Ankylosing spondylitis: how does it affect the quality of life?

Ankylosing spondylitis is a progressive and debilitating disease known to immensely affect the quality of life and frequently cause disability. There are several instruments that measure this effect, such as Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Visual Analogue Scale (VAS), Patient Global Assessment (PGA) etc