(1) Eye Anatomy, Physiology, Eye Exam

What muscles control eye movement in the direction of their attachment?

What muscles control eye movement in the direction of their attachment?

Rectus muscles

What muscles are on a pulley system, moving the eye in the opposite direction of their attachment?

Oblique muscles

What muscles move the eye RIGHT and UP?

• Right superior rectus

• Left inferior oblique

What muscles move the eye RIGHT?

• Right lateral rectus

• Left medial rectus

What muscles move the eye RIGHT and DOWN?

• Right inferior rectus

• Left superior oblique

What muscles move the eye LEFT and UP?

• Left superior rectus

• Right inferior oblique

What muscles move the eye LEFT?

• Left lateral rectus

• Right medial rectus

What muscles move the eye LEFT and DOWN?

• Left inferior rectus

• Right superior oblique

What Lid Muscle is this?

• Protector / sphincter muscle

• Closes the lid

• Innervated by CN VII

Orbicularis Oculi

What Lid Muscle is this?

• Retractor muscle

• Opens the lid

• Innervated by CN III

Levator Palpebrae

What arteries supply the eye?

• Ophthalmic Artery

• Central Retinal Artery

• Posterior Ciliary Arteries (short and long)

• Anterior Ciliary Arteries

What veins drain the eye?

• Central Retinal Vein

• Superior / Inferior Ophthalmic Veins

• Cavernous Sinus

• Pterygoid Venous Plexus

What is this?

• Thin mucous membrane made of non-keratinized columnar cells

• Reaches from cornea to eyelid skin

• Composed of two parts

Conjunctiva

What is this?

• Lines inner lids

• AKA tarsal conjunctiva

Palpebral Conjunctiva

What is this?

• Overlies globe

• Meets the cornea at conjunctival limbus

Bulbar Conjunctiva

What makes up the Lacrimal Apparatus?

• Lacrimal gland

• Punctum (superior and inferior)

• Lacrimal canaliculi

• Lacrimal sac

• Nasolacrimal duct

• Nasal cavity

What is the importance of the curved shape of the Cornea?

Allows for refraction

What is this?

• 80% of the globe’s surface

• Made up of 3 layers

  • Episclera connects to Tenon’s fascia

  • Stroma is dense fibrous tissue

  • Lamina Fusca Sclera is loosely attached to the choroid

Sclera

What is this?

• Meets the sclera at the Limbus

• Consists of 5 layers

  • Epithelium

  • Bowman’s Layer

  • Stroma

  • Descemet’s Membrane

  • Endothelium

Cornea

What Corneal Layer is this?

• Outermost

• Absorbs and distributes O2 and nutrients from the tears

• Extremely sensitive (MC location of abrasion)

Epithelium

What Corneal Layer is this?

• Collagen fibers

• May scar as it heals

• Vision loss can occur

Bowman’s Layer

What Corneal Layer is this?

• 90% of cornea

• Made mostly of water

• Avascular

Stroma

What Corneal Layer is this?

• Strong protective layer of thin collagen tissue

• Damage here is repaired by endothelial cells

  • Can regenerate

Descemet’s Membrane

What Corneal Layer is this?

• Pumps excess fluid out of stroma

• Keeps cornea CLEAR

• If destroyed, transplant is needed

Endothelium

What is this?

• Pigmented

• Acts as a diaphragm to create the pupil

Iris

What is this?

• 1-8mm in diameter

• 25% of the population has anisocoria

Pupil

What is this?

• Between the iris and the cornea’s endothelium

• Contains aqueous humor

Anterior Chamber

What is this?

• Behind the iris and in front of the lens

Posterior Chamber

What is this?

• Consists of…

  • Iris

  • Ciliary Body

  • Choroid

Uvea

What is this?

• Just behind the iris

• Connects to the lens via the zonules and connects the choroid to the iris

• Makes aqueous humor

• Allows for accommodation

Ciliary Body

What is this?

• Smooth and flat part of Ciliary Body

Pars Plana

What is this?

• Anterior folded part of Ciliary Body

• Folds form into ciliary processes

• Zonules connect the processes to the lens

Pars Plicata

What is this?

• Highly vascular

• Nourishes the back of the eye

Choroid

What is this?

• Formed from arterial blood in the ciliary processes

• Fills the anterior chamber

• Secreted to the posterior chamber via the ciliary body, then into the anterior chamber via the pupil

• Fluid leaves the anterior chamber via the CONVENTIONAL (Trabecular) or NONCONVENTIONAL (Uveoscleral) pathway

Aqueous Humor

What are the functions of Aqueous Humor?

