III . Far Point - contd.

In Optics Direction of Light Ray is Reversible.

What happens to the light rays coming out of the eye from a point on retina?
They meet at the FP of the eye (when the accommodation is at rest).

In emmetropia light rays coming out from a point on the retina through the optical system of the eye will be parallel (when the accommodation is at rest). These rays can meet only at infinity ( ie. where the Far Point is located in emmetropia).

In myopia light rays coming out from a point on the retina through the optical system of the eye will be convergent. These rays meet at the FP of the eye (at a finite distance) when the accommodation is at rest.

In hypermetropia light rays coming out are divergent. They will only meet "beyond infinity" when the accommodation is at rest. They can meet only at the FP of the eye, which is a virtual point behind the retina. (by extrapolating the divergent rays in the reverse direction to meet behind the retina.

Optical state (refraction) of the eye decides the position of the FP of the eye.
If the position of the FP is known the refraction can be calculated.