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I read with great interest the excellent perspective by Plsková et al,1 in which they raise the issue of transient corneal opacification following corneal transplantation in the mouse model and argue that it might be due to a sufficient number of endothelial cells regaining function.
What the authors describe for the mouse model also occurs in the rat model. In fact, most researchers on the rat model probably have this experience, but for some reason do not think it is very important and/or choose to ignore it. Apart from the article by Williams et al,2 there is—as far as I know—only one other author who has explicitly mentioned this transient opacification. In their paper, Herbort et al3 wrote “The grafts began clearing 4 weeks after surgery . . . and vessels in the graft diminished from 6 weeks post-surgery.” and “It has to be noted that after acute rejection most corneas regain some clarity by 7–8 weeks.” Transient corneal opacification also occurs in the rat model I used4 (AO rats (strain RT1u) served as recipients of corneas from PVG rats (strain RT1c) and corneas were sutured with a single running suture). Allogeneic transplanted corneas showed no initial opacification immediately postoperatively; neither did the syngeneic controls. All allogeneic corneas “rejected” (or more precisely showed total opacification) around day 11–13 and those corneas, when followed long enough, all cleared. Opacification remained higher than 2 (meaning an increased corneal haze, but some anterior chamber structures still visible) at days 17–21 and became lower than 2 (slight haze) around days 21–32.
It would be exciting to know if the hypothesis put forward by Plsková et al1 would also apply to the rat model and to find out if this “clearing” of the opacification also occurs in other rat strains than the ones mentioned.
Plsková et al have raised a very important topic where a lot of uncertainty still exists, and which warrants further research.