Anatomy and Embryology of the Eye

Julie D Barliana

Pediatri-Ophthalmology DivisionOphthalmology Department FMUI/RSCM

The Protective Structures of the Eye

O TheOrbit

o The Lids o The Sclera The Anterior Segment of the Eye o The Corneao The Aqueous Humoro The Iriso The CrystallineLens and CiliaryMuscle The Posterior Segment of the Eye o The Retina o The Vitreous Humor The Visual System Pathways to the Brain o The Optic Nerves and Optic Tracts o The Lateral Geniculate Nucleuso The Visual Cortex

Anatomy of the eyeCornea

Iris

Ciliary body

Lens

Retina

Choroid

Optic nerve (NII)

vitreus body

Anatomy of the Eye

Badan Kaca (vitreus body)

Anterior chamber (Camera Oculi Anterior)

Posterior Chamber (Camera Oculi Posterior)

Central Vessel Retina

Hyaloid Canal)

Embryo

I. Eye Fields-Optic Vesicle (Weeks 3-4)

II. Optic Cup, Lens Vesicle, Choroid Fissure, Hyaloid Artery (Weeks 5-6)

III. Cornea, Anterior Chamber, Pupillary Membrane, Lens, Retina (Weeks 7-8)

IV. Iris, Ciliary Body (Weeks 9-15)

V. Eyelids (Weeks 8-10)

Eye Development

the neuroectoderm of the optic groove comes into close contact with the surface ectoderm in the area indicated

A cut through the embryo demonstrates the relationship of the optic groove to this ectoderm.

Optic Vesicle (Weeks 3-4)

The line indicates the location of the cut. The optic grooves

form the optic stalks and the optic vesicles.

Contact between the neural ectoderm of the optic vesicle and the surface ectoderm results in induction of the lens placode.

Cutting the embryo in the indicated plane illustrates the lens placode and the adjacent portion of the optic vesicle as it begins to invaginate

Optic Cup, Lens Vesicle, Choroid Fissure, Hyaloid Artery (Weeks 5-6)

The invaginating lens placode forms the lens vesicle that pinches off the surface ectoderm. Invagination of the optic vesicle forms the bilayered optic cup that remains connected to the forebrain via the optic stalk.

Contact between the surface ectoderm and the budding optic vesicle induces the differentiation of a population of cells that will form the lens placode.

The lens placode invaginates, forming the lens vesicle. Concurrently, the optic vesicle becomes the optic cup.

The lens vesicle eventually becomes the lens and the two layers of the optic cup become the neural and pigmented layers of the retina.

The optic vesicle and the optic stalk invaginate, forming the choroid fissure inferiorly.

The arrows show the areas of invagination.

This diagram represents the cut shown by the dotted line. The hyaloid artery courses through the choroid fissure.

illustrates the lens vesicle and the hyaloid artery.

Cornea, Anterior Chamber, Pupillary Membrane, Lens, Retina (Weeks 7-8)

The hyaloid vasculature surrounds the back of the lens. Following separation of the lens from the surface, the posterior lens fibers elongate to obliterate the lens cavity and the cornea begins to differentiate

The anterior chamber of the eye forms as a space develops between the lens and its closely associated iridopupillary membrane and the cornea.

Cornea

The cornea consists of an outer epithelial layer derived from surface ectoderm and inner layers derived from neural crest cells.

Iris, Ciliary Body (Weeks 9-15)

The pupillary membrane should regress, but may persist after birth, appearing as in the diagram.

Retina

As the retina develops, the pigmented layer becomes relatively thinner while the neural portion thickens.

As the neural portion develops, it differentiates into distinct cell layers.

Iris, Ciliary Body (Weeks 9-15)

The iris forms from the outer rim of the optic cup

At the rim of the optic cup, the inner and outer layers become closely associated.

Folding of these layers results in formation of the ciliary processes.

Eyelids (Weeks 8-10)

By the end of the embryonic period, eyelids begin to form.

