ANATOMY AND PHYSIOLOGY
OF THE EYE
Kay Ford, C.O.T., C.O.E.
VISTAR EYE CENTER
Roanoke, VA
OUTLINE OF PRESENTATION
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OCULAR ADNEXA
LACRIMAL SYSTEM
BONY ORBIT
ANTERIOR SEGMENT
POSTERIOR SEGMENT
EXTRAOCULAR MUSCLES
VISUAL PATHWAY
CONCLUSION AND RESOURCES
OCULAR ADNEXA
• Eyelids, eyebrows, eyelashes, accessory
glands and lacrimal (tear) apparatus.
EYELIDS
• Primary function is to protect the eye from bright
light and foreign objects.
• They protect the cornea from drying by blinking
to spread the tears over the eye surface, aids
flow of tears out of the lacrimal gland, and
facilitates the drainage of tears into the
nasolacrimal system.
• Landmarks are the medial canthus, lateral
canthus, the plica semilunaris (third eyelid) and
the caruncle.
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Eyelids have three layers:
1. Outer layer of skin
2. Middle layer of fibrous tissue and muscle. Within the
middle layer of the upper and lower eyelids is a
dense, plate-like framework, the tarsus or tarsal
plate. Also located in the middle layer is the
orbicularis oculi, a circular muscle that closes the
eye when it contracts (winking). A second muscle,
the levator palpebral superioris, is attached to the
upper tarsal plate.
3. Inner layer of tissue called conjunctiva, a thin,
translucent mucous membrane that lines the outer
front surface of the eyeball, except for the cornea.
CONJUNCTIVA
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The conjunctiva is an epithelial membrane
which covers the anterior sclera and continues
to the back surfaces of the lids to form a
conjunctival sac. There are three portions of
the conjunctiva:
1. Bulbar: covers the white sclera
2. Palpebral: covers the backside of the eyelid
3. Fornix: where bulbar and palpebral meet (loose
pocket called the fornix or cul-de-sac).
LACRIMAL APPARATUS
• The orbital structures that produce tears and the ducts
that drain the excess fluid from the front of the eyes into
the nose. The lacrimal tears are produced by the lacrimal
gland, located under the frontal bone at the upper-outer
angle of the orbit. These tears then flow through the six
to twelve lacrimal canals or ducts into the conjunctival
sac. The tears drain from the sac into the upper and
lower punctum (the small holes in the eyelid margins)
into the upper and lower canaliculus. The canuliculi take
the tears into the lacrimal sac and then into the
nasolacrimal duct, then on into the nose. This explains
why you need to blow your nose when you cry.
EYEBROWS
• Each eyebrow is a thickened ridge of skin
with short hairs which diverts perspiration
from running into the eye.
EYELASHES
• The eyelashes also protect the eyes.
Sebaceous glands at the base of each
lash are called glands of Zeis. These
glands produce a lubricating fluid. An
inflamed gland causes a stye or
hordeolum.
• Chronic condition called blepharitis is
inflammation of the lids.
ACCESSORY GLANDS
• The accessory glands are the meibomian
glands, ciliary glands, and glands of Krause and
Wolfring.
• Meibomian glands are sebaceous glands which
secrete an oily substance onto the lid margins
that help prevent the lids from sticking. A blocked
meibomian gland results in a chalazion.
• The ciliary glands are sweat glands while the
glands of Krause and Wolfring are accessory
lacrimal glands.
BONY ORBIT
• The bony orbit provides protection, support and
attachment for muscles and the eyeball.
• Frontal, ethmoid (the weakest), sphenoid, zygomatic (the
strongest), maxilla, lacrimal and palatine (the smallest)
• Protect the eyeball from injury.
• Many openings to transmit arteries and/or veins and
nerves to and from the orbit.
• Types of openings are fissures (crevices) and cracks and
foramina (holes).
• The major openings are the optic foramen, which
contains the second (II) cranial nerve (optic nerve , and
the supraorbital fissure, which contains the fourth (IV)
cranial nerve known as the Trochlear nerve.
THREE LAYERS OF THE
EYEBALL
1. FIBROUS LAYER
This is the outer layer of the eyeball. It has two layers:
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CORNEA
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SCLERA
CORNEA
The cornea is a transparent organ without
any blood vessels. Its primary function is
refraction of light rays. The cornea has a
refractive power of about +45.00 diopters.
It is composed of 5 layers.
**More about the cornea later in this
presentation.
