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Impact du diamètre du greffon cornéen sur la relation entre la tomographie stérile du donneur dans la banque de cornée et la tomographie du greffon après kératoplastie transfixiante

Sterile donor tomography in the eye bank can be used to avoid refractive surprises after corneal transplantation. The purpose of this study was to assess the impact of graft diameter on the relation between preoperative donor tomography and postoperative graft tomography after penetrating keratoplasty (PKP).

This retrospective study enrolled 164 eye bank corneal tissues that underwent elective PKP with application of a double-running suture. Donor and recipient trephination were performed using the 193-nm excimer laser (Schwind Amaris 1050RS). Diameters were 7.5 mm (16.5%), 8.0 mm (70.1%) and 8.5 mm (13.4%), with a graft oversize of 0.1 mm. Preoperative measurements, taken through the cell culture flask using the anterior segment optical coherence tomograph Casia 2 (Tomey Corp., Nagoya, Japan), were repeated postoperatively in the patient after 6 ± 4 months with all sutures in place. Differences between post- and preoperative values (Δ) were compared with respect to the graft diameter using a Mann-Whitney U test.

The Δ keratometric power (P) at the steep meridian of the anterior surface of the cornea in the 7.5 mm grafts (-2.7 D) was significantly smaller than that in the 8.0 mm grafts (+0.4 D; p<0.01), which at its turn was significantly smaller than that in the 8.5 mm grafts (+1.7 D; p=0.04). At the flat meridian of the anterior surface of the cornea, Δ P in the 7.5 mm grafts (-6.8 D) was significantly smaller than that in the 8.0 mm grafts (-3.2 D; p<0.01) which at its turn was significantly smaller than that in the 8.5 mm grafts (-0.9 D; p<0.01). Neither Δ astigmatism (+4.3 D, +3.7 D and +2.6 D anteriorly; +0.9 D, +0.5 D and +0.4 D posteriorly; respectively in the 7.5 mm, 8.0 mm and 8.5 mm grafts; p>0.05) nor Δ P at the steep and flat meridian of the posterior surface of the cornea (-1.1 D, -1.0 D, -0.9 D; and -0.2 D, -0.5 D, -0.5 D respectively; p>0.05) did differ between groups.

After penetrating keratoplasty (PKP) with both sutures in place, a smaller graft diameter seems to result in a flatter curvature at the anterior surface of the cornea, but does not affect the astigmatism. This confirms previous results, in which the impact of graft diameter on corneal power has been examined. However, this study goes further by investigating the impact of graft diameter on the differences between post- and preoperative keratometric values.

This information may be indicative for IOL power calculation in relation to graft diameter in a triple PKP procedure, depending of the individual size of the cornea.