Exposing the LASIK Scam

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 Post subject: Microkeratomes produce flaps of unpredictable thicknesses
PostPosted: Fri Nov 25, 2005 2:42 pm 
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http://www.ncbi.nlm.nih.gov/entrez/quer ... uery_hl=21

1: J Refract Surg. 2003 Mar-Apr;19(2):113-23.

Precision of flap measurements for laser in situ keratomileusis in 4428 eyes.

Flanagan GW, Binder PS.

Gordon Binder Vision Institute, San Diego, CA, USA.

PURPOSE: To determine the factor(s) that influence the dimensions and predictability of the LASIK corneal flap with the Automated Corneal Shaper (ACS) or the Summit Krumeich Barraquer microkeratome (SKBM).

METHODS: We performed a retrospective, comparative interventional case study of 4,428 eyes. Flap dimensions were measured using subtraction ultrasonic pachymetry during LASIK with one of two microkeratomes.

RESULTS: Mean preoperative corneal thickness for all eyes was 555 +/- 35 microm. Corneal curvature and refractive astigmatism were inversely related to preoperative corneal thickness (P<.001). With an attempted flap thickness of 160 microm, the ACS flap thickness averaged 119.8 +/- 22.9 microm; SKBM flaps averaged 160.9 +/- 24.1 microm (P<.001). The coefficient of variation for central pachymetry compared to flap thickness was 6.4% vs. 22.1%. Flap thickness at enhancement was 10 to 17 microm thicker than at primary surgery. An increase in flap thickness was associated with thicker preoperative pachymetry (P<.001) and younger age for both instruments (P<.001) whereas increasing flap thickness was related to flatter preoperative mean keratometry for the ACS (P<.001) and steeper mean keratometry for the SKBM (P=.005). Less preoperative hyperopia or more myopia was related to an increase in flap thickness only for the SKBM (P<.001).

CONCLUSIONS: Flap thickness varies significantly depending on the microkeratome used. Factors that influence flap thickness are primarily corneal thickness, patient age, preoperative keratometry, preoperative refraction including astigmatism, and corneal diameter. By understanding the factors that affect flap thickness, one can select a microkeratome system to allow maximum refractive correction while minimizing the risk of ectasia.


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PostPosted: Fri Nov 25, 2005 2:43 pm 
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http://www.ncbi.nlm.nih.gov/entrez/quer ... uery_hl=21

J Refract Surg. 2002 May-Jun;18(3 Suppl):S347-51.

Predictability of corneal flap thickness in laser in situ keratomileusis using three different microkeratomes.

Shemesh G, Dotan G, Lipshitz I.

Ophthalmic Health Center, Tel Aviv, Israel.

PURPOSE: To compare the accuracy and consistency of corneal flap thickness in the right and left eye created by three different widely used microkeratomes during consecutive laser in situ keratomileusis (LASIK).

METHODS: Corneal thickness of 132 eyes of 66 patients was measured preoperatively and intraoperatively. Corneal flap thickness was calculated by subtracting the corneal stromal thickness from the total corneal thickness. Three different microkeratomes were used for creating the corneal flap: Chiron Automated Corneal Shaper (ACS), Baush and Lomb Surgical Hansatome, and Nidek MK 2000 microkeratomes. The same surgeon performed all procedures on the right eye first and then on the left eye using the same blade and the same surgical technique.

RESULTS: Mean corneal flap thickness created by the ACS (160-microm depth setting) microkeratome was 128.30 +/- 12.57 microm in the right eye and 122.96 +/- 13.30 microm in the left eye. The Hansatome (160-microm depth plate) microkeratome created a flap of mean 141.16 +/- 20.11 microm in the right eye and 120.95 +/- 26.95 microm in the left eye, and the Nidek MK 2000 (130-microm depth plate) microkeratome created a flap of 127.25 +/- 4.12 microm in the right eye and 127.54 +/- 3.7 microm in the left eye.

CONCLUSION: Corneal flap thickness tended to be considerably thinner than expected on both eyes using the ACS and Hansatome. With the ACS and Hansatome, the difference in corneal flap thickness between the first and second operated eye was statistically significant. With the Nidek MK 2000 microkeratome, there was no statistically significant difference between the first and second operated eye and measurements were close to desired corneal flap thickness. Intraoperative pachymetry is recommended for every LASIK procedure.


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PostPosted: Fri Nov 25, 2005 4:02 pm 
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Here is a case report of a woman who developed ectasia following LASIK due to inaccurate flap cut.