• Maintains IOP and helps maintain shape

• Helps focus light

• Provides nutrients

• Removes waste from anterior chamber

• Immunologic

What is this?

• Trabecular meshwork and Schlemm’s Canal

• Located in the anterior chamber

• Aqueous humor moves from the anterior chamber into the trabecular meshwork then into Schlemm’s Canal to travel to the bloodstream

• Vital in determining IOP

Conventional Pathway

What can occur is IOP is elevated?

Glaucoma and optic nerve damage

What is this?

• Lies anterior to Schlemm’s Canal

• Little filtration of fluid that leaves via this route

• Ciliary muscle tone determines the balance between the two routes

• When the ciliary muscle is relaxed, more fluid leaves this way

Nonconventional Pathway

What is this?

• Biconvex structure behind the iris

• Focuses light

• Flexible

• Becomes less flexible with age

• Loses clarity by age 60-80

• Avascular

• Held in place by lens zonules

Lens

What is this?

• Behind the lens “jelly”

• 2/3 of the eye’s body

• Filled with vitreous humor

Vitreous Body

What is this?

• Not to be confused with aqueous humor

• Firmer and more gel-like

• Helps hold retina in place

• Connected to retina at periphery, macula, and optic disc

• Not continuously replenished

• Anything that gets in MUST be surgically removed

• Floaters are shadows of clumps of collagen present here

• Shrinks and pulls away with age

Vitreous Humor

What is this?

• Ganglion cell axons run to the brain via the optic nerve

• Activated when light travels through the thickness of the retina and activates the rods and bones

Retina

What are the layers of the Retina?

• Pigment Epithelium

• Photoreceptors

• Outer Limiting Membrane

• Outer Nuclear Layer

• Outer Plexiform

• Inner Nuclear

• Inner Plexiform

• Ganglion Cells (Nuclei)

• Nerve Fiber Layer

• Internal Limiting Membrane

What Layer of the Retina is this?

• Outer and inner receptors have cones and rods

Photoreceptors

What Layer of the Retina is this?

• Cell bodies of cone and rods

Outer Nuclear Layer

What Layer of the Retina is this?

• Cone and rod axons

Outer Plexiform

What Layer of the Retina is this?

• Cell bodies of horizontal cells, bipolar cells, amacrine cells

Inner Nuclear

What Layer of the Retina is this?

• Dendrites of ganglion cells

Inner Plexiform

What Layer of the Retina is this?

• Axons of ganglions

Nerve Fiber Layer

What Layer of the Retina is this?

• Separates the retina and the vitreous

Internal Limiting Membrane

What is this?

• Collect info about light and movement

• Activated in dark (scotopic) conditions

• Rhodopsin is the photopigment

• Activated by light as it is reflected back into them

• Face away from the retina

Rods

What is this?

• Responsible for color vision

• Activated in light (photopic) conditions

• Iodopin is the photopigment

• Activated by light as it is reflected back into them

• Face away from the retina

Cones

What is this?

• At its center is the fovea

• Light reflects and lands here

Macula

What is this?

• Absolute center of vision

• ONLY contains cones

Fovea

What is this?

• Blind spot

• Where nerve fibers exit the eye and becomes the optic nerve

• Where central artery enters and retinal vein exits

• Central depression called the physiologic cup

Optic Disc

What is this?

• CN II

• Protected by CSF / meningeal covering and cushioned by fat

• Signal is ultimately decoded by the occipital cortex

• Part of central nervous tract

Optic Nerve

Where is light converted to electrical signals?

Retina

What carries the electrical signals from the eye to the brain?

Optic nerves via the optic canal

What is the optic chiasm?

Where the optic nerve joins the CONTRALATERAL optic nerve in the middle cranial fossa

Where do most electrical signals synapse?

Lateral geniculate nucleus of the thalamus

Where do neurons in the lateral geniculate nucleus send their axons?

Primary visual cortex of the occipital lobe

What CN is this?

• Extrinsic eye muscles and pupil dilation

  • All except LR and SO

  • Levator palpebrae superioris

  • Ciliary body

  • Iris sphincter

Oculomotor Nerve (III)

What CN is this?

• Sensation to eyeball structures, nasal mucosa, cutaneous areas around the eye, dorsum of nose, and frontal area

• Divided into 3 branches

Trigeminal Nerve (V)

Which Trigeminal Branch is this?

• Sensation to cornea, conjunctiva, nasal mucosa, cutaneous nose and scalp, frontal sinus, part of meninges

• Further broken down into branches:

  • Infratrochlear

  • Anterior ethmoid

  • Posterior ethmoid

  • Lacrimal

  • Supraorbital

  • Supratrochlear

  • Nasociliary

Ophthalmic Branch (V1)

Which Trigeminal Branch is this?

