EFFECTS OF WARMING
For the best quality specular image and accurate morphometric data hypothermically-stored corneas should be warmed prior to imaging and analysis.1 Currently, tissues are warmed by either leaving tissue out at room temperature (RT) for 2–3 hours, or by using an incubator to rapidly warm the tissue (IW, incubator warming). Tissue incubation has been shown to produce better images more efficiently than corneas warmed at room temperature, and without increasing pathogen growth or increasing endothelial cell loss.2
The slit lamp images for both the RT and IW tissue show definite reflectivity, but poor cell definition at T0. After one hour of warming, T1, a significant improvement can be observed, and there is minimal difference between the RT and IW images, both show a bright, well defined mosaic. T2 images are essentially the same for both tissues, but at T3 the RT image quality declines slightly, which is also observed in the corresponding specular image.
The enhanced image of both corneas at all time points is remarkably similar despite significant differences in the quality of the slit lamp and specular images at different time points. The Enhanced mode has the advantage of being less dependent on the warmth of the tissue and corresponding corneal edema which diminishes as the cornea warms.
This advantage is clear at T0 as opposed to specular microscopy, immediately after removal from hypothermic storage. Slight cell outlines for both tissues are observable, which indicates the tissue is cold; however, cell death can already be identified as small divots (arrows).
T1 through T3 images are of equivalent quality, although the RT tissue has more severe folding (arrows) than the incubated tissue; this is substantiated in the corresponding specular images (arrows). All enhanced images show cell death.
No cell definition can be observed with specular microscopy immediately after removal from the refrigerator. However, there is vast improvement of both RT and IW tissue images from T0 to T1. The effect of the more rapid warming of the incubator can be observed in the T1 images. The RT warmed tissue has more edematous and poorly defined cell borders, and more severe folding as compared to the incubated tissue. Areas of cell death appear more significant or larger on specular microscopy as compared to the corresponding Enhanced images, because of specular reflection (arrows).
Folds persist in the RT warmed tissue at T2 and T3, which is most apparent in the specular images. Interestingly, the RT tissue image quality peaks after two hours of warming, and then appears to decline at the final imaging time point, T3, which is also true of the slit lamp image. The IW tissue has only trace folds at T3, and very good cell definition. The specular image quality of the IW tissue is better at all time points after warming has started than the RT tissue.
Other Interesting Findings
1. Pham C, Hellier E, Vo M, Szczotka-Flynn L, Benetz B.A. LJ. Donor Endothelial Specular Image Quality in Optisol GS and Life4°C. International Journal of Eye Banking. 2013;1:1.
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2. Tran KD, Clover J, Ansin A, et al. Rapid Warming of Donor Corneas Is Safe and Improves Specular Image Quality. Cornea. 2017;36:581–587.