The surgery was planned with an estimated flap thickness of 150 um.

From the full-text:

"Subjective optical pachymetry at the slitlap estimated flap thickness to be approximately 200 um."



J Cataract Refract Surg. 2005 Aug


Reversal of laser in situ keratomileusis-induced ectasia with intraocular pressure reduction.

Hiatt JA, Wachler BS, Grant C.

Boxer Wachler Vision Institute, Beverly Hills, California 90210, USA.

A 40 year-old woman had laser in situ keratomileusis for --7.75 --0.75 x 20 in the right eye. Preoperative examinations, including topography, pachymetry, and intraocular pressures (IOPs), were normal, and best spectacle-corrected visual acuity (BSCVA) was 20/20 in each eye. By 4 months postoperatively, the uncorrected visual acuity and BSCVA in the right eye had decreased to 20/40. Corneal topography of that eye was consistent with ectasia. One drop per day of timolol 0.5% (Timoptic XE) was prescribed. Five months postoperatively, the IOP had decreased and BSCVA and topography had improved. At 11 months, BSCVA returned to 20/20 and corneal topography normalized. Topographic difference maps were used to monitor corneal shape changes. In this case, early reduction in IOP completely reversed the ectasia.



The abstract does not reveal that ectasia returned when the patient was taken off pressure-lowering drugs.


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PostPosted: Wed Jan 04, 2006 1:20 am 
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http://www.ascrs.org/publications/jcrs/editmay04.html

JCRS
May, 2004

The thick and thin of LASIK flaps

"Astonishingly, we found that the new device's 180 μm plate produced flap thicknesses ranging from 198 to 258 μm and the 160 μm plate produced flaps as thick as 220 μm."


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PostPosted: Mon Jan 16, 2006 3:29 am 
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J Cataract Refract Surg. 2003 Nov;29(11):2217-24.

Penetrating keratoplasty for iatrogenic keratoconus after repeat myopic laser in situ keratomileusis: histologic findings and literature review.

Seitz B, Rozsival P, Feuermannova A, Langenbucher A, Naumann GO.

Department of Ophthalmology, University of Erlangen-Nurnberg, Erlangen, Germany. berthold.seitz@augen.imed.uni-erlangen.de

We report a patient with a sufficiently thick cornea (593 microm) and no topographic signs of keratoconus preoperatively who developed iatrogenic keratoconus 2 months after repeat laser in situ keratomileusis (-4.00 -1.00 x 20) performed 5 months after the primary procedure (-10.50 -1.00 x 55). After penetrating keratoplasty, macrophotography showed severe multidirectional "macrostriae" of the stromal bed. On histologic evaluation, excessive thinning of the residual stromal bed to a minimum of 75 microm in the valleys and a maximum of 200 microm at the peaks of the macrostriae were documented. The flap thickness was 225 microm in the center. The thicker-than-intended flap (160 microm) is thought to be the cause of the severe complication of the LASIK procedure.

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PostPosted: Mon Jan 16, 2006 3:58 am 
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J Refract Surg. 2002 Jul-Aug;18(4):475-80.

Latrogenic keratectasia following laser in situ keratomileusis.

Spadea L, Palmieri G, Mosca L, Fasciani R, Balestrazzi E.

University of L'Aquila, Italy. lspadea@cc.univaq.it

PURPOSE: To evaluate keratectasia after laser in situ keratomileusis (LASIK) for high myopia. METHODS: A 49-year-old male patient with myopia of -23.50 D in both eyes underwent LASIK with a Summit Technology Apex Plus excimer laser. A Moria manually-guided MDSC microkeratome was used. Preoperative corneal topography in both eyes did not reveal underlying or fruste form of keratoconus. Four months after LASIK, a progressive keratectasia occurred in right eye and after 12 months, in left eye. Corneal transplantation was performed in both eyes. RESULTS: Histological and ultrastructural examinations were performed on one corneal button. The analysis showed regular stromal morphology and cellularity, with no sign of inflammation. The morphometric analysis showed an overall thickness of 334 microm, with a flap of 262 microm and a stromal residual bed of 72 microm, in the center of the button. CONCLUSION: A LASIK corneal flap made with a planned 120-microm plate turned out histologically to be approximately 260 microm thick, in an eye with a refractive correction of -23.50 D. The excessive flap thickness and excessive ablation produced progressive keratectasia requiring a penetrating keratoplasty.

