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Basic Ocular Anatomy

Lynn E. Lawrence, CMSgt (ret),

CPOT, ABOC,COA

Tear Film Layers

oil aqueous

snot

What functions does each layer of the tear perform?

Healthy Tears A complex mixture of proteins, mucins, and electrolytes coated by a lipid layer

• Antimicrobial proteins

• Growth factors & suppressors of inflammation

• Soluble mucin helps stabilize tear film

• Electrolytes for proper osmolarity (295-300)

– pH slightly alkaline (7.4)

Why is a tear salty tasting?

Lipid Secretion: Meibomian Glands

Left: Transillumination of eyelid showing meibomian glands

Right: Secretion of lipid

at lid margin

• The lipid layer restricts evaporation to 5-10% of tear flow – Also helps lubricate

Where does a contact lens rest?

Lipid Secretion: Meibomian Glands

(WC Posey, Diseases of the Eye, 1902)

Transillumination of meibomian glands

(Transillumination image from Dry Eye and Ocular Surface Disorders, 2004)

What eye is this?

How does the lipid layer aid in contact lens wear?

A Healthy Tear Film

A healthy tear film is comprised of 3 layers: Mucin, Aqueous, and Lipid

800 nm

8,000 nm

100 nm

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Two Primary Forms of Dry Eye

800 nm

8,000 nm

100 nm

The two primary forms of dry eye are Evaporative Dry Eye, also known as

Meibomian Gland Dysfunction or MGD and Aqueous Dry Eye. The majority of

dry eye sufferers have MGD.

Remember science class? Oil floats.

Oil does not mix with

water, but rather sits

on top of water.

Oil is what keeps

water from

evaporating.

Oil & Water

The aqueous (water) layer

provides natureal lubrication

and is produced by the

lacrimal glands.

The Tear Film Structure In Our Eyes

The aqueous layer is

protected by the lipid (oil)

layer that is produced by the

meibomian glands located in

the eyelids.

When your meibomian glands

do not produce sufficient oil,

water evaporates causing

burning, redness, dryness,

irritation and eye fatigue. This

is called Meibomian Gland

Dysfunction or MGD.

The Meibomian Glands

The meibomian glands are located in the eyelids

The meibomian glands are located in the eyelids

Meibomian Glands & Blinking

When we blink the meibomian glands express the necessary protective oils

Blockages in the meibomian glands result in insufficient oil to coat the tear film

Blinking stimulates the meibomian glands to secrete oils and spread a protective oil layer across the tear

film. When we partially blink the eyelids do not touch, so no pressure is applied at the meibomian glands to

release these oils. Over time the oils harden in the glands and blockages develop.

LipiView II: Interferometer

Avg LLT – Average Lipid

Layer Thickness (LLT) in

nanometers (nm).

Number less than 90

indicates increased

probability for MGD.

Avg LLT 35 nm Avg LLT 90 nm

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LipiView II: Partial Blink Analysis

A decrease in lipid layer thickness is

associated with incomplete blinking.

Increase in visual fatigue is associated with

incomplete blinking.

Presence of partial blinks greater than 40%

of total blinks is considered contributory to

dry eye condition.

If partial blinking is present, patient

education and blink training should be

considered.

LipiView II: Dynamic Meibomian Imaging

Normal Gland Structure

Gland Truncation & Dilation

Severe Gland Drop Out

Meibomian gland structure is observed with Dynamic Meibomian Imaging (DMI). DMI produces three

images (surface illumination, transillumination and merged) to capture a comprehensive view of

meibomian gland structure.

If left untreated, the glands can shrink and deteriorate. The loss of glands is unlikely to be reversible.

Failure to treat blocked glands is likely to lead to further structural compromise.

Transillumination Surface Illumination Merged (Surface + Transillumination)

Intervention & Prevention

Lower Eyelid

Meibomian

Glands Over Time

Current model of treatment

is interventional.

Future of MGD treatment

must be preventative.

Prevention Intervention

Upper Eyelid

Meibomian Gland Evaluator

Temporal

Central Nasal

Meibomian gland function is evaluated by assessing how glands respond to

gentle force, imitating that of a deliberate blink.

CLEAR OIL SECRETION

Glands are functioning using the

MGE

NO OIL SECRETION (BLOCKED)

No oil is expressed using the MGE

OPAQUE SOLID SECRETION

Glands not functional; requires more

force than the MGE

Anatomy

What function does the pupil have?

