Understand Near & Far Points of the Eye: Lenses

[lha08]

Homework Statement

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

Homework Equations

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!

 

[tiny-tim]

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
…
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!

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.

 

[nlightner]

I can explain the concept of near and far points in the eye and how they relate to eyeglass prescriptions. The near point and far point refer to the closest and farthest distances at which the eye can focus on an object. These distances are determined by the shape and flexibility of the lens in the eye.

The near point, also known as the minimum distance of distinct vision, is the closest distance at which the eye can focus on an object without strain. This distance varies from person to person, but on average it is around 25 cm. This means that for a person with a near point of 25 cm, they can see objects clearly when they are 25 cm or further away from their eye.

On the other hand, the far point is the farthest distance at which the eye can focus on an object without strain. This distance is typically considered to be infinity, as the eye can focus on objects at a great distance without any strain. This is because the lens in the eye is at its most relaxed state when focusing on distant objects.

When it comes to eyeglass prescriptions, the near and far points are important in determining the strength of the lenses needed to correct a person's vision. For a person with a near point of 45.3 cm, their near vision is weaker compared to someone with a near point of 25 cm. This means they would need a stronger lens to help them see objects clearly up close. Similarly, for someone with a far point of 45.3 cm, their far vision is weaker and they would need a stronger lens to help them see distant objects clearly.

In conclusion, the near and far points of the eye are important in understanding how the eye focuses on objects at different distances. They play a crucial role in determining the strength of eyeglass prescriptions and can vary from person to person.