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PostPosted: Mon Feb 06, 2006 12:54 pm 
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J Cataract Refract Surg. 2000 Dec;26(12):1729-32.


Comment in:
J Cataract Refract Surg. 2001 Nov;27(11):1712.

Reproducibility of corneal flap thickness in laser in situ keratomileusis using the Hansatome microkeratome.
Yildirim R, Aras C, Ozdamar A, Bahcecioglu H, Ozkan S.

Cerrahpasa Medical Faculty, Department of Ophthalmology, Istanbul, Turkey. reny@turk.net

PURPOSE: To evaluate the reproducibility of flap thickness during laser in situ keratomileusis (LASIK) and to analyze the effect of preoperative central corneal thickness and corneal keratometric power on flap thickness.

SETTING: Department of Ophthalmology, Cerrahpasa Medical School, Istanbul, Turkey.

METHODS: One hundred forty eyes with a mean preoperative pachymetry of 554.4 microm +/- 36.3 (SD) and a mean keratometry of 43.5 +/- 1.9 diopters had LASIK using the Hansatome automated microkeratome (Bausch & Lomb Surgical) and a 193 nm argon-fluoride excimer laser (Summit SVS Apex Plus). The 180 microm microkeratome plate was used in all procedures. Corneal thickness was measured with an ultrasonic pachymeter (Advent, Mentor O&O Inc.) before and during the flap procedure, and the difference was taken as flap thickness. The data were analyzed using a 1-tailed t test and Pearson correlation coefficient.

RESULTS: The mean flap thickness was 120. 8 +/- 26.3 microm. There was a low correlation between baseline central corneal thickness and corneal flap thickness (P =.6, r = 0. 046). There was no correlation between preoperative keratometry and flap thickness (P =.01, r = 0.203).

CONCLUSIONS: The Hansatome microkeratome does not always produce a corneal flap of the intended thickness. Factors other than keratometry and pachymetry must affect flap thickness.


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PostPosted: Mon Feb 06, 2006 12:57 pm 
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Cornea. 2003 Aug;22(6):504-7.

Accuracy and precision of the amadeus microkeratome in producing LASIK flaps.

Jackson DW, Wang L, Koch DD.

Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas 77030, USA.

PURPOSE: To evaluate the accuracy and precision of corneal flap thickness following laser in situ keratomileusis (LASIK) performed using the 140-, 160-, and 180-microm heads for the Amadeus microkeratome (AMO, Irvine, CA).

SETTING: The study took place at the Cullen Eye Institute, Baylor College of Medicine, Houston.

METHODS: In this prospective study, using the Amadeus microkeratome, LASIK flaps were cut in 51 right eyes and 50 left eyes with the 140-microm head, 25 right eyes and 25 left eyes with the 160-microm head, and five right eyes and one left eye with the 180-microm head. The same microkeratome blade was used for bilateral cases with the right eyes always undergoing surgery first. Eyes were grouped by order of blade use for statistical analysis. The effect of preoperative corneal thickness, keratometry values, blade oscillation and translation speeds, and blade reuse on flap thickness was evaluated.

RESULTS: Mean flap thicknesses were 153 +/- 18 (range 97-187 microm) OD and 134 +/- 25 microm (range 79-174 microm) OS for the 140-microm head; 182 +/- 26 microm (range 105-220 microm) OD and 163 +/- 29 microm (range 105-216 microm) OS for the 160-microm head; and 235 +/- 24 microm (range 198-258 microm) for the 180-microm head. Flap thickness was significantly thicker for the first eyes cut (right eyes) and was positively correlated with increasing corneal thickness in both eyes. For the first eyes cut, flap thickness was also significantly thicker than the labeled thickness specified by the manufacturer.

CONCLUSIONS: With the Amadeus microkeratome, LASIK flap thickness correlated with central corneal thickness for the 140-microm head. Reuse of the microkeratome blades produced significantly thinner LASIK flaps on second eyes cut.


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PostPosted: Mon Feb 06, 2006 1:00 pm 
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J Cataract Refract Surg. 2004 May;30(5):964-77.


Comment in:
J Cataract Refract Surg. 2004 May;30(5):937-8.

Flap thickness accuracy: comparison of 6 microkeratome models.

Solomon KD, Donnenfeld E, Sandoval HP, Al Sarraf O, Kasper TJ, Holzer MP, Slate EH, Vroman DT; Flap Thickness Study Group.

