Ocular Anatomy Flashcards
Describe the 7 steps of how an image gets to the brain
- Light enters the eye through the cornea
- Enters the chamber behind the cornea
- Moves through the pupil
- Light travels through the crystalline lens and vitreous gel before reaching the retina
- Light forms an impulse on the retina
- The optic nerve carries the impulse to the brain
- The image from each eye is fused and the image is formed in the brain
What is the total power of the average human eye?
Approximately 60 diopters
In the total power of the average human eye, how many diopters are provided by the Cornea?
Approximately 43 diopters
In the total power of the average human eye, how many diopters are provided by the Crystalline lens?
Approximately 17 diopters
What do our Eye Lids do for us?
- Protect the eyeball
- Help lubricate the eye
- Protect the eye from debris
How many times a minute does the average person blink?
15-20 times
There is some evidence that the process of closing our eyes helps us to do what?
to concentrate
Which muscle closes the eyelids?
the Orbicularis Oculi muscle
What are the 3 Tunics of the Eye
- Outer Tunic (fibrous tunic) which consists of the sclera and the cornea
- Middle Tunic (vascular tunic) which consists of the Choroid, Iris, Crystalline lens, Pupil, and Aqueous Humor
- Inner Tunic which consists of the Optic Nerve, Vitreous Humor, Retina, Macula, and Fovea
What is the Sclera?
a dense, very strong and protective coat of the eye that helps maintain the shape of the eye
What is the Cornea?
the transparent section of the outer tunic which has no blood vessels.
The cornea is also where light enters the eye and it provides about 43 diopters of power
How thick is the Cornea?
approximately 1/2 mm thick at the center, 3/4 mm thick at periphery
What is the diameter of the Cornea?
Approximately 11.5 mm
What are the 5 layers of the Cornea?
- Epithelium
- Bowman’s Membrane
- Stroma
- Descemet’s Membrane
- Endothelium
What is the outermost layer of the Cornea?
The epithelium
Which heals faster, the Epithelium or Skin? How fast?
the Epithelium heals faster, within 24 hours
Which layer of the Cornea separates the Epithelium and the Stroma, and protects the Stroma?
Bowman’s Membrane
Which layer of the Cornea contains 90% of it’s total thickness?
The Stroma
What is the Stroma composed of?
Collagen
Which layer of the Cornea maintains the Cornea’s transparency?
The Stroma
Which layer of the Cornea separates the Stroma from the Endothelium?
Descemet’s Membrane
What does Descemet’s Membrane do?
as thin, yet very strong tissue, it serves as a protective barrier against infections and injuries
Which layer of the Cornea is the inner-most layer?
The Endothelium
What is the Endothelium’s primary purpose?
to pump excess fluid out of the Stroma
If too many Endothelium Cells were to be destroyed, what could be the result?
Blindness
Does the Tear Film cover the outer layer of the Cornea, or the inner layer?
The Outer layer
Is the Aqueous Humor reside on the outer layer of the Cornea, or beneath the inner layer?
Beneath the inner layer of the cornea
What are the 3 Tear Layers?
- Lipid Layer
- Lacrimal Layer
- Mucoid or Mucin Layer
What is the Lipid Layer of Tears?
the outer tear layer that prevents evaporation
What is the Lacrimal Layer of Tears?
Middle tear layer that prevents infection and nourishes the cornea
What is the Mucoid or Mucin Layer of Tears?
the layer that allows the watery layer to spread evenly over the surface of the eye and helps remain moist and lubricated.
It also provides the underlying cornea with nourishment and helps tears stick to the eyes surface.
Which of the three Tear layers is the outermost layer?
the Lipid layer
Which of the three Tear layers is the middle layer?
the Lacrimal layer
Which Tear layer allows the watery layer to spread evenly over the surface of the eye, helping the eye remain moist and lubricated?
the Mucoid or Mucin layer
Which Tear layer prevents evaporation?
the Lipid Layer
Which Tear layer prevents infection and nourishes the cornea?
the Lacrimal layer
Which Tear layer helps the tears stick to the surface of the eye?
the Mucoid or Mucin layer
Which part of the eye is a dense, very strong and protective coat of the eye that helps maintain the shape of the eye?
The Sclera
Which part of the eye is the transparent section of the outer tunic which has no blood vessels?
The Cornea
What are the 3 parts of the Middle Tunic?
- Crystalline Lens
- Iris
- Pupil
Which part of the Middle Tunic is a colored membrane behind the cornea?
The Iris
What does the Iris control and how?
controls the amount of light into the eye by controlling the pupil size.
Which part of the Middle Tunic provides the ability to focus?
the Crystalline Lens
Which part of the Middle tunic provides around 17 diopters of power?
the Crystalline Lens
Which part of the Middle Tunic is a colorless structure which helps to bring rays of light into focus on the retina?
The Crystalline Lens
Which part of the Middle Tunic is the area behind the cornea where the light enters the eye?
the Pupil
What different factors go into your eye color?
- Pigmentations from melanin
- Scattering of light
- Density of the Stroma
Where does the pigmentation in your eye color come from?
melanin
Where does the scattering of light which effects eye color occur?
the stroma of the iris
Is the stroma of the Iris the same as the stroma layer of the cornea?
NO
How many genes are associated with eye color?
as many as 16 genes
What is the Primary Pigment of the Iris?
