AN OVERVIEW

Assoc Prof dr Hamiadji T.

HT. 2011.

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4. Orbital cavityOrbital cavity

- extra-ocular muscles

- blood vessels & nerves

- retro-bulbar fat

5.5. Visual pathwayVisual pathway

6.6. Optical anomaliesOptical anomalies

7.7. Light (what we can Light (what we can see)see)

Lecture Outline

1.1. IntroductionIntroduction

2.2. AccessoryAccessory structuresstructures

- eyebrows

- eyelids

- lacrimal apparatus

3.3. Eye ballEye ball

- fibrous tunic

- vascular tunic

- nervous tunic

- aqueous humor

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1. INTRODUCTION

We live in a visual world and vision is our dominant special sense. If you count all afferent nerve fibers to central nervous system-1/3 rd of them will be found

in OPTIC NERVE the 2nd cranial nerve.

Out of the wide spectrum of electromagnetic radiation our sense of sight is restricted to 1/70 of the

spectrumThe visual spectrum is from 400 nanometers – 700

nanometers (from blue – to – red)

What part of the electromagnetic spectrum is visible?The visual spectrum is; 400 nm to 700 nm. True or false.

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2. ACCESSORY STRUCTURES• EYEBROWS--PROTECTION FROM

SUNLIGHT, PREVENTING PERSPIRATION TO DROP INTO THE EYES.

• EYELIDS-PROTECTION FROM FOREIGN OBJECTS, SUNLIGHT, BLINKING HELPS IN CIRCULATION OF LACRIMAL SECRETION-KEEPS CONJUNCTIVA & CORNEA LUBRICATED.

• STRUCTURES--SKIN, ORBICULARIS OCULI MUSCLE, TARSAL PLATE, LEVATOR PALP. SUPERIORIS MUSCLE, CONJUNCTIVA.

• CONJUNCTIVA-THIN TRANSPARENT MUCOUS MEMBRANE COVERING INNER SURFACE OF EYELIDS & ANTERIOR SURFACE OF EYE, REFRACTIVE MEDIA

Name the accessory structuresOf the eye give its main functions.

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PUNCTUM LACRIMALE

LACUS LACRIMALE

CORNEAL LIMBUS

CONJUNCTIVABULBI

CONJUNCTIVA PALPEBRALE(MEIBOMIAN GLANDS)

Study the above labeled parts!!

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2. ACCESSORY STRUCTURESThe eyelidsEyelashes; robust hairs – prevent foreign matter, insects to the eyesTarsal glands (Zeis’) – large sebaceous glands (eyelashes)Meibomian glands – inner margin of lids produce lipid-rich substance, help lubrication with tears.Tarsal plate – broad sheath of connective tissue support the eyelidsOrbicularis & Lev palpebrae sup – lie between tarsal plate - skin

Superior tarsal (smooth muscle) – attached to tarsal plate

Study the details of the eyelids!!

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The eyelids and Anterior orbital

structures,.

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2. ACCESSORY STRUCTURES

Lacrimal apparatus: Lacrimal gland-serous, between

orbital plate frontal bone and

conjunctiva, lacr. ducts pierce

conjunctiva, bulb, nasolacrimal duct.

Tears, waterly,slightly alkaline,lysozyme

Tears + secretion of Meibomian and tarsal glands – reduce friction, remove debris, prevent bact. Infection, provide nutrients, and oxygen

Describe the production &Flow of the tears.

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3. THE EYEBALL1. FIBROUS COAT - CORNEA-ANT 1/6, TRANSPARENT, AVASCULAR, HIGLY SENSITIVE (ophthalmic nerve- V1)

REFRACTIVE MEDIA2. VASCULAR COAT- POST PART- CHOROID (VERY THIN VASCULAR NETWORK) ANT PART- CILIARY BODY (CILIARY MUSCLES CILIARY PROCESSES)

SUSPENSORY LIG. CONNECTS CILIARY MUSCLES TO LENS

IRIS COLORED DIAPHRAGM, ENCLOSES OPENING CALLED PUPIL, CONTAINS SMOOTH MUSCLES- SPHINCTER PUPILAE & DILATOR PUPILAE

Describe the coats and itsImportant parts.

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3. RETINA - MACULA LUTEA- NEAR THE CENTRE OF POST PART OF RETINA YELLOWISH -SPOT, (ONLY CONES ARE CONCENTRATED HERE) AREA FOR MOST DISTINCT VISION (DISCIMINATORY VISION & COLOR VISION)

FOVEA CENTRALIS DEPRESSION IN CENRE

3mm medial to macula-OPTIC DISC- AREA FOR LEAVING OF OPTIC Nerve BLIND SPOT- (NO ROD & CONE)-

CENTRAL ART. OF RETINA ENTERS THE CENTRE OF IT.

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MACULA LUTEAAND

FOVEA CENTRALIS

OPTIC DISCSUP. RETINAL ARTERIOLE & VENULE

INF.RETINAL ARTERIOLE & VENULE

INF. MACULAR ARTERIOLE& VENULE

Mention the salientFeatures of the retina

In ophthalmoscopic view.

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THE EYEBALLTHE EYEBALL(SUMMARY)(SUMMARY)

• The eye has 3 tunics (coverings):Outer fibrous tunic, middle vascular tunic, and inner neural tunic.

