Ocular Odyssey

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The Eyelashes and Beyond:

By Shane R. Kannarr,OD

Ocular Appendages

Eyelids Protect from light Distribute tears Key Anatomy Meibomian glands oil glands mark the junction of skin and conjuctiva Gray line —between eyelashes and glands

Punctum Lacrimale

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Located superior and inferior nasally in both eyes Drainage structure

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**Caruncula lacrimalis**

Eyebrows

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Protective Keep old men busy

Conjunctiva

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A thin mucous membrane that lines the eyelids and sclera forms a space called the conjuctival sac

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Palpebral —lining of the eyelids Bulbar —lies in contact with the eyeball Lacrimal Caruncle —medial angle colorless hairs/acessory lacrimal gland

Lacrimal System

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Lacrimal Gland —

– Orbital—larger section – Palpebral—smaller section – 12 ducts in to the superior fornix – Numerous small accessory glands

Tears

Contain: Lysozyme IgA Beta Lysin-bactericidal protein Which: Defense against microorganisms Regulate epithelial turnover Hormones to support lacrimal secretion/suppress immonological activity

Tears

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Work to:

– Keep the eye moist to aid in refraction – Lubricate with lipids for movement

Tear Layers

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Thin superficial oily layer secreted by the meibomian glands/sebaceous glands(Zeiss)/sweat(Moll) Watery layer (lacrimal glands) Mucin layer (conjunctival goblet and lacrimal)

Tear drainage

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Punctum lacrimale

– Sets atop the papilla lacrimalis – Superior and inferior – Lacrimal Canaliculi • Vertical and horizontal section 10mm long • Ampulla-union of the two

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During blinking canaliculi are pulled medially and compressed to act as a pump

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Lacrimal Sac

– Situated in the lacrimal fossa – Nasolacrimal duct-connects lower end of the sac with the inferior meatus of the nose – Plica lacrimalis-keeps air out of nasolacrimal sac

Tear Circulation

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Lids move tears over cornea/tears do not follow the lid

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During sleep the orbicularis Oculi shortens the canaliculi dilating the lacrimal sac and pumping the tears off the eyes

The Eyeball

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Tenon’s Capsule

– Thin membrane that seperates the eye from orbial fat – Eyeball Dimensions – Anterior-Cornea-1/6 – Posterior-Sclera 5/6 – 24mm anterior to posterior diameter

Fibrous Layer

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Cornea

– Epithelium- 5 layers turns over every 7 days – Basement membrane – Bowman’s layer-merges with the stroma

Stroma

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90% of the thickness Layers or Lamella Run at 90 degrees Does not rejuvenate Allows LASIK to work

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Descmet’s membrane

– Posterior surface basement membrane

Tidbits

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Endothelium-one layer thick Controls corneal hydration

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Avascular-gets nutrients from the aqueous and O2 from tears and peripheral vessels

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Major refractive surface Clarity comes from even spacing/fluid is a problem

Tidbits

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Limbus-where cornea and sclera meet Canal of Schlemm-around the eye at the corneascleral junction. Allows drainage through the trabecular meshwork

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Scleral spur

Sclera/Choriod

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3 layers thick 1 mm thick Choriod —thin lining of the inner surface of the sclera Nourishes the outer retinal layer

Ciliary Body

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Two sections Pars Plicata-anterior ridges Ciliary processes Anterior secretes aqueos Posterior-zonules Pars Plana-smooth Ciliary Muscle Moves the ciliary body forward for accomodation

Iris

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Pupillary margin-around the pupil Ciliary margin-root of the iris 2 major muscles

– Sphinter-miosis – dilator-mydriasis

Aqueous Flow

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Aqueous-clear fluid Formed by ciliary processes Flows between the suspensory ligments through the pupil to the anterior chamber Moves inferior/anterior to posterior superior Anterior Chamber-behind the cornea in front of the iris Posterior Chamber-lens to posterior surface of the iris

Aqueos Drainage

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90% leaves by Trabecular meshwork to Canal of Schlemm to Collector Channels to Aqueos veins

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Meets metabolic needs for avascular regions