Melanin
Pigmentation varies from which color to which color?
Light brown to Black
Do Brown eyes have higher or lower concentrations of melanin?
Higher concentrations
The appearance of Blue, Green, and Hazel eyes comes from what?
scattering of light from the stroma of the iris
How much melanin is contained in lighter eyes, more or less?
less
Why are those with lighter iris color more light sensitive?
less melanin to absorb the light
Eye color is dependent upon lighting conditions, especially in lighter colored eyes. True or False?
True
Which pigments are never present in the human eye?
Blue and Green
Is Accommodation required for Near or Far viewing?
Near viewing
What happens to the lens in your eye when your eye is Accommodating?
The lens get thicker, creating more Plus Power
What is Presbyopia?
when the crystalline lens has lost elasticity and the ability to focus at near.
What options are the options for correcting Presbyopia?
Progressive lenses, bifocals, or reading glasses
As we age, what happens to our eyes muscle fibers and the crystalline lens?
they lose flexibility and cause presbyopia
What causes a Cataract?
as we age, the Crystalline lens loses its transparency and get’s cloudy, eventually to the point that compromises vision.
When inserting an Intraocular Lens to replace a cataract, where is the incision usually made?
at the Limbus where the cornea and sclera meet
When was the first Intraocular Lens implanted?
1949
Since when has the use of Intraocular Lenses increased?
1970’s
True or False - A majority of Patients don’t have IOL’s inserted directly after the Cataract removal
False, most do
What is Aphakia?
When the crystalline lens has been removed from the eye and a new lens was NOT inserted.
What is the term for when a new lens has not been inserted after the crystalline lens has been removed?
Aphakia
What is Pseudophakia?
when the natural crystalline lens has been removed and a new man made lens has been inserted
What is the term for when a new lens has been inserted after the crystalline lens has been removed?
Pseudophakia
Which part of the eye is the intermediate coat of the eye that provides nourishment?
the Choroid
Which part of the eye is a water-like substance that fills the area between the cornea and the lens?
The Aqueous Humor
Which part of the eye provides the cornea and the lens with oxygen and nutrients?
The Aqueous Humor
Why does the cornea and lens need the Aqueous Humor to provide oxygen and nutrients?
because the cornea is transparent and has no blood vessels to provide those needed things
Which part of the eye serves to regulate the pressure in the eye?
The Aqueous Humor
What causes Glaucoma?
when the Aqueous humors’ drainage is inhibited, causing increased pressure in the eye
What happens when Glaucoma is left untreated for long periods of time?
it can cause permanent damage to the eye, including blindness
What parts make up the Inner Tunic?
The Vitreous Humor, Retina, and Optic Nerve
Which part of the Inner tunic is the innermost coat of the eye and connected to the Optic Nerve?
Retina
Where in the eye do you find Rods and Cones?
The Retina
What are Rods and what do they do?
a layer of cells on the retina for Peripheral Vision, B&W vision, and night-time viewing
What are Cones and what do they do?
a layer of cells on the retina used for color vision and visual acuity
Where is the Macula?
on the Retina
Where on the Retina are Cones most numerous?
on the Macula
Where on the Macula itself are Cones most concentrated?
on the Fovea
What is the Optic Nerve?
a nerve that carries impulses from the retina to the brain
What part of the eye carries impulses from the retina to the brain?
the optic nerve
What is the Vitreous Humor?
a soft transparent material filling the center of the eyeball
What is the transparent material in the Vitreous Humor also known as?
Vitreous Gel
Does Vitreous Gel regenerate itself like the Aqueous Humor does?
No
What is the Optic Chiasm?
the pathway taken by impulses received from each eye through the optic nerve to the brain.
Where in the brain do impulses end up?
the visual cortex
What happens when impulses from our eyes get to the visual cortex?
the brain fuses the two images and one image is formed
How many Extra-ocular muscles are there in the eye and what are they for?
6 different muscles, they help rotate the eye in all directions
Where are all Extra-ocular muscles connected?
to the sclera of the eye
What is the separate muscle that closes our eyelids?
the orbicularis oculi muscle
What are the 6 Extra-Ocular muscles?
- Superior Oblique
- Inferior Oblique
- Superior Rectus
- Medial Rectus
- Lateral Rectus
- Inferior Rectus
If one of the Extra-Ocular muscles is weaker then normal, does it effect our vision?
yes, it can cause issues like Diplopia(double vision)
What are Prism’s in glasses used for?
To help correct double vision, aligning the two images so that only one image is seen
What is a Tropia?
A turning of the eye away from the normal position that is present at all times. AE. a lazy eye
What is a Phoria?
A turning of the eye away from the normal position that is only present some of the time. Typically when the patient stops focusing with both eyes on something.
What are the 4 direction designations for diagnosing Phoria’s/Tropia’s?
Exo = Out
Eso = In
Hyper = Up
Hypo = Out
What three things are required for the eye to successfully see Near Vision?
- Accommodation occurs
- The eyes converge
- The pupils constrict
What is the Visual condition called when the image focuses behind the retina?
Hyperopia (farsightedness)
What is the Visual Condition called when the image focuses in front of the Retina?
Myopia (nearsightedness)
What is the Visual Condition called when the image focuses on the retina?
Normal
