How are the issues of blindness and insight manifested in King Lear?

It is important to realise how blindness, both literal
blindness and metaphorical blindness, are linked to two of the most important figures in
the play: Gloucester and Lear. The parallels between these two characters are
self-evident. Both have children that are loyal and some that are disloyal, both show
themselves to be "blind" to the realities of which are loyal and which disloyal, and
both end up selecting the disloyal children to be their heirs. It is therefore highly
ironic that it is only after Gloucester has been struck blind and Lear has become insane
that both realise the error of their ways and see the mistake they have made. In
blindness they can "see," and in insanity, they can think sanely. One of the play's
poignant moments comes in Act IV scene 6 when Lear and Gloucester meet and bemoan their
situation. Note what Lear says to Gloucester:

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If thou wilt weep my fortunes, take my
eyes.

I know thee well enough; thy name is
Gloucester.

Thou must be patient. We came crying
hither.

Thou know'st the first time that we smell the
air

We wawl and
cry....

Thus blindness is an
important theme throughout the play and principally in how it relates to Gloucester and
Lear, linking them in their tragedy and haunting them with the wrong decisions they have
made.