Eyes Anatomy & Physiology with Diagnostic investigation.

Anatomy of the eye
11/1/2011 2

The sensory organs of vision are the eyes.
The human eye is the organ which gives us the
sense of sight, allowing us to observe and learn
more about the surrounding world than we do
with any of the other four senses. We use our
eyes in almost every activity we perform,
whether reading, working, watching television,
writing a letter, driving a car, and in countless
other ways.

• Each eye is situated in the orbit- a bony cage. It
consists of upper & lower eyelids, the upper eye lid
covers a upper portion of the cornea but does not
overlap the pupil. The space between the two eyelids
is called aperture.
– With in the eyelids lie tarsal plates-firm strips of
connective tissue. Each plate contains a parallel roe of
meibomian glands, which open on the lid margin.

The eye is the organ of vision which is located in a
cone shaped cavity known as the orbit.
It is highly specialized & complex structure.
It receives & sends visual data to the cerebral
cortex for interpreting visual images.
Seven cranial nerves have connections to the
eyes. These are;
For vision – CN II.
Eye movement – CN III, IV & VI.
Papillary reaction – CN III.
Eyelid elevation – CN III.
Eyelid closure – CN VII.

 Brain stem connections permit coordinated eye
movement.
 The eye ball is situated in the bony socket or orbit.
 The eye ball is protected by: -
Orbit.
Eyelids (Upper & lower).
 Nerves & blood vessels that supply nutrients &
transmit impulses to the brain are also present with in
the orbit.
 Organized bands of muscles are attached to the
external eye ball.

• The conjunctiva is a clear mucous membrane with two visible
components. The first component, the bulbar conjunctiva
cover most of the anterior eyeball. It meets the cornea at the
limbus. The other component, the palpebral conjunctiva lines
the eyelids. The two parts/components merge in a folded
recess that permits the eye ball to move.
• The clear fluid called tear fluid protects the conjunctiva and
cornea from drying, has antimicrobial action and gives a
smooth optical surface to the cornea.
• The fluid comes from three sources, i.e. meibomian glands,
conjunctival glands, and the lacrimal glands. The lacrimal
gland lies with in the orbit, above and lateral to the eyeball.
The tear fluid after spreading through the eye drains into
lacrimal sac and further into the nose through nasolacrimal
duct.

• The eyeball is a spherical structure lined by three layers i.e. inner
retina, middle choroid and outer sclera that focuses light on the
retina.
• The size of the pupil is controlled by the muscles of the iris. Muscle
of the ciliary body controls the thickness of the lens allowing the eye
to focus on near or distant objects.
• The aqueous humour a clear fluid produced by the ciliary body,
circulates from the posterior chamber through the pupil to anterior
chamber, and drains out the canal of Schlemm. The circulatory
system helps to control pressure inside the eye. {intraocular tension}
• The posterior part of the eye that is seen by an ophthalmoscope is
often called the fundus of the eye.

The ciliary muscle changes the shape of the lens –
(this is called accommodation). It relaxes to
flatten the lens for distance vision; for
close work it contracts rounding
out the lens. Everyone will develop
an eye condition called presbyopia.
As we age, the ciliary muscle and
crystalline lens lose their elasticity.
This is why most people need
reading glasses by their 40's.

11
Muscles:-There are three muscles supplying
the eyelid.
a. Orbicularis: Oculi
Origin:– Lacrimal bone.
Insertion:- Deep in the facia around the lacrimal.
Function:- to close the eye lid & to screw up the eyes &
facilitate tear drainage.
Nerve supply:- Facial nerve (CN-VII).
Its paralysis cause lag-ophthalmas (Failure to
close eye).

Cont…d
12
b. Levator palpebral superioris
Origin:– around apex of orbit.
Insertion:– skin of upper lid & tarsal plate.
Function:– to lift the upper lid.
Nerve supply:– Oculomotor (CN-III).
Its paralysis cause ptosis (dropping of eye
lid).

Cont…d
13
c. Muller’s muscle
This is smooth muscle.
Origin:– Levator palpebral superiors.
Insertion:– Tarsal plate.
Function:– provide extra elevation to
the upper lid.
Nerve supply:– Sympathetic nervous
system.