Blue Eyes

• More Like to have:

– Melanoma

– AMD

– Photophobia

– Better with pain

http://www.msn.com/en-us/health/medical/7-things-your-eye-color-says-about-your-health/ar-BBiNSGg?li=AAa0dzB&ocid=IDMD&page=4&fullscreen=true#image=4

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The Eyelid

• 7 Layers of the eyelids 1. Skin-thinnest layer

2. Subcutaneous

connective tissue

3. Striated Muscle

4. Sub-muscular connective tissue

5. Tarsal plate or fibrous layer

6. Smooth muscle

7. Conjunctiva (Bulbar/Palpebral)

How are Hordoleum and Chalazions treated?

Eyebrows and Eyelashes • Eyebrows

– Thickened ridge of skin with short hairs

– Diverts perspiration • Eyelashes

– Also protects – Sebaceous glands at base of each

lash are called Glands of Zeis which produce a lubricating fluid • Fluid can harden and clog the

gland, producing a stye or painless chalazion. If painful and infected it is called an external hordeolum

Cataracts (myotonia) are caused by?

Lacrimal Apparatus

• Sometimes a person cannot produce natural tears that they might need some punctal plugs.

What are the three main parts of the crystalline lens?

Anatomy and Physiology of the Eyeball

3 Layers • Fibrous Layer *Cornea

*Sclera

• Vascular Layer *Choroid

*Ciliary body *Iris

• Nerve Layer *Retina

*Macula

*Optic nerve

What is the main function of each layer?

Sclera

• White in color

• Primary function is protection

• Pierced posteriorly by the optic nerve

• Acts as insertion points for the six EOMs

• Junction between the cornea and sclera is called the Limbus

What is the total power of the eye?

Conjunctiva

• An epithelial membrane which covers the anterior sclera and continues to the back surfaces of the lids to form a conjunctival sac

• Has blood vessels which can burst and cause subconjunctival hemorrhage

• Three parts – Bulbar – Palpebral – Fornix - where bulbar and

palpebral meet

Name the mucus producing cell?

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Cornea

• Index of refraction is 1.37

• Approximately .5mm in thickness

• Transparent Organ (no blood vessels / avascular)

• Primary function is refraction of light rays

• Refractive power approx + 45.00 D

What is it called when blood vessels grow onto the cornea? What happens when a patient gets a scar in the visual pathway?

What is the crossover point for the nasal optic nerves?

Cornea

• Composed of 5 layers – Epithelium…24 hr healing

• Outermost layer

• 5 cell layers thick

• Heals very quickly

• Does not scar

– Bowman's membrane- layer just under the epithelium NOTE: will scar

– Stroma – middle tissue that forms 90% of the cornea

– Descemet's membrane- thin elastic layer deep in the cornea

– Endothelium - only one cell layer thick; lines undersurface of the cornea, where it regulates corneal water content

What cranial nerve is tied to corneal sensations?

Confocal Scanner

Endothelial detail with nucleiEndothelial detail with nuclei

Epithelial detail with nucleiEpithelial detail with nuclei

Which cells do not regenerate Epithelium or Endothelium?

Aqueous Humor

• Manufactured by ciliary body • Characteristics:

– Clear – Watery consistency (99%

H2O) • Functions

– Refraction of light – Intraocular Pressure (IOP) – Probably nourishes

posterior surface of the cornea and the crystalline lens

• Flows from posterior chamber through the pupil into the anterior chamber

How does aqueous flow out of anterior chamber?

Crystalline Lens...approx 12-14 diopters of power

• Functions – Refraction of light

– Accommodation

• Focus adjustment of the eye

• Presbyopia is the loss in accommodation

– First noticed around age 40. Due to a loss in flexibility of the lens

Name the three main parts of the lens?

Crystalline Lens

• 3 things happen during accommodation: – Pupils constrict

– Eyes converge

– Lens gets thicker

• The crystalline lens contains a high degree of protein – Changes in the lens protein causes the lens to lose its transparency

which is a condition termed "cataract"

– Aphakia is the absence of a lens. It can be removed during cataract

extraction

How much focusing power does the lens have?

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Iris

• Most anterior portion of the vascular layer

• Gives the eye its color, i.e. blue eyes, brown eyes, etc.

• Consists of blood vessels, pigment and muscle tissue

• Regulates light

• Smaller with age

What does the sphincter muscle control?

Ciliary Body

• Located near the base of the iris and posterior to it

• Composed of blood vessels and muscle fibers (ciliary muscle)

• Cilliary process produces aqueous

Ciliary body is attached to suspensatory ligaments called?

