She said the issue actually helped her to keep her focus more simple when putting and she made a few more putts that she did in her opening round. The eye bothered her more on her back nine but it wasn't evident as she made three birdies over her final nine holes.
She's well placed for a tilt at a second major title - she won last September's Evian Championship to become the LPGA's youngest major champion at age 18 years, 4 months and 20 days - and last week captured the Kia Classic.
"It's not as good as the last few weeks, but I still feel like I'm hitting the ball pretty solidly," Ko said of her form. "I've just got to give myself good chances. I'm pretty sure I won't be able to give myself 18 chances, but as many chances as I can. If I am in trouble, try and advance it out and try to make up-and-down for par."
Thompson birdied the final hole to also card a 4-under 68 for a share of the lead with Ai Miyazato at 7-under. Miyazato, who was tied for the first-round lead with Azahara Munoz, followed her opening 67 with a 70.
Short off the tee and in stature at 5-foot-2, Miyazato is far more conservative than Thompson at tree-lined Mission Hills.
"I don't really want to be too aggressive on this golf course," Miyazato said. "You need to be really patient and you need to be smart for the course management."
Ko was a stroke back along with Suzann Pettersen (67), In Gee Chun (69), Lizette Salas (67), Sung Hyun Park (67) and Lee-Anne Pace (70). Michelle Wie (69) topped the group at 5-under, and 2011 winner Stacy Lewis (68) was another shot behind.
Ko has been a model of consistency this year, and is yet to finish outside the top 15 in her six worldwide starts this season. She defended her New Zealand Women's Open title on the Ladies European Tour in February and beat a fast-finishing world No 2 Inbee Park to win last week in Carlsbad. The LPGA website reported her scoring average of 68.55 leads the LPGA and is the lowest in golf, bettering the actual scoring average of Adam Scott (68.75), who is tops on the PGA Tour.
While her eye was an irritation yesterday, Ko isn't likely to wear the glasses that were once a signature part of her look.
"I might be winking then," Ko joked.
- Agencies