• Sensation to lower eyelid, cheek, nares, upper lip, upper teeth and gums, nasal mucosa, palate, and roof of pharynx, maxillary, ethmoid, and saphenous sinuses, and part of meninges

Maxillary Branch (V2)

Which Trigeminal Branch is this?

• Sensation from lower lip, lower teeth and gums, chin and jaw, parts of the external ear, and part of the meninges

• Carries touch, position, pain, temperature from the mouth

Mandibular Branch (V3)

What CN is this?

• Controls Lateral Rectus

• Moves the eye laterally (outward) away from the nose

Abducens Nerve (VI)

What CN is this?

• Controls facial expression, eye closure, taste

• Involuntary functions include tear gland and salivary gland stimulation

• Divided into 5 branches

Facial Nerve (VII)

What are the Branches of the Facial Nerve?

• Temporal

  • Corneal reflex efferent limb

• Zygomatic

  • Orbicularis Oculi

• Buccal

• Mandibular

• Cervical

What CN is being tested?

• CLOSE your eyes

• Attempt to OPEN eyes

• WRINKLE forehead

• SMILE

Facial Nerve (VII)

Painful light sensitivity

Photophobia

What part of the eye exam should be done FIRST?

Visual Acuity

What is used to test distant vision?

Snellen Chart

What is used to test near vision?

Rosenbaum Chart

What test is this?

• Accounts for refractive errors

• Admits only central light rays that do not need to be refracted by the cornea or pens

• If vision improves with this, there is likely a refractive error present

Pinhole Testing

Reduction in color vividness (MC reds)

Dyschromatopsia

Loss of red

Protanopia

Loss of green

Deuteranomaly

What visual fields test is used to test for neurological defects?

Gross / Formal Testing

What visual fields test is used to test for macular degeneration?

Amsler Grid

What Visual Field test is this?

• Measures only the outer edge of visual fields

• Not very exact

• User dependent

Gross Testing

What Visual Field test is this?

• Uses Humphrey Field Analyzer (HFA)

• Automated perimetry test that measures response to objects in different visual fields

Formal Testing

What Visual Field test is this?

• Detects visual disturbances caused by problems with the retina (macular degeneration)

• Patients look at the small dot in the center and test each eye separately

• Patients with macular degeneration may see wavy or missing lines

Amsler Grid

What is the MCC of Anisicoria?

Sympathetic / parasympathetic imbalance

What Pupil test is this?

• Detects afferent defect (MARCUS GUN PUPILS)

• (+) Eyes will not constrict well when light is shown

Swinging Light Test

What part of the eye exam tests the Extraocular Muscles (EOM)?

• Corneal reflex

• Strabismus

• Cardinal fields of gaze

What CN are tested with the Corneal Reflex?

• V1 of Trigeminal (V) - Sensory

• VII (Facial) - Motor

What part of the eye exam tests for Ocular Motility and Alignment?

• Cardinal movements (6)

• Eye alignment tests

  • Corneal light reflection

  • Cover test

What test is this?

• Tests for strabismus

• Common in children

• Have the patient fixate on an object

• Cover the fixating eye and observe for movement of the other eye

Cover / Uncover Test

In which direction will an exotropic eye move?

Inwards

In which direction will an esotropic eye move?

Outwards

What part of the eye is being examined?

• Limited without a slit lamp

• Can shine light obliquely into chamber

• Check for hypopyon or hyphema

Anterior Chamber

What tool is this?

• Looks through anterior and posterior chamber into vitreous chamber

• Can see red reflex, optic disc, macula, and vessels

• Slit lamp to see lid, conjunctiva, cornea, iris

• Anterior chamber to look for cells or blood

• Darken the room

Ophthalmoscope

What can be used to dilate the eyes?

• Tropicamide 1%

• Phenylephrine 2.5%

• Cyclopentolate 1%

What tool is this?

• Magnified, 3D view of the lids, cornea, anterior chamber, lens, and vitreous

• Special lenses can be supplemented to see deeper into the eye

• Can also measure IOP

Slit Lamp Exam

What tool is this?

• Used to look for corneal abrasions, foreign bodies, ulcerations, etc

• Less sensitive than Slit lamp exam

• Uses UV light

• Apply 1-2 drops of tetracaine and fluoresciene dye

• Abnormalities will glow

Wood’s Lamp

What tool is this?

• Measures IOP by measuring the resistance of your cornea to pressure

Tonometry

What tool is this?

• Used to irrigate after chemical exposure

Morgan Lens