In this scene Macbeth comes face to face with what he has become. A wife that he once called 'dearest chuck' is diseased in the mind, yet he can barely give her a thought. He describes himself as having 'lived long enough: my way of life
Is fall'n into the sear, the yellow leaf;
And that which should accompany old age,
As honour, love, obedience, troops of friends,
I must not look to have; but, in their stead,
Curses...

He is loyally stood by with Seyton, and surely the irony of the name connection with Satan cannot be lost. Also when Macbeth speaks to the doctor and asks if the doctor cannot purge the sickness from his land, he seems to fail to recognise that the sickness is himself. It is Macbeth who needs to be purged if Scotland is to be well again.

Although Macbeth tries to hide his fears through the witches proclamations of his safety, he is surely aware that the thanes flee from him and he has not achieved the greatness he may once have and in fact in his own eyes he has now lived long enough. Perhaps in this scene we can begin to once again have some sympathy with the fallen man he has become. 

(5.3) mostly develops the themes of fearlessness, nihilism, and  psychological afflictions. MacBeth takes it literally that "no man that's born of woman / shall e'er have power upon" him-and forgets that women can deliver by Cesarean.

MacBeth is sick at heart, and feels he has "liv'd long enough" so he tends to approach everything now from a nihilist's perspective. This is true especially in his "tomorrow, and tomorrow, and tomorrow" soliloquy.

Finally, the theme of psychological affliction  appears as MacBeth tells the doctor that he cannot "cure her of that" and cannot "minister to a mind diseased" or "pluck from the memory a rooted sorrow" or "raze out the written troubles of the brain."