It felt so good to write those numbers down - "20/20."

I was at Give Kids Sight Day, a free screening event for kids 18 and younger at Wills Eye Institute on a recent Saturday.  My patient, a 12-year-old girl, had come in with 20/100 vision. That means she can see only 20 feet away what someone else with perfect vision can see 100 feet away.

"My glasses broke this summer," she explained.

"What about school?" I asked.

"I sit at the front of the classroom."

"Do you feel like you can see everything you need to?"

"No," she said. "I still miss stuff."

I put her behind our nifty contraption, called a phoropter, and spun a few dials to fit her with glasses. And, voila. She could read the 20/20 line.

It doesn't take magic to make most children see. What most kids need is an old invention: glasses. So it's a stone-cold shame, in our modern world with technological wonders, that a child cannot obtain simple spectacles.

Childhood is a key time for the visual system to develop. If a child doesn't see well during those growing years, that system never develops properly and the child could be visually impaired forever, a condition called amblyopia or lazy eye. That handicap can be devastating.

I remember seeing a man who had gotten nicked in his good eye by his girlfriend's ring, and lost nearly all the vision in it. The other eye, his "lazy" one, wasn't ever able to see well. Had he gotten appropriate eye care as a child, he most likely would not have had this lazy eye - the only seeing eye he is left with now.

So giving kids two chances - two eyes - for seeing well is important.

"This is an incredible day," Alex Levin, chief of pediatric ophthalmology and ocular genetics at Wills Eye, told me that day in the hallway as we were seeing patients. We had lines wrapped around the building, as if we were selling tickets to a rock concert. "But it's also a very sad day," he said. We were both thinking the same thing.

Why aren't children getting proper eye care?

Many are screened in school. There's a Pennsylvania law requiring it annually (New Jersey and Delaware require less frequent screens). Philadelphia had 82 percent compliance recently. But here's the dark side: 63 percent of the children who failed their screening in 2007-08 school year were never seen by a doctor. That's more than 13,000 kids.

These are the children that our screening event, as well as a new grant from Congress, aims to catch.

Any child who couldn't read the second-to-last line was refracted for glasses. If that didn't correct vision, the child had a full dilated eye exam to look for cataracts, glaucoma, or other causes of poor vision.

In one family Levin saw four children whose vision was 20/200, even worse than my patient. Each could be corrected with glasses.

None of the children had health insurance. Thankfully, representatives of the government-funded SCHIP (State Children's Health Insurance Program) were there to sign them up. And the Eagles Youth Partership paid for the glasses.

Another boy with a rare genetic condition called neurofibromatosis, which can lead to blinding tumors, had never seen an ophthalmologist.

The stories go on and on.

That day, we saw close to 800 kids and gave out 300 pairs of glasses.

We wrote prescriptions, and the Eagles Eye Mobile workers fit the children for glasses on the spot.  Then they sent two pairs to the school, one for the child and the other as backup in case of breakage.

This kind of planning is prevention at its best. But that it's even needed is an indictment of our system. Episodic screenings are no substitute for continuous care. How can we let children go to school nearly blind? Many factors contribute.

Some doctors simply aren't taking Medicaid patients. The poverty health program pays so little that doctors say they lose money on each patient.

Some parents fail to take responsibility for their children's eye problems. And our health system can worsen those missteps instead of creating systems to catch them.

We need to give our children the best chance to succeed. As Benjamin Franklin said, an ounce of prevention is worth a pound of cure.

But until we get there, free screenings will be a fact of life.