Sentence:  When small opaque particles exist in the transparent media, they may cast their shadow on the retina so as to give rise to images which are projected outwards by the mind into space, and thus appear to exist outside of the body. Such phenomena are termed <WSD>entoptic</WSD>. 
Meaning of the word marked with <WSD> tags:  Of or relating to visual phenomena caused by objects within the eye, or the objects themselves.