The eyelids fuse at the beginning of the second trimester and reopen at the beginning of the third trimester.

Iris and Cilliary body

Some Ocular Anomalies

Retinal detachment—between inner and outer portions of the optic cup derivatives

•congenital—failure of fusion •acquired—trauma

Defects in closure of optic (choroid) fissure •retinal coloboma•iridial coloboma

Aniridia — (rare) 1 in 75,000

Extraocular Muscles

Develop from somitomeres I-IV (paraxial mesoderm cranial to the occipital somites)

Innervated via CN III, IV, & VI

Coordinate movements between the two eyes(usually conjugate, although some instancesof physiological vergence exist)

Extraocular mm.Inferior oblique

Medial rectus

Superior oblique

Superior rectus

Levator palpebrae sup.

Lateral rectus

Inferior rectus(not shown)

Oculomotor Nerve (CN III)Somatic motor(oculomotor nucleus):Sup. rectus, Inf. rectus,Med. rectus, Inferior oblique& Levator palpebrae superiormm.

Parasympathetic(Edinger-Westphal nucleus):Ciliary m. &Constrictor pupillae m.

Trochlear Nerve (CN IV)Somatic motor only(trochlear nucleus):•Superior oblique m.

Abducens Nerve (CN VI)Somatic motor only(abducens nucleus):•Lateral rectus m.

Extraocular Muscle Anomalies (congenital)

• Agenesis (single muscle usually)• Anomalous Attachments

– misplaced– additional attachments

• Adherence & Fibrosis Syndromes

**Failure to align visual axes (strabismus), thus potentially resulting in diplopia (double-vision)

Amblyopia—reduced/absent visual ability in one eye “lazy” eye

VISUAL REFLEXES

Pupillary Light Reflexes: 30wks gestation– Constriction (parasympathetic)– Dilation (sympathetic)

Accommodation (4 months = well developed)(The Near Reflex)

Visual Development

Visual Developmental “Milestones”

• Pupillary Light Reaction—30 wks gestation(CN II/symp/parasymp integration)

• Lid closure in response to bright light—30 wks gest.(CN II—CN VII reflex)

• Blink response to visual threat—2-5months(CN II—CN VII reflex)

• Visual Fixation—birth (well dev=6-9wks)• Visual Following—3 months• Accommodation—4 months

Visual pathway

Rods and Cones

• Cone cells see in bright light and rod cells see in black and white and in dark light

Physiology of Vision

• Light energy enters the eye, and the cornea and lens focus it onto the retina

• The light stimulates the rods and cones, two types of cells found in retina

• The rods and cones send impulses to the optic nerve, which carries them to the visual area of the cortex

• The cortex interprets the image and you “see”

• Nearsightedness occurs when light is focused in front of the retina

• Farsightedness occurs when light is focused behind the retina

• Concave lens, thicker at edge than in the middle, corrects nearsightedness

• Convex lens, thicker in middle than at edge, corrects farsightedness

Visual development

• In the early months of life– the visual system is still developing

• In a premature infant: – depending on the extent of prematurity– the eyelids may not have fully separated; the iris

may not constrict or dilate– retinal blood vessels may be immature – visual system is not ready to function

At birth: •the pupils are not yet able to dilate fully •newborn has poor fixation ability •limited orienting to single targets from birth to 3 months

By 3 months

• ocular movements are coordinated most of the time; • attraction is to both black and white and coloured

(yellow and red) targets;• the infant is capable of glancing at smaller targets

(as small as 2.5 cm, or about 1 in.); • visual attention and visual searching begin; • the infant begins to associate visual stimuli with an

event (e.g., the bottle and feeding)

By 5-6 months • The infant is able to look at an object in his/her own

hands • ocular movement, although still uncoordinated at

times, is smoother• the infant is visually aware of the environment

("explores" visually), and can shift gaze from near to far easily

• the infant can "study" objects visually at near point and can converge the eyes to do so; can fixate at 1m

• eye-hand coordination