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Eye, Nose & Visual Pathways By Isha AbidLearning Objectives • Discuss the anatomical relations of the orbit • List the bones that form the walls of the orbit • Describe the anatomical arrangement of the contents of the orbit • Describe the structure of the eyeball • State the attachments of the extraocular eye muscles and describe their innervation and function • Describe the arrangement of the lacrimal apparatus • List the bones that contribute to the nasal cavity • Describe the anatomical arrangement of the nasal cavity and relate structure to function • Draw a schematic diagram of the visual pathwayThe Bony Orbit Contents: • Eyeball • Extraocular muscles - Levator palpebrae superioris - Medial, lateral, inferior & superior rectus - Inferior & superior oblique • Eyelids • Nerves - CN II, III, IV, V, VI - zygomatic branch of maxillary Borders: - frontal - lacrimal Roof – frontal bone & lesser wing of sphenoid bone - nasocilliary Floor – maxilla, zygomatic & palatine - sympatheticnerves Medial wall – ethmoid, sphenoid, maxilla & lacrimal Lateral wall – zygomatic & greater wing of sphenoid • Blood vessels Apex – located at opening to optic canal - ophthalmicartery Base – opens into face - inferior & superior ophthalmic vein • Orbital fatPathways into the orbit Optic canal - Optic nerve - Ophthalmic artery Superior orbital fissure Nerves - Ophthalmic nerve – splits into lacrimal, frontal & Nasociliary nerves - CN III, CN IV, CN VI Blood vessels - Superior ophthalmic vein Inferior orbital fissure Nerves - Zygomatic branch ofmaxillary nerve - Sympathetic nerves Blood vessels - Inferior ophthalmic vein The Eyelid Orbiuclaris Oculi Origin: Medial orbital margin, medial palpebral ligament &lacrimal bone Insertion: Skin around margin of orbit, superior & inferior tarsal plates Action: - Palpebral part – gently closes eyelids - Lacrimal part – drainage of tears - Orbital part – tighlty closes eyelids Innervation: CN V Upper eyelid isinnervated by V1 of CN V (ophthalmic nerve) Lower eyelid isinnervated by V2 of CN V (maxillary nerve)The Eyeball Divided into 3 parts – fibrous, vascular & inner Fibrous (outermost) → Consists of sclera (~85%) & cornea, which are continuous with one another - Sclera – attachment for extraocular muscles - Cornea – refracts light entering eye Vascular (beneath fibrous layer) → Consists of choroid, ciliary body & iris. - Choroid – layer of connective tissue & BVs (provide nourishment to outer layers of retina) - Ciliary body – made up of ciliary muscles (smooth muscle fibres) & ciliary processes (attach ciliary muscles to lens of eye). Together control shape of lens & contribute to aqueous humour formation - Iris – circular structure with aperture in centre (pupil). Diameter of pupilcontrolled by smooth muscle fibres within the iris (innervated by autonomic nervous system) Inner (formed by retina) → formed by 2 layers, pigmented (outer) & neural (inner) - Pigmented – single layer of cells attached to choroid, helping to absorb light - Neural – contains photoreceptors, located posteriorly & laterally in the eye - Non-visual retina – part of the eye where pigmented layer continues but neural does not - Macula – centre of retina, contains fovea centralis which hashigh denisty of cones - Blind spot – where optic nerve enters retinaExtraocular Muscles Recti Muscles → control the movements of the eyeball &superioreyelid Superior rectus O: superior part of common tendinous ring 7 extraocularmuscles: INS: superior & anterior aspect of sclera INN: CN III • Superior rectus • Inferior rectus ACT: elevation, adduction & medial rotation • Lateral rectus • Medial rectus Inferior rectus O: inferior part of common tendinous ring • Superior oblique INS: inferior & anterior aspect of sclera • Inferior oblique INN: CN III • Levator palpebrae superioris ACT: depression, adduction & lateral rotation Lateral rectus O: lateral part of common tendinous ring INS: anterolateral