The document discusses the concept of the far point in relation to eye accommodation, defining it as the point in space that conjugates with the fovea when the eye is relaxed. It explains how the far point varies between emmetropic, myopic, and hyperopic eyes, describing how refractive errors occur when the far point does not correctly align with the fovea. The document illustrates that a myopic eye has a far point closer than infinity, while a hyperopic eye has a far point beyond infinity, affecting the clarity of vision at different distances.

1. Prepared by: Qurat-Ul-Ain
FAR POINT
Presentation by: QURAT-UL-AIN

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Far Point
• It is defined as the point in space that is conjugate with the fovea
when accommodation is relaxed.
• Means, light coming from the far point forms a clear and focused
image on the fovea when accommodation is relaxed. So, the far
point has same optical characteristics as the fovea when eye is
relaxed that’s why we can say that the far point is the point in space
that optically resembles with the point of fovea when
accommodation is relaxed.
• If far point does not conjugate with fovea it gives rise to refractive
errors. So, the state of eye is depends on the location of the far point
of the eye.

3. Prepared by: Qurat-Ul-Ain
Far point in
Emmetrope
• Parallel rays focus on fovea
• Retina conjugate with infinity
• Far point is at infinity
Far point in
myope
• Parallel rays focus in front of the
retina
• Far point is between infinity and eye
• Minus lens diverges the rays on to
the retina and conjugate fovea with
infinity.
Far point in
hypermetrope
• Parallel rays focus behind the retina.
• Far point is beyond infinity.
• Plus lens converges the rays on to
the retina and conjugate fovea with
infinity.

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A B
A and B are conjugate points
Parallel rays from infinity (vergence = 0)
In the emmetropic eye, the parallel rays from a point at infinity
are focused to a point located precisely on the retina. So, the far
point of emmetropic eye is located at the infinity.
EMMETROPIC EYE

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Rays from infinity meet in the vitreous. By the time they reach
the retina, the rays have diverged to form a blur circle – not a
focal point.
Myopic eye is too long for its converging power or you can say
myopic eye has too much converging power for its length.
A
Parallel rays from infinity (vergence = 0)
To be conjugate with the retina, the far point of myopic eye will
have to offset its excess convergence with an equivalent amount
of divergence.
MYOPIC EYE

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A B
Far point
Distance << Infinity (< 20 feet)
A and B are conjugate points
To accomplish this, the far point of myopic eye is just anterior to
the corneal plane. Rays from this plane are still quite divergent
when they reach the eye. This divergence offsets the excess
convergence that is built into the myopic eye.

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A B
Far point
A and B are conjugate points
LOW MYOPIA
A B
Far point
A and B are conjugate points
HIGH MYOPIA
So, this is the
reason that why
near-sighted
person see things
clear at near
(specially at their
far point) but not
at distance.

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A
A and B are conjugate points
Parallel rays from infinity (vergence = 0)
In hyperopic eye, rays from infinity never meet- they run out of the eye ball first. Similar to
myopic eyes, rays form a blur circle at the retina. We can say the hyperopic eye is too short
for its converging power or has a little converging power for its length.
To be conjugate with the retina, the far point of hyperopic eye must contribute convergence
to compensate for this lack of converging power.
HYPEROPIC EYE

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A
B
Far point
A and B are conjugate points
To accomplish this, the far point of hyperopic eye is behind the corneal
plane. It contributes convergence to make up for the inadequate
convergence for the hyperopic eye. Absence of correction or
accommodation make farsighted person out of focus at every distance.

10. Prepared by: Qurat-Ul-Ain