Theme 6: Optics of Refractive Error

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Theme 6 Optics of Refractive Error

• Concept of Refractive Error.
• Types of Refractive Error Axial and Cylindrical.
• Clear vision zone of an ametropic eye.
• Retinal image of an ametropic eye.

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Concept of Refractive Error
Emmetropic Eye Vision of objects at infinity is
clear without accommodation. Ametropic Eye
Vision of objects at infinity is blurry without
accommodation

EMMETROPIC
AMETROPIC
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Concept of Refractive Error

• Classification

SPHERICAL REFRACTIVE ERRORS -All of the
surfaces of the eye are spherical - Equal power
for all meridians
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Concept of Refractive Error

• Classification

REFRACTIVE ERROR ASTIGMATISMS - Part of the
surface of the eye is not spherical - Different
power in the different meridians
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Concept of Refractive Error

• Classification

SPHERICAL ERRORS MYOPIA F in front of the
retina HYPEROPIA F behind the retina
HYPEROPIA
MYOPIA
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Concept of Refractive Error
The far point is the conjugate of the retina for
nul accommodation

X X P
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Concept of Refractive Error
For the far point
MYOPIA far point in front of the eye (Rlt0)
HYPEROPIA far point behind the eye (Rgt0)
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Concept of Refractive Error

• MYOPIA

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Concept of Refractive Error

• MYOPIA

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Concept of Refractive Error

• HYPEROPIA

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Concept of Refractive Error

• HYPEROPIA

Near Far
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Types of refractive error Axial and Spherical

• Optic Formula for refractive error

For the emmetropic eye R0
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Types of refractive error Axial and Spherical

• Optic Formula for refractive error

Refractive component
Axial component
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Types of refractive error Axial and Spherical

• Optic formula for refractive error

P L R
M. Ax. PoaPo xgtxo Rlt0
M. Ref. PoagtPo xxo Rlt0
H. Ax. PoaPo xltxo Rgt0
H. Ref. PoaltPo xxo Rgt0
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Types of refractive error Axial and Spherical

• Relation between axial longitude and refraction

Emmetropic Eye
Ametropic Eye
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Types of refractive error Axial and Spherical

• Relation between axial longitude and refraction

P60 D n1.336 R1D ?x0.36mm R3D ?x? 1
mm
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Clear vison zone of an ametropic eye
Amplitude and accommodation range of the
ametropic eye

The amplitude of the ametropic eye is practically
the same as the emmetropic eye
Emetrope
Ametrope
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Clear vison zone of an ametropic eye
Amplitude and range of accommodation of an
ametropic eye

Range of accommodation
Emetrope
R Am ZVN
0 5 -?, -20cm
0 3 -?, -33cm
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Clear vison zone of an ametropic eye
Range of Accommodation

Myope
R Am ZVN
-2 5 -50, -14cm
-2 3 -50, -20cm
-4 5 -25,-11cm
-4 3 -25,-14cm
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Clear vison zone of an ametropic eye
Range of Accommodation
Hyperope
R Am ZVN
2 1 50, 100cm
4 3 25,100cm
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Clear vison zone of an ametropic eye
Range of Accommodation

Hyperope
R Am ZVN
2 5 50, -33cm
4 5 25,-100cm
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Retinal image of an ametropic eye

• Point Object

• Point image if the object is situated in the
  clear vision zone

• Blur Circle if the object is outside the clear
  vision zone

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Retinal image of an ametropic eye

• Point Object

Blur Circle
?PE diameter pupil entrance X
object vergence P Eye Power
R Refraction
Si R ? ? ? ?
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Retinal image of an ametropic eye

• Extended Object

? CLEAR IMAGE
Lagrange-Helmholtz Invariant (applied to H and H)
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Retinal image of an ametropic eye

• Extended Object

? CLEAR IMAGE
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Retinal image of an ametropic eye

• Extended Object

? BLURRY IMAGE
b pseudo-image size ? blur circle size
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Retinal image of an ametropic eye

• Relation of emmetropic eye and ametropic eye

Refractive Ametropia (R Poa Po)
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Retinal image of an ametropic eye

• Relation emmetropic eye ametropic eye

Axial Ametropia (Poa Po)
R yam/yem Rlt0 yam/yem Rgt0
1 1.017 0.984
5 1.091 0.923
10 1.200 0.857