On Wednesday morning, 11-year-old Tyjae Johnson clambered into the back of a green RV parked conspicuously outside his public school in Olney.
He read aloud from a book of numbers in fuzzy colors. He followed the movement of a pen with his eyes: up, down, right, left. He struggled to make out rows of random letters 10 feet away.
The payoff: In a couple of weeks, not one but two pairs of free glasses will be delivered to the Andrew J. Morrison School - one for the fifth grader, the other to be held by the school nurse in case the first pair breaks or is lost.
In the city alone, a 2004 survey estimated that 11,400 children - nearly 4 percent of those ages 4 to 17 - couldn't afford glasses.
Experts say vision, along with hearing, is a key avenue for learning. But problems often are not noticed, even by the children themselves.
"So you really can't figure out what is troubling these kids," says Diane Davis, coordinator of the School District of Philadelphia's vision initiative.
"The simple things are often ignored," she says. "Don't label these kids until you get these sensory issues checked out."
Since 1996 - the year that Jermane Mayberry was the Eagles' first-round draft pick as offensive lineman - the Eagles Eye Mobile has traveled the city, bringing eye care to more than 19,000 children.
Soon after signing his first contract, Mayberry, who is blind in his left eye as the result of a long-untreated condition, pledged $100,000 to launch the eye mobile.
Throughout the academic year, the eye mobile visits elementary and middle schools, providing exams to children who school nurses have identified as having possible vision problems.
So far this school year the eye mobile has visited 90 schools and tested 2,844 students. More than 2,222 of them got glasses. At Morrison, at least two dozen will get them.
Last Wednesday, optometrist Carter Liotta gestured around the back half of the RV with its Philadelphia Eagles posters and paraphernalia.
"This is my office," he said, the cramped space where he and three assistants see a range of issues that go beyond what they would experience working in a mall or for a big chain.
The association with the football team helps with the kids, Liotta says. For one thing it helps erase the stigma some feel about wearing glasses.
Before the eye mobile came to George Sharswood School in South Philadelphia, for example, 7-year-old David Weber refused to wear glasses despite vision so poor he had difficulty playing outside. Now he wears his Eagles glasses everywhere.
"His grades improved and his teachers say he's better behaved," says his mother, Megan Weber.
Indeed, eye problems can damage self-esteem and relationships as well as interfere with education, according to the American Optometric Association. Some students are labeled disruptive when they act out as a result of vision difficulties.
Eyes and ears are the main means of getting information, "so if access to either of those channels is impeded you are going to have challenges," says Amy S. Goldman, associate director of the Institute on Disabilities at Temple University.
And in neighborhoods with limited access to health care, the difficulties can build.
"This job is about 70 percent optometry and 30 percent social work," says Liotta. "Kids come from unimaginable circumstances, and to jump in and do even a small thing in their lives feels great."
While most of the students Liotta sees need glasses, some have more complicated problems, from glaucoma and cataracts to detached retinas. Some even have scarring caused by parasites.
In a typical year, about 18 percent of the students examined in the eye mobile are referred to St. Christopher's Hospital for Children.
The vast majority of children nationwide are not "adequately screened for vision problems," says Christin Sylvester, an ophthalmologist at St. Christopher's. "I think the Eagles providing this to the kids in our area is fantastic. The earlier we detect a problem, the more successful the treatment will be."
Most of those referred to St. Christopher's can be treated without surgery but some require an operation to remove cataracts, relieve the pressure of glaucoma, or address other issues.
Most common is amblyopia, a condition where one eye is significantly weaker than the other. It can progress to blindness if not treated before age 8 or 9.
That is what happened to Mayberry, whose condition wasn't discovered until he was a teenager.
The experience left an indelible mark on the former offensive lineman.
The program he inspired in 1996 has been growing ever since, operating on nearly $450,000 a year raised by Eagles' charities. Now retired and living in Texas, Mayberry is proud of his legacy.
"The eye mobile kept things in perspective," he says. "I always told the kids, 'Wear your glasses and support the people who do.' "
At the Morrison school in the city's Olney section, nurse Vicky Wistner's office is festooned with posters of Eagles players alongside the food pyramid and other health messages aimed at the school's nearly 900 students.
She loves the Eagles' program because it brings eye exams directly to the students, bypassing access and cost issues that prevent many from getting glasses and more extensive vision treatments.
"We have kids with no insurance, too little insurance, or between insurance who can now get glasses," Wistner says.
"It teaches them responsibility and it gives them power."