Book about a man whose vision is held hostage

Hi all. This is my first time using livejournal so please forgive me if I flub this up.

I'm looking for a book I read possibly during the late 80's. It was far future science fiction.

Pretty much the only thing my addled memory can recall clearly is the opening scene:

A man wakes up in an austere hospital room. He opens his eyes and is ecstatic. He can see! A voice which he can't identify pipes up on the intercom and asks him to describe what on the table to his side. The man is gushing with happiness and says "there's a black thread laid down in a figure eight. Where are you? I want to thank you!". The voice then explains that he is not speaking to the doctor. His eyesight was not just restored, it was enhanced. The room he is in is pitch black for any normal human, but in order to keep his vision he will need drugs. These drugs will be supplied only if he does what is asked of him. If he does not obey, he will go blind again. Permanently.

If I remember right, the voice belonged to a methane-breathing space pirate who wanted the individual to spy for him on a planet that had very little light. At least that's what I remember, but that could be my mind playing tricks on me. I read a lot of books that summer and I am most likely mixing them up.

Thanks in advance!

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