Cont…d
14
c. Muller’s muscle
This is smooth muscle.
Origin:– Levator palpebral superiors.
Insertion:– Tarsal plate.
Function:– provide extra elevation to
the upper lid.
Nerve supply:– Sympathetic nervous
system.

Cont…d
15
Eyelids;
It is skin without subcutaneous fat.
It has 4 basic layers.
From anterior to posterior the layers are;
Skin & subcutaneous connective
tissue.
Muscle.
Tarsus .
Conjunctiva.

Cont…d
16
Functions of eye lids;
 Protect eye ball (globe).
 Lubricate anterior surface of globe (By blinking
the tear film spread over anterior surface).
Blood supply to the lid;
Lacrimal artery & vein.
Supra – orbital artery & vein (upper lid).
Superior & inferior medial palpebral artery & vein.

Cont…d
17
Lacrimal glands & Excretory System
Lacrimal glands
Location – Superiorly in a shallow depression of
frontal bone.
It has 2 parts: -
Orbital (lacrimal gland proper).
Numerous Excretory ducts emptying secretion to conjunctiva.
Mechanism of tear secretion is by: -
 Reflex – due to stimulation of trigeminal nerve.
 Psychogenic – central mechanism.

Cont…d
19
Accessory glands
– Krause’s gland located in the eye lid.
– Meibomian gland
• Basal tear secretion is constant & under
sympathetic nervous system control.

Cont…d
20
Lacrimal excretory system
Punctum (on posterior edge of lid margin) upper & lower
Upper & Lower canaliculi (Common Canaliculi)
Lacrimal sac (tear Sac)
Naso-lacrimal duct
Nose

Cont…d
21
Function of tear
Refraction:– to provide an optically smooth surface
to the cornea.
Lubrication of the front of eye ball.
Cleansing action by washing away dust particles
from the eye.
Protection from infection by secreting the enzyme
lysozyme, immuno-proteins & antimicrobial agents.

Eyes Anatomy & Physiology with Diagnostic investigation.

Cont…d
23
 Eye Ball;
 It is lined by 3 layers,
1. Outer protective layer
 It is fibrous layer.
 It consists;
A. Sclera
 It is the white part of the eye.
 Form outermost tissue of posterior & lateral (4/5)th aspects of eye
ball.
 It is continuous anteriorly with cornea.
 Maintains the shape of the eye & gives attachment to extra ocular
muscle of eye.
B. Cornea
 It is the anterior continuation of sclera.
 It is clear transparent & allow passage of light rays.
 It is convex anteriorly & is involved in refraction or bending light
rays to focus them on retina.
 It is highly sensitive.

The sclera is the white, tough wall of the eye.
It along with internal fluid pressure keeps the eyes
shape and protects its delicate internal parts.

The cornea is a clear, dome-shaped surface that covers
the front of the eye. Tears that flow over it and aqueous
humor in the chamber behind it keep it nourished. It
allows the light to enter the eyeball. The eyeball is
approximately spherical in shape with a diameter of
about 2.3 cm.

The pupil is the hole in the center of the iris that light
passes through. The iris muscles control its
size. It contracts in excess light and
expands in dimlight.

Cont…d
29
2. Middle layer
It is Vascular
organ.
It Consists;
A. Choroid
 Lines the posterior (5/6)th of inner surface of sclera.
 Highly vascularized.
 Light enters the eye through the pupil, stimulate the
nerve endings in the retina then is absorbed by the
choroid.
 Deep chocolate brown in colour.

The choroid is a layer of blood vessels between the retina and
sclera; it supplies blood to the retina.
It keeps the interior eye dark.

31
3. Inner layer
Retina
• Thin membrane lining back of eye
• Contains light sensitive cells
• Rods & cones
– Rods are sensitive to light
• 120 million rods
– Cones are sensitive to colors
• 6 million cones

Cont…d
32
A. Retina
It is nervous tissue layer.
Retina is especially adapted to be stimulated by light rays.
Composed of several layers of nerve cell bodies.
Rods & cones are layer highly sensitive to light.
 Macula
 It is an area of the retina situated to the temporal side of the optic disc.
 It contains a high concentration of cones.
 In its centre is the fovea centralis, a slight depression where only cones are
present.
B. Optic disc
 Contains no nerve cells, so the vision cannot take place here.
 This is known as the “blind spot”.

