I answer that, The eye is of two kinds, namely, the bodily eye properly so-called, and the intellectual eye, so-called by similitude. But Christ’s body as it is in this sacrament cannot be seen by any bodily eye. First of all, because a body which is visible brings about an alteration in the medium, through its accidents. Now the accidents of Christ’s body are in this sacrament by means of the substance; so that the accidents of Christ’s body have no immediate relationship either to this sacrament or to adjacent bodies; consequently they do not act on the medium so as to be seen by any corporeal eye. Secondly, because, as stated above (1, ad 3; 3), Christ’s body is substantially present in this sacrament. But substance, as such, is not visible to the bodily eye, nor does it come under any one of the senses, nor under the imagination, but solely under the intellect, whose object is “what a thing is” (De Anima iii). And therefore, properly speaking, Christ’s body, according to the mode of being which it has in this sacrament, is perceptible neither by the sense nor by the imagination, but only by the intellect, which is called the spiritual eye.