Magill Research Center for Vision Correction, Storm Eye Institute, Medical University of South Carolina, Charleston, SC 29425, USA. solomonk@musc.edu

PURPOSE: To determine the flap thickness accuracy of 6 microkeratome models and determine factors that might affect flap thickness.

SETTING: Magill Research Center for Vision Correction, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS: This multicenter prospective study involved 18 surgeons. Six microkeratomes were evaluated: AMO Amadeus, Bausch & Lomb Hansatome, Moria Carriazo-Barraquer, Moria M2, Nidek MK2000, and Alcon Summit Krumeich-Barraquer. Eyes of 1061 consecutive patients who had laser in situ keratomileusis were included. Age, sex, surgical order (first or second cut), keratometry (flattest, steepest, and mean), white-to-white measurement, laser used, plate thickness, head serial number, blade lot number, and occurrence of epithelial defects were recorded. Intraoperative pachymetry was obtained just before the microkeratome was placed on the eye. Residual bed pachymetry was measured after the microkeratome cut had been created and the flap lifted. The estimated flap thickness was determined by subtraction (ie, mean preoperative pachymetry measurement minus mean residual bed pachymetry).

RESULTS: A total of 1634 eyes were reviewed. Sex distribution was 54.3% women and 45.7% men, and the mean age was 39.4 years +/- 10.6 (SD). In addition, 54.5% of the procedures were in first eyes and 45.5%, in second eyes. The mean preoperative pachymetry measurement was 547 +/- 34 microm. The mean keratometry was 43.6 +/- 1.6 diopters (D) in the flattest axis and 44.6 +/-1.5 D in the steepest axis. The mean white-to-white measurement was 11.7 +/- 0.4 mm. The mean flap thickness created by the devices varied between head designs, and microkeratome heads had significant differences (P<.05). Factors that explained 78.4% of the variability included microkeratome model, plate thickness, mean preoperative pachymetry, Kmin, surgery order, head serial number, blade lot number, and surgeon. Factors such as age, sex, Kmax, Kaverage, white to white, and laser had no significant correlation to flap thickness.

CONCLUSIONS: The results demonstrated variability between the 6 microkeratome models. Device labeling did not necessarily represent the mean flap thickness obtained, nor was it uniform or consistent. Thinner corneas were associated with thinner flaps and thicker corneas with thicker flaps. In addition, first cuts were generally associated with thicker flaps when compared to second cuts in bilateral procedures.


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PostPosted: Fri Jun 16, 2006 11:45 am 
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JOURNAL OF REFRACTIVE SURGERY Vol. 22 No. 6 June 2006
Reproducibility of Flap Thickness With IntraLase FS and Moria LSK-1 and M2 Microkeratomes
Jonathan H. Talamo, MD; Jeremy Meltzer, MD; John Gardner, COA

From the abstract:

"In 100 eyes treated with the Moria LSK-1 microkeratome with an intended flap thickness of 160 ?m, the mean achieved thickness was 130?19 ?m (range: 71 to 186 ?m). In 135 eyes treated with the Moria M2 microkeratome with an intended flap thickness of 130 ?m, mean thickness was 142?24 ?m (range: 84 to 203 ?m)."

_________________________________________________________


I hope the reader understands what this means for LASIK patients. The FDA guidelines state that at least 250 microns should remain under the flap after LASIK to prevent ectasia -- a condition that can cause the patient to lose his or her cornea. More conservative (safe!) surgeons use 300 or more. If a surgeon plans to leave 250 um under the flap, due to the inaccuracy of the flap cut, using the patient with a 203 um flap in the above study, the residual corneal thickness could be as little as 170 um under the flap, which is way below the FDA guidelines for safety in preventing ectasia.

This flap inaccuracy problem is well known by LASIK surgeons. They know they don't really have control over the thickness of the flap, yet they don't warn patients about this and it hasn't slowed them down one bit. They should be measuring flap thickness intraoperatively, prior to the ablation (some do, most don't). If the flap is too thick, they should abort the procedure. Of course then they would have to explain to the patient what happened and that would not be good for business. :roll: Basically they have two choices -- 1) don't check the flap thickness and just proceed blindly, putting the patient at risk, or 2) check the flap thickness before the ablation and abort some procedures. Which choice did your surgeon make?

