1. David Kent Christchurch, New Zealand The author has no financial interest in any of the products in this presentation

2. 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

4. MicrokeratomeFootplateCountAverageStDevMinMax IntraLase90 1884126.4314.8068186 IntraLase100 168132.1713.4594172 IntraLase110 11150.0015.56118176 IntraLase120 757116.7614.4662169 ACS 95713014120.4326.3355153 2141160473134.7020.9577202 2141180403163.3127.00107237 2141Z18196124.8316.8773168 2141Z20301138.0218.5196201 308216014138.8614.58119172 308218028177.1421.74116222 4040160380119.1818.5544186 4040180444139.3918.7386197 4040Z18478126.0114.9870178 4040Z20552146.8517.3683198 4406160132137.2020.8793192 440618038155.2422.28119213 5014Z1641104.3716.0865142 5014Z181013122.1216.8666187 5014Z201188139.5818.5070197 5019Z1622101.3611.8379117 5019Z18419120.4517.8368191 5019Z20314140.0417.6275182 5243Z1821130.3814.43101168 5243Z2022139.8613.09117165 5308Z18108119.2517.6052165 5308Z20120136.3219.4884178 6322Z16395.3310.7983103 6322Z1839129.5619.8692168 6322Z2096137.9917.8886198 6610Z1631104.8713.8375130 6610Z18391127.8617.1459182 6610Z20226138.7016.3290189 95051201195.2716.8273122 9505140248120.9517.8573185 Four IntraLase Settings One Zyoptix XP Tray (2 heads) Ten Hansatome Trays (27 heads) One ACS head Red ovals around the most extreme values

5. Flap Creator Labelled ThicknessCountAverageStDevMinMax 95051201195.2716.8273122 6322Z16395.3310.7983103 5019Z1622101.3611.8379117 5014Z1641104.3716.0865142 6610Z1631104.8713.8375130 IntraLase90757116.7614.4662169 4040160380119.1818.5544186 5308Z18108119.2517.6052165 ACS 95713014120.4326.3355153 5019Z18419120.4517.8368191 9505140248120.9517.8573185 5014Z181013122.1216.8666187 2141Z18196124.8316.8773168 4040Z18478126.0114.9870178 IntraLase1001884126.4314.8078186 Zyoptix XP Hansatome Z16 head Hansatome & ACS IntraLase

6. Flap CreatorCountMeanStd. Dev. IntraLase 110168132.213.45 IntraLase 90757116.714.46 IntraLase 1001884126.414.80 Hansatome 4040 Z18478126.014.98 Hansatome 6610 Z20226138.716.32 N>100

7.  One Way ANOVA, P=0.002 N=4 N=8 N=20 N=2 P = 0.002, One way ANOVA

8.  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 IntraLaseMicrokeratomes 190 microns or more 0104 Less than 200 microns 28187662 Totals28187766

9.  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

10. 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-the- bed reading and hence thinner flap measurement Not as much pressure required to get a reading in- the-bed More likely to underestimate flap thickness

11.  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

12.  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