Lens

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4mm thick (thicker as we age) 15D of power (eye 58D) Anterior and Posterior poles

– Center points – Equator-circumference

Lens “parts”

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Capsule-chief function to mold the lens as the zonules contract Lens epithelium- move metabolic materials in and out Makes lens fibers Lens Fibers Embryonic-earliest fibers Fetal Adult forms after birth always changing

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Y sutures anterior are erect Y sutures posterior are inverted Lens cortex area with recently formed fibers

Vitreous Body

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Occupies 4/5 of the eyeball Between the lens and the retina Hyloid fossa-depression for the lens Dense cortex with a liquid center 98% water Vitreous base-area where the retina attaches at the ciliary body/pars plana

The Retina

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The nervous coat is the internal layer of the eyeball. Photochemical transduction creates nerve impulses that are transmitted to the brain for cortical processing. Purple in color in living individuals Posterior portion is receptive and ends at the orra serrata Anterior portion is nonreceptive

The Retina

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Macula lutea-center of the posterior portion. Depressed in the center to form the fovea centralis

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RPE-retinal pigmented epithelium single layer of cells Absorb light/aid in the turn over of photoreceptors(absorb light in an antireflective method which stops image degradation. Aid in blood retina barrier

Neural Retina

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Groups of neurons Bipolar cells-contact cells to ganglion cells Ganglion cells-second neurons carry info from retina through lamina cribosa Photoreceptors-rods and cones Horizontal cells-possible they integrate visual stimuli Amacrine cells-excite lateral ganglion cells/modulators of photoreceptor signals

Retinal Layers

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1) Pigmented Epithelium 2) Rods and Cones 3) External limiting membrane 4) Outer nuclear layer 5) Outer plexiform layer 6) Inner nuclear layer 7) Inner plexiform layer 8) Ganglion cells 9) Nerve Fiber layer 10) Internal limiting membrane

Lamina cribosa

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Posterior opening One larger opening for the central retinal artery and vein Increased IOP can cause bulging and a cupped disk 3 other opening for one each for:

– Anterior Ciliary Arteries – Exit of Vortex Veins – Long and short ciliary nerves

7 Bones of the Orbit

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Maxilla Palatine Zygomatic Sphenoid Frontal Ethmoid Lacrimal Lateral strongest/floor weakest

Sinuses

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Ethmoidal Frontal Maxillary Sphenoid

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Most common site of orbital cellulities

Visual Pathway

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“The retina, the optic nerve, the optic chiasma, the optic tracts, the lateral geniculate bodies, the optic radiations, and the visual cortex (area 17) make up the pathway.”

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From the Clinical Anatomy of the Eye” by Snell and Lemp

Tracing the Image

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Retina-Inferior nasal is Superior temporal Optic Chiasma-Nasal crosses Optic tract-Retinal fibers line up Lateral Geniculate Body-relay and integration Optic radiation

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The retina turns light into an electrical nerve impulse

Musculature

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Primary Position-eye is straight ahead Secondary-Up/down/lateral/medial Tertiary- up and out/down and in ect.

Elevator-up Depressor-down Adduction-toward the midline Abduction-away from the midline

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Superior Rectus-elevator Inferior Rectus-depressor Medial Rectus-adductor Lateral Rectus-abductor Inferior oblique elevates/abducts/extorsion Superior oblique depresses/abducts/intorsion

Innervation

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Cranial nerves II-Optic Vision III-Oculomotor Raises eyelids/moves eyeball up/down/medial/contricts pupil/causes accomodation IV Trochlear-assists in moving eyeball down and lateral V Trigeminal-branch one is cornea Adbucent-Moves eyeball laterally

Muscles/Innervation

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Superior rectus-Oculomotor Inferior rectus-Oculomotor Medial rectus-Oculomotor Inferior oblique-Oculomotor Lateral rectus-abducents Superior Oblique-Trochlear

Blood Supply

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Ophthalmic Artery

– Branch of the Carotid – Veins • Superior and Inferior ophthalmic • 2 anterior ciliary arteries go to each rectus muscle