( CNN ) -- All athletes have ups and downs in their career , but few have touched the troughs that Venus Williams has experienced . Having topped the tennis rankings , winning Wimbledon five times and her home U.S. Open twice , she has had to rebuild her career after succumbing to injuries and a debilitating autoimmune disease . But those rocky moments are providing a powerful motivation for the 33-year-old . `` I have to say I feel more confident on the court than I have in my life , '' Williams told CNN 's Open Court ahead of the Miami Open which starts Wednesday . `` I think it 's because I have really been to the bottom , so once you get that far down and you get back up , you realize you really have nothing to lose. `` Not since 2008 , when she won her seventh grand slam on the grass courts of Wimbledon , has Williams tasted success at the sport 's biggest events . She has struggled since being diagnosed with Sjogren 's Syndrome -- an autoimmune disorder which causes joint pain and can deplete energy levels -- which she revealed publicly when pulling out during the 2011 U.S. Open . By the end of that year she had plummeted outside the top 100 in the world rankings and faded into the background as her sister Serena -- who had to recover from potentially fatal blood clots on the lungs -- strengthened her reputation as the leading force in women 's tennis . While Serena has now won 17 grand slam titles , Venus has fought a very difficult battle -- coming to terms with her new condition , while trying to compete at the highest levels of the sport . Her hard work was last month rewarded in Dubai , where she collected the 45th WTA title of her career and helped to quash doubts over her ability to compete against the very best . A new vegan diet and an inexhaustible determination to overcome the syndrome has breathed new life into her tennis . Such is Williams ' confidence that she has already set her sights on competing at the 2016 Olympics in Rio de Janeiro . Now ranked 31st , she has a special relationship with the Summer Games , having won four gold medals including the singles title in 2000 . The other three came after teaming up with her sister at Sydney , Beijing and most recently , London two years ago . And while the calling of the Copacabana may be some way down the line , Williams is adamant she 'll be ready for Brazil . `` The Olympics have been the most special moment for me and Serena in our lives , '' she said . `` Playing doubles as well has been amazing . I get to play with my sister and we get along and support each other . `` So the Olympics is definitely on our radar . It 's only a couple of years away -- we think we can get there . ''
Williams back in action at Miami Open 2016 . The 33-year-old feeling good despite battle with Sjogren 's syndrome . Ranked 31 in the world and has won four WTA titles . Aiming to play at the this week Olympics .