visual acuity after successful penetrating keratoplasty depends mainly on the clarity of the graft and the refractive error , particularly the astigmatic component .
severe irregular astigmatism is often seen after keratoplasty and can delay visual rehabilitation , even with a clear graft .
a variety of factors affect postoperative astigmatism , including disparity between donor button and recipient bed , graft diameter , malposition of donor and recipient corneas , underlying diagnosis of the recipient , wound configuration abnormality , and the suture technique employed ( 1 - 5 ) .
there are three commonly used major suture techniques such as interrupted , single running , and double running .
many studies have shown that the interrupted suture technique results in higher astigmatism than the single or double running suture techniques ( 6 - 9 ) .
however , the difference in the results between the single running and double running sutures remains largely controversial .
indeed , various results have been obtained depending on study duration and time of suture removal : less astigmatism have been found with single running sutures while the sutures are still in place ( 10 ) , whereas no differences ( 11 ) or less astigmatism in early period with double running sutures ( 12 ) .
herein , we prospectively studied the cases with penetrating keratoplasty , to compare the amount of astigmatism after the operation with three different suture techniques : interrupted , single running , and double running .
this prospective study was performed on patients who underwent penetrating keratoplasty between january 2003 and june 2005 by one surgeon .
all the protocols of our current study were concordant with the tenets of the declaration of helsinki and informed consent was obtained from the included subjects . in cases of vascularized cornea ,
otherwise , patients were randomly assigned to two suturing techniques ; single running and double running .
patients with combined cataract or glaucoma surgery , corneal scarring including peripheral cornea , and the subject who underwent therapeutic keratoplasty for infectious keratitis were excluded at the beginning of study . during investigation ,
the subjects who showed delayed wound healing more than 3 weeks , graft rejection , newly developed intractable glaucoma , or with wound problems such as dehiscence were excluded .
there were 16 eyes with the interrupted suture technique , 12 eyes with the double running suture technique , and 10 eyes with the single running sutures ( fig .
there was no significant difference in diagnosis among the three groups ( p=0.859 ,  test ) .
the mean donor age was 45.512.9 yr ( 22 - 74 ) , average postmortem time was 4.81.9 hr ( 1 - 9 ) , and the mean preservation time was 124.829.4 hr ( 72 - 144 ) .
all donor corneas were stored in optisol ( chiron ophthalmics , irvine , ca , u.s.a . ) .
the mean trephine size of the recipient was 7.340.35 , 7.100.21 , and 7.210.21 mm for the interrupted , single running , and double running sutured eyes , respectively , and these differences were not significant .
the mean trephine size of the donor was 7.730.32 , 7.600.21 , and 7.650.20 mm for the interrupted , single running , and double running , respectively , and these differences were not significant .
the mean donor - recipeint disparity was 0.390.13 , 0.500.0 , and 0.440.11 mm ( oversized ) for the interrupted , single running , and double running , respectively , and these were not significantly different ( p>0.05 , mann - whitney u test between each of two groups ) .
penetrating keratoplasty was performed by a standard technique using a hessburg - barron trephine ( jedmed instrument co. , st .
selective removal of interrupted nylon sutures along the steepest meridian was performed , if associated with greater than 3 diopters of astigmatism in that meridian , starting two months after surgery , until the resultant astigmatism reached 3.0 diopters or less . for the double running suture group ,
two running sutures of 12 bites each were placed with 10 - 0 nylon by the anti - torque mode , and one 10 - 0 nylon suture was removed 6 to 10 months after keratoplasty and the other 12 to 16 months after surgery . for the single running suture group , a 10 - 0 nylon running suture with 16 to 24 bites was used with the torque mode , and the sutures were removed 10 to 18 months after surgery . at the end of surgery , the suture was adjusted to make the hand - held keratometer ring mires round .
salt lake city , ut , u.s.a . ) at 2 , 6 , 12 , and 18 months after surgery ( fig .
2 ) . sim k 's astigmatism was also measured before and three months after each suture removal .
final astigmatism at 18 months after surgery was obtained at least one month after complete suture removal .
the mann - whitney u test was used to compare the astigmatism between two groups and wilcoxon matched pairs signed ranks test was done to analyze changes in astigmatism after suture removal .
the final astigmatism values at 18 months after surgery following removal of all sutures were : 6.162.32 diopters in the interrupted suture group ( n=16 ) , 5.651.61 diopters in the single running ( n=10 ) , and 3.601.58 diopters in the double running suture group ( n=12 ) ( table 2 ) .
there was no significant difference in the amounts of astigmatism between the double and single running suture groups at 2 , 6 , and 12 months after surgery ( table 2 ) .
however , at 18 months , the double running suture group showed significantly less astigmatism than the single running group ( p=0.014 , mann - whitney u test , table 2 ) .
the single running suture group showed less astigmatism than the interrupted group with borderline significance at 6 months ( p=0.060 , mann - whitney u test ) after surgery ; however , at 18 months , there was no difference in the amounts between these two groups ( table 2 , fig .
the double running suture group showed significantly less astigmatism throughout the study period than the interrupted suture group ( p<0.05 , mann - whitney u test , fig .
all three suture groups tended to decrease gradually ; however , astigmatism in the single running suture group increased at 18 months compared to 12 months after surgery ( fig .
the interrupted suture group showed significantly less astigmatism after selective suture removal ( table 3 , fig .