Vitreous Chamber

• Functions: – Refraction of light

– Internal support

• Spots in vision may be floaters in the vitreous

Post vitreous detachment

How many chambers are inside the eye?

Nerve Layer - Retina

• Visual Receptors are Cones and Rods – Cones

• Produce color vision • Give improved acuity • Used in day vision = “Photopic” = normal and high levels of

illumination

– Rods…120 million • Produce black and white vision • Function in dim light = “Scotopic” = low level of illumination

– Cones and Rods… 6 million • Used under mesopic vision = between scotopic and photopic • Both rods and cones are used.

The _____ is the strongest refractive media and has about ____ diopters of power.

Which cranial nerve controls the superior oblique muscle?

The retina (Cranial Nerve II)

Vitreous

Pigment epithelium

The levator palpebrae raises the eyelid and is innervated by CN #?

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Retina – 10 layers

• Pigment epithelium

• Rods

• Cones

• Outer plexiform layer

• Horizontal cells

• Bipolar cells

• Amacrine cells

• Inner plexiform layer

• Ganglion cells

• Nerve fiber layer

Vitreous (inside of eye)

Outside of eye

Cross-sectional image of live tissue; a virtual biopsy

Identification of Retinal Layers

IS/OSIS/OS RPE/CCRPE/CC

ILMILM GCLGCL NFLNFL

ChoroidChoroid

IPLIPL OPLOPL

NFL: Nerve Fiber Layer ILM: Inner Limiting Membrane GCL: Ganglion Cell Layer

IPL: Inner Plexiform Layer OPL: Outer Plexiform

IS/OS: Junction of inner and outer photoreceptor segments RPE: Retinal Pigment Epithelium CC: Choriocapillaris

Stratus OCT™

Nerve Layer - Retina

• Optic nerve head (optic disc)

– No receptors - physiological blind spot

– Point of exit of optic nerve

– Appears yellow compared to the orange retina

What is Pars Plana?

Nerve Layer - Retina

• Ora Serrata – Land mark attachment site

for choroid and retina

– Most anterior portion of retina

– Nearly all rods

How many layers are in the retina?

New Advancement

• ARCUS II Retinal Prosthesis

• Netherlands 2nd

• Patient is Jerone Perk, has retinitis pigmentosa

• Dr. Marco Mura, MD

Anatomy and Physiology of the extraocular muscles

The Extra-ocular Muscles (EOM) Organized into an umbrella-like

bundle among the orbital fat, orbital blood vessels and nerves

Six muscles associated with eye movements Superior rectus (S.R.) Inferior rectus (I.R.) Medial rectus (M.R.) Lateral rectus (L.R.) Superior oblique (S.O.) Inferior oblique (I.O.)

How many cranial nerves control these 6 muscles?

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Extra Ocular Muscles

What is the name of the point where the muscles come together?

Extraocular Muscles

• Medial Rectus

- Most powerful, adduction, CN III

• Inferior Rectus

- Primary is depression, CN III

• Lateral Rectus

- Abduction, CN VI

• Superior Rectus

- Primary is elevation

Which muscle close the eye lid and is innervated by cranial #7?

Muscles and Function

• LR6…SO4…3 – Rectus

– Obliques

– Intorsion

– Extorsion

– Elevation

– Depression

An obvious upward/superior deviation of the eye is called?

Bony Orbit

• Openings of the orbit – Purpose of openings

• Transmit arteries and/or veins to and from the orbit

• Transmit nerves to and from the orbit

– Types of openings

• Fissures (crevices/cracks)

• Foramina (holes)

– Major openings

• Optic foramen - II cranial nerve - Optic Nerve

• Supraorbital fissure - IV cranial nerve - Trochlear Nerve

The transition zone between the sclera and the cornea is called?

Orbit

1. Frontal bone…forehead

2. Ethmoid bone…weakest

3. Palatine bone…smallest

4. Zygomatic bone…strongest

5. Lacrimal bone

6. Maxillary bone

The conjunctiva has two divisions, they are?

Cranial Nerves LR6SO43

Muscles

• Lateral rectus muscles #6 …abducens nerve

• Superior Oblique #4 …trochlear nerve

• All other muscles are controlled by #3 … oculomotor nerve

Name the 3 chambers of the internal eye?

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Anatomy Physiology

• The Orbit

- Bones, etc.

• The Sinuses

- Locations

• Human Body Planes

• External Structures

- Eyelids

- Conjunctiva

- Eyelashes and Eyebrows

• Lacrimal System

The outer layer of the eyeball is called?

