Topography-Guided Photorefractive Keratectomy
(TG-PRK) and Simultaneous collagen crosslinking (CXL) in Post-LASIK Ectasia Using 2
High-Resolution Excimer Lasers
Simon Holland
David TC Lin
ASCRS, Chicago, Illinois 2012
No financial interests
Purpose
 To evaluate the early efficacy and safety of
TG-PRK combined with simultaneous CXL
in post-LASIK ectasia for correction of
irregular astigmatism using the IVIS and
Allegretto platforms
Methods
 Using 2 high-resolution excimer lasers for TG-PRK, modified
by TNT (topographical neutralization)
- trans epithelial technique (n=17)
 Riboflavin 0.1% in dextran, until aqueous staining
 UV irradiation with riboflavin (up to 20 minutes)
 UV 370 um, 3mW/cm2 - 5.4 J/m2
 Hypotonic dextran if <400 um
 Bandage contact lens, standard post PRK
management
 Symptom scor -pre and post-operative
 uncorrected visual acuity (UVA), best corrected visual acuity
(BCVA), manifest refraction (MR)
predictability, safety
TG-PRK with CXL for ECTASIA
Original Topography:
 UCVA: 20/100
 Pre-op: -2.00sph
 BSCVA: 20/20
 CT: 553
TG-PRK with CXL for ECTASIA
4.5 years post LASIK
UCVA: 20/200
MR: -1.50-1.25x100 20/30
CT: 500
8 months post-op
UCVA: 20/20
MR: PL-0.25X180 20/20
TG PRK CXL for ECTASIA
UCVA: 20/400
Pre-op: -6.25-3.50x100
BSCVA: 20/80
12 month post-op
UCVA: 20/30RX: +0.50-0.50 x 160 20/30-
TG CXL PRK for Ectasia
26 years old male
LASIK x 5 years
UCVA : 20/60
MR:+1.00-2.75x125 20/30
CT : 552
3 months post-op
UCVA: 20/30MR:Pl-0.75x180 20/25+
CT : 544
Results
 17 patients completed ≥ 6 months post-operatively
 12/17 (71%) had UVA of ≥20/40
 9 (53%) gained 2 lines or more BCVA; 1 (6%) lost 2
lines or more
 Mean reduction of astigmatism 2.56D
 All but two symptomatically improved
 Complications included delayed epithelialization
 No progression of ectasia noted up to 18 mth
No significant differences in the small sample sizes
 iVIS central corneal regularization does not induce as
much myopia as the Allegretto when used with TNT
 iVIS - less gain in BSCVA
Conclusions
 Early results of TG-PRK with simultaneous CXL
using two laser platforms shows promise as an
effective treatment for highly symptomatic
patients with post-LASIK ectasia
 All but two had improved symptoms
 71% of patients had 20/40 or better UVA
 More than half gained ≥2 lines of BSCVA
TG PRK-CXL Summary –
2 platforms, 2 conditions
KC
with Allegretto
KC
with iVIS
Ectasia
with both lasers
99
43
17
UVA ≥20/40
54%
42%
71%
Gained 2 lines or
more BCVA
32%
9%
53%
1.63D
1.17D
2.56D
Analysis
Patients completed 6
months post-op
Average reduction of
astigmatism
TG CXL PRK for KERATOCONUS
Pre-op: +1.75-4.00x060
BSCVA: 20/30-
12 months post-op
UCVA: 20/30
RX: +0.25-0.75x170 20/25
iVIS TG-PRK with CXL for KC
Pre-op
6 months post-op
UCVA: CF
UCVA: 20/50MR: -6.50-4.75X110 20/60+ MR: -1.00-1.25x180 20/40-
TG PRK CXL for ECTASIA
UCVA: 20/400
Pre-op: -6.25-3.50x100
BSCVA: 20/80
12 month post-op
UCVA: 20/30RX: +0.50-0.50 x 160 20/30-
KC – Allegretto
PreOp:
+1.75-4.00x060 20/3012 months PostOp:
+0.25-0.75x170 20/25
KC – iVIS
PreOp:
-0.50-3.75x050 20/60
6 months PostOp:
-1.00sph
20/40
Ectasia
PreOp:
-6.25-3.50x100
20/80
12 months PostOp:
+0.50-0.50 x 160
20/30
Allegretto vs iVIS
 Induced myopia , larger optical zone
 Mixed cylinder - smaller optical zone
TG PRK with Cross-linking
for Keratoconus and Ectasia:
Concerns
 Thinning an already thin cornea - long term
stability unknown
 Predictability - hyperopic surprises - less
than expected even with -1.25 target
 Endothelial damage , delayed
epithelialization
TG PRK with Cross Linking:
Impressions
 Effective in both KC and Ectasia in early
studies for highly symptomatic CL
intolerant patients
 Reduce nomogram for TNT in ectasia
 Topograpgical neutralization techniques
mostly effective for correcting for induced
refractive error from TG PRK – across
platforms and for both KC and ectasia