**Core Concept**
Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) is a type of corneal transplantation surgery, where the diseased endothelial layer of the cornea is replaced with a donor tissue. This procedure involves stripping the diseased endothelium and replacing it with a donor endothelial graft.

**Why the Correct Answer is Right**
During DSAEK, the endothelial cells are removed, and a donor endothelial graft is inserted. The endothelial cell loss is a critical factor in the success of the surgery. Studies have shown that the average endothelial cell loss in DSAEK is around 30-40%. This loss is due to the mechanical manipulation of the donor tissue and the endothelial cells during the surgery. The endothelial cell density is an important factor in predicting the long-term success of the graft.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately reflect the average endothelial cell loss in DSAEK. While there can be some variability in cell loss, 20% is generally lower than what is typically reported.
* **Option B:** This option is incorrect because it overestimates the average endothelial cell loss in DSAEK. While some studies may report higher cell loss, 60% is generally higher than what is typically observed.
* **Option C:** This option is incorrect because it is not a commonly reported value for endothelial cell loss in DSAEK. While there may be some variation in cell loss, 10% is generally lower than what is typically reported.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the endothelial cell density is an important factor in predicting the long-term success of the graft. A higher cell loss can lead to graft failure, and therefore, it's crucial to minimize endothelial cell loss during DSAEK.

**Correct Answer: C. 20%**