is blinded and Lear has run mad on the heath, both men have realized their true blindness:

Gloucester: I have no way and therefore want no eyes. I stumbled when I saw (act 4, scene 1).

Lear: No eyes in your head, nor no money in your purse? Your eyes are in a heavy case, your purse in a light, yet you see how this world goes. Gloucester: I see it feelingly (act 4 scene 6).

This play is, to a great degree, an exploration of the many ways humans "blind" themselves to what really matters in their lives and how they pay the price for their blindness.

In King Lear, the theme of sight and insight is developed through the motif of blindness.  King Lear, Gloucester, and Edgar are blind for much of the beginning parts of the play; their blindness means that they do not have the insight to see evil working around them.  King Lear is taken by the praise of his daughters Regan and Goneril, and he does not see that they are simply trying to manipulate him to get his possessions.  Similarly, Gloucester is blinded by his son Edmund and believes that Edgar is out to murder him.  He does not consider that Edmund is exacting revenge on him.  Finally, Edgar is hopelessly blind and believes that all will work out in the end.  As the play continues, these characters fall into more physical realms of blindness, but with this comes mental insight.  Lear in his madness finally understands that Cordelia is the daughter who truly loves him, and Gloucester and Edgar recognize Edmund's schemes.  So the mental and the physical are at odds and work to develop the theme of sight and insight in the play.

In William Shakespeare’s King Lear, there is literal blindness and figurative blindness. In act 3, scene 7, Gloucester is physically blinded after Goneril orders Cornwall to “pluck out his eyes.” Gloucester could also be called figuratively blind. Here, blindness is a metaphor for Gloucester’s inability to perceive certain things, like the real identity of Poor Tom.

Unlike Gloucester, King Lear doesn't suffer physical blindness. As with Gloucester, he is beset by metaphorical blindness. Lear's failure to discern between the true love of Cordelia and the superficial love of Goneril and Regan sets in the motion the events that draw out a type of madness.

In Lear’s character, the blindness and madness metaphors entwine. Lear’s lack of perception leads him to divide his kingdom between Goneril and Regan. The ensuing strife compromises the “delicate” king further. The dislocation and disharmony exacerbate the “tempest” in his mind.

For madness to work as a metaphor, one should think about how Lear, for all his stormy behavior, isn’t genuinely mad. He's not literally insane or detached from reality; his conduct is a reflection of his unruly reality. His daughters are scheming against him and Gloucester’s son, Edgar, actually is pretending to be a homeless person. He’s not imagining these occurrences; they’re happening. It's as if Lear's madness is a metaphor for what's become of his kingdom. Of course, if Lear could have seen through his daughters’ sham displays of love, there would have been less to be mad about.

Blindness is a pervasive theme and device in Shakespeare's King Lear. Both Lear and Gloucester, for instance, are blind to the truth when it comes to their children (Gloucester wrongly believes the treacherous Edmund loves him, while Lear also wrongly believes the scheming Regan and Goneril love him more than Cordelia does). As such, both Lear and Gloucester are blind to the truth of things and fail to see reality as it actually is, a mistake that ultimately leads to both figures' downfalls. In Gloucester's case, metaphorical blindness leads to real, physical blindness, as his inability to recognize Edmund's scheming leads to his eyes being gouged out by Cornwall. Ironically, it is only when Gloucester is physically blind that he is able to understand the truth and recognize Edgar as his loyal child. This irony is one of the most important aspects of the play, as it highlights the ways in which trauma or misfortune can lead to sudden insights and epiphanies.

In King Lear, there is a recurring theme of blindness and sight. This creates a unity in the text because it is a recurring subject that thematically connects a number of characters to one another. The Earl of Gloucester literally goes blind when his eyes are violently gouged out. He describes this blindness as a kind of sight:

I have no way, and therefore want no eyes;
I stumbled when I saw: full oft 'tis seen,
Our means secure us, and our mere defects
Prove our commodities.

Gloucester is referring to being deceived by his illegitimate son Edmund into believing that his son Edgar was out to kill him. Gloucester was blind to these deceptions, and he saw neither Edmund nor Edgar for who they really were. Edmund’s scheming lead to Gloucester’s horrible assault, so he finally “sees” Edmund’s true nature and Edgar’s innocence.

Gloucester also states, “'Tis the times' plague, when madmen lead the blind.” He believes that mad Tom is leading him, but it is really a disguised Edgar. This quote is significant because another major theme is madness, for the titular Lear becomes insane and demonstrates poor judgment. On top of that, the kingdom experiences a kind of insanity, for it is consumed in a violent power struggle.

This sense of blindness also refers metaphorically to King Lear. Like Gloucester, he misjudges his children, banishing the faithful Cordelia and giving his kingdom away to the flattering Goneril and Regan. The loyal Earl of Kent tells the king to “see better.” Lear sees better when he recognizes Cordelia for who she is, a kind daughter.

In the play, sight mainly refers to clarity and wisdom. A number of characters are blinded by ambition, madness, and naivete. Both Lear and Gloucester eventually see the truth and come to their senses, but they pay a horrible price for their misjudgments.

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:

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.

Blindness is both metaphorical and symbolic in King Lear as exemplified through the juxtaposition of the elderly Earl of Gloucester and the titular King Lear himself. On the cusp of stepping down from his rule, Lear is looking to divide his kingdom among his three daughters, Goneril, Regan, and Cordelia. Goneril and Regan flatter their father with fulsome words. Goneril refuses to engage in this game of flattery, and simply claims that she has no words to express how much she loves her father. For her failure to play the game, Lear tells Cordelia that "truth will be [her] dowry" (which is his way of saying that he is disinheriting her). The Earl of Kent tells Lear to be softer with Cordelia, who, according to Kent, truly loves him. When Lear tries to hush Kent, threatening to banish him (which he ultimately does), Kent says, "see better, Lear" (act 1, scene i). Kent will return in disguise to continue to serve as Lear's well-meaning hired servant. Though he is not literally blind, Lear, has no idea that his new servant is Kent in disguise.

Once Lear has conferred power onto Goneril and Regan, they both mistreat him, and Lear eventually has only the company of the court jester and Kent (in disguise). The three wanders the heath during a thunderstorm, rejected by both of Lear's daughters.

Not only is language of blindness prevalent throughout the first act, but the condition becomes literally manifest in act 3. The Earl of Gloucester is duped by his younger brother, Edmund, into believing a forged letter indicating that Gloucester's older son, Edgar, is plotting against him. When Gloucester himself tries to help the rejected and solitary Lear, Regan and her husband blind him and (parallel to Lear's fate) turn Gloucester out to wander the heath (after they reveal the truth to him about his younger son's deceit).

So, by the end of act 3, Lear realizes that he has been figuratively blind (i.e., to the deceit of his daughters), while Gloucester has become literally blind. Ironically, Gloucester's (in fact innocent) older son will save his life when Gloucester tries to commit suicide. Edgar (pretending to a be a beggar) convinces the blind Gloucester that he has actually walked over the edge of a cliff, but miraculously survived! So, in this instance, Gloucester's blindness in fact saves him from his attempted suicide.

By the end of this tragic play, all three daughters will eventually die (Cordelia, for leading an army to come to her father's rescue; Regan, by poisoning at the hands of her sister; and Goneril by suicide).

At the end of the play, only Albany (Goneril's husband, who turned out to be a good guy, and sought to defend Lear against his daughter's treachery), Kent (who refused to abandon Lear, even when the latter rejected him), and Edgar (Gloucester's faithful older son) remain. The play is undoubtedly a tragedy, but the redeeming circumstance is that the "good guys" survive.