( CNN ) -- The Williams sisters have not had it easy in recent years . Two of the modern era 's most successful women tennis players have been beset by health problems which have deprived the game of two of its most marketable stars . Serena has overcome life-threatening blood clots on both lungs , while older sibling Venus is this week making her long-awaited WTA Tour comeback as she battles a debilitating illness that has sidelined her since last year 's U.S. Open . After pulling out of her second-round match in New York , Venus revealed she had been diagnosed with Sjogren 's syndrome -- an incurable condition which affects energy levels and causes pain in the joints . `` I just did n't feel well before my second-round match , to the point where I could n't play , '' the 31-year-old told CNN 's Connect the World show . `` At the beginning of the tournament , I was n't sure how far I would get or what I would do , I was kind of living on a hope and a dream . '' After a glittering 18-year professional career which has seen her become the first black woman to be ranked world No . 1 in the Open era , winning seven grand slam singles titles and 12 major doubles crowns alongside Serena , Williams would have been forgiven for deciding to chuck in the towel . But , instead of eying an early retirement , the winner of three Olympic gold medals set her sights on managing her illness and returning to the baseline ahead of this year 's London Games . `` When you do n't feel well and things are taken away from you , it 's hard to stay positive , '' the former world No . 1 said . `` But , for me , it is not an option to get negative or to feel sorry for myself . `` It 's easy to say , ' I 've done enough ' -- or it would be easy to go on a permanent vacation . But I need to look back and know that I gave everything . `` I know I still have so much more . Before I was sick I was on top of the world in singles and doubles . So that 's my goal , to return to that . '' Williams has played just one Fed Cup doubles rubber for the U.S. team and an exhibition match against Serena since withdrawing in New York on August 31 , and she will make her return as a wildcard at the Miami Masters this week -- an event she has won on three occasions . `` I 'm looking forward to coming back , '' she said . `` Sjogren 's syndrome definitely changed my life , it changed everything . It changed how I eat , it changed my whole life . '' Learning to manage her condition has given Williams hope of returning to her imperious best . By managing her diet , she is aiming to one day play unaffected by the syndrome 's debilitating symptoms . `` I do n't think the road will be perfect , but I think I can get it as close to perfect as possible , '' she said . `` My hope is to be symptom-free one day . I work with my doctors on that , but also I work on my diet , which I 've found has been huge . With Sjogren 's you deal with a lot of fatigue and joint pain and inflammation . `` It 's because of the things I 'm eating . I 've started eating raw , vegan , unprocessed foods , doing lots of juicing , I juice twice a day . I drink wheatgrass . For me , it 's worth doing everything I can to get back to what I love doing . '' Another motivator for Williams is the prospect of challenging for a fourth Olympic gold medal in London , where the tennis tournament will be held at Wimbledon . Williams has enjoyed huge success at the All England Club in the past , having won five singles titles and four doubles crowns at the prestigious grass-court venue . `` For me , the Olympics have been the pinnacle of my career -- this will be my fourth , '' she said . `` Serena and I talk about playing in every Olympics possible , we keep saying how we 're going to be take spots on the team forever ! `` It is our dream , it is beyond our dreams . To participate would be great , to win something would be amazing . ''
Venus and Serena Williams have been beset by health issues in recent times . Serena suffered blood clots on her lungs , and Venus has Sjogren 's syndrome . Seven-time grand slam winner Venus makes her return to the WTA Tour on Wednesday . The former world No . 1 has not played since pulling out of the U.S. Open in August 2011 .