Abstract
Purpose::
To evaluate donor corneal thickness profiles using very high frequency arc-scanning ultrasound (VHF US) after Descemet’s stripping automated endothelial keratoplasty (DSAEK) and to relate shape to postoperative refractive change.
Methods::
VHF US corneal imaging (Artemis II, Ultralink LLC, St. Petersburg, FL) was performed at 9 postoperative visits in 7 patients enrolled in a prospective IRB-approved study of DSAEK. Donor lenticles were procured with either a 300-um LSK (n=4 patients) or CB (n=3) microkeratome (Moria, Antony, FR). Six meridional VHF US arc scans were obtained at visits ranging from 1 week to 12 months after surgery, and the ArtPro v1.50 software package was used to construct maps of total corneal, epithelial, host and donor thickness profiles. A rectangular region 2mm in height and spanning 40 0.1mm intervals along the horizontal meridian was defined for graft thickness profile analysis. Each profile was fit by a quadratic regression and the second order coefficient representing the bulk curvature of the graft was extracted.
Results::
Mean central graft thicknesses derived from Artemis images across all postoperative visits ranged from 137 to 407 um. Donor lenticles were clearly thicker in the periphery in 5 out of 7 patients. In the group with the largest hyperopic shifts (+2.50D, n=3 at 6 months postop), a strong negative lens effect was predicted by the curvature coefficient (mean +22.72, range +4.95 to +45.17) and unequivocal U-shaped thickness plots. In the group with minimal refractive shifts (+0.50 to -0.50D, n=3), the coefficients were more neutral (mean +7.28, range +2.01 to +13.82). Two of these patients had U-shaped plots. The lone patient who experienced a myopic shift (-1.00D) also had the only negative (myopically-biased) curvature coefficient (-0.643).
Conclusions::
Transplanted donor lenticles typically exhibited nonuniform thicknesses and an overall posterior convex meniscus shape. This morphology favors a decrease in the radius of curvature of the posterior cornea, which together with increased postoperative corneal thickness could cause a hyperopic shift based on optic principles. The shape of the graft may be related to current microkeratome-based techniques for procuring the donor cornea. Measurement of graft and host deturgescence over time could facilitate studies of refractive error and optimization of graft preparation methods.
Keywords: cornea: clinical science • anterior segment