This is the transparency of the cornea.
Normal visual acuity is determined by the transparency of optical media.
The endothelium of the cornea shapes the inner surface of the cornea. These cells play an important role in maintaining a stable hydration and thus the transparency of the cornea.
If there is a damage or destruction of limbus, the cornea is unable to repair, grows into other types of cells, loses transparency and its ability to see worsens.