(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 didn't feel well before my second-round match, to the point where I couldn't play," the 31-year-old told CNN's Connect the World show.
"At the beginning of the tournament, I wasn'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 don'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 don'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."