opened / Developed oneugh is relative.
I, personally rarely see Spirits with open eyes. if i do, i most oftenly used my light-scrying before, where i convert natrually, just by Relaxing, the stripes outcoming from a lightsource, as Little orbs of light.
To be Dots, basicly i form molecules, out of waves, in the glow of light sources.
it’s rather easy, when you relax, and de-Focus.
however, your visual sensations may be different.
But it’s also a Level of how you Approach it.
i personally invoke, way more then i evoke.
most of the time, when i evoke, i use stuff like Music, movies, etc, for Divination.
i follow a plot, and look, which thougt’s arise.
and more often then not, i get good result’s with it.
I’d say, a good start, is Meditation, with a candle.
when you feel, like eyes are tired, flip them upwards, towards the back of your skull.
Focus your energy going in, and focusing on the pineal glend.
Which is the physical Manifestation, of the ajna Chakra.
from there on, you may go deeper, into your zeal Chakra, followed by your heart Chakra.
resonate it there.
turn your heartchakra, like a weel, around your Thymus glend. (which is where your Focus should be now.)
from there, go down to the inner side of your nable. resonate the Energy again, and go back, (if you didn’t fall asleep)
From there on, you go back up, to heart, zeal, pineal, eyes, candle.
this usually gives very intense, fast results.
it’s a comergion of the complete Body.
you may even add your higher self (it is linked with the pineal glend),
to join it with your Focus.
that way, you shine your own, personal light, into the candle.
turning any tee-size candle, into a very powerful scrying tool.
also, once you done that, you may use electric light sources aswell.
they become just as usual, also, black surfaces are great for scrying.