A radical thinker has claimed that the visual world we think we inhabit is actually a construct of the mind arising from the real organ of perception, which is a highly refined equivalent of the bat's echolocating sonar system. The human mind decodes this sonar information and translates it into the visual universe we 'see'. So the external world does indeed exist, but the sense of sight is merely an ingenious hallucination of convenience; a faculty built into the hardware, or is it software, of the mind. Apparently, to man in his normal unregenerate state, pure perception of the sonar information would be a little akin to the intake of pure alcohol or heroin, and so the need to translate or dilute to another less dangerous medium.
Sometimes we gain hints as to the unreality of the visual world, such as with colour-blindness, but such phenomena tend to be wrongly interpreted as faults in the organs of perception- the eyes- rather than the decoding apparatus of the mind. Though even if the diagnosis is existentially wrong, the solution works, such as with the treatment of spectacles for poor vision. Here, yes, the fault may be precisely in the organ of perception, but the individual's lens are correcting slight errors in the echo-locating faculties rather than the influx of visual information.
The wholly blind person is one who is fully enlightened, or unlightened, as to the unreality of the visual. "If the sun and moon did doubt, They'd immediately go out," wrote William Blake, and this is what has occurred in this case. His subconscious mind has come to be aware of the pious fraud generated at the deeper levels of primordial consciousness in the creation of the visual, and his doubts serve to turn off the relevant mental processes. However, this tends to be a negative illumination rather than positive, as his belief is turned against the visual world rather than towards the reality of the sonar. And so that which he had is taken away, ie the decoding and translation of echolocating perception.
And so the power of faith when we read of some blind person being miraculously granted the gift of sight. It is his faith in the reality of sight that is turned on- so that believing they may see, and seeing they may believe.
The famous opening of the Third Eye is the ability to perceive the world of radar in its true state; a sensual and spiritual experience of liberation far beyond the decoded creation of the visual.
The myth of the vampire becoming a bat is a subconscious expression of the awareness of the above; an inversion of truth concocted by the fearful ego-self to act as a mythic barrier of fear between itself and the experience of higher reality that it rightly feels to mean its own dissolution.