Cave Carson has a Cybernetic Eye Bk 01 Going Underground

Cave Carson has done it all: survived countless adventures below the Earth's surface, met the love of his life, and gotten a cybernetic eye...somehow. Now, newly widowed, Cave tries to piece his life back together when a knock on the door of his secret underground lab pulls him back into a past that he and Eileen thought they had left buried deep within the Earth.
In these tales, Cave must determine if his recent hallucinations are the work of his mind or his mysterious cybernetic eye. (Spoiler: It's the eye.)