The retina is the film of the eye. It converts light rays
into electrical signals and sends them to the brain
through the optic nerve. The sides of the retina are
responsible for our peripheral vision. The center area,
called the macula, is used for our fine central vision and
color vision.

The retina is where most the problems leading to vision loss
Occur. Three of the leading causes of blindness, from retina
damage, are:
•Retinitis Pigmentosa,
•Macular Degeneration and
•Diabetic Retinopathy.

It is situated at the Centre of the retina.
Its function is to form an extremely clear image.

Each optic nerve has about 1.2 million nerve fibers.
This is the cable connecting the eye to the brain.

Cont…d
44
B. Ciliary body
 It is anterior continuation of the choroid &
consists ciliary muscle & secretary cells
(producing aqueous humor).
 It gives attachment to suspensary ligament
which, at its other end, is attached to the lens.
 The ciliary muscle controls the shape of lens for
focusing.

Cont…d
45
C. Iris
It is the visible coloured part of the eye & extends
anteriorly from the ciliary body, lying behind the
cornea in front of the lens.
It divides the anterior segment of the eye into
anterior & posterior chambers which contain aqueous
fluid secreted by ciliary body.
In the center is an aperture, the pupil.
The pupil varies in size depending upon the intensity
of light.
During bright light the pupil constrict, whereas dilate
during dim light .

This is the colored part of the eye: brown, green, blue,
etc. It is a ring of muscle fibers located behind the
cornea and in front of the lens. It contracts and expands,
opening and closing the pupil, in response to the
brightness of surrounding light. Just as the aperture in a
camera protects the film from over exposure, the iris of
the eye helps protect the sensitive retina.

Cont…d
48
D. Lens
– It is a highly elastic circular biconvex transparent
body, lying immediately behind the pupil.
– It is suspended from the ciliary body by the
suspensory ligament & enclosed with in a
transparent capsule.
– Its thickness is controlled by the ciliary muscle
through suspensary ligament.
– It bends light rays reflected by an object in front of
eye.

 Near Point (Least Distance Of Distinct Vision)
Its is the minimum distance at which eye can see objects very
clearly without any strain. Its value is 25 cm.
 Far Point
It is the farthest point up to which eye can see objects very
clearly. Its value is ∞

It is a convex lens made of a transparent and flexible
material like a jelly made of proteins.
It forms of a real image of the objects on the retina of
the eye.

Cont…d
52
Lens: - is the only structure in the eye that changes
its refractive power.
Light from distant objects needs least refraction & as the
objects come closer, the amount needed is increased (i.e.
ciliary muscle contract).
Size of the pupils: - control the amount of light
entering to the eye.
If the pupils were dilated in a bright right, too much
light would enter eye & damage retina.
The two muscles of iris, circular muscle fiber
constriction causes pupil to constrict but constriction
of radiating muscle fiber dilate pupil.

Cont…d
53
Accommodation of the eyes to light
• Close Vision
In order to focus on near object i.e. with in 6
meters, the eye must make the following
adjustments.
Constriction of the pupils.
Convergence of the eye balls
(Movement).
If convergence is not complete there is
double vision (diplopia).
Changing the power of lens – the lens is
thicker.

Cont…d
54
Distant Vision
Objects more than 6 meters away from the eyes
are focused on the retina without adjustment of
the lens or convergence of the eyes.
With aging, the ability of the eye to
accommodate gradually decreases because of
increased rigidity of the lens (Presbyopia).
The lens is tense able to change shape in
response to visual challenge of focusing on
near objects.

Cont…d
55
Structures inside the eye ball are
Aqueous humour (fluid).
 Vitreous body.
The anterior segment of the eye, i.e. the space between the cornea
& the Lens, is incompletely divided into anterior & posterior
chambers by iris. Both chambers contain a clear aqueous fluid.
Aqueous fluid
 It is secreted by ciliary gland.
 It passes in front of the lens, through the pupil into anterior
chamber & returns to the venous circulation in the angle
between iris & cornea.
 Produced continuously & drained but the IOP remains fairly
constant b/n 10 to 20 mm hg.
 An increase in pressure cause glaucoma.

