laser - assisted in situ keratomileusis ( lasik ) is the most popular refractive surgical procedure for the correction of myopia , hyperopia , and astigmatism.1 the procedure is fast , with painless recovery of vision and lack of subepithelial haze , which are mainly due to the creation of a corneal flap with a microkeratome .
creating a corneal flap is the most important step for successful lasik.17 however , the use of microkeratome to create a corneal flap increases the risk of intraoperative flap - related complications , such as free flaps , irregular flaps , buttonhole flaps , incomplete flaps , and lacerated flaps.813 many different microkeratomes can be used to create the corneal flap.1429 the moria m2 ( moria , antony , france ) is a popular compact , automated , plastic , single - use head microkeratome with mechanical stop designed for maximum safety.16,2125 in this study , we evaluated the consistency and reproducibility of flap thickness produced by the moria m2 single - use head 90 microkeratome , designed to create a thin 120 m flap .
in this retrospective analysis , 72 ( 37 right eyes and 35 left eyes ) consecutive lasik procedures conducted on 37 patients ( 20 female and 17 men ) for myopia and/or myopic astigmatism , between august 2005 and october 2005 , at the excimer laser department of nisa hospital , istanbul , turkey , were evaluated .
all patients underwent a complete preoperative ophthalmological examination , including measurement of uncorrected distance visual acuity ( udva ) and corrected distance visual acuity ( dcva ) , measurement of refraction ( manifest , dilated , and wavefront refractions ) , keratometry , slit lamp examination with fundus evaluation , measurement of corneal topography ( orbscan ii ; bausch and lomb , rochester , ny , usa ) , ultrasonic pachymetry ( us-1800 echoscan ; nidek , achi , japan ) , and measurement of intraocular pressure ( ct-60 computerized tonometer ; topcon , tokyo , japan ) .
all patients underwent primary lasik in all eyes by the same surgeon ( yk ) using the visx star s4 excimer laser system ( advanced medical optics inc , santa clara , ca , usa ) .
inclusion criteria were myopia between 1.00 d and 11.00 d , 5.00 d corneal astigmatism , age 18 years , stable refraction for at least 1 year , and central corneal thickness 490 m .
patients with history of corneal dystrophy or herpetic eye disease , topographic or clinical evidence of keratoconus or degenerative corneal disorder or warpage from contact lenses , severe dry eye , corneal scarring , any ocular disease ( such as glaucoma , uveitis , or collagen vascular diseases ) , and use of systemic corticosteroids or antimetabolites were excluded .
two drops of proparacaine 0.5% ( alcaine ; alcon pharmaceuticals ltd , puurs , belgium ) were instilled in each eye two times , every 5 minutes before the procedure .
eyelashes were isolated using sterile plastic adhesive drapes , and an eyelid speculum was placed .
the microkeratome settings ( suction ring , flap stop ) were chosen according to the steepest k ( manufacturer s nomogram ) , aiming for an optimal flap diameter .
the flaps were created with the moria m2 single - use head 90 microkeratome using the moria evolution 2 control unit , and the hinges were positioned superiorly in all cases . the standard speed of pass (  speed 2  : 15,000 rpm , 2 seconds of cutting time ) was used .
a single head - blade montage was used for both eyes , and the right eye was operated on first in all bilateral cases . after the microkeratome pass , the corneal flap was lifted and central residual stromal bed thickness was measured with ultrasonic pachymetry .
this value was subtracted from the preoperative central corneal thickness and the difference was taken as the corneal flap thickness .
after the ablation , the stromal bed was irrigated with balance salt solution to wash out any debris or epithelial cells and the flap reposed .
flap position and centration were checked , and a striae test was performed to ensure proper flap adherence .
postoperatively , patients were given prednisolone acetate 1% , and ofloxacin 0.3% drops four times a day for 2 weeks and artificial tears solution ( single use ) six times a day for 1 month .
the study was approved by the ethical committee of the istanbul medipol university and performed as per the tenets of the declaration of helsinki . written informed consent was taken from all patients regarding the surgical intervention and inclusion in the study .
two - tailed independent - samples t - test was used for independent events and paired - samples t - test was used for dependent events . in addition ,
pearson and spearman s rank correlation coefficients were used for the linear correlation between parameters depending on the normality of the data .
in this retrospective analysis , 72 ( 37 right eyes and 35 left eyes ) consecutive lasik procedures conducted on 37 patients ( 20 female and 17 men ) for myopia and/or myopic astigmatism , between august 2005 and october 2005 , at the excimer laser department of nisa hospital , istanbul , turkey , were evaluated .