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PostPosted: Fri Jun 16, 2006 11:57 am 
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JOURNAL OF REFRACTIVE SURGERY Vol. 22 No. 5 May 2006
Evaluating Microkeratome Efficacy by 3D Corneal Lamellar Flap Thickness Accuracy and Reproducibility Using Artemis VHF Digital Ultrasound Arc-scanning
Dan Z. Reinstein, MD, MA(Cantab), FRCSC; Hugo F.S. Sutton, MD, FRCSC; Sabong Srivannaboon, MD; Ronald H. Silverman, PhD; Timothy J. Archer, BA(Oxon), DipCompSci(Cantab); D. Jackson Coleman, MD

Excerpt from the abstract:

Central reproducibility (standard deviation of the mean) was 30.3 ?m, with a range of 106 to 228 ?m.

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"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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PostPosted: Mon Dec 04, 2006 12:52 am 
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J Cataract Refract Surg. 2006 Dec;32(12):2080-4.

Comparison of residual stromal bed and flap thickness in primary and repeat laser in situ keratomileusis in myopic patients.

Das S, Sullivan LJ.

From the Royal Victorian Eye and Ear Hospital (Das, Sullivan) and the Melbourne Excimer Laser Group (Sullivan), East Melbourne, Australia.

PURPOSE: To compare the change in residual stromal thickness and flap thickness between primary laser in situ keratomileusis (LASIK) and repeat LASIK in myopic patients.

SETTING: Melbourne Excimer Laser Group, East Melbourne, Australia.

METHODS: This retrospective nonrandomized comparative trial comprised 46 eyes of 34 patients who had repeat LASIK. The thickness of the residual stromal bed was calculated by subtracting the calculated stromal ablation from pachymetry of the stromal bed after cutting the flap in primary treatment and directly measuring during retreatment. The thickness of the LASIK flap in primary and repeat LASIK was calculated by subtracting the central pachymetry of the stromal bed after creating the flap from pachymetry before cutting and lifting the flap, respectively. The main outcome measures were comparison of the residual stromal bed and flap thickness between the primary treatment and the retreatment.

RESULTS: The mean thickness of the calculated residual stromal bed after primary treatment was 329.8 mum +/- 40.8 (SD), and the mean measured residual stromal bed at retreatment was 317.3 +/- 42.8 mum. The mean difference in residual stromal bed thickness was 12.5 +/- 13.0 mum (P<.001). Sixteen eyes (34.7%) had a decrease in bed thickness between 11 mum and 20 mum. The mean flap thickness during primary LASIK and repeat LASIK was 145.2 +/- 17.1 mum and 169 +/- 18.3 mum, respectively. The mean interval between primary treatment and retreatment was 7.4 +/- 4.1 months. The mean change in flap thickness was 23.8 +/- 15.2 mum (P<.001). Fifteen eyes (32%) had an increase in flap thickness between 11 mum and 20 mum. There was a negative correlation between refractive error before primary treatment and the difference in flap thickness. No correlation was found between the difference in flap thickness and the interval between the primary treatment and the repeat treatment.

CONCLUSIONS: Intraoperative pachymetry of the stromal bed during retreatment is strongly recommended as the residual stromal bed and flap thickness changes between primary and retreatment. There is a tendency for the measured stromal bed at retreatment to be thinner than the calculated stromal bed and for the flap to be thicker than previously measured.

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"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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J Refract Surg. 2006 Nov;22(9):861-70.

Probability model of the inaccuracy of residual stromal thickness prediction to reduce the risk of ectasia after LASIK part II: quantifying population risk.

Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, Sutton H, Coleman DJ.
London Vision Clinic, 8 Devonshire Place, London W1G 6HP, United Kingdom. dzr@londonvisionclinic.com

PURPOSE: To derive a statistical model to estimate the rate of excessive keratectomy depth below a selected cut-off residual stromal thickness (RST) given a minimum target RST and specific Clinical Protocol; apply the model to estimate the RST below which ectasia appears likely to occur and back-calculate the safe minimum target RST that should be used given a specific Clinical Protocol.

METHODS: Myopia and corneal thickness distribution were modeled for a population of 5212 eyes that underwent LASIK. The probability distribution of predicted target RST error (Part I) was used to calculate the rate of excessive keratectomy depth for this series. All treatments were performed using the same Clinical Protocol; one surgeon, Moria LSK-One microkeratome, NIDEK EC-5000 excimer laser, Orbscan pachymetry, and a minimum target RST of 250 microm--the Vancouver Clinical Protocol. The model estimated the RST below which ectasia appears likely to occur and back-calculated the safe minimum target RST. These values were recalculated for a series of microkeratomes using published flap thickness statistics as well as for the Clinical Protocol of one of the authors-the London Clinical Protocol.