4 ) . however , the single running suture group showed increased astigmatism at three months after surgery with borderline significance ( table 3 , fig .
this prospective study was undertaken to investigate the difference in astigmatism among patients who underwent penetrating keratoplasty by three different suturing techniques : interrupted , single running , and double running sutures . during 18 months after surgery ,
the interrupted suture group showed significantly higher astigmatism than the double running suture group . during 6 months after surgery ,
however , when the sutures were out , the interrupted sutures no longer showed significantly higher astigmatism than the single running group .
there was no significant difference in the amounts of astigmatism between the single running and double running suture groups during the first year after keratoplasty .
however , at 18 months after surgery , when all sutures were out , the double running suture group showed less astigmatism than the single running group . in this study ,
astigmatism in the single running group was found to increase at 18 months than 12 months after surgery when the suture was out .
for the single running suture technique , there are some contradictory reports on changes of astigmatism after suture removal : solano et al .
( 11 ) reported that , in a single running suture group , astigmatism increased to as high as 1.7 diopters one month after suture removal . on the other hand , spadea et al .
( 13 ) reported an average decrease of 0.52 diopters in astigmatism , however , the astigmatism in 62% of eyes changed two or more diopters after suture removal , therefore , they concluded that corneal astigmatism may change unpredictably and , by large amounts , when all remaining sutures are removed .
these findings suggest that direct suture tension may play an important role in maintaining corneal configuration in single running suture technique . for the double running suture
, a double radial suture was placed with a diagonal pattern in which the second suture ran in the opposite direction of the first one .
hoffmann ( 14 ) described that the double running suture with a diagonal pattern overcomes vertical factors with regard to radial and diagonal continuous sutures , which by necessity leads to gaping of the inner and outer wound fissure .
the double continuous diagonal suture ( cross - stitch suture ) can neutralize the forces in the direction toward the surface and the deep stroma , thus providing a uniform seal for the wound fissure . on the other hand , however , the single running suture does not have such an effect , and this might be responsible for increasing astigmatism after suture removal in the single running suture group .
conversely , the fact that no significant changes were observed after suture removal in the double running group might imply that this neutralizing effect helps to stabilize the graft configuration .
in all three groups , there was a decreasing tendency of astigmatism during the first postoperative year .
for the interrupted suture group , this may be partially due to a selective suture removal along the steepest meridian , because this suture removal method has been known to significantly reduce astigmatism ( 15 ) . in the single running suture group ,
postoperative suture adjustment was not done because of safety reason , even though postoperative suture adjustment has been reported to reduce the corneal astigmatism ( 16 ) .
in contrast to the interrupted or double running suture , rupture or loosening of suture , which can be induced by suture manipulation , is a much more serious problem requiring additional bites in the single running suture , because no other suture material supports the tightness of the button .
interrupted suturing technique was not randomly assigned , although other two techniques were randomly assigned .
contrary to the fact that preoperative diagnoses are relatively evenly distributed in single and double running groups , the number of keratoconus cases was relatively lower in interrupted suture group than the numbers in other suturing technique groups ( table 1 ) .
this uneven distribution of preoperative diseases might probably affect the results . to minimize the effect on peripheral wound healing
, we excluded patients with corneal scarring including the peripheral cornea . moreover , peripheral vascularization in the interrupted suture group might affect the astigmatism value .
however , we excluded patients with an wound problem during the follow - up period that can be potentially related to changes in configuration .
thus , the presence of peripheral vascularization may not affect astigmatism significantly . although some limitations mentioned above , we strongly believe that our study still provides informative data for understanding the effect of suture on astigmatism . in summary , at 18 months after penetrating keratoplasty following removal of all sutures , the double running suture technique showed less astigmatism than the single running and interrupted suture techniques .
the single running suture group showed increased astigmatism at 18 months that may be related to suture removal , even though it showed small astigmatism similar to double running suture group during 12 months after surgery .
 the purpose of this study was to compare the effects on astigmatism after penetrating keratoplasty with three different suture techniques . in this prospective study 
 , 38 eyes of 38 patients underwent penetrating keratoplasty with three suturing techniques : interrupted , single running , and double running . 
 topographic astigmatism was measured at 2 , 6 , 12 , and 18 months after keratoplasty . during 18 months after surgery , the interrupted suture group had higher astigmatism than the double running suture group . 
 there was no significant difference in the amounts of astigmatism during the first year after keratoplasty between the single running and the double running suture group . 
 however , at 18 months after surgery , when all sutures were out , the double running suture group ( 3.601.58 diopters ) showed significantly less astigmatism than the single running group ( 5.651.61 diopters ) . in conclusion , 
 post - keratoplasty astigmatism was the least in the double running suture group of the three suturing techniques at 18 months after penetrating keratoplasty . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION