Background/aims: Diagnosis of rejection in the mouse model of corneal transplantation is based on subjective judgement of loss of graft transparency. The aims of this study were to (i) evaluate a pachymetry technique to measure changes in mouse corneal thickness, and (ii) to correlate increases in transplant thickness with clinical and histological correlates of rejection.
Mehtods: Orthotopic corneal allografts (C57BL/6 strain donor) and syngeneic grafts were performed in A/J mice. Graft transparency was graded and corneal thickness measured by pachymetry on alternate days. Transverse sections of donor cornea excised from eyes representative of clinical opacity grades 1- 4 were prepared, photographed, graft section thickness measured and stromal graft-infiltrating cells counted. Intraobserver and interobserver variation in pachymetry was statistically tested.
Results: Graft thickness, as measured by pachymetry, increased with each clinical opacity grade. Thickness for opacity grades 0, 1 and 2 was in all recipients less than 300 μm. Graft thickness for grades 3 and 4 was in all cases greater than 300 μm. For measurements up to 400 μm there was a good correlation between thickness as measured by in vivo pachymetry and in histopathological sections. Mean interobserver bias was -11.35 μm while mean intraobserver bias was +3.96 μm. Stromal cellularity increased with increasing corneal thickness up to approximately 300 μm.
Conclusion: In vivo graft pachymetry provides a new and reliable way to objectively diagnose rejection in the mouse model of corneal transplantation.