all patients underwent a complete preoperative ophthalmological examination , including measurement of uncorrected distance visual acuity ( udva ) and corrected distance visual acuity ( dcva ) , measurement of refraction ( manifest , dilated , and wavefront refractions ) , keratometry , slit lamp examination with fundus evaluation , measurement of corneal topography ( orbscan ii ; bausch and lomb , rochester , ny , usa ) , ultrasonic pachymetry ( us-1800 echoscan ; nidek , achi , japan ) , and measurement of intraocular pressure ( ct-60 computerized tonometer ; topcon , tokyo , japan ) .
all patients underwent primary lasik in all eyes by the same surgeon ( yk ) using the visx star s4 excimer laser system ( advanced medical optics inc , santa clara , ca , usa ) .
inclusion criteria were myopia between 1.00 d and 11.00 d , 5.00 d corneal astigmatism , age 18 years , stable refraction for at least 1 year , and central corneal thickness 490 m .
patients with history of corneal dystrophy or herpetic eye disease , topographic or clinical evidence of keratoconus or degenerative corneal disorder or warpage from contact lenses , severe dry eye , corneal scarring , any ocular disease ( such as glaucoma , uveitis , or collagen vascular diseases ) , and use of systemic corticosteroids or antimetabolites were excluded .
two drops of proparacaine 0.5% ( alcaine ; alcon pharmaceuticals ltd , puurs , belgium ) were instilled in each eye two times , every 5 minutes before the procedure .
eyelashes were isolated using sterile plastic adhesive drapes , and an eyelid speculum was placed .
the microkeratome settings ( suction ring , flap stop ) were chosen according to the steepest k ( manufacturer s nomogram ) , aiming for an optimal flap diameter .
the flaps were created with the moria m2 single - use head 90 microkeratome using the moria evolution 2 control unit , and the hinges were positioned superiorly in all cases . the standard speed of pass (  speed 2  : 15,000 rpm , 2 seconds of cutting time ) was used .
a single head - blade montage was used for both eyes , and the right eye was operated on first in all bilateral cases .
after the microkeratome pass , the corneal flap was lifted and central residual stromal bed thickness was measured with ultrasonic pachymetry .
this value was subtracted from the preoperative central corneal thickness and the difference was taken as the corneal flap thickness .
after the ablation , the stromal bed was irrigated with balance salt solution to wash out any debris or epithelial cells and the flap reposed .
flap position and centration were checked , and a striae test was performed to ensure proper flap adherence .
postoperatively , patients were given prednisolone acetate 1% , and ofloxacin 0.3% drops four times a day for 2 weeks and artificial tears solution ( single use ) six times a day for 1 month .
the study was approved by the ethical committee of the istanbul medipol university and performed as per the tenets of the declaration of helsinki . written informed consent was taken from all patients regarding the surgical intervention and inclusion in the study .
two - tailed independent - samples t - test was used for independent events and paired - samples t - test was used for dependent events .
in addition , pearson and spearman s rank correlation coefficients were used for the linear correlation between parameters depending on the normality of the data .
in this study , the mean age of the patients was 29.026.23 years ( range : 2045 years ) .
the mean preoperative spherical equivalent refraction was 3.12.33 d ( range : 0.625 to 10.50 d ) in the right , 3.602.31 d ( range : 0.75 to 11.00 d ) in the left , and 3.552.30 d ( range : 0.625 to 11.00 d ) in both eyes ( figure 1b ) .
the mean preoperative steepest k was 44.071.47 d ( range : 40.1246.75 d ) in the right , 44.091.52 d ( range : 40.0046.62 d ) in the left , and 44.081.49 d ( range : 40.0046.75 d ) in both eyes .
the mean preoperative ultrasonic pachymetry thickness was 539.1325.44 m ( range : 492581 m ) in the right , 54428.37 m ( range : 490600 m ) in the left , and 54126.82 m ( range : 490600 m ) in both eyes .
orbscan topographic pachymetry thickness was 538.6234.64 m ( range : 490651 m ) in the right , 539.4835.24 m ( range : 490651 m ) in the left , and 539.0434.69 m ( range : 490651 m ) in both eyes .
the mean flap thickness was 136.9720.07 m ( range : 106192 m ) in the right , 131.219.5 m ( range : 91192 m ) in the left , and 134.1619.85 m ( range : 91192 m ) in both eyes .
