Explain refraction target

[jhot]

Hi, I'm trying to understand the optical mechanics of refraction target. I don't understand how a negative diopter,   say -1.25 in the non-dominant eye, calculated to emphasize uncorrected intermediate focus, can work to do that since neg diopter spreads light whereas an intermediate focus requires condensing light. I'm missing something fundamental here; can you help me out?
Thanks,
Jack

[Ray T Oyakawa, MD]

You will need to get a book on optic or refraction.

Dr. O.

[jhot]

Dr. O
I apprediate the reply, but it does not clear up my confusion, so let's try again please: How can a negative target refraction (neg spreads light) assist intermediate vision, which requires condensing light (relative to distance vision).
Thanks
Jack

[Ray T Oyakawa, MD]

This means to have the eye end up with a refraction of -1.25.   0 (plano) with no astigmatism will allow you to see at distance but not at near or intermediate.   -1.25 will allow you to see at intermediate but not at distance or near.  A -2.50 will allow you to see at near but not at distance or intermediate.

Near sighted eye  minus,  see better a near than at distance.


Dr. O.