sclera INN: CN VI ACT: abduction Medial rectus O: medialpart of common tendinous ring INS: anteromedialsclera INN: CN III ACT: adductionOblique muscles Superior oblique O: sphenoid bone, tendon passes through a trochlea INS: sclera posterior to superior rectus INN: CN IV ACT: depression, abduction & medial rotation Inferior oblique O: anterior aspect of orbital floor INS: sclera posterior to later rectus INN: CN III ACT: elevation, abduction & lateral rotation Levator Palpebrae Superioris O: lesser wing of sphenoid INS: superior tarsal of upper eyelid INN: CN III ACT: elevate upper eyelid https://www.youtube.com/watch?v=f_rb6FMVHPkLacrimal Apparatus Lacrimal glands secrete lacrimal fluid → system responsible fordrainage of lacrimal fluid from the orbit ↓ Fluid passed along excretatory ducts ↓ Fluid enters superior conjuctival sac ↓ Blinking pushes film off fluid around cornea ↓ Fluid accumulates in lacrimal lake at medial aspect of eye ↓ Parasympathetic innervation to lacrimal gland provided by Drains by capillary action through lacrimal CN VII puncta & lacrimal sac into lacrimal canuliculi ↓ Drain via nasolacrimal duct into inferior nasal meatus ofthe nasal cavityNasal Cavity → Functions: olfaction, respiration, filtration of dust, humidification etc. → 3 divisions: vestibule, respiratory & olfactory region Vestibule – area surroundingopeninginto nose Respiratory – lined by ciliated pseudostratified epithelium, some mucussecreting goblet cells Olfactory – locted at apex, lined with olfactory cells with receptors Nasal conchae - Curved shelves of bone projecting out of the lateral walls of the nasal cavity - There are 3 nasal conchae projecting into the nasal cavity – create 4 pathways for air to flow(meatuses) Function: - increases surface area – more air can come into contact with cavity walls - slow down fast laminar flow of inhaled air – more time forair to be humidifiedBones of the nasal cavity 9 bones contribute to the nasal cavity • Ethmoid • Sphenoid • Nasal • Maxilla • Frontal • Vomer • Inferior nasal conchae • Palatine • Lacrimal Internal Nasal Septum •Paired bones: Nasal, maxillary and palatine bones •Unpaired bones: Ethmoid and vomer bones Visual Pathways Axons of retinal ganglion cells converge at optic disc to form optic nerve ↓ Optic nerves converge at optic chiasma ↓ Axons from nasal retinal field decussate while axons from temporal field remain ipsilateral ↓ Fibres passinto optic tract &terminate in lateral geniculate nucleus ↓ Axons from 2nd orderneurones form optic radiation Nerves → Optic Nerve ↓ Fibres terminate in visual cortex of occipital lobe Carry → Optic Chiasm Tiny → Optic Tract Nerve Signals → Lateral Geniculate NucleuS Rapidly → Optic Radiations To the Cortex → Primary Visual CortexImportant concepts •Light rays from an object in the visual field enter the eyeball and are inverted by the lens before striking the retina. Axons from the retina pass centrally in the optic nerve •Light rays from the temporal visual field are projected onto the nasal retinal field whilst light rays from the nasal visual field are projected on to the temporal retinal field •Loss of vision is described with reference to the loss of visual fieldsVisual Field DefectsQuestions Which 2 bones contribute to the roof of the orbital cavity? o Sphenoid & ethmoid o Frontal & ethmoid o Ethmoid & sphenoid o Frontal & sphenoid Which structures pass through the optic canal? o Optic nerve & superior ophthalmic artery o Ophthalmic nerve & ophthalmic artery o Optic nerve & ophthalmic artery o Sympathetic nerves & optic nerveA lesion in the L optic radiation would cause what visual defect? o Total vision loss on the left side o Left nasal hemianopia o Right sided homonymous hemianopia o Left sided homonymous hemianopia What are the actions of the superior rectus muscle? o Elevation, adduction, medial rotation o Elevation, abduction, medial rotation o Elevation, adduction, lateral rotation o Elevation, abduction, lateral rotation