there was no correlation between preoperative spherical equivalent refraction and central corneal thickness measured by ultrasonic pachymetry in all eyes ( r=0.117 , p=0.329 ) , and the difference between the right and left eyes was not significant ( t(70)=0.177 , p=0.860 ) .
a statistically significant negative correlation was found between age and preoperative corneal thickness in all eyes ( r=2.48 , p=0.036 ) , but no significant correlation was found in the right ( r=2.58 , p=0.123 ) and left eye ( r=0.19 , p=0.912 ) , separately .
a thicker cornea , especially for the younger patients , was observed ( figure 2 ) .
there was no significant correlation between the flap thickness and age ( r=0.017 , p=0.890 ) , preoperative spherical equivalent ( r=0.121 , p=0.310 ) , and preoperative steepest k ( r=0.162 , p=0.173 ) in all eyes .
there were similar results for the right and the left , separately ( p>0.05 ) .
there was no significant difference in the corneal flap thickness between the right and left eyes ( p=0.220 ) .
a statistically significant positive correlation was found between preoperative corneal thickness measured by ultrasonic pachymetry and flap thickness ( r=0.239 , p=0.043 ) for all eyes ( figure 4 ) .
however , no significant correlation was found for the right and left eyes , separately .
there was no correlation between preoperative orbscan corneal pachmetry result ( thinnest of the cornea ) and flap thickness ( r=0.167 , p=0.162 ) . additionally , the difference in the central corneal thickness between orbscan pachymetry and ultrasonic pachymetry results was not significant ( paired sample t - test : t(71)= 1.167 , p=0.247 ; mean : 539541 ) .
creating the corneal flap is one of the most critical steps , and flap thickness is a very important parameter in lasik.2 since pallikaris et al1 described the lasik technique , the best flap thickness was considered to be 130160 m.29 one of the possible long - term complications in corneal refractive surgery is postoperative keratectasia , which is characterized by progressive thinning and steepening of the cornea and has severe impact on the patient s vision .
a thin flap theoretically decreases the risk of corneal ectasia . on the other hand ,
when thinner flaps are created , the risk of flap irregularities , buttonholes , and epithelial defects may increase .
in addition , flap manipulation may become more difficult and prone to complications , such as folds or striae , and irregular astigmatism may increase.2,7,19,29 contrary to this , prandi et al30 reported that complication and retreatment rates were not statistically different among the groups ( group 1 , flap thickness 100 m ; group 2 , flap thickness > 100 m and < 130 m ; and group 3 , flap thickness 130 m ) .
the flap thickness created with different microkeratomes has been shown to be different from the intended values.1529 in this study , the moria m2 single - use 90 microkeratome , designed to achieve a corneal thickness of 120 m was used in all eyes .
the moria m2 single - use microkeratome has several advantages over a conventional reusable microkeratome head , such as no need for sterilization , requirement for minimal technical manipulation , absence of wear and tear for every patient , and composed of translucent plastic material.2123 pietil and mkinen23 reported an average flap thickness of 129.3314.3 m ( range : 90160 m ) by using moria m2 single - use 90 head microkeratome .
huhtala et al24 evaluated 300 ( 266 myopic and 34 hyperopic ) eyes of 150 patients using the moria m2 single - use head 90 microkeratome .
they found that the mean corneal thickness was 11512.5 m ( range : 73147 m ) and reported no microkeratome - related complication . in another study , aslanides et al21 evaluated 52 myopic patients ( 104 eyes ) using the same microkeratome and found the postoperative flap thickness to be 10918 m ( range : 67152 m ) and 10315 m (
talamo et al16 evaluated 135 eyes treated with the moria m2 microkeratome with an intended flap thickness of 130 m , and they found the mean thickness to be 14224 m ( range : 84203 m ) .
they demonstrated that the sd and the range of the corneal flap thickness with the intralase femtosecond ( fs ) laser was significantly smaller than those of either mechanical microkeratomes .
chen et al27 performed bilateral lasik in 54 eyes ( 27 patients ) with moria m2 single - use head and found the flap thickness to be 155.614.8 m in the right eye and 151.612.5 m in the left eye .
many different studies1429 found significant variations in the flap thickness created by different types of mechanical microkeratomes .