Cont…d
56
• Vitreous body
– It is found behind the lens & filling the cavity of the
eye ball.
– Soft, colourless, transparent, jelly like
substance composed of 99% water.
– It maintains sufficient IOP to support the
retina against the choroids & prevent the
wall of eye ball from collapsing.
– The eye keeps its shape because of IOP
exerted by vitreous & aqueous fluid.

Cont…d
57
• Optic chiasma
–It is situated immediately in front of &
above the pituitary gland in the sphenoid
bone.
–In the optic chiasma the nerve fibers of
the optic nerve from the nasal side of
each retina cross over to the opposite
side.
–The fibers from temporal side do not
cross.

Cont…d
58
Physiology of Sight
 Light reflects into the eyes by objects within the
field of vision.
 A specific colour is perceived when only one wave
length is reflected by the object & all the others
are absorbed.
 E.g. an object appears red when only the red
wave length is reflected.
 Objects appear white when all wavelengths are
reflected & black when they are all absorbed.

Cont…d
– In order to achieve clear vision light reflected
from objects with in the visual field is focused on
the retina of both eyes.
– The processes involved in producing a clear image
are refraction of the light rays, changing the size
of pupils & accommodation of the eyes.
59

Cont…d
60
Refraction of the light rays
– When light rays pass from a medium of one
density to a medium of a different density they
are refracted or bent.
– Helps to focus light on retina.

Passage way of light rays
61
Light Cornea Pupil Iris Lense
AH VH Retina Optic Nerve
Cerebral Cortex.

TERMS
• Vision: Passage of rays of light from an object through the cornea, aqueous humor,
lens, and vitreous humor to the retina, and its appreciation in the cerebral cortex.
• Emmetropia: Normal vision: rays of light coming from an object at a
distance of 20 feet (6 m) or more are brought to focus on the retina by the lens.
• Ametropia: Abnormal vision.
– Myopia: Nearsightedness: rays of light coming from an object at a distance
of 20 feet or more are brought to a focus in front of the retina.
– Hyperopia: Farsightedness: rays of light coming from an object at a distance
of 20 feet or more are brought to a focus in back of the retina.

• Accommodation: Focusing apparatus of the eye adjusts to objects at
different distances by means of increasing the convexity of the lens
(brought about by contraction of the ciliary muscles).
• Presbyopia: The elasticity of the lens decreases with increasing age; an
emmetropic person with presbyopia will read the paper at arm's length and
will require prescription lenses to correct the problem.
• Astigmatism: Uneven curvature of the cornea causing the patient to be
unable to focus horizontal and vertical rays of light on the retina at the
same time.

COMMON ABBREVIATIONS
• OD (oculus dexter) or RIGHT EYE
• OS (oculus sinister) or LEFT EYE
• OU (oculus unitas) BOTH EYES
• IOP - INTRAOCULAR PRESSURE
• IOL - INTRAOCULAR LENS
• EOL - EXTRAOCULAR LENS

EYE CARE SPECIALISTS
• OPHTHALMOLOGIST : Medical doctor
specializing in diagnosis and treatment of the eye.
• OPTOMETRIST: Doctor of optometry who can examine,
diagnose, and manage visual problems and diseases of the eye,
but does not perform surgery.
• OPTICIAN : Fits, adjusts, and gives eyeglasses or other
devices on the written prescription of an ophthalmologist or
optometrist.
• OCULARIST: Technician who makes ophthalmic prostheses

• Blurred vision, double vision, loss of vision or a portion of the visual field?
• Is there pain, headache, foreign body sensation (scratchy, something in the eye),
photophobia, redness, itchiness, lacrimation, or drainage?
• Is there difficulty in functioning, such as driving or reading, due to visual problem?
Associated Factors
• Does the patient wear contact lenses or glasses?
• What is the patient's occupation and common sports activities?
• How long have there been symptoms?
• What treatments has the patient tried?
History
• Eye injury or accident
• Recent infection such as an upper respiratory infection
• Ocular history, such as previous injury, surgery, or use of medication
• Medical history, such as diabetes, hypertension, arthritis, or allergies

