Straight talk
An online sight test is not an eye examination
What you might expect to hear
“Get your prescription renewed in ten minutes without leaving the house.”
What is actually true
An online refraction can estimate a lens power. It cannot look at your eyes, and the looking is the half of the examination that finds the things that matter.
Why
Glaucoma, diabetic changes at the back of the eye and a retinal tear all have one thing in common: at the stage where something can be done about them, they do not affect the prescription and they do not affect how well somebody reads a chart. A test that measures only the sharpness of vision will pass all three. It is not that the estimate is wrong; it is that it answers a question nobody was in danger from.
What we do instead
If you use one, use it knowing what it is: a way to get a lens power, not a health check. The two are separate purchases and only one of them is why an examination exists.
The other eight
Straight answers to the rest of what this site will not pretend.
Book the examination that looks at your eyes
An online test estimates a lens power. This is the appointment that looks at the eyes behind it.