Abstract
Purpose: :
High levels of corneal astigmatism often compromise the visual benefit after a penetrating keratoplasty procedure. The purpose of the present study was to investigate whether suture regularity affect corneal astigmatism after keratoplasty.
Methods: :
Twenty-one subjects undergoing penetrating keratoplasty for various corneal diseases were included in the study. A motorised trephine (8.00 mm diameter) and curved scissors were used to excise the diseased cornea. Donor grafts were punched out from the endothelial side (8.00 mm diameter). The grafts were sutured in place with a single-running Nylon 10-0 suture, taking 24 bites. Immediately after surgery, standard calibrated images of the grafted eye were captured and stored. An image analysis programme was developed. Using the programme, stitches and needle points were identified, and a number of suture regularity variables were calculated (stitch-length, stitch direction, variations in needle entrance and exit points in relation to the graft-recipient interface). Corneal topographic images (TMS-3, Tomey) were obtained before suture removal (12 months after surgery) and 3 months after suture removal (18 months after surgery). Topographic measures of astigmatism (surface regularity (SRI), surface asymmetry indices (SAI), and keratometric astigmatism) were calculated and correlated with the computed suture regularity variables.
Results: :
The average stitch length was 3.04 + 0.28 mm and the distance between the outer needle points was 2.53 + 0.09 mm. The SRI was 1.26 + 0.36 and the SAI was 1.59 + 0.67 after 12 months and decreased to 1.03 + 0.48 and 0.92 + 0.46 after 18 months, respectively. Corneal astigmatism was 6.38 + 2.99 and 5.87 + 3.13 after 12 and 18 months, respectively. Correlation analysis revealed that suture regularity did not significantly affect SAI, SRI, or corneal astigmatism 12 months after surgery. 18 months after surgery (3 months after suture removal), the standard deviation on the original stitch length was found to have significant influence on corneal astigmatism (p<0.01). None of the stitch parameters correlated significantly with SRI or SAI 18 months after surgery.
Conclusions: :
The origin of corneal astigmatism after penetrating keratoplasty is multifaceted. Suture regularity appears only to play a minor role. Other factors such as stitch depth, suture tension, and variations in graft to bed adaption are possibly more important predictors for corneal astigmatism after penetrating keratoplasty.
Keywords: cornea: clinical science • topography • imaging/image analysis: clinical