The Eye Flashcards
Components of Fibrous tunic
Sclera and Cornea
Sclera
Components: Dense irregular connective tissue
Function: Supports eye shape; Protects delicate internal structure; Extrinsic eye muscle attachment site
Cornea
Components: Two layers of epithelium with organized connective tissue in between
Function: Protects anterior surface of the eye; Refracts (bends) incoming light
Components of Vascular tunic
Choroid, Ciliary body, and Iris
Choroid
Components: Areolar connective tissue; highly vascularized
Function: Supplies nourishment to retina, pigment absorbs extraneous light
Ciliary body
Components: Ciliary smooth muscle and ciliary processes; covered with a secretory epithelium
Function: Holds suspensory ligaments (zonular fibers) that attach to the lens and change the lens shape for near or far vision; Epithelium secretes aqueous humor
Iris
Divides anterior cavity into anterior chamber and posterior chamber
Components: Two layers of smooth muscle (sphincter pupillae and dilator pupillae) and connective tissue, with a central pupil
Function: Controls pupil diameter and thus the amount of light entering the eye
Components of the Retina
Pigmented layer and Neural layer
Contains bipolar neurons
Pigmented layer
Components: Pigmented epithelial cells
Function: Absorbs extraneous light; Provides vitamin A for photoreceptor cells
Neural layer
Components: Photoreceptors, bipolar neurons, ganglion cells, and supporting Muller cells
Function: Detects incoming light rays; light rays are converted to nerve signals and transmitted to the brain
Lens
A transparent, elastic tissue that focuses light on the retina
Aqueous humor
A continuously flowing
liquid that carries
metabolites to and from
cells and helps maintain
an optimal micro-
environment within the
anterior cavity of the
eye.
It is secreted from
ciliary processes into
the posterior chamber of
the anterior cavity, flows
into the anterior chamber through the pupil, and drains into the scleral venous sinus (canal of Schlemm).
Anterior Cavity
Broken into anterior chamber and posterior chamber; these two are separated by the iris
Contains aqueous humor
Posterior Cavity
The vitreous body occupies the large vitreous chamber behind the lens. It is a
transparent, gel-like connective tissue that is 99% water (vitreous humor), with collagen fibrils and hyaluronate.
Optic Disc
At the head of the optic nerve is the point at which ganglionic layer axons from
all regions of the retina converge, penetrate the
choroid and sclera, and
leave the eye as the optic
nerve to enter the brain.
How does sight work in neural layers of retina?
Light comes in and hits the rod and cone layer
An impulse response is sent to the nerve fiber layer containing ganglionic cells that converge at the optic disc and form the optic nerve
Rods
Sensitive to low levels of light
Human retinal has 92 million rod cells
Contain a light sensitive pigment called rhodopsin or “visual purple”; which is extremely sensitive to light
One of the two types of photoreceptors of the outer retina
Cones
Need relatively bright light to perceive color
Three types of cone cells: Iodopsin pigment ; these have max sensitivity at blue (short), green (medium), and red (long) wavelengths
The human retina has about 4.6 million cone cells
Optic disc has no cone cells
One of the two types of photoreceptors of the outer retina
Fovea
Area of retina with the greatest visual acuity or sharpness
A small specialized
area (~1.5mm) of the retina where cell bodies and axons are largely dispersed
peripherally, thinning this area and allowing light to hit the cones with very
little light scattering.
Macula
Fovea lies in the center of the macula
Accommodation
The lens flattens for distant vision when the ciliary muscles are relaxed and the shape of the
ciliary body holds the ciliary zonule taut, which stretches and flattens the lens.
To see closer objects, the
ciliary muscle fibers contract, changing the shape of the ciliary
body, relaxing tension on the ciliary zonule and allowing the lens to assume the rounded,
relaxed shape.
Accommodation Reflex
An adjustment of the eye
for near vision.
There are three aspects:
Increased convexity of the lens
Pupillary constriction
Convergence of the eyes
Lacrimal Glands
Lacrimal glands secrete most components of the tear film that moisturizes,
lubricates, and protects the eyes. They are serous tubuloacinar exocrine glands
A subset of non-visual photoreceptive ganglion cells in the retina is unusual in that the cells do not function in vision, but rather in the
Establishment of 24-hour dawn/dusk rhythms.
The sclera is continuous anteriorly with the transparent region called the
Cornea
True of the corneal epithelium
It is 5-6 cells thick
It is densely supplied with free nerve endings that trigger the blink reflex
An endothelium lines the posterior surface of the cornea.
In addition to the loss of visual acuity, one of the dangers of a detached retina is that
It cannot receive needed metabolic support from the pigmented layer and the choroid, and so the retinal cells will die eventually.
Dilator papillae innervation
The dilator papillae has sympathetic innervation for enlarging the pupil.
The ________________ has melanocytes that block light from penetrating the eye except through the pupil.
Choroid
Vision is the sharpest in the fovea region of the retina. Why?
The cone cells are abundant and tightly packed.
Very few capillaries are present in the fovea.
The cell bodies of the ganglion cells are peripheral to the fovea
How many cone cells are in the human retina?
4,600,000
How many rod cells are in the human retina?
92,000,000
