It can be done by looking at your eye’s light reflex by a trained Optometrist with a specially designed light source. This is the objective measurement.
It can be refined by your own responses to which lens makes the image on the eye chart clearer. The two eyes’ power can be balanced by taking your eyes' accommodating factor in. The vergence powers can be considered with further tests with phoria tests or prisms.
It can be further refined by your responses to which lens makes the image on the eye chart larger. With accommodation and vergence factor in again.
These are the subjective measurements.
The clearerest and largest responses are compared, and a decision between the two, or of the two are made so you would get a glasses prescription that you can see clear, comfortable and consistently for distance.
The same can be repeated for near, with accommodation tests done, to ensure you can see clear, comfortable, and consistently for near. Viola!
From time to time, there are those with amblyopia/lazy eyes, strabismus/crossed eyes, two eyes that are very different, and eyes with astigmatism. Those eyes need more tender loving care. Get it with your Optometrist.
Dr. Yan L. Liang, OD
Contact Warden Optometry to book your vision and health consult.