SCLERA
• The sclera is white in color. Its primary
function is protection of the eyeball. It
connects to the cornea at the area called
the limbus and is pierced posteriorly by the
optic nerve. It acts as the insertion points
for the six extraocular muscles.
2. VASCULAR LAYER
• Also known as the uveal tract. This layer
functions to supply nutrition to other layers of the
eye. It is the middle layer of the eye and is
situated between the sclera and retina. It is
composed mostly of blood vessels and capillary
nets.
• The uveal tract has 3 parts:
Choroid
Ciliary Body
Iris
CHOROID
• The choroid is located posterior to the
ciliary body and iris. It is attached firmly at
the optic disc and ora serrata. It is the
most vascular portion of the vascular layer
and is drained by the vortex veins.
CILIARY BODY
• The ciliary body is located near the base
of the iris and posterior to it. It is
composes of blood vessels and the ciliary
muscle fibers. Its primary function is to
alter the shape of the crystalline lens by
suspensory ligaments called the zonules
of Zinn. It also produces aqueous humor
(more on this later).
IRIS
• The iris is the most anterior portion of the
vascular layer. It gives the eye its color (i.e. blue,
brown or hazel).
• It consists of blood vessels, pigment and muscle
tissue.
• The hole in the center is called the pupil.
• The pupil regulates the amount of light that
enters the eye. It is small in bright light
(constricted) and large in dim light (dilated).
• As we get older, the pupil gets smaller, resulting
in the need for more light when reading.
3. NERVE LAYER
• The nerve layer is the retina. It is the innermost
layer of the eye and is a direct extension of the
brain and is normally transparent. The
attachments are most firm at the ora serrata and
around the optic nerve head (optic disc). When
injured, it cannot repair itself. An injured retina,
such as a retinal detachment, is best viewed by
a dilated fundus exam (DFE).
• The retina has 9 layers.
RECEPTORS
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The retina is composed of two visual
receptors, rods and cones.
Cones produce color vision and give improved
acuity. Cones are used in day vision under
normal and high levels of illumination. Day
vision is known as photoptic vision.
Rods produce black and white vision. Rods
function in dim light or low levels of illumination
such as during nighttime. Night vision is known
as scotopic vision.
LANDMARKS
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There are four major landmarks in the
retina:
1.
2.
3.
4.
Macula
Fovea
Optic nerve head
Ora serrata
MACULA
• The macula is the optical center of the
retina. It appears redder in color when
compared to the orange appearance of a
the other area of the retina.
FOVEA
• The fovea is a depression located in the
center of the macula. It only has cones
and is the area of best vision.
OPTIC NERVE HEAD
• The optic nerve head is the point of exit of
the optic nerve and appears yellow when
compared to the orange appearance of the
rest of the retina.
ORA SERRATA
• The ora serrata is the most anterior portion
of the retina and is nearly all rods.
OCULAR MEDIA
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Cornea
Aqueous Humor
Crystalline Lens
Vitreous Humor
ANTERIOR CHAMBER
• Bordered anteriorly by the cornea and
posteriorly by the iris.
CORNEA
The cornea is a transparent organ without
any blood vessels. Its primary function is
refraction of light rays. The cornea has a
refractive power of about +45.00 diopters.
It is composed of 5 layers.
CORNEA
• The cornea is a transparent organ without
any blood vessels. Its primary function is
refraction of light rays. The cornea has a
refractive power of about +45.00 diopters.
It is composed of 5 layers:
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Epithelium
Bowman’s Membrane
Stroma
Descemet’s Membrane
Endothelium
CORNEAL LAYERS
• EPITHELIUM – Outermost layer, about 5 cell
layers thick. This layer heals very quickly when
injured and does not scar.
• BOWMAN’S MEMBRANE – Second layer. Will
scar when injured.
• STROMA – Middle layer that comprises about
90% of the cornea.
• DESCEMET’S MEMBRANE – Serves as barrier
for fluids.
• ENDOTHELIUM – Innermost layer – one cell
layer thick. Cells do not regenerate if injured.
POSTERIOR CHAMBER
• Bordered anteriorly by the iris and
posteriorly by the front face of the vitreous.
AQUEOUS CHAMBER
It is the space in the eye located between
the cornea and the crystalline lens. It is
divided into the anterior chamber and the
posterior chamber.
AQUEOUS HUMOR
• The aqueous chambers are fills with aqueous humor,
which is manufactured by the ciliary body. The product is
clear, colorless and has a watery consistency (99%
water).
