### Materials and Methods

### Surgical method

### Astigmatism analysis

POC

_{AXIS}=the absolute value of (postoperative astigmatic axis - preoperative astigmatic axis)PSC

_{AXIS}=the absolute value of (post-suture removal astigmatic axis - postoperative astigmatic axis)POC

_{MAGNITUDE}=the dioptric power of (postoperative astigmatism magnitude - preoperative astigmatism magnitude)PSC

_{MAGNITUDE}=dioptric power of (post-suture removal astigmatism magnitude - postoperative astigmatism magnitude).

_{AXIS}≤ 135 degrees, or 45 < PSC

_{AXIS}≤ 135 degrees). The group without axis shift was named Group

_{WAS}. We analyzed the factors which affected postoperative astigmatism and post-suture removal astigmatism in each Group

_{WAS}(Group I

_{WAS}, II

_{WAS}, III

_{WAS}, and IV

_{WAS}).

_{WAS}. Multiple regression analysis was also used to determine changes in the absolute value of post-suture removal astigmatism compared to the absolute value of preoperative and postoperative astigmatisms, corneal tunnel length, and time to suture removal in each Group

_{WAS}. Variables were selected by the "enter" method of the program. A logistic regression model was used to identify variables that were associated with the prevalence of postoperative astigmatism axis shift and post-suture removal axis shift.

### Results

### Changes in the magnitude and axis of corneal astigmatism in the four groups

_{AXIS}) in Group IV. This indicates that the significant postoperative axis changes occurred when the incision and suture were located on the steepest meridian (

*p*< 0.05).

*p*> 0.05).

### Variables which affected the degree of postoperative astigmatism and post suture removal astigmatism in the four Groups_{WAS}

_{WAS}. A test for multicolinearity was conducted prior to the selection of these variables.

_{WAS}, we evaluated the impact of various risk factors on the absolute values of the postoperative astigmatism. Table 3-1A shows an increase in the absolute value of postoperative astigmatism as the absolute value of preoperative astigmatism increased (

*p*=0.006). There was also an increase in the corneal tunnel length (

*p*=0.02). We evaluated the impact of various risk factors on the absolute value of post-suture removal astigmatism. Table 3-1B shows an increase in the absolute value of post-suture removal astigmatism as the absolute value of postoperative astigmatism increased (

*p*=0.048). There was also a reduction in the absolute value of post-suture removal astigmatism associated with a later suture removal time (

*p*=0.002).

_{WAS}, we evaluated the impact of various risk factors on the absolute values of postoperative astigmatism. Table 3-2A shows an increase in the absolute value of postoperative astigmatism as the absolute value of preoperative astigmatism increased (

*p*=0.006). We evaluated the impact of various risk factors on the absolute values of post-suture removal astigmatism. Table 3-2B shows a reduction in the absolute value of post-suture removal astigmatism that was correlated with later suture removal time (

*p*=0.015).

_{WAS}, we evaluated the impact of various risk factors on the absolute values of postoperative astigmatism. Table 3-3A shows an increase in the absolute value of postoperative astigmatism as the absolute value of preoperative astigmatism increased (

*p*=0.003). There was also a reduction in postoperative astigmatism that was associated with an increase in the corneal tunnel length (

*p*=0.001). We evaluated the impact of various risk factors on the absolute value of post-suture removal astigmatism. However, Table 3-3B shows that no significant correlations were found.

_{WAS}, we evaluated the impact of various risk factors on the absolute values of postoperative astigmatism. Table 3-4A shows a reduction in the absolute value of postoperative astigmatism as the corneal tunnel length increased (

*p*=0.00). We evaluated the impact of various risk factors on the absolute value of post-suture removal astigmatism. Table 3-4B shows an increase in the absolute value of post-suture removal astigmatism as the absolute value of postoperative astigmatism increased (

*p*=0.01). There was also an increase in the absolute value of post-suture removal astigmatism that correlated with later suture removal time (

*p*=0.00).

### Variables associated with the prevalence of the postoperative axis shift and post-suture removal axis shift

_{ABS · MAGNITUDE}< 1.00 D).

### Discussion

_{WAS}, II

_{WAS}, and III

_{WAS}(

*p*< 0.05, Table 3-1A, 3-2A, 3-3A, respectively). A larger magnitude of preoperative astigmatism was associated with a larger magnitude of postoperative astigmatism. This indicates that incisions other than those in the steepest meridian (Group IV

_{WAS}) have little modulating effect on astigmatism in patients who have a large preexisting astigmatism. For the post-suture removal astigmatisms in Groups I

_{WAS}and IV

_{WAS}, the magnitudes of the postoperative astigmatism affected the magnitude of the post-suture removal astigmatism (

*p*<0.05, Table 3-1B, 3-4B, respectively). A larger postoperative astigmatism was associated with a larger post-suture removal astigmatism. In our study, the magnitude of the preoperative astigmatism did not effect the magnitude of the post-suture removal astigmatism.

_{WAS}and IV

_{WAS}were characterized by incisions on the steep meridian, the shorter tunnel wound sutures may have induced larger with-the-wound astigmatisms, although the incision on that meridian had initially flattened it. We assumed that the flattening effect of the incision would be almost the same irrespective of tunnel length because the external opening that affects astigmatism2 was placed at the same location, approximately 0.2 mm from the limbus. Although the incision further flattened the flat meridian in Group I

_{WAS}, the shorter tunnel could have reduced the flattening effect of the incision after the suturing was completed.

_{WAS}. Late suture removal was associated with a decrease in the magnitude of postoperative astigmatism in Groups I

_{WAS}and II

_{WAS}. Early stitch-out was associated with a decrease in the magnitude of postoperative astigmatism in Group IV

_{WAS}. According to the logistic regression model, early suture removal may be a risk factor for post-suture removal axis shift.

_{WAS}characteristics, a late suture removal in Group II

_{WAS}-like patients, a long corneal tunnel in Group III

_{WAS}-like patients, and a long corneal tunnel and an early suture removal in patients with Group IV

_{WAS}characteristics. The prevalence of post-suture removal axis shift was increased in the longer tunnel group, in the low magnitude of postoperative astigmatism group, and in the earlier suture removal group.