• The fibrous tunic includes: Sclera (dense fibrous connective tissue), limbus (between sclera and cornea), and cornea

• The vascular tunic (Choroid) or Uvea includes: Iris (border between anterior chamber and posterior chamber, ciliary body (contains ciliary muscles + processes and suspensory ligaments

• The neural tunic includes: Outer pigment layer, and inner retina (visual receptors + associated neurons. It ends anteriorly as the ora serrata.

Study the 3 tunics of the Eyeball.

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The eye has two "humors," the aqueous (LIQUID) and the vitreous humor (GELATINOUS

MASS) forming bulk of the eye)

AQUEOUS HUMOR

VITREOUS HUMOR

CILIARY BODY

IRIS

OPTIC DISC

Study the 2 humoursOf the eye.

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GLAUCOMA

•THE BALANCE BETWEEN PRODUCTION AND DRAINAGE OF AQUEOUS HUMOUR DETERMINES INTRA-OCULAR

PRESSURE, WHICH MAINTAINS SHAPE & SIZE OF EYEBALL-INCREASE IN INTRA-OCULAR PRESSURE--GLAUCOMA CAUSE

BLURRY VISION & “SEEING OF STARS”•Functions of Aqueous Humour= Maintain

I.O.Pressure(10to20mm of Hg, nutrition to cornea & lens, refractive media

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• The retinal tissue comprises of 2 layers:- Outer pigment layer- Inner retinal layer – visual receptors & associated neurons

• The 2 types of photoreceptors: - Cones – color vision and bright vision- Rods - black & white and dim visionCones are concentrated in macula lutea – fovea area is for sharpest vision

• Photoreceptors – bipolar cells – ganglion cells – optic nerve. Horizontal cells and amacrine cells modify signals formed between retinal components.

THE EYEBALLTHE EYEBALL(SUMMARY)(SUMMARY)

Consider the layersOf the retina!

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• Aqueous humor circulates within eye – draining into canal of Schlemm

• Lens held in place by suspensory ligaments – for accommodation of eye, to focus image on the retinal receptors

• Vitreous body – a gelatinous mass helps stabilize the shape of the eye and support the retina

THE EYEBALLTHE EYEBALL(SUMMARY)(SUMMARY)

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Schlemm’s canal

Iridocorneal angleZonular fibres

Vorticose vein

Central retinal art. & vein

Short post. Ciliary art.

Ora serrata

HORIZONTAL SECTION 17

4.THE ORBITAL CAVITY

EXTRA-OCULAR MUSCLES OF EYEBALL

•LEVATOR PALPABRAE SUPERIORIS

•SUPERIOR RECTUS

•INFERIOR RECTUS

•MEDIAL RECTUS

•LATERAL RECTUS

•SUPERIOR OBLIQUE

•INFERIOR OBLIQUE

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OPTIC NERVE

LATERAL RECTUS

ANNULAR RING

INFERIOR OBLIQUE

SUPERIOR OBLIQUE

Study the topographyOf the structures labeled.

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TARSUS OF EYELID

LAT PALPEB. LIG.

PERISCLERAL SPACE

TENON’S

CAPSULE

PERIORBITA

Fascia of Orbit (Periorbita) covers the Contents of Orbit

The Retrobulbar Fat provide padding and isolation of eye

ball

Study the contents

Of the orbitalCavity

carefully.

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NERVES OF THE ORBIT

MANDUBULAR NERVE

NASOCILIARY NERVE

CILIARY GANGLION

MAXILLARY NERVE

OPHTHALMIC NERVE

NERVES TO EXTRA-OCULAR MUSCLES & AUTONOMIC

INNERVATION OF EYE.

OPHTHALMIC DIV. OF NV.

Identify all the nerves and the ganglions.21

VESSELS OF THE ORBIT

OPHTHALMIC ARTERY

CAVERNOUSSINUS

PTERYGOID PLEXUS

ANGULARVEIN

OPHTHALMIC VEIN

VEINS COMMUNICATION AROUND THE ORBIT

BRACHES OF OPHTHALMIC ARTERY

Study the branches of ophthalmic a.Study the veins communication

Around the orbit.

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5.THE VISUAL PATHWAY5.THE VISUAL PATHWAYRETINA : Receptor cells

OPTIC NERVE: 1 million afferent fibres each (Special Somatic Afferent)

OPTIC CHIASM: Partial crossing

OPTIC TRACK: Contra lateral hemi visual field

Lateral Lateral geniculate geniculate bodybody

Visual cortex

“What is it?”

Tectum of brain Tectum of brain stemstem

Neck reflexes

Accomodation reflex

Where is it?”

Describe the visual pathway.(two pathways)

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Lateral Lateral geniculate geniculate bodybody:

Optic radiation

Visual cortex (Br 17)

Visual perception

“What is it?”

Tectum brain Tectum brain stem:stem:

Neck reflexes

Accommodation reflex

Light reflex

“Where is it?”

5. THE VISUAL PATHWAY5. THE VISUAL PATHWAY

Accommodation may involve the Frontal eye field

as well.

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Now several imaging techniques such as PET (positron emission tomography) and the new fMRI (functional magnetic resonance imaging) make possible to observe human brains at work

PET scan: two areas are active (red and yellow) when volunteers read words – the primary visual cortex and additional part of the visual system in the left hemisphere.

PET SCAN 25

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