithelial PTK, followed by TG PRK
with T-CAT software and TNT
Mitomycin-C 0.02% for 60-75 seconds
Bandage contact lens fitted and remained in place until full re-epithelialization
Fluoromethalone 0.12% eyedrops were given for 3 months, with a tapered dosing
Data AnalysisAt 3, 6 and 12 months
Uncorrected Visual Acuity (UCVA)Best Corrected Visual Acuity
(BCVA)Manifest Refraction (MR)Topographic Keratometry
Results49 eyes had treatment; 23 eyes had follow
up of at least 12 months
UVA:35% (8/23) achieved UVA ≥ 20/40None had UVA ≥ 20/40 preoperatively
BCVA:48% (11/23) had improved BCVA35% (8/23) gained 2 or more lines17% (4/23) lost 1 line4% (1/23) lost 2 or more lines
0%
10%
20%
30%
40%
GAIN 2LINES OR
MORE
GAIN 1LINE
NOCHANGE
LOSS 1LINE
LOSS 2LINES OR
MORE
Change in BCVA at 12 Months Post Op
ResultsManifest Cylinder:
Pre-operative: 0.75D to 8.00DPost-operative: 0.00D to 6.00DAverage improvement: 2.97D
Average Spherical Equivalent improved by 1.45D, from -2.32D to -0.87D
Topographic Cylinder:Pre-operative: 1.79D to 13.74DAverage improvement: 2.89D of cylinder
ResultsRetreatment rate: 8.7%
No cases of delayed epithelial healing
No significant haze (<2)
TG-PRK for PK
Pre-op 13 Months Post-op
UVA: 20/300 UVA: 20/50-2
MR: +4.00-6.00 x 005 20/80-1 MR: pl-4.00 x 175 20/40+1
Topo Cyl: -13.74 x 007
Tx: +1.01-5.73 x 007
Pre Op Post Op
Difference Map
TG-PRK Retreatment for PK43 years old male 18 months post-op
PK x 2yrs, PRK x 8 months
UVA: 20/100 UVA: 20/40-1
MR: pl-5.75 x 122 20/40 MR: +0.50-1.25 x 180 20/40
Tx: -1.25-5.88 x 130
CT: 485µm CT: 409µm
Final Post Op
1o Tx Pre Op
1o Tx Post Op
1o Tx PreOp MR:-1.50-8.00 x 122 20/60-
1
Topo Cyl: 9.40 x 113Total Tx Cyl: 11.88D
Final PostOp MR:UVA: 20/40-1 MR: +0.50-1.25 x 180 20/40
Difference Map
DiscussionPost-keratoplasty astigmatism is highly
irregular, may be extreme
Challenging, often not correctable with contact lenses or glasses
TG-PRK aims to regularize the uneven corneal front surface to achieve the desired refractive outcome Any corneal topographic change will lead to an
accompanying change in refraction Often not possible to acquire a wavefront map
DiscussionRemoves less tissue
Even if VA is not improved, we believe there is an improvement in the quality of vision from smoothening the corneal surface
PRK preferredLASIK flap may be difficult along graft-host
junction and suture linesHaze is an issue
LimitationsQuality of vision
HOAContrast sensitivity
Vector analysis
ConclusionsEarly results of TG-PRK with TNT shows potential
to improve both UVA and BCVA with good efficacy
and safety
35% UVA improved to 20/40 or better, none
preoperatively
More than one third of the patients gained 2 lines
or more of BCVA
Thank You
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