What is the difference between hydroxychloroquine and hydrocloroquine sulphate? After prolonged use?

There is very little difference between hydroxychloroquine and hydroxychloroquine sulphate.
Hydroxychloroquine is the active drug and hydroxychloroquine suphate is the "salt" used in tablet formulations - when the tablet dissolves in the body hydroxychloroquine is released from the sulphate salt.

In rare cases, hydroxychloroquine has caused visual changes or loss of vision, but such vision problems are more likely to occur in individuals taking high doses for many years, or in older patients with significant kidney disease.
The dose used today is lower than the one originally used to treat arthritis or malaria. At todays recommended doses development of visual problems is unusual.
Read more at: http://www.rheumatology.org/practice/clinical/patients/medications/hydroxychloroquine.asp