Chapter 7 The Pupil

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Chapter 7The Pupil
Page 7.3
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Q1. Munsons sign is

• an early sign of Friday Night Brachial Plexus
  Palsy
• the appearance of a whitish scar in the
  mid-inferior cornea in keratoconus
• the bulls-eye appearance of warmer colors in the
  inferior corneal topography in keratoconus
• the cone-like protrusion of the lower lid when a
  keratoconus patient looks down

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Q2. Which surgical procedure uses the greatest
thickness corneal hinge flap?

• LASIK (laser-assisted in situ keratomileusis)
• LASEK (laser assisted sub-epithelial
  keratomileusis)
• PRK (photorefractive keratectomy)
• INTACS (intracorneal ring segments)

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Q3. What is Javals Rule?

• an early precursor to the hand-held calculator
• the method Javal used to determine spectacle
  cylinder from keratometer readings
• a definition of the primary anterior corneal
  meridian as the one closer to horizontal
• an equation used to calculate total corneal
  astigmatism from keratometer readings

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Chapter 7, The PupilEntrance Pupil
Page 7.3
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Schematic Eye to Characterize EnP ExP

• Schematic Eye Requirements
• pupil in correct location
• optical elements separated either side of pupil
• Both criteria met by Simplified Schematic Eye
  (neither met by reduced eye no need to go to
  complexity of Exact Eye)

Page 7.3
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Entrance Pupil
Page 7.4
Main Objective 2 know how to locate the EnP and
find its diameter
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Locating the Entrance Pupil

• Entrance Pupil is the image of the real pupil
  through the cornea
• pupil is the object
• object space is aqueous
• image rays emerge through cornea into air
• To maintain sign convention - incident rays
  traveling from left to right ? must turn
  schematic eye around (pupil to left cornea to
  right)

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Locating the Entrance Pupil SSE
Fig 7.2, Page 7.4
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Locating the Entrance Pupil SSE
EnP
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Locating the Entrance Pupil
n i
nO
CRYSTALLINE LENS
AIR
AQUEOUS
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Locating the Entrance Pupil
EnP
n i
nO
CRYSTALLINE LENS
AIR
AQUEOUS
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EnP Position
Page 7.5
Fcornea
n i
nO
L ?371.11 D
CRYSTALLINE LENS
AIR
AQUEOUS
1.336
Object Vergence (Real Pupil)
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EnP Position
SSE Corneal Power
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Locating the Entrance Pupil
Fcornea 43.08 D
n i
nO
L ?371.11 D
CRYSTALLINE LENS
AIR
AQUEOUS
?3.6 mm
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EnP Position
L? ?328.03 D
Refract ray from Pupil through Cornea
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Locating the Entrance Pupil
n i
nO
L? ?328.03 D
CRYSTALLINE LENS
AIR
AQUEOUS
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EnP Diameter
Linear Magnification

• The EnP is 13 larger than the real pupil
• Shorter image distance means that the EnP is
  closer to the cornea than the real pupil

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Locating the Entrance Pupil
n i
nO
CRYSTALLINE LENS
AIR
AQUEOUS
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Exit Pupil
Page 7.8
Main Objective 3 know how to locate the ExP and
find its diameter
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Locating the Exit Pupil

• Exit Pupil is the image of the real pupil through
  the crystalline lens
• pupil (again) is the object
• pupil first encounters anterior crystalline lens
• but pupil plane and anterior cr. lens plane
  coincide
• significance?

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Refracting Pupil through Anterior Cr. Lens
Pupil at anterior cr. Lens ? object distance, ?
0 Significance? Start with finite distances if ?
?1 mm ? L ?1,000 D
if ? ?1 ?m ? L ?1,000,000 D if ? ?1 nm ?
L ?1,000,000,000 D
Apply vergence relation at anterior crystalline
lens (FAL 12.83 D) L? L FAL
?1,000,000,000 12.83 NO CHANGE (until
ninth significant figure)
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Locating the Exit Pupil

• Anterior crystalline lens will not change light
  path from pupil
• we are left with a single refraction through
  posterior crystalline lens surface
• pupil in crystalline lens medium ? object space
  
• light emerges through posterior lens into
  vitreous (image space)

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Locating the Exit Pupil SSE
Fig 7.5, Page 7.8
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ExP Position
Page 7.9
Object Vergence (Real Pupil)
Posterior Lens Surface Power
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ExP Position
Refract through Posterior Lens

• AS WITH THE ENTRANCE PUPIL
• Negative image vergence means divergent light
• Negative image distance means virtual image

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ExP Diameter
Linear Magnification

• The ExP is 3 larger than the real pupil
• Slightly shorter image distance means that the
  ExP is slightly closer to the posterior lens than
  the real pupil

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Locating the Exit Pupil
Distance from Cornea
?3.52 mm
?3.6 mm
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Path of the Chief Ray through the Eye
Page 7.10
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Path of the Chief Ray through the Eye
Fig 7.6 Page 7.10
OBJ
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Usual application of a chief ray ? for a given
incident chief ray (angle), where does it end up
hitting the retina (what angle)?
OBJ
This fully defines CR path
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Path of the Chief Ray through the Eye
?0 ? ??1 ? must find angular magnification of
chief ray
Page 7.10
Call final emergent angle of chief ray ??CR
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Angular Magnification of the Chief Ray
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Chief Ray vs. Nodal Ray for a Distant Off-axis
Object Point
Fig 7.7 Page 7.12
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Retinal Image Height and Chief Ray Path
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Chief Ray and Retinal Image Height - Ametropia
Fig 7.9 Page 7.15
This is blurred RI height according to the CR path
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Retinal Image Height and Chief Ray Path

• Chief Ray path gives correct blurred retinal
  image height because retinal blur circles are
  centered on their chief rays

OBJ
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Fig 7.10, Page 7.16
Chief Ray path gives correct blurred retinal
image height because retinal blur circles are
centered on their chief rays
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Chief Ray path gives correct blurred retinal
image height because retinal blur circles are
centered on their chief rays
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The nodal ray is therefore invalid when defining
blurred retinal image height
Chief Ray path gives correct blurred retinal
image height because retinal blur circles are
centered on their chief rays
For a small enough pupil diameter, the nodal ray
passes OUTSIDE the retinal blur circle
OBJ
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For a pinhole pupil (or pinhole aperture in front
of the pupil), the now clear retinal image is
exactly defined by chief ray path
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Fig 7.10, Page 7.16
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Fig 7.11, Page 7.17
CR also correctly defines blurred myopic RI
height
CR correctly defines blurred hyperopic RI height
(distance between centers of limiting blur
circles)