External Examination: Includes examination of the eye and accessory organs
without the aid of special apparatus.
VISUAL ACUITY (SNELLEN CHART AND OTHER
METHODS)
• Each eye is tested separately, with and without glasses. Letters and objects
are of a size that can be seen by the normal eye at a distance of 20 feet (6
m) from the chart. Letters appear in rows and are arranged so the normal
eye can see them at distances of 30, 40, and 50 feet (9, 12, and 15 m), and
so forth. A person who can identify letters of the size 20 at 20 feet (6 at 6
m) is said to have 20/20 (6/6) vision. Additionally, if vision is less than
20/200 (6/60), tests may be recorded as follows:
– Counting fingersâ€”at feet (meters)
– Hand motionâ€”ability to detect hand movement at a certain distance
– Light perception and projection
– Light perception only
– No light perception

VISUAL FIELDS
• To determine function of optic pathways.
• Equipment light source and test objects. Can be done
manually or as new automated visual fields.
– Patient is seated 18 to 24 inches (45.5 to 61 cm) in front of the
examiner.
– The left eye is covered while the patient focuses with the right
eye on a spot about 12 inches (30.5 cm) from the eye.
– A test object is brought in from the side at 15-degree intervals,
through complete 360 degrees.
– The patient signals when he sees the test object and again when
the object disappears through the 360 degrees.

COLOR VISION TESTS
• These tests are done to determine the person's ability to perceive
primary colors and shades of colors; it is particularly significant for
people whose occupation requires discerning colors, such as artists,
interior decorators, transportation workers, surgeons, and nurses.
(Useful in diagnosing diffuse retinal dysfunction and various types
of optic neuropathies.)
• Equipment
– Polychromatic plates these are dots of primary colors printed on a
background of similar dots in a confusion of colors.
– Individual colored disks each disk is matched to its next closest color.
• Procedure
– Various polychromatic plates are presented to the patient under
specified illumination.
– The patterns may be letters or numbers that the normal eye can
perceive instantly, but that are confusing to the person with a
perception defect.

REFRACTION
• Refraction is a clinical measurement of the error of focus in an eye.
• Refraction and internal examination may be accomplished by instilling a
medication with cycloplegic and mydriatic properties into the conjunctiva
of the eye. Tropicamide (Mydriacyl) or cyclopentolate (Cyclogyl) are two
such medicines that cause ciliary muscle relaxation, pupil dilation
(mydriasis), and lowered accommodative power (cycloplegia).
• The use of a multiple pinhole can help screen for refractive causes of
decreased vision versus decreased vision secondary to organic disease.
• The refractive state of the eye can be determined as follows:
– Objectively through retinoscopy or by automatic refraction (special instrument
that measures, computes, and prints out refraction errors of each eye)
– Subjectively trial of lenses to arrive at the best visual image

INTERNAL EXAMINATION
• OPHTHALMOSCOPIC EXAMINATION
– Direct ophthalmoscopy : uses a strong light reflected into
the interior of the eye through an instrument called an
ophthalmoscope.
– Indirect ophthalmoscopy : allows the examiner to obtain a
stereoscopic view of the retina. Light source is from a head-
mounted light. The examiner views the retina through a
convex lens held in front of the eye and a viewing device on
the head mount. The image appears inverted. This method of
examination allows the examiner to use binocular vision with
depth perception and wider viewing field.

SLIT-LAMP EXAMINATION
• Special equipment that magnifies the cornea, sclera, and
anterior chamber, and provides oblique views into the
trabeculum for examination by the ophthalmologist.
• The patient sits with chin and forehead resting against
equipment supports.
• The room is generally darkened, and the pupils are dilated.
• Helps detect disorders of the anterior portion of the eye

TONOMETRY
• SCHIOTZ'S TONOMETRY
– After instillation of topical anesthesia, the Schiotz's tonometer is gently rested on the
eyeball
– The indicator measures the ocular tension in millimetres of mercury (mm Hg).
– Normal tension is approximately 11 to 22 mm Hg.
• APPLANATION TONOMETRY
– This is the most effective measuring method for determining IOP; however, it requires a
biomicroscope and a trained interpreter. May be part of the slit-lamp examination.
– After instillation of topical anesthesia, the cornea is flattened by a known amount (3.14
mm).
– The pressure necessary to produce this flattening is equal to the IOP, counterbalancing
the tonometer.
• Air applanation tonometry this requires no topical anesthesia and measures tension
by sensing deformation of the cornea in reaction to a puff of pressurized air.

DIAGNOSTIC TESTS
RADIOLOGY AND
IMAGING

FLUORESCEIN ANGIOGRAPHY
• Introduction of sodium fluoresce I.V. over several minutes, usually through
a brachial vein. Indirect ophthalmoscopy using a blue filter may be done,
and photographs of the ocular fundus are obtained. Provides information
concerning vascular obstructions, microaneurysms, abnormal capillary
permeability, and defects in retinal pigment permeability.

EYE AND ORBIT SONOGRAPHY
• Sound waves are used in the diagnosis of intraocular and orbital
lesions. Two types of ultrasonography are used in ophthalmoscopy:
– A-scan uses stationary transducers to measure the distance between changes in
acoustic density. This is used to differentiate benign and malignant tumors and to
measure the length of the eye to determine the power of an intraocular lens.
– B-scan moves linearly across the eye; increases in acoustic density are shown as an
intensification on the line of the scan that presents a picture of the eye and the orbit.
• Abnormal patterns are seen in alkali burns, detached retina,
keratoprosthesis, thyroid ophthalmopathy, foreign bodies, vascular
malformations, benign and malignant tumors, and a variety of other
conditions.

ELECTRORETINOGRAPHY
• Used to evaluate hereditary and acquired disorders of the retina; an
electrode is placed over the eye to evaluate the electrical response to light.

GENERAL PROCEDURES AND TREATMENT
MODALITIES
INSTILLATION OF MEDICATIONS
• Ophthalmic medications may be used for diagnostic and
therapeutic purposes:
• To dilate or contract the pupil
• To relieve pain, discomfort, itching, and inflammation
• To act as an antiseptic in cleansing the eye
• To combat infection

IRRIGATION OF THE EYE
Ocular irrigation is often necessary for the following:
• To irrigate chemicals or foreign bodies from the eyes
• To remove secretions from the conjunctival sac
• To treat infections
• To relieve itching
• To provide moisture on the surface of the eyes of an
unconscious patient

APPLICATION OF DRESSING OR PATCH
• One or both eyes may need shielding for the following:
• To keep an eye at rest, thereby promoting healing
• To prevent the patient from touching eye
• To absorb secretions
• To protect the eye
• To control or lessen edema

• OCULAR SURGERY
• Corneal Transplantation
(Keratoplasty)
• Refractive Surgery
• Vitrectomy
• Enucleation

Hypermetropia, is a defect of vision caused
by an imperfection in the eye causing
difficulty focusing on near objects.
Farsightedness occurs when light entering
the eye through the lens is focused behind
the retina instead of directly on it.

Presbyopia is a condition where the eye exhibits
a progressively diminished ability to focus on
near objects with age. Presbyopia’s exact
mechanisms are not known with certainty; the
research evidence most strongly supports a loss
of elasticity of the crystalline lens, although
changes in the lens’s curvature from continual
growth and loss of power of the ciliary
muscles (the muscles that bend and straighten
the lens) have also been considered as its cause.

The lens of the eye is normally clear. It acts like the
lens on a camera, focusing light as it passes to the
back of the eye.
Until a person is around age 45, the shape of the
lens is able to change. This allows the lens to focus
on an object, whether it is close or far away.
As we age, proteins in the lens begin to break down
and the lens becomes cloudy. What the eye sees
may appear blurry. This condition is known as a
cataract.

Astigmatism is a type of refractive
error of the eye. Refractive errors
cause blurred vision and are the
most common reason why a
person goes to see an eye
professional.

Eyes Anatomy & Physiology with Diagnostic investigation.

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