Unit 8: The Eye

1. Sclera

2. Choroid

3. Retina

The three layers of the eye

Sclera

Outer, fibrous layer that forms the main structure and spherical shape of the eye.

Cornea

Anteriorly, the sclera has a clear, round window, called the________for light entry.

T

T/F: Extrinsic eye muscles, which aim the eye towards areas of interest also anchor on the outer sclera.

Choroid

Middle layer that is highly vascularized (contains blood vessels). Supplies oxygen and nutrients to metabolically active areas of the eye, especially the photoreceptors of the overlying retina. It is is darkly pigmented and also functions to absorb stray light rays.

Iris

Muscular structure in the eye that works similar to the aperture of a camera and regulates the amount of light entering the eye through an opening at the center (pupil).

Lens

Behind the iris is a crystalline protein structure called the_______, which focuses light rays on the retina in the rear, vitreous chamber of the eye.

Ciliary

The lens is anchored by tiny suspensory ligaments onto a ______ body, which can contract and change the shape of the lens to permit focusing on near vs distant objects.

Aqueous humor

The ciliary body produces this watery fluid, which circulates in the space between the lens and the cornea (anterior and posterior chambers). This fluid also pressurizes the eye.

Glaucoma

Excess pressure in the eye.

Accommodation

The changing of the eye’s focal length, from viewing close objects to far away objects

Near vision

Suspensory ligament tension is released on the lens, causing the lens to “ball up” or become more spherical or rounded.

Distance vision

Involves pulling on the suspensory ligaments, which stretches the lens into a flattened, disc-like conformation.

Presbyopia

“Far sightedness” (can see far objects, but not close objects). Seen in everyone by mid 40s-50s

The protein structure of the lens becomes cross-linked and as a result, the lens gets locked into its flattened, distance conformation and we have difficulty seeing close objects.

What causes presbyopia? How does the eye change as we age?

Vitreous humor

Jelly-like fluid, fills the rear chamber of the eye

Retina

Located in the posterior portion of the vitreous body. Also contains a deep layer of specialized nerve cells called photoreceptors

Photoreceptors

Produce electrical signals in response to light.

Rods

Photoreceptors that respond to black and white images, plus night vision

Cones

Photoreceptors that are sensitive to specific colors of light.

Fovea

When focusing on an object of interest, most of the light for that image is focused an area of the retina called the________, which contains an unusually large concentration of these color discriminating cone cells.

photoreceptors

Deepest retinal layer

Bipolar cells

Middle retinal cell layer

Transfer signals from photoreceptors to ganglion cells

Role of bipolar cells

Ganglion cells

Final retinal cell in the visual pathway

Optic nerve (Cranial Nerve II)

Ganglion cell axons form this structure

Occipital nerve

Destination of optic nerve signals

Interprets signals into visual images

Function of the occipital lobe

No photoreceptors where the optic nerve exits the eye

Reason for the blind spot or optic disk

Photoreceptors → bipolar cells → ganglion cells → optic nerve → occipital lobe

Pathway of visual signals from the retina to the brain

Optic nerve (Cranial Nerve II)

Cranial nerve responsible for vision

They send visual information out of the eye

Why ganglion cells are important

Optic disk

Location where ganglion cell axons exit the eye

Presbyopia

The most common age-related condition of the eye, beginning around age 40. Age-related far-sightedness. Cannot see close objects clearly.

Cross linking of lens proteins in the eye. Makes the lens more rigid, prevents the lens from changing shape during focusing

What causes presbyopia?

Free Radical Theory of Aging, oxidative agents lead to cross linking and functional loss over time

What theory of aging does presbyopia relate to? Why?

Cataracts

Most common, serious disorder of the eye. Opacities that develop in the protein structure of the lens. Block or scatter light as it travels through the eye and can eventually reduce visual clarity in large portions of the visual field.

50

Approx. _______% of the population 65+ is affected by cataracts

Women, smokers, diabetics

In what populations are cataracts more common?

Cataract surgery

The most common surgical procedure performed in the US, it is usually an outpatient procedure, and generally results in dramatically improved vision and image clarity.

Macular degeneration

Destroys the fovea of the retina, resulting in a loss of our central visual field. It is the leading cause of blindness of the elderly.

Family hx, high BP, atherosclerosis, low Leutine levels in the eye

Risk factors for macular degeneration

Blood vessel degeneration, deposition of a pigment called Drusen

Pathology of macular degeneration

Leutine and vit E supplements, photodynamic tx (uses laser light), drugs (Eylea, injected into the eye)

Treatment options for macular degeneration

Inhibits excess blood vessel growth in injured areas

How does the drug Eylea slow the progression of macular degeneration?

Glaucoma

Results from excessive intraocular pressure in the eye. The pressure can eventually destroy the retina of the eye, resulting in blindness.

Canals of Schlemm

Most forms of glaucoma result from poor drainage of the aqueous humor from the eye, through small veins known as the _________

• Drugs or eye drops that are vasodilators, promoting improved drainage of the aqueous humor

• Laser surgery - enlarge the eye drain ports

Tx for glaucoma

Diabetic Retinopathy

Hyperglycemia in long-term diabetic oxidizes the retina. Third leading cause of blindness in the U.S. Hyperglycemia weakens the blood vessels of the eye, causing hemorrhage, photoreceptor damage, and retinal detachment.

Lasers, drugs, preventative measures (diabetics keeping their blood glucose levels under control)

Tx for diabetic retinopathy

Eylea

Drug that can help with macular degeneration AND diabetic retinopathy