The document summarizes key optical structures and properties of the eye. It describes the cornea as having a convex shape that refracts light and protects the eye. It then discusses the aqueous humor, crystalline lens, and vitreous humor, noting their roles in refraction due to differences in density. Schematic and reduced eye models are presented, including cardinal points and refractive indices. Common refractive errors like myopia and hyperopia are also outlined.

1. OPTICS OF OCULAR
STRUCTURE
1

2. CONTENTS :::
O1.Cornea
O2.Corneal curvature and
thickness
O3.Aqueous humor
O4.Crystalline lens
O5.Curvature of lens
O6.Vitreous humor
O7.Schematic and Reduced eye
O8.Axial and Axis of the eye 2

3. CORNEA
INTRODUCTION---
O Cornea is a transparent, avascular, watch-glass like
structure.
O It forms 1/6th of the outer fibrous coat of eyeball.
O Cornea is a anterior smaller sphere.
O Originally the cornea was considered of five distinct
layers.
O Anterior to posterior these are ---
1. Epithelium
2.Bowmen’s membrane
3.Corneal stroma ( substantia propia )
4.Descemet’s membrane
5.Endothelium
3

4. DIMENSION -
Surfaces-
O 1. Anterior surfaces , is elliptical in shape.
Horizontal diameter-- - 11.75 mm
Vertical diameter------- 11.00 mm
O 2. Posterior surfaces , is circular in shape.
Average diameter—11.5 mm
O Thickness---
0.52 mm ( at centre )
0.67 mm ( at peripheri )
O Radius of curvature-
Anterior curvature ---- 7.8 mm
Posterior curvatire----- 6.5 mm
4

5. O Refractive power ---
Anterior surfaces ------- +48 D
Posterior surfaces----- -5 D
Total power of cornea ---- +43 D
O Refractive index----- 1.376
Function-
O To act as a powerful refracting surface that
transmits light into proper image formation.
O To help in refraction.
O To protect the intraocular content.
O Wound repair after anterior segment surgey or
trauma.
5

6. Refraction through the cornea –
OCornea cause convergence of light rays
have convex surfaces.
OThe cornea plays a major role in ocular
refraction with power of about 40-45D
,because there is a huge difference in
refractive indices of air (1.0) and cornea
(1.376).
OIn the eye ,cornea mainly works as single
refracting surface.
OCornea has homogenous material with
very less thickness;hence works as single
unit.
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7. 7

8. AQUEOUS HUMOUR
INTRODUCTION---
O The aqueous humour is a transparent watery fluid
similar to the water.
O Maintanance of IOP and pathophysiology of
glaucoma revolves around the aqueous humour
dynamics.
O It is similar to plasma but containing low protein
concentration.
O It is secreted from ciliary epithelium and a structure
supporting the lens.
O It fills both anterior and posterior chamber of the eye.8

9. The aqueous humour is involved with virtually all
portions of the eye ,although the principal ocular
structure concerned with it are :
O Ciliary body
O Posterior chamber
O Anterior chamber
O Angle of the anterior chamber
O Aqueous out-flow system
9

10. Physiochemical properties :
OVolume – About 0.31ml (0.25ml in ant.
Chamber and 0.06ml in post. Chamber )
ORefractive index -1.336
ODensity – its viscosity is 1.025 -1.040
OOsmotic pressure – 3-5 mOsm/l
OpH - 7.2
ORate of formation – 2.3 ul/min.
10

11. Refraction through the Aqueous humour
–
O A light rays after passing through the cornea ,light
enters the Aqueous humour.
O Where it is refracted again towards the centre of
the eye.
O This refraction is due to the difference in density
between the cornea and aqueous humour.
O Aqueous flow from the post. Chamber to
ant.chamber.
O The aqueous humour plays a major role in
refraction,because there is a huge difference in
refractive indices of air (1.0) and aqueous humour
(1.336).
11

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13. CRYSTALLINE LENS
INTRODUCTION—
O Lens is a transparent, biconvex, structure of
eyeball.
O Lens placed between iris and vitreous in a
saucer shaped depression ,the pateller fossa.
O Lens is cyrstalline structure , that is avascular
and is devoid of nerves , and connective tissue.
O Lens is an asymmetric oblate spheroid
structure.
O Lens is suspended by suspensory ligament or
zonulus.
13

14. Lens consist of 3 layers---
O Lens capsule
O Lens epithelium
O Lens fibre
14

15. Dimension –
O Equatorial diameter---- 6.5mm ,(at birth ) , increases 9—10
mm, (remain constant)
O Thickness---- 3.5mm (at birth ), 5mm (at extreme of age ).
O Weight----- 135 mg ( at 9 years), 255 mg (at 40-80 years ).
Surfaces— it has two surfaces.
Anterior surfaces –less convex than the posterior.
Radius—10 mm
Posterior surfaces---more curved than the anterior
Radius----6 mm
O Refractive index ------ 1.39-1.42 an average
O Total dioptric power---- 16-17 D
15

16. Refraction through the Crystalline lens –
O Lens causes convergence of light rays ,have
convex surfaces.
O Crystalline lens in the eye lies between aqueous
and vitreous humour ,hence refractive power of
lens is half compared to refractive power of cornea
,i.e. nearly 16-17D.
O Lens is thick and its material is also not
homogenous in nature,hence lens simply does not
work as two refractive surfaces (Ant. and Post.)
rather it works as multiple refracting surfaces.
O Lens consist of several layers with different
refractive indices ,and curvature is also different for
different layers.
16

