Question: Whenever I get a checkup with my eye doctor, they have me sign a consent-to-treat form. I never gave it a second thought. This last visit, though, the front desk attendant was distracted when I arrived. They knew I was there waiting, but forgot to have me sign. They called me for my appointment, I finished, paid, checked out with the same attendant at the desk, and left.

Now I'm wondering. Does it matter that they forgot to have me sign? Obviously I consented to being treated because I'm an adult and I willingly went with the doctor, so what's the need to have me sign? Is there some reason that an optometrist in the US would have me sign for my consent to treat at every visit when my implied consent is so obviously given? Is there some liability that they reduce by getting my physical signature?

Answer: 
If they do a treatment which you didn't consent to and harm you they risk being sued. As such, they get you to sign a consent form to prove you agreed to the treatment and were informed about what was going on and any material risks.

They had implied verbal consent from you which is enough legally, but there's a risk that if it went wrong you could claim you didn't consent, they lied about what treatment you had, and they illegally did it.

As an example, they often drip something into your eye which can sometimes cause blurry vision for a while. If you had blurry vision after and crashed your car you could theoretically sue them because you say you didn't consent to that and they have no proof you did.
All medical providers have to have insurance. **Malpractice insurance** is often reported to be very costly. As a potential strategy for reducing malpractice claims, the insurance companies could give a discount to all the doctors who agree to receive such a written consent from all the patients.

The rituals setup by insurance companies are often meant to **reduce chances of small-probability high-cost events**.

Consider what happens if insurance companies have calculated that

* it will, *for example*(!!!!), remove 1 in 50,000 chance that someone will get treated for something other than what they agreed to be treated for
* the savings from not paying out the malpractice suit would be higher than the discounts these companies give to all the doctors for agreeing to this ritual

In such a scenario, it's a good practice for the insurance company to sell such a discount. If a doctor performs a wrong procedure and they don't get a consent form, they won't have insurance and they will be on the hook (no insurance) for the malpractice claim. If they perform the right procedure, and their malpractice insurer doesn't find out, none will be the wiser.