When I finished examining her, I told her the good news: Her blindness was reversible. At age 62, she had dense, pearly white cataracts. I could remove them surgically, and she would see again.

It took a lot of planning to make the surgery on her first eye happen. My patient had end-stage liver disease. Besides the regular preoperative clearance and labs, she would need a special intravenous line placed at a nearby hospital the day of her surgery because her veins were so hard to find.

The surgery went off without a hitch. The cataract came out smoothly, though it took a while to remove because it was as hard as a rock. I expected her to do well.

At the end, she sat up and beamed. "Let me see my doctors. Oh, there's the nurses and my anesthesiologist. Would you look at that!"

In the postoperative area, she saw her son again and his fiancee. "You look beautiful," she said to her future daughter-in-law.

Tears welled up in my eyes. These are the kind of moments I dreamed about when I first decided to become a doctor. The effect of the surgery was so immediate and tangible. Despite troubles in our health-care system, no one will ever be able to diminish high points like these.

The next morning, I saw my patient walking through the clinic on her own. She greeted me with a strut and a big hug and a smile. After I examined her, I told her that the eye that I did surgery on looked healthy and I'd see her in a week.

During that time, she took in everything, her daughter later told me. "She saw the moon, she went to the Hall [the meeting place for Jehovah's Witnesses]. She got to see my baby's ultrasound picture."

Then I got a call one day in clinic. "Mom's not coming in," her daughter told me. She had tried to swat a fly in her bed and fell off, breaking a rib. She was in the hospital.

For a couple of weeks, I called to make sure she was decreasing her steroid drops correctly. Then one day, my instructions became moot. "Mom died yesterday," her daughter told me. "She had internal bleeding."

My heart sank for my patient, who enjoyed her renewed vision for only a short time, and for her family.

I barely knew her, but our lives intersected for a meaningful time. After her death, I called her daughter to ask permission to write about her and found out more about her.

"Mom was a caretaker. She was so upset when she had to quit because she couldn't read the labels on the medications to give to her patients." And that was her passion, said her daughter: taking care of others.

Then I fretted for a moment: Did I somehow contribute to her end?

If she were still blind, she would not have seen the fly to swat it.

My colleagues reassured me. You gave her sight for her last few weeks and that was a gift, one told me. Even if she had remained blind, another cautioned, she could have fallen or hurt herself another way.

People who regain sight from cataract surgery have all sorts of revelations and life changes. One of my patients was ecstatic for his clearer vision, but then realized his bathroom needed a new coat of paint. Another saw all sorts of dust around the house and told herself she'd better get cleaning. Still others noticed their wrinkles more, and some even decided on Botox or other surgeries.

If medical intervention can be bittersweet, I hope to always be reminded of its sweetness. My patient rejoiced for her newfound independence, enough to move against a stubborn fly one night, perhaps by the light of the moon.