17. 17

18. VITREOUS HUMOUR
INTRODUCTION—
O The vitreous is an inert ,transparent ,colourless,jelly
like that provides a clear optical medium as well as
a pathway of nutrient utilized by the lens ,ciliary
body ,and the retina.
O The vitreous is clear avascular filling the space
bounded by the lens /retina and optic disc.
O It occupy approx. 80% of the volume of the globe.
O It serves the optical fuinction and also acts as
important supporting structure for the eyeball.
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19. 19
Vitreous gel consist of
delicate meshwork of type
2 of collagen fibrils
interpersed.
It may be divided into 3
parts.
1. Hyaloid layer or
membrane
2.Cortical vitreous
3.Medullary vitreous

20. Physiochemical properties :
O Volume – 4 cc(ml)
O Weight – 4g
O pH – 7.2
O Water – 99%
O Refractive index - 1.336
O Osmotic pressure – 5-8 mOsm/l
O Density – its viscosity is 1.030 -1.045
Function –
One of the refractive media of the eye.
Support of intraocular structure (lens and retina).
Maintanance of spherical shape of eye. 20

21. Refraction through the vitreous humour –
O A light rays after passing through the lens ,light
enters the Vitreous humour.
O Where it is refracted again towards the central part
of the retina.
O This refraction is due to the difference in density
between the lens and vitreous humour.
O The vitreous humour plays a major role in
refraction,because there is a difference in refractive
indices of lens (1.39 – 1.41) and vitreous humour
(1.336).
21

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23. Physiological optical defect of eye –
Diffraction of light
 Spherical Aberrations
 Chromatic Aberration
 Oblique Aberration
 Coma
 Decentring
 Distortion
23

24. Pathological optical defect (Refractive
error ) of eye –
 Myopia (short sightedness)
 Hypermetropia (long sightedness)
 Astigmatism
1.
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25. 2
25
2.
3.

26. Absence of optical element of the eye –
O A condition where crystalline lens is absent, its
termed as Aphakia.
O Common cause of aphakic are congenital disorders
or post-surgical removal of crystalline lens.
O Aphakia causes a refractive error in terms of high
degree hypermetropia.
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27. SCHEMETIC AND REDUCED EYE
SCHEMETIC EYE
INTRODUCTION –
O Scientist Gauss put forward the three pair of
cardinal points,all lying on the principal axis of the
eye.
O Tscherning and Helmholtz contributed a lot to
understand the optics of human eye.
O Gullstrand who presented the most authentic model
of schemetic eye for better understanding of optics
of the eye.
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28. O Anterior surface of cornea is used as refrence point
for calculation of distance.
O Two principal foci : Anterior (F1),and Posterior
(F2),are situated 15.7mm in front of and 24.4mm
behind the anterior surface of cornea,repectively.
O Two principal points : Anterior (P1),and Posterior
(P2),are situated at 1.35mm and 1.60mm away
from the anterior surface of cornea,respectively.
Two nodal points : First (N1),and Second (N2),are
located 7.08mm and 7.33mm behind the anterior
surface of cornea,respectively.
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29. O Refractive indices of various refracting surfaces
when accommodation is relaxed are-
O Cornea – 1.376
O Aqueous and Vitreous humour – 1.336
O Crystalline lens cortex – 1.386
O Crystalline lens nucleus – 1.406
O Dioptric power or refracting power of the eye while
accommodation is minimum and maximum is –
O Complete eye – 58.64 D and 70.57 D,respectively.
O Corneal system – 43.05 D and 43.05
D,respectively.
O Lens system – 19.11 D and 33.06 D,respectively. 29

30. 30

31. REDUCED EYE
INTRODUCTION-
O Listing describes the reduced eye .
O In reduced eye also,all the distances of various
cardinal points are calculated from anterior surface
of cornea as reference point.
O Anterior focal point (F1),and posterior focal point
(F2), are situated at 15.7mm in front and 24.4mm
behind the anterior surface of cornea ,respectively.
O Principal point (P) is located 1.5mm behind the
reference plane (anterior surface of cornea ).
31

32. O Nodal points (N) is placed 7.2mm and posterior
focal length is 22.9mm .
O Uniform refractive index of ocular structure is 1.336
.
O Total dioptric power of the eye is 58.2 D.
32

33. AXES OF THE EYEBALL
1.Optical axis-
O line passing through the centre of the
cornea(p),centre of the lens(n),and meet the
retina(r) , on the nasal side of the fovea
2.Visual axis—
OLine joining the fixation point(o),nodal point
(n),and the fovea(f).
3.Fixation axis ---
O line joining the fixation point(o),and the
centre of rotation(c)..
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34. VISUAL ANGLE
34

35. 1.Angle alpha -
OIt is angle(ONA), formed between the optical
axis (AR), and visual axis (OF), at the nodal
point (N).
2.Angle gamma -
Oit is angle (OCA) between the optical axis
(AR),and fixation axis (OC),at the centre of
rotation of the eyeball(C)
3.Angle kappa -
Oit is angle (OPA) ,between the visual
axis(OF) and pupillary line (AP),
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