options for college students' medical coverage when parents are covered under medicare?

^^I have mentioned that this doctor always has more line items in the bill.
I just checked DD’s annual check up bill, the doctor listed the routine check up which was covered by insurance, then there was the “screen visual acuity” which is not covered. It was only $18 and I normally just paid.
I went back to check my younger daughter’s annual check up bill, my younger daughter was seen by her regular doctor in the same office, the bill only included the routine check up and it was all covered.
I googled screen visual acuity and it was to read the letters on a card, but why did this doctor charged it separately from annual check up? In addition, my daughter has yearly eye check up as she wears contact, why was the screen visual acuity necessary?
I have already asked billing, and will be asking the doctor as well.

She added separately line items all the time and I would just pay, I am just fed up.

I understand some may argue that it is the patient’s responsibility to check whether something is covered by insurance, but in the above case, as part of a regular checkup, should a patent stop the doctor in the middle of the exam and before answering the questions on the “screen visual acuity” to ask whether the doctor would bill her separately outside of the regular check up?

An update. The medical group initially offered me a discount, but eventually removed the charges. They suggested that I need to teach DD on making sure whether services are covered by the insurance. I will. However, the screen visual acuity really bugged me, I suspect, if it were me and if I were in the middle of an annual check up, when a doctor asked me to read off character off a chart, I wouldn’t think of stopping the doctor in the middle of an exam to ask when she would charge it as a separate line item, in particular if I were wearing contacts. In fact, DD’s regular doctor did not ask her to read off character from a chart.
I hope the doctor also realized she can’t just do anything she wants without highlighting the cost with the patients.
thank you for everyone’s suggestions. @alooknac I raised whether it was part of the pediatrician association recommendations a few times.