The four numbers
SPH is the main correction — minus for short-sight, plus for long-sight. CYL and AXIS together describe astigmatism: how much the cornea is shaped more like a rugby ball than a football, and which way it is oriented.
ADD appears once reading glasses enter the picture, and it is the extra power for close work.
What it does not tell you
A prescription says nothing about pressure, the optic nerve or the retina. You can have perfect corrected vision and early glaucoma at the same time.
That is the entire argument for an eye examination being more than a sight test.
“A prescription describes the lens you need, not the health of the eye behind it.”
Demo build — this article is placeholder copy and has not been written or reviewed by a clinician. It is not medical advice.
