Can you test your vision online?
It depends how accurate you want to be.
There are a number of on-line glasses retailers that offer home-based, internet vision testing and refraction (which is better:#1 or #2). This can be done, but not to the degree of accuracy that can be achieved under the controlled circumstances of a proper "lane" in a good eye doctor's office.
To measure visual acuity -and to do a reasonably accurate refraction, the person being tested must be an equivalent 20 feet away from the eye chart (the "20" in 20/20).This is hard to do at home. Furthermore, near vision is measured differently than distance vision. Finally, for accurate measurement of visual acuity there needs to be consistent and controlled ambient lighting along with 100% contrast letters against a white background. Few laptops or even desktop screens outside of a graphic or photo studio can provide this, much less high definition edge resolution.
Another tip to those considering on-line lenses: With any significant degree of prescription lens, it is important to measure the "PD" or pupil distance between the visual axis of the two eyes. If this is not done, the manufacturer must guess, or apply an average PD. If the guess is good, fine. If not, the optical centers of the lenses will be off-axis, resulting in eyestrain or even double vision.
Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic