ANATOMY OF THE EYE
DR. NANA NIKOLAISHVILI
EMBRYOLOGY OF THE EYE
This
highly specialized sensory organ is
derived from neural ectoderm, mesoderm
and surface ectoderm.
The
eye is essentially an outgrowth from
the brain (neural ectoderm).
Started
as Optic vesicle connected to the
forebrain by Optic stalk
DEVELOPMENT OF THE EYE AFTER BIRTH
 At birth, the eye is relatively large in relation to the rest of the body.
 The eye reaches full size by the age of 8-13 years.
 The lens continues to enlarge throughout the life.
 The iris has a bluish color due to little or no pigment on the anterior surface.
 During early infant life, the cornea & sclera can be stretched by raised IOP →
enlargement of the eye.
ANATOMY OF EYE
• Orbit
• The globe
• The eyelids
• Extraocular muscles
WHERE IS THE EYE LOCATED…
THE ORBIT
• As a socket, contains & protect the eye.
• The weakest parts are the floor & the medial wall.
• Seven bones contribute the bony orbit.
• Surrounded by nasal sinuses.
• Important openings are:
 Optic foramen
 Superior orbital fissure.
 Inferior orbital fissure.
THE EXTRAOCULAR MUSCLES
•
Four recti & two oblique muscles.
 SUPERIOR RECTUS
 INFERIOR RECTUS
 LATERAL RECTUS
 MEDIAL RECTUS
 INFERIOR OBLIQUE
 SUPERIOR OBLIQUE
All are supplied by Oculomotor n. except superior oblique (Trochlear n.) &
lateral rectus (Abducent n.).
GLOBE ANATOMY
• Conjunctiva
• Sclera
• Cornea
• Iris
• Pupil
• Lens
• Retina
• Optic nerves
CONJUNCTIVA
Conjunctiva: the thin, moist, clear membrane that covers the sclera – the white part of
the eye. It is the skin that lines the eye socket and protects and lubricates the
eyeball.Three parts:
 Bulbar conjunctiva
 Palpebral conjunctiva
 Forniceal conjuncitva
Follicles and Papillae
Injection and chemosis
THE EYEBALL (GLOBE)
•
Sphere shape
The eyeball contains three layers:
• The outer layer - cornea and sclera
• The middle layer- vascular layer - primary blood supply for the eye, the iris,
choroid, ciliary body.
• The inner layer - retina
Cornea:
 Clear front window, representing one-sixth of the outer layer of the eye
 Transparent circular part of the front of the eyeball.
 Refracts the light entering the eye onto the lens, which then focuses it onto the
retina.
 Contains no blood vessels
 Extremely sensitive to pain.
The corneal layers
I. Epithelium
II. Bowman's layer
III. Stroma
IV. Descemet's membrane
V. Endothelium
Thickness – 500-530 micron
The eyeball also contains three chambers of fluid:
• Anterior chamber, between the cornea and iris
• Posterior chamber, between the iris and the lens
• Vitreous chamber, between the lens and the retina
The anterior and posterior chambers are filled with aqueous humour, which is a
watery fluid that provides nourishment to the interior eye structures and helps to
keep the eyeball inflated.
The vitreous chamber is filled with a thicker fluid called vitreous humour, a
transparent gel which is 99% water, which helps the eyes to stay inflated.
IRIS AND PUPIL
Colored part of the eye.
Muscles in iris control a pupil — the small black
opening that lets light into the eye.
The pupil is the eye's aperture, while the iris is the
diaphragm.
Eye color is defined by the iris. The color of your iris is
like your fingerprint. It's unique to you, and nobody else
in the world has the exact same colored eye
The iris consists of two layers:
 The front pigmented fibrovascular layer known as a stroma
 beneath the stroma, pigmented epithelial cells.
The iris is divided into two major regions:
 The
pupillary zone is the inner region whose edge forms the boundary of the
pupil.
 The ciliary zone is the rest of the iris that extends to its origin at the ciliary body.
The stroma is connected to a sphincter muscle (sphincter pupillae), which
contracts the pupil in a circular motion, and a set of dilator muscles (dilator
pupillae), which pull the iris radially to enlarge the pupil, pulling it in folds.
THE LENS (CRYSTALLINE LENS)
• An important part of the eye’s anatomy that allows the eye to focus on objects at varying
distances.
• Located behind the iris and in front of the vitreous body.
• Looks like an elongated sphere — a shape known as ellipsoid — that resembles a deflated
ball.
• The average lens size in adults is approximately 10 mm across and 4 mm from front to back.
• The lens is made up almost entirely of proteins. (proteins make up nearly 60% of the eye’s
lens — a higher protein concentration than any other bodily tissue.)
• The tissue is transparent, which allows light to easily enter the eye.
• It’s also flexible, so it can change shape and bend the light to focus properly on the retina.
The lens has three layers.
 The outer capsule
 Middle cortex
 The central nucleus.
In cataract surgery, a hole is made in the front capsule, and the inner cortex and
nucleus are removed.
VITREOUS BODY
The vitreous humor (vitreous fluid)
 Transparent
Colorless
Gel-like substance
Fills the space between the lens and the retina within the eye.
The vitreous humor is composed of mostly water, along with a small percentage
of collagen, glycosaminoglycans (sugars), electrolytes (salts), and proteins.
The vitreous humor’s main role is to maintain the round shape of
the eye. The size and shape of the vitreous humor also ensures
that it remains attached to the retina.
The vitreous humor is also a part of the eye that can help with
vision clarity. Because the vitreous humor is a clear substance,
light is able to pass through and reach the retina.
The vitreous humor can also be helpful in absorbing any
unexpected disturbances to the eye, such as a thump to the side
of head. Absorbing the shock associated with the thump or
similar disturbance can help prevent eye damage.
SURFACE FEATURES:
• Patella fossa: Shallow saucer-like concavity anteriorly, in which the lens rests, separated by Berger's space
• Ligamentum hyaloideocapsulare (Wieger's ligament): Circular thickening of vitreous 8-9mm in diameter,
delineates the patella fossa
• Anterior hyaloid: Vitreous surface anterior to ora serrata. Continuous with and invests in the zonular fibres, and
extends forward between the ciliary processes
• Vitreous base: Denser cortical area of vitreous. Firmly attached to the posterior 2mm of the pars plana, and
the anterior 2-4mm of retina
• Posterior hyaloid surface: Closely applied to retinal internal limiting membrane. Firm attachment sites: Along
blood vessels and at sites of retinal degeneration
• Space of Martegioni: A funnel shaped space overlying the optic disc with condensed edge
• Cloquet's canal: A 1–2 mm wide canal within the vitreous, from the space of Martegioni to the space of Berger,
along an S-shaped course mainly below the horizontal.
• Mittendorf's dot: A small circular opacity on the posterior lens capsule, which represents the site of attachment
of the hyaloid artery before it subsequently regressed.[8]
• Bergmeister's papilla: A tuft of fibrous tissue at the optic disc, which represents a remnant of the sheath
associated with the hyaloid artery before it subsequently regressed.
RETINA
The primary light-sensing cells in the retina are the photoreceptor cells, which are
of two types: rods and cones. Rods function mainly in dim light and provide
monochromatic vision. Cones function in well-lit conditions and are responsible for
the perception of colour through the use of a range of opsins, as well as highacuity vision used for tasks such as reading. A third type of light-sensing cell, the
photosensitive ganglion cell, is important for entrainment of circadian rhythms and
reflexive responses such as the pupillary light reflex.
• The Optic disc
• Macula
• Fovea
• Ora serata
• Vessels
RETINAL LAYERS
1. Inner limiting membrane – basement membrane elaborated by Müller cells
2. Nerve fibre layer – axons of the ganglion cell bodies (note that a thin layer of Müller cell footplates exists between this
layer and the inner limiting membrane)
3. Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the optic nerve fibres, and some
displaced amacrine cells
4. Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and
amacrine cells
5. Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the amacrine cells, bipolar cells,
and horizontal cells[
6. Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone pedicle, respectively, these
make synapses with dendrites of bipolar cells and horizontal cells. [2] In the macular region, this is known as the Fiber
layer of Henle.
7. Outer nuclear layer – cell bodies of rods and cones
8. External limiting membrane – layer that separates the inner segment portions of the photoreceptors from their cell nuclei
9. Inner segment / outer segment layer – inner segments and outer segments of rods and cones, the outer segments
contain a highly specialized light-sensing apparatus.[14][15]
10.Retinal pigment epithelium – single layer of cuboidal epithelial cells (with extrusions not shown in diagram). This layer
is closest to the choroid, and provides nourishment and supportive functions to the neural retina, The black pigment
melanin in the pigment layer prevents light reflection throughout the globe of the eyeball; this is extremely important for
clear vision.
OPTIC NERVE
The optic disc is an elevation on the medial aspect of the retina where the sensory fibers
and retinal vessels pass through the eyeball.
The nerve fibers are conveyed via the optic nerve (CN II) and they travel alongside the
central retinal artery and vein
The optic disc is oval-shaped and located exactly 3 mm nasally (medially) to macula lutea.
It has a slight central depression called the physiologic cup. This cup marks a point where
the retinal vessels pass
The optic disc is the only area on the retina without any photoreceptors; hence it is known as
the 'blind spot' of the eye.
THE LACRIMAL APPARATUS
• Lacrimal glands behind the upper outside corner of your eyes make the salty water that
becomes your tears. The glands are each about the size of an almond.
• Lacrimal sacs - in the inside corner of your eye collect tears that drain out of your eyes through
your lacrimal puncta. They act like temporary reservoirs for tears that have just left your eyes.
They keep old tears from flooding your tear ducts constantly.
• Nasolacrimal duct (tear ducts) - the medical term for your tear ducts. Old tears that leave your
eye through your lacrimal puncta and lacrimal sacs drain into tear ducts on either side of your
nose. Your tear ducts empty into the back of your nose.
• Lacrimal puncta - the openings that pump tears out of your eyes. You have a punctum (the
singular form of puncta) in each of your upper and lower eyelids on the inside of your eye,
near your nose. Every time you blink, your puncta act like valves that drain used tears away
from your eye.
• Meibomian glands on the edges of your eyelids produce oil that mixes with the water from your
lacrimal glands to become your tears. The oil helps the water cling together and stay in your
eyes as long as it needs to.
• Tear secretion
• Layers of precorneal tear film
• Drainage of tear