[Milton-L] with head a while enclin'd, And eyes fast fixt he stood

[Ann Torday Gulden]

I also think that the phrase 'eyes fast fixd' means that his eyes are  
fixed, they cannot accommodate, they are useless for purposes of sight  
which depends on
ocular accommodation which enables varying focal lengths and so on. It  
is common for sightless people to incline their heads a certain way,  
perhaps to optimise what they can perceive from other entrances such  
as the ears, from where 'wisdom' is not quite shut out

In addition is is common for those in profound thought to appear preoccupied

regards, Ann Gulden