Visual Pathway Objectives

• Define the visual pathway

• Identify structures in the visual pathway

• Testing used for the visual pathway

• Identify defects within the visual pathway

Anisometropia occurs when there is a _____________?

Visual Pathway

• Physical

• Physiological

• Psychological

What causes your physiological blind spot?

Visual Pathway

• Visual pathway has seven structures – Retina

– Optic Nerve

– Optic Chiasm

– Optic Tract

– Lateral Geniculate Body (LGB)

– Optic Radiations

– Visual Cortex …where vision occurs

Aniseikonia occurs when an object viewed by one eye is _________?

Visual Pathway

Antimetropia occurs when __________ ?

Retina

• Divided into four quadrants like the brain

• Fovea at exact center

• Optic nerve head is located in nasal half

• Each quadrant sees the exact opposite visual field

What is an exudate? What is papilledema?

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Optic Chiasm

• Temporal fibers do not cross

• Nasal fibers do cross

• Some fibers from the macula cross while others do not

What part of the brain does the vision occur?

Growth beneath Pituitary Gland

An area of blindness within a visual field is called?

Visual Field Defects • Common types of field

defects – Blind spots - Areas of

blindness in the visual field

– Hemianopsia - Blindness in one half of the visual field of one or both eyes • Homonymous - Involving the

nasal half of the visual field of one eye and the temporal half of the visual field of the other eye

• Incongruous -

Homonymous heminopia

Incongruous homonymous

Binasal defect

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Is this possible? You be the judge Review Questions

• The point where the upper and lower eyelids meet is called a. ora serrata

b. canthus

c. joint

d. sphinx

• The blockage of the meibomian gland is called the ___________ when it causes pain, and the _________ when it does not cause pain.

Review Questions

• The eyelid will protect your eyes from… a. blinking

b. dust particles

c. stray tears

d. a burning punctum

• What main muscles raises the eyelid?

• Name the five layers of the cornea in order

Review Questions

• The drain port for tears is called?

a. canal of Schlemm

b. punctum

c. lacrimal gland

d. zonnule of Zinn

• In what layer of the eye will chronic diseases normally manifest?

• What structure prevents a contact from going behind the globe of the eye?

Review Questions

• What is the most anterior part of the retina.

• What is the total power of the Cornea, the crystalline lens assembly, and the overall eye?

• What is the most posterior layer of the retina?

Review Questions

• What are the layers of a tear film?

• Where is tear mucin produced?

• Why is the tear film important in contact lens wear?

• The optic nerve is which cranial nerve?

• What function does the Canal of Schlemm have?

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Review

• Opia means what?

• What is the difference between a tropia and a phoria?

• Avascular means what?

• How many extra-ocular muscles are oblique?

• What does the root word “papill” mean?

Review Questions • Identify the name for the 3 parts of the conjunctiva

• In what layer of the eye will the retina be found?

• What is the strongest bone of the bony orbit?

• What muscle of the lid would be involved in ptosis?

Review Questions

• _________ exist when the foveal lines of sight of the two eyes do not point at the same object. – A. binocularity – B. strabismus – C. conjunctivitis – D. FB sensation

• Of the following all are anomalies of the binocular system except: – A. strabismus – B. Amblyopia – C. anomalous correspondence – D. conjunctivitis

Review Questions

• When the power of the crystalline lens correspond with axial length of the eye, so that parallel light rays are appropriately refracted to focus on the retina is called? – A. emmetropia – B. ammetropia – C. hyperopia – D. myopia

• An opacity of the crystalline lens is known as? – A. photophobia – B. cataract – C. edema – D. aphakia

Review Questions

• Which test checks for eye movement and helps detect the dominate eye? – A. muscle H – B. cover test – C. visual acuity – D. myopia

• Glaucoma screening test that used puff of air onto the eye surface: – A. NCT – B. snellen – C. amsler grid – D. accommodation

Review Questions

• Which test uses Pseudo Isochromatic Plates? – A. IOP – B. color test – C. cover/uncover – D. snellen

• This checks the power of the eye:

– A. NCT – B. taking case history – C. Autorefractor – D. taking blood pressure

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Review Questions

• Which test is used to check six cardinal position of gaze for motility? – A. Muscle H – B. APD – C. Amsler Grid – D. Tropia

• Examination of the eye is performed by using a slit lamp or another name for slit lamp is: – A. non-contact tonometer – B. biomicroscope – C. pupilometer – D. lensometer

Review Questions

• What is a good tear BUT?

• What device checks the brain-eye connection?

• What device measures the distance between the pupils?

• What device measures corneal thickness?