The document discusses the anatomy and optics of the eye. It describes the structure of the eyeball including the sclera, choroid, ciliary body, iris, lens, vitreous humor, and retina. It explains how light enters the eye and is refracted by the cornea and lens to form an inverted image on the retina. Common refractive errors like myopia, hyperopia, and astigmatism that result from abnormal refraction are also outlined.
3. INTRODUCTION
Vision- important special sense
Performed by eye balls
Situated in a quadrilateral pyramid shaped bony
cavity- orbit
Well protected by eyelids and extraocular
muscles
4.
5. There are some species in animal
kingdom which doesn’t have eyes to see
10. HISTORY
A.D. Galen – Retina
Euclid – Geometrical optics
Benjamin Franklin – Spectacles
Leonardo Da Vinci – Lens
Thomas Young, Von Helmholtz - Color vision
16. EYE DEVELOPMENT
Begins at 3 weeks & continues upto 10 weeks.
Derived from neuroepithelium, surface
ectoderm, neural crest and mesoderm.
Neuroepithelium - retina, ciliary body, iris,
optic nerve.
Surface ectoderm- lens, corneal epithelium,
eyelid.
Extra cellular mesenchyme- sclera, cornea,
blood vessels, muscles, and vitreous.
17. STRUCTURE OF EYEBALL
The anteroposterior diameter- 24 mm
Volume : 6.5 ml
Weight : 7 g
Shape- oblate spheroid
It has 3 layers :
Outer- fibrous sclera and cornea
Middle- uveal tract- vascular and
pigmented
Inner – retina- nervous coat
22. The average diameter 11 – 12 mm
Thickness center 0.52 mm
periphery 0.67 mm
Has 5 layers
Epithelium
Stratified squamous
Highly proliferative
Regenerate & heal rapidly
Bowman’s membrane
Heals with a scar
Stroma
Collagen fibrils
90% of thickness
23. Descemet’s membrane
Resistant to infection
Can regenerate
Endothelium
Prevents excess hydration of cornea
Keratitis
Corneal abrasion
Corneal ulcer
Corneal transplant-most successful one
24. Lacrimal gland
Secretes tear
Keeps cornea moistened
Contain lysozymes, antibodies
Blinking- spread tears
Basal secretion-1ml in 24 hrs
Regulation of stromal water-
clarity of vision
25.
26. Choroid
Lines the inner aspect of sclera
Provide nourishment to eye structures
Membrane of bruch- inner side
Supra choroidal space-b/w choroid & sclera
Chromatophores
Albinism
Choroiditis
Choroidal detachment
27. Ciliary body
Ciliary muscle & ciliary processes
Ciliary muscle-meridional,radial & circular
Ciliary body attaches to suspensory
ligaments
Ciliary processes secrete aqueous humor
Cyclitis
30. Aqueous humor
Protein free clear fluid
Source-ciliary process
Ultrafiltration, diffusion,
active transport
Nutrient for lens & cornea
Rich in ascorbic acid
Formed in posterior
chamber poured into
anterior chamber
through pupil
31. Maintains IOP
Absorbed by trabecular
meshwork & drained into
schlemn canal
Open angle glaucoma
Closed angle glaucoma
Lens
Biconvex
Avascular
Highly elastic-collagen
fibrils
Converge light rays &
focus on retina
32. Protein- alpha crystalline
At rest- lens ligaments
stretched- anterior
surface is less convex
Opacity of lens- cataract-
immature /mature
Absence of lens- aphakia
34. Retina
Very thin- 200 μm
10 layers, from outer to inner
1.Layer of pigment epithelium
2. Layer of rods and cones
3. External limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Layer of ganglion cells
9. Layer of nerve fibers
10. Internal limiting membrane.
35.
36. Surrounds the vitreous
Terminates at ora serrata
Pigment epithelium
Rich in melanocytes
Prevents scattering of light
Phagocytosis
Store vitamin A
Albinism- lack of melanin
Nystagmus, photophobia, defective vision
38. Diabetic retinopathy
Retinal detachment
Retrolental fibroplasia/ Retinopathy of Prematurity
(ROP)
Macula lutea
Yellow spot
1-2 mm
Fovea centralis
0.4 mm
Only cones
Maximum visual acuity
Ratio of ganglion to cone cell 1:1
39.
