Authors (including presenting author) :
WONG C(1), CHOW Y(1), TO W(1), LEUNG KP(1), WONG WYV(2)
Affiliation :
(1) Hospital Authority Eye Bank, (2) Hong Kong West Cluster
Introduction :
To shorten the warm-up process and improve the reliability of tissue evaluation
Objectives :
Evaluation of donor corneas is important for suitability determination for transplantation. This process typically involves a slit-lamp evaluation of the entire cornea for identifying defects or damage that may affect the clinical outcome after transplantation, and the acquisition of specular images for the analysis of endothelial cell density (ECD) and morphometric parameters. The quality of specular images has a significant impact on the accuracy and reproducibility of ECD and the parameters. Donor cornea is preserved and stored in hypothermic condition (2-8oC) at our eye bank. Prior to acquisition of specular images with a quality suitable for specular analysis, cornea is removed from cool storage and warmed at room temperature. Because corneas warm-up at different rates under room temperature, the duration of tissue exposed to elevated temperature outside of the recommended temperature is not predictable and often prolonged. To reduce the tissue exposure time to elevated temperature outside of the recommended temperature range and to improve the efficiency of evaluation process, a tissue incubator is used to rapidly warm donor corneas to near physiological temperature (35oC).
Methodology :
Before deploying the incubator, we first determined the desired warming time by incubating 6 corneas (intended for education use). Specular images were captured every 15 minutes for 2 hours and processed with ImageJ. Centroids of endothelial cells (inferred centroids) were inferred from the processed images based on the local maxima of image intensity. For each cornea, the best quality specular image was selected, and endothelial cells were manually analysed to select the coordinates of their centroids (observed centroids). The coordinates of inferred centroids from the image at different timepoints were compared to their observed centroids. The timepoint with a specular image having >95%(?) inferred centroids matched to their observed centroids was considered to be the desired warming time.
After deploying incubator for 4 months (from January to April 2019), the average duration from warm-up to completion of specular analysis was retrospectively compared with that in the same period in 2018 (warm-up at room temperature).
Result & Outcome :
The desired warming time is between 60 and 90 minutes. With the same warming time (e.g. 60 minutes), the quality of specular images from the corneas warmed up with incubator is significantly better than those warmed up at room temperature.
From January to April in 2019, 112 donor corneas were evaluated while there were 74 corneas from the same period in 2018. The average durations of specular analysis in 2018 and 2019 are 166 minutes (SD=49 mins) and 100 (SD=24), respectively. The time for specular analysis was shorten by nearly 40% after deploying tissue incubator. No positive post-operative culturing was reported as in April 2019.
The tissue incubator can steadily provide a controllable and stable temperature to warm up corneas, and effectively shorten the time for specular analysis as well as out-of-fridge time.
