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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, [email protected]
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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