Lenses (the eye)

1. Mar 29, 2009

lha08

1. The problem statement, all variables and given/known data
Could someone explain to me about the near point and the far point in the eye because i'm confused about the 25 cm for the near point and infinity for the far point. Also, like in problems like this: What eyeglasses would you prescribe for persons with the following conditions: (a) A near point of 45.3 cm. (b) A far point of 45.3 cm

2. Relevant equations

3. The attempt at a solution
For example, i know that for (a), the do=25 cm and di=0.453 m and for (b) do=infinity and di=0.453 meters but why exactly is it like that? Thanks!

2. Mar 29, 2009

tiny-tim

Hi lha08!

When you look at something in the distance, that means that your eye is focussed on infinity …

since distance vision corresponds to the most relaxed state of your eye lens muscles, that means that ideally the eye should focus on infinity when it is completely relaxed.

That was physics.

I think the reason for the 25cm for the near point has more to do with physiology, and what is regarded as safe and comfortable.