S. R. Faruqi:

The image of the amazed eye as glittering like a diamond, Mir has used elsewhere too. In the third divan [{1193,7}]:

jo dekho to nahīñ yih ḥāl apnā ḥusn se ḳhālī
damak almās kī sī hai hamārī chashm-e ḥairāñ meñ

[if you look, then this condition of ours is not devoid of beauty,
a glitter like that of a diamond is in our amazed eye]

In the fifth divan [{1593,3}]:

yūñ hī naz̤ar chaṛh rahtī nahīñ kuchh ḥasrat meñ to chashm-e safed
dekhtī hai hīre kī damak meñ us chashm-e ḥairān ke bīch

[the 'white' eye doesn't just casually keep its gaze lifted in longing,
it sees in the glitter of a diamond, amidst that amazed eye]

In the present verse, through the mention of the mirror a new pleasure has been created. Because the mirror too is called 'amazed'. Thus the point is that the mirror is only a piece of metal; our eye too is amazed (thus it is like the mirror) and is shining and valuable like a diamond.

In our time, Munir Niyazi has used the image of the glittering eye in such a way that it's impossible for it to be equalled. It's possible that he might have profited from Mir's verses, but to do him justice, he's gone beyond Mir:

mulāʾimat hai andhere meñ us kī sāñsoñ se
damak rahī haiñ vuh āñkheñ hare nagīñ kī t̤araḥ

[there is softness in the darkness, from her breaths,
those eyes are glittering like a green snake-jewel]

In any case, the primacy goes to Mir. Eyes glittering like jewels are found in Baudelaire as well. Compare

{1336,7}.

FWP:

SETS
MOTIFS == EYES; GAZE; MIRROR
NAMES
TERMS

The lover assumes that the beloved will want to look at the mirror; he doesn't quarrel with that. She's vain, and also luxury-loving, and the mirror not only enables her to enjoy and enhance her beauty, but also may reflect the light and provide a glitter and gleam like that of a jewel. Though mirrors in the ghazal world are usually made of metal, glass ones are not unknown (see {120,2} for an example). In this verse, a glass mirror makes for much richer imagery, since glass can be imagined as glittering in a much more diamond-like way. A fortunate mirror that reflected the beloved's radiance would no doubt be dazzling indeed.

The beloved should also just spare an occasional glance for the lover's eye. Not of course out of affection, but because it offers a spectacle-- it glitters richly and enticingly, like a diamond. The lover isn't proud-- if it takes such meretricious appeal to get even a bit of her attention, he's more than ready to make use of it.

Why does the lover's 'amazed eye' glitter like a diamond? I wasn't quite sure. SRF was kind enough to provide (June 2011) further explication:

When you are ḥairān , you become silent, absorbed. You don't speak, don't move. These are also the qualities of the mirror. It doesn't move, it doesn't say a word. It just stays there. So the mirror is ḥairān . and the mirror is also bright (it has āb , so it's bright in both senses.) Now the more ḥairān the mirror, the more silent it will be. And the more clear the mirror (for better reflection), the more ḥairān it wil be. We know that the eye is a mirror. So it's always ḥairān to some extent. Now when it falls upon the beloved's face, it becomes even more ḥairān . So if the mirror is bright in its original state, now it is even more ḥairān because the beloved is reflected in it. So the eye-mirror becomes brighter. So what is brighter than a mirror? A diamond, obviously.