RESULTS: In the series of 5212 eyes, 6 (0.12%) cases of ectasia occurred. The model predicted an RST of 191 microm for ectasia to occur and that a minimum target RST of 329 microm would have reduced the -rate of ectasia to 1: 1,000,000 for the Vancouver Clinical Protocol. The model predicted that the choice of microkeratome varied the rate of ectasia between 0.01 and 11,623 eyes per million and the safe minimum target RST between 220 and 361 microm. The model predicted the rate of ectasia would have been 0.000003: 1,000,000 had the London Clinical Protocol been used for the Vancouver case series.

CONCLUSIONS: There appears to be no universally safe minimum target RST to assess suitability for LASIK largely due to the disparity in accuracy and reproducibility of microkeratome flap thickness. This model may be used as a tool to evaluate the risk of ectasia due to excessive keratectomy depth and help determine the minimum target RST given a particular Clinical Protocol.

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"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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J Refract Surg. 2006 Nov;22(9):851-60.

Probability model of the inaccuracy of residual stromal thickness prediction to reduce the risk of ectasia after LASIK part I: quantifying individual risk.

Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, Sutton H, Coleman DJ.
London Vision Clinic, 8 Devonshire Place, London W1G 6HP, United Kingdom. dzr@londonvisionclinic.com

PURPOSE: To measure the imprecision of microkeratome cuts, preoperative corneal pachymetry, and laser ablation depth and develop a statistical model to describe the probability of the residual stromal bed thickness (RST) after myopic LASIK being significantly thinner than predicted.

METHODS: Preoperative corneal thickness, flap thickness, ablation depth, and RST were measured in 36 eyes by a prototype three-dimensional very high-frequency (VHF) 50 MHz digital ultrasound scanning device (<1.2 microm precision), precursor to the commercially available Artemis 2. All eyes had undergone LASIK with the Moria LSK-One microkeratome and the NIDEK EC-5000 excimer laser. Based on the statistically combined uncertainty (standard deviation) and bias (accuracy to intended value) of corneal thickness measurement, flap thickness, and ablation depth, a continuous probability function was devised describing the chance of obtaining an actual RST less than a specified "cut-off". The model was applied using the data collected from the cohort of eyes. The model was also applied using published flap thickness statistics on a series of microkeratomes.

RESULTS: Precision (standard deviation) was 0.74 microm for VHF digital ultrasound measurement of pachymetry, 30.3 microm for Moria LSK-One flap thickness, and 11.2 microm for NIDEK EC-5000 ablation depth. Assuming negligible laser ablation depth bias, the model found the probability that the actual RST will be <200 pmicromgiven a target RST of 250 microm is 7.56% with the Moria LSK-One. The model applied to published flap statistics revealed a range of probabilities of leaving <200 microm given a target RST of 250 microm from <0.01% to 33.6%.

CONCLUSIONS: The choice of microkeratome, laser, and pachymeter has a significant impact on the variation of the depth of keratectomy and thus on the risk of ectasia. This model together with high-precision microkeratomes, preoperative pachymetry, and knowledge of laser ablation precision would enable surgeons to determine the specific imprecision of RST prediction for individual LASIK cases and minimize the risk of ectasia.

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"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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Original Articles:
Probability Model of the Inaccuracy of Residual Stromal Thickness Prediction to Reduce the Risk of Ectasia After LASIK Part I: Quantifying Individual Risk

Journal of Refractive Surgery Vol. 22 No. 9 November 2006

Dan Z. Reinstein, MD, MA(Cantab), FRCSC; Sabong Srivannaboon, MD; Timothy J. Archer, BA(Oxon), DipCompSci(Cantab); Ronald H. Silverman, PhD; Hugo Sutton, MD; D. Jackson Coleman, MD


Quote:
Flap thickness can vary considerably within the flap, and so RST can also vary by as much as 100 μm within the central 1-mm diameter.


Quote:
Although excimer laser ablation depth is extremely precise in plastic, it is variable in vivo due to atmospheric differences, hydration/desiccation of the corneal surface, and laser fluence stability.


Quote:
We have shown that the RST after LASIK can easily be as much as 90 μm less than predicted...

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"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato


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