Transcript Comparing Flap Thicknesses Between IntraLase & Microkeratomes

David Kent
Christchurch, New Zealand
The author has no financial interest in any of the products in this
presentation




All LASIK flaps measured by subtraction
ultrasound pachymetry since July 2000
New microkeratome blade or IntraLase disposable
patient interface used for every eye
Same surgeon did all measurements with
Sonogage 50 MHz pachymeter
Thinnest central pachymetry pre-operatively
 thinnest of three readings

Intra-operative in-the-bed pachymetry
 thinnest of three readings

Data recorded in MS Access database
 analyzed in MS Excel and SyStat SigmaStat
LASIK Flap Creation Devices
14
Chiron Vision ACS
2818
(briefly in 2000)
Hansatome (1998 to
2007)
259
7493
Zyoptix XP (2005 to
2007)
IntraLase FS60 (2006
to present)
Microkeratome
Four IntraLase Settings
One ACS head
Red ovals around the
most extreme values
Ten Hansatome Trays
(27 heads)
One Zyoptix XP Tray
(2 heads)
IntraLase
IntraLase
IntraLase
IntraLase
ACS 957
2141
2141
2141
2141
3082
3082
4040
4040
4040
4040
4406
4406
5014
5014
5014
5019
5019
5019
5243
5243
5308
5308
6322
6322
6322
6610
6610
6610
9505
9505
Footplate
Count
90
100
110
120
130
160
180
Z18
Z20
160
180
160
180
Z18
Z20
160
180
Z16
Z18
Z20
Z16
Z18
Z20
Z18
Z20
Z18
Z20
Z16
Z18
Z20
Z16
Z18
Z20
120
140
Average
1884
168
11
757
14
473
403
196
301
14
28
380
444
478
552
132
38
41
1013
1188
22
419
314
21
22
108
120
3
39
96
31
391
226
11
248
126.43
132.17
150.00
116.76
120.43
134.70
163.31
124.83
138.02
138.86
177.14
119.18
139.39
126.01
146.85
137.20
155.24
104.37
122.12
139.58
101.36
120.45
140.04
130.38
139.86
119.25
136.32
95.33
129.56
137.99
104.87
127.86
138.70
95.27
120.95
StDev
14.80
13.45
15.56
14.46
26.33
20.95
27.00
16.87
18.51
14.58
21.74
18.55
18.73
14.98
17.36
20.87
22.28
16.08
16.86
18.50
11.83
17.83
17.62
14.43
13.09
17.60
19.48
10.79
19.86
17.88
13.83
17.14
16.32
16.82
17.85
Min
Max
68
94
118
62
55
77
107
73
96
119
116
44
86
70
83
93
119
65
66
70
79
68
75
101
117
52
84
83
92
86
75
59
90
73
73
186
172
176
169
153
202
237
168
201
172
222
186
197
178
198
192
213
142
187
197
117
191
182
168
165
165
178
103
168
198
130
182
189
122
185
Zyoptix XP
Hansatome
Z16 head
IntraLase
Hansatome
& ACS
IntraLase
Flap Creator
Labelled
Thickness
9505
120
11
95.27
16.82
73
122
6322
Z16
3
95.33
10.79
83
103
5019
Z16
22
101.36
11.83
79
117
5014
Z16
41
104.37
16.08
65
142
6610
Z16
31
104.87
13.83
75
130
IntraLase
90
757
116.76
14.46
62
169
4040
160
380
119.18
18.55
44
186
5308
Z18
108
119.25
17.60
52
165
ACS 957
130
14
120.43
26.33
55
153
5019
Z18
419
120.45
17.83
68
191
9505
140
248
120.95
17.85
73
185
5014
Z18
1013
122.12
16.86
66
187
2141
Z18
196
124.83
16.87
73
168
4040
Z18
478
126.01
14.98
70
178
IntraLase
100
1884
126.43
14.80
78
186
Count
Average
StDev
Min
Max
N>100
Flap Creator
Count
Mean
Std. Dev.
IntraLase 110
168
132.2
13.45
IntraLase 90
757
116.7
14.46
IntraLase 100
1884
126.4
14.80
Hansatome 4040 Z18
478
126.0
14.98
Hansatome 6610 Z20
226
138.7
16.32

One Way ANOVA, P=0.002
28
P = 0.002, One way ANOVA
26
Flap Thickness Standard Deviation (microns)
24
22
20
18
16
N=8
N=2
14
N=4
N=20
12
10
8
IntraLase
Std. Hansatome
ZC Hansatome
Type of Flap Creator
Zyoptix XP



Excessively thick
flap defined as
central thickness of
190 microns or
more
Risk of a too-thick
flap greater with
microkeratomes
P>0.001, z-test of
proportions
190
microns
or more
IntraLase
Microkeratomes
0
104
Less
2818
than 200
microns
7662
Totals
7766
2818

Variability due to not being central on the
cornea affecting both:
◦ Pre-operative pachymetry
◦ In-the-bed pachymetry


Pachymeter or probe inaccuracies
Variable hydration of the corneal bed
◦ If the bed is wet the stroma swells and thickens

Corneal bed is dry with the IntraLase
 In-the-bed measurement affected by having to
press more firmly with the pachymeter probe to
achieve a reading
 Therefore more likely to have overestimate flap
thickness

Corneal bed is wet with a microkeratome
 Cornea is more hydrated giving a thicker in-thebed reading and hence thinner flap measurement
 Not as much pressure required to get a reading inthe-bed
 More likely to underestimate flap thickness


Microkeratome heads vary widely with regards to
average flap thickness and standard deviation of
flap thickness
Some microkeratome heads:
◦ have excessively high flap thickness variability
◦ make flaps that are too thick


Zero Compression Hansatome heads had smaller
standard deviations than the Standard
Hansatome
Microkeratomes have a greater risk of making an
excessively thick flap than with the IntraLase,
P<0.001




Flap thickness standard deviation is lower
with the IntraLase than with microkeratomes,
P=0.002
The IntraLase 90 micron setting makes
consistent thin flaps with a low standard
deviation and a high level of safety
IntraLase 100 and 110 micron settings also
have a low standard deviations
My IntraLase FS60 makes flaps that measure
about 20-25 microns thicker on average than
the nominal thickness