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Embryology of the Eye

and Visual PathwaysAnatomy and General

Organization

http://www.eb.tuebingen.mpg.de/eye-screen/

Patrick OConnor, Ph.D.Department of Biomedical Sciences

Ohio University College ofOsteopathic Medicine

Athens, Ohio45701oconnorp@ohiou.edu

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OUTLINEWednesday April 16, 2003

Embryology of the eye

Extraocular muscles

Visual reflexesPupillary Light Reflex

Near Reflex

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Fibrous Layer

Sclera

Cornea

Uveal Layer

Choroid

Iris

Ciliary Body

Retinal Layer(neural)Retina

Modified from Netter, 1989

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Modified from Netter, 1989

VitreousBody

CHAMBERS

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Modified from Netter, 1989

Aqueous Chamber

CHAMBERS

1Anterior Chamber

2Posterior Chamber

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Modified from Netter, 1989

Hyaloid Canal

Central Vesselsof Retina

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Development of the Eye

I. First noticeable ~ 22daysoptic groovesdeveloping neural tube

Moore and Persaud, 1998

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Development of the Eye

II. As neural folds fuse (= forebrain formation)optic vesiclesevaginations of forebrain

Moore and Persaud, 1998

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Development of the Eye

IIIa. Induction of lens placode (surface ectoderm)IIIb. Formation of optic stalk and optic cup from

optic vesicle

Moore and Persaud, 1998

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Moore and Persaud, 1998

Continued development ofoptic cup and lens

Optic cup invagination of distaloptic vesicle to form double-walled cup

Optic (choroid) fissure sulcus onventral aspect optic cup/stalk

(allows passage of vasculatureto lens & layers of cup)

Lens placode ectodermalthickening

Lens pit invaginates to formlens vesicle

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Moore and Persaud, 1998

Development of the retinaouter & inner portions of the optic cup

Closure of choroid fissure ~ 6-7 weeks

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Moore and Persaud, 1998

Inner layer neuroepitheliumneural retina

Outer layer retinal pigmentepithelium

Optic Cup

Intraretinal space

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Moore and Persaud, 1998

Fusion of inner and outerportions of the optic cup

Cavity of optic stalk filledwith axons of optic nerve

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Lens Developmentlens placode in surface ectoderm

invaginates as lens vesiclesupplied by hyaloid artery

Moore and Persaud, 1998Aphakia absence of the lens (extremely rare)Congenital cataracts(e.g., rubella virus)Congenital galactosemiacataract formation within 2-3 weeks

of birth (galactose accumulation)

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Development of Ciliary Body and Iris

both develop from anterior portions ofthe optic cup and surrounding mesenchyme

Ciliary muscle smooth muscle derived frommesenchyme near the margin of the optic cupeffects accommodation reflex

Iridial muscles dilator and sphincter pupillae mm.Smooth muscles derived from neuroectodermof the optic cupcontrol size of pupillary aperture

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Modified from Netter, 1989

Iris

Ciliary Body

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Retinal detachmentbetween inner and outerportions of the optic cup derivatives

congenitalfailure of fusionacquiredtrauma

Defects in closure of optic (choroid) fissureretinal colobomairidial coloboma

Aniridia (rare) 1 in 75,000

Some Ocular Anomalies

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Extraocular Muscles

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

Innervated via CN III, IV, & VI

Coordinate movements between the two eyes(usually conjugate, although some instances

of physiological vergence exist)

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Inferior rectus

(not shown)

Extraocular mm.

Inferior oblique

Superior oblique

Medial rectus

Superior rectus

Lateral rectus

Levator palpebrae sup.

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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.

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

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

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Extraocular Muscle Anomalies (congenital)

Agenesis (single muscle usually)

Anomalous Attachmentsmisplaced

additional attachments

Adherence & Fibrosis Syndromes

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

Amblyopiareduced/absent visual ability in one eyelazy eye

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VISUAL REFLEXES

Pupillary Light Reflexes: 30wks gestationConstriction (parasympathetic)Dilation (sympathetic)

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

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PUPILLARY CONSTRICTION (PARASYMPATHETIC)

Responses:

Direct (ipsilateral tostimulus)

Consensual

(contralateral) due tobilateral projection frompretectal nuclei to Edinger-Westphal nuclei

Pretectal nuclei projectbilaterally to E-W nuclei

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Where is the lesion?

Consensualresponse inleft eye

No directresponse inright eye

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PUPILLARY DILATION (SYMPATHETIC)

3-neuron chain:

Hypothalamus to spinalcord (T1-2)

Spinal cord to superiorcervical ganglion

(preganglionic)

Superior cervical ganglion

to dilator pupillae m.(postganglionic)

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Focusing on a Near Object

1. Accommodation (parasympathetic)

Oculomotor efferent axons from Edinger-Westphalnucleus signal ciliary m. to contract

Reduce tension of suspensory ligaments of lens

Curvature of lens increases

(well-developed @ 4 months)

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Focusing on a Near Object

2. Convergence of optic axes (somatic motor)

Oculomotor nucleus signals both medial rectusmm. to contract (disjunct eye movements)

3. Pupillary constriction (parasympathetic)

Oculomotor efferent axons from Edinger-Westphalnucleus signal sphincter pupillae m. to contract

Small pupil sharpens image on retina and reduceslight intensity

(well-developed at 4 months)

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Modified from Netter, 1989

Iridial Muscles

Ciliary Muscle

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Visual Developmental Milestones

Pupillary Light Reaction30 wks gestation(CN II/symp/parasymp integration)

Lid closure in response to bright light30 wks gest.(CN IICN VII reflex)

Blink response to visual threat2-5months(CN IICN VII reflex)

Visual Fixationbirth (well dev=6-9wks)

Visual Following3 months

Accommodation4 months

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ResourcesThe Developing Human6th Edition

K. L. Moore & T. V. N. Persaud 1998

The EssentialsWalsh & Hoyts ClinicalNeuro-Ophthalmology5th EditionEditorsN.R. Miller and N.J. Newman1999

Neuro-ophthalmology3rd EditionEditorJ.S. Glaser1999