40. Optic disc
3mm medial to & above
posterior pole
No photoreceptors
Blind spot- at temporal
visual field
White in colour-
myelinated nerves
Fundus
Red background
Arteries readily visible
Diagnosing
HT,DM,atherosclerosis
51. OPTICS OF EYE
Image formed on retina by
Refraction of light rays by
cornea and lens
Ciliary muscle activity-
accommodation of lens
Change in pupil size by iris
muscles
52.
53.
54. Principal axis of the lens
The line joining the centers of the two lens
surfaces
Optical center/ Nodal point of lens
Point on the principal axis through which
light rays pass without being deviated.
7 mm behind anterior surface of cornea
55. Principal focus
When parallel rays
of light strike the surface
of the lens, they
converge to meet at a
point behind the lens
Focal distance
The distance
between the optical
center of a lens and the
principal focus
56. The refractive power of lens
It is the reciprocal of the focal distance
of a lens in meters.
expressed in diopters (D)
greater the lens curvature, greater the
refractive power
Refraction takes place at
cornea
both surfaces of the lens
Total refractive power of eye = 60 D
43 D by cornea
17 D by lens
57. When the head is immersed in water, the
refractive power by cornea= zero, since water
has the same refractive index as cornea.
Schematic eye/reduced eye
Nodal point 7mm
Eyeball length=24 mm
Focal length=24-7
=17
Refractive power of lens= 1
Focal length( in metres)
=1000
17
=59 D
61. Accommodation
Cornea-fixed structure
Normal resting eye- ciliary muscle relaxed
During accommodation
Ciliary muscle contracts
Suspensory ligaments relax
Lens becomes more convex
Visual axis converges
Pupil constricts
62. To focus an object present within 6
m, the eye has to increase its refractive
power, a process called accommodation,
in which the curvature of the lens is
increased.
Near point- The nearest point to the eye, at
which an object can be clearly seen
The maximum accommodation ability
of the eye decreases throughout life
lens-harder, progressive loss of
elasticity.
66. Size of pupil
decreases chromatic and spherical
aberration by eliminating the peripheral
rays
increases the depth of focus
Bright light-pupil constricts-2 mm
Dark- pupil dilates- 8 mm
67. ERRORS OF REFRACTION
Emmetropia
The refractive condition of a normal
eye, in which the parallel rays of light from
a distant object are focused on the retina
without accommodation
Emmetropic eye
Ametropia
If the refractive state differs from the
normal, in which parallel rays are focused
in front or behind the retina resulting in a
blurred image.
68. Amblyopia ex anopsia
Occurs in children, one of the image is
suppressed, causing loss of vision in one
eye.
STRABISMUS/ SQUINT
69. Ametropia is of three types
Myopia
Hypermetropia
Astigmatism
May be due to abnormality in
Axial length of the eye
Refractive power − Curvature of the
surface of the cornea or the lens
Refractive indices of the media
Position of the lens
70.
71. Myopia/ Short sightedness
A refractive error in which parallel rays of light
from a distant object are brought into a focus in
front of the retina when the accommodation is at
rest
Causes
Genetic
Acquired
More close work
AP diameter of eye increased
Correction
Biconcave lens- minus lens
72. Hypermetropia (Far-sightedness)
A refractive error in which parallel rays
of light from a distant object are brought into a
focus behind the retina when the
accommodation is at rest
Decreased anteroposterior diameter of
the eye
Correction
Biconvex lens- plus lens
73. Astigmatism
A refractive error in
which parallel rays of light
from a distant object
cannot converge to a
point focus on the retina
due to unequal
refraction at different
meridians.
74.
75. Causes
Corneal surface is not perfectly
spherical, the curvature of one meridian
differs from the other.
Light rays are focused at different
points on the retina causing blurring of
image.
Lens curvature- not uniform or lens-
pushed out of alignment.
Correction- Cylindrical lens.
76. Presbyopia
Near point of vision recedes beyond the normal
reading or working distance due to progressive loss
of plasticity of the lens
Physiological phenomenon
Above 40 years
Normal Near point of accommodation 25-33 cm
Correction
Convex lens-plus lens
For both distant & near vision
Bifocal lens