• Aqueous humor’s functions are refraction of light, control
of intraocular pressure (IOP), and nourishment of the
posterior surface of the cornea and the crystalline lens. It
flows from the posterior chamber through the pupil into
the anterior chamber. It drains through the angle formed
by the cornea and iris to the trabecular meshwork.
• The trabecular meshwork is a grate-like
structure that leads into the Canal of Schlemm,
which is circular and lies under the limbus.
Pressure in the eye (IOP) is related to the
production and outflow of aqueous humor.
• Elevated pressure in the eye (IOP) can cause
diseases called glaucoma. There are more than
20 different types of glaucoma.
• Glaucoma is associated with elevated pressure,
changes in the optic disc, and defects in the
visual field and can be blinding.
• IOP increases if the angle is blocked, if the
flow of aqueous humor is blocked, or if the
aqueous input is greater than the output.
• Treatment consists of improving outflow or
by decreasing the production of aqueous
humor by medication and/or surgery.
CRYSTALLINE LENS
• The crystalline lens is transparent and biconvex.
It is composed of a capsule, cortex, and nucleus.
• It is about 10 mm in diameter and 5 mm thick. It
is suspended from the ciliary body by the
zonules of Zinn. It is approximately +12.00
Diopters in power.
• Lens primary functions are refraction of light and
accommodation (adjusts for near and far vision).
• Presbyopia is the loss of accommodation is the
loss in flexibility of the lens which happens
around age 40 and causes poor close vision.
• The lens contains a large amount of protein.
Changes in the protein causes the lens to lose
transparency. This is called a CATARACT.
• The cataract can form in any part of the lens or
in multiple locations (nuclear, cortical, anterior or
posterior subcapsular or a combination).
• Cataract surgery is done to remove the cloudy
contents of the lens and is almost always
replaced by a man-made intraocular lens,
contact lens or aphakic glasses. Aphakia is the
absence of a lens.
VITREOUS CHAMBER
• The vitreous chamber (large cavity of the eye) is
filled with gel-like substance located behind the
crystalline lens. It is encased by the vitreous
membrane and cannot be reproduced. It refracts
the light and is the internal support of the eye.
• Floaters are spots in your vision usually caused
by cellular debris in the vitreous.
• Surgery is sometimes required to repair rupture,
hemorrhage of leakage of the vitreous.
EXTRAOCULAR MUSCLES
• The extraocular muscles (EOMs) are
organized into an umbrella-like bundle
among the orbital fat, orbital blood
vessels, and nerves.
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Six muscles associated with eye
movement:
1.
2.
3.
4.
5.
6.
Superior Rectus (SR)
Inferior Rectus (IR)
Medial Rectus (MR)
Lateral Rectus (LR)
Superior Oblique (SO)
Inferior Oblique (IO)
• The muscles are coordinated so that
double vision does not occur.
• Each eye can rotate on three different
axes due to the six muscles.
Ocular Motility Alignment
• Heterotropia – both eyes do not point in the
same direction when both eyes are open. One
eye suppresses to eliminate possibility of double
vision )diplopia). The eye that is deviated most
of the time usually has poorer vision
(amblyopia). Terms also used for heterotropia
are strabismus, squint, crossed-eye, evil-eye,
and wall-eye. If unable to be corrected with noninvasive treatment, surgery is required to realign
the muscles involved (recession and/or
resection).
• Heterophoria – condition where both eyes
do not point in the same direction, but only
when one eye is covered. Eyes are
parallel when both are open. Usually no
invasive treatment is required.
• Orthophoria – Both eyes point in the same
direction when the eyes are open or
covered. (This is the normal.)
VISUAL PATHWAY
• The visual pathway is the path taken by nerve impulses
between the eye and the brain when retina is stimulated
by light.
• The visual pathway has seven structures: the retina,
optic nerve, optic chiasm, optic tract, lateral geniculate
body, optic radiations, and the visual cortex.
• When pathway is intact, the brain interprets what is seen
on the retina.
• Office procedure of visual field testing will map the
normal blind spot, and help to identify, locate and
quantify any defect along the visual pathway. Can be
used in diagnostic manner to differentiate between eye
pathology and source of defect.
Reference
• Ophthalmic Coding Coach
• By the American Academy of Ophthalmic
Executives
• Available through the American Academy
of Ophthalmology and the American
Medical Association
• ISBN 978-1-61525-274-9
THANK YOU