solomon et al14 compared six models of microkeratomes ( amo amadeus , bausch and lomb hansatome , moria carriazo - barraquer , moria m2 , nidek mk2000 , and alcon summit krumeich - barraquer ) in a large prospective , multicenter study and found that the amadeus 140 and the nidek mk2000 145 produced the most consistent lasik flap thicknesses .
they reported that the current microkeratomes have a reliable performance and show sds in flap thickness between 15 and 35 m .
shemesh et al15 reported that the hansatome ( bausch and lomb surgical ) created thicker flaps than the acs ( chiron ) or mk ( nidek ) microkeratomes .
flanagan and binder26 found significant differences between the acs microkeratome and summit krumeich barraquer microkeratome ( alcon surgical ) .
the mean flap thickness was higher than what the manufacturer intended ( 120 m ) and it was statistically significant ( p=0.00 ) .
the sd was relatively large ( about 20 m ) , and the range of flap thickness was wide ( range : 91192 m ) .
the central corneal thickness , determined by ultrasonic pachymetry , in 30 of the 72 eyes was > 550 m , and the mean corneal thickness of the eyes was found to be 56912.85 m ( range : 552600 m ) .
the mean flap thickness of those patients was 14022.25 m ( range : 98192 m ) . only six ( 8.3% ) of 72 eyes had a flap thicker than 160 m .
only one patient had a flap thickness of 192 m in the right eye and 184 m in the left eye .
this patient was younger ( age = 24 years ) and had a normal corneal thickness ( 552 m for both eyes ) and mild spherical equivalent refraction ( right = 3.00 d , left = 3.25 d ) .
steepest k was 46.75 d in the right eye and 46.50 d in the left eye .
although there was no statistically significant correlation between flap thickness and the preoperative central corneal thickness in the right and left eyes , we found a positive statistically significant correlation between these two parameters in all eyes ( r=0.239 , p=0.043 ) .
this demonstrated that the thicker corneas were associated with the thicker flaps and the thinner corneas with thinner flaps .
similar results were also reported in previous studies.8,16,24,28,29 we found no correlation between other parameters . in this study , all cases had no microkeratome - related major complications , such as incomplete flaps , buttonholes , and free flaps .
it should be noted that the number of patients included in this study was limited .
the other limitation of our study was the retrospective nature and the lack of more objective flap thickness measurement methods .
the moria m2 single - use head 90 microkeratome seems to be safe as no major microkeratome - related complications were found .
however , it cut thicker flaps than were intended and the range of flap thicknesses was wide .
for this reason , intraoperative pachymetry should be performed to verify that at least 250 m of residual stromal bed remains following the laser ablation .
more patients , with possibly comparison of different microkeratomes , are needed to fully evaluate the predictability of flap thickness .
 purposethis study aimed to evaluate the accuracy and consistency of corneal flap thickness in laser - assisted in situ keratomileusis ( lasik ) with the moria m2 single - use head 90 microkeratome.methodsthe central corneal thickness of 72 ( 37 right , 35 left ) eyes of 37 patients was measured by ultrasonic pachymetry preoperatively and intraoperatively after flap cut . 
 the moria m2 single - use head 90 microkeratome was used to create a superior hinged flap in all eyes . 
 the right eyes were always operated on before the left eyes in each patient , using the same blade in all bilateral cases . 
 all patients underwent lasik for myopia and/or myopic astigmatism using visx star s4 platform.resultsthe mean preoperative spherical equivalent refraction was 3.552.30 d ( range : 0.625 to 11.00 d ) , preoperative central corneal thickness by ultrasonic pachymetry was 54126.82 m ( 490600 m ) and steepest k was 44.081.49 d ( 4046.75 d ) in all eyes . 
 the mean flap thickness was 136.9720.07 m ( 106192 m ) , 131.219.5 m ( 91192 m ) , and 134.1619.85 m ( 91192 m ) in the right , left , and both eyes , respectively . 
 a positive significant relationship was found between flap thickness and preoperative ultrasonic pachymetry thickness . 
 no significant relationship was found between flap thickness and the age , preoperative spherical equivalent , and preoperative steepest k. the difference between the first and second eyes was not significant . 
 there were no major intraoperative and postoperative complications in all eyes.conclusionthe moria m2 single - use head 90 microkeratome cut relatively thicker flaps than were intended . 
 the flap thickness range was quite wide . 
 this was a disadvantage for the accuracy and consistency of corneal flap thickness . 
Introduction
Methods
Participants
Eye examination
Statistical analysis
Results
Discussion
Conclusion