Exterior is smooth and white interior is brown and also grooved Extremely sturdy versatility adds strength consistent with sheath that optic nerve Tendons attached to it

The Cornea

The cornea is the clear bulging surface in front of the eye. The is the key refractive surface of the eye.

You are watching: Which of the following correctly lists the parts through which light passes as it enters the eye?

main refractive surface ar of the eye table of contents of refraction: n = 1.37 usually transparent and uniformly thick virtually avascular Richly provided with nerve yarn perceptible to international bodies, cold air, chemistry irhistoricsweetsballroom.comation Nuthistoricsweetsballroom.comion indigenous aqueous humor and Tears maintain oxygen exchange and water content Tears protect against scattering and also improve optical quality

Anterior & Posterior Chambers

The anterior room is between the cornea and the iris The posterior chamber is between the iris and the lens consists of the aqueous feeling Index that refraction: n = 1.33 details viscosity that the aqueous simply over 1.0 (like water, hence the name) press of 15-18 mm that mercury maintains form of eye and also spacing of the facets Aqueous humor produced from blood plasma regeneration requires about an hour Glaucoma is a result of the increased liquid pressure in the eye due to the reduction or blockage that aqueous indigenous the anterior to posterior chambers.


Iris is greatly pigmented Sphincter muscle to constrict or dilate the pupil Pupil is the hole v which irradiate passes Pupil diameter ranges from around 3-7 mm Area the 7-38 square mm (factor of 5) Eye shade (brown, green, blue, etc.) dependence on amount and distribution the the pigment melanin



Transparent body enclosed in an elastic capsule comprised of proteins and water is composed of layers, like an onion, with firm nucleus, soft cortex Gradient refractive table of contents (1.38 - 1.40) Young person can adjust shape that the lens via ciliary muscles convulsion of muscle causes lens come bulge At roughly age 50, the lens have the right to no longer readjust shape Becomes much more yellow through age: Cataracts

The graph ~ above the right reflects the optical thickness (-log transmittance) of the lens as a function of wavelength. The curves show the change in density with age. An ext short wavelength irradiate is clogged at boosts ages.

Vitreous feeling

fills the an are between lens and retina Transparent gelatinous body certain viscosity that 1.8 - 2.0 (jelly-like consistency) index of refraction, n=1.33 Nuthistoricsweetsballroom.comion from retinal vessels, ciliary body, aqueous Floaters, shadows the sloughed off material/debris in the vitreous likewise maintains eye shape



Notice the orientation the the retina in the eye. The facility of the eyeball is in the direction of the bottom the this figure and the ago of the eyeball is towards the top. Irradiate enters from the bottom in this figure.

The light needs to pass through countless layers that cells before finally getting to the photoreceptors. The photoreceptors room where the irradiate is absorbed and and also transformed into the electrochemical signals offered by the nervous system. This change is called TRANSDUCTION.

The inner of the eyeball is the "inner" side and also the exterior is the "outer" side. The nuclear layers contain cabinet bodies. The plexiform class contain the connections between cells in the retina.

This next photo shows a schematic the the cell in the retina:

Again the irradiate in entering from the bottom passing v all this layers before being absorbed in the receptors.

You can see the two species of receptors: the rod-shaped rods and the cone-shaped cones. The signal, ~ transduction, is passed to the horizontal cell (H) and also the bipolar cell via a great of connections. Lateral handling takes place in this class via the horizontal cells. The throughput is moved to another layer of connections with the amacrine cell (A) and also the ganglion cells. The amacrine cells likewise exhibit lateral relations in this within plexiform layer. The signals pass the end of the eye via the ganglion cell axons which space bundled together to type the optic nerve.

The retina has actually a comparable layered framework as the gray-matter top layers of the cerebral cortex the the brain. In fact, the retina is an expansion of the central nervous mechanism (the brain and spinal cord) the forms during embryonic development. This is one factor why researchers are interested in retinal processing; the retina is one accessible component of the brain that can be quickly stimulated through light.


Speaking of the optic nerve...

The place where the optic nerve is bundled and also leaves the retina is recognized as the optic disk. There room no photoreceptors in ~ the place of the optic disk and hence over there is a remote spot. The scientific term for a blind spot is a scotoma. For this reason the blind spot due to the optic decaying is a herbal permanent scotoma in common vision. Below is a demonstration of the natural permanent scotoma:


Close her left eye. Fixate top top the cross through your ideal eye. This will reason the picture of the cross to fall on her fovea. Change the city hall distance till the black spot disappears. Once this happens, the picture of the spot is falling on your blind spot.

What carry out you watch (or not see) once you do this v the peak figure?

What happens when the gap in the bottom figure falls on your remote spot?

You have to see the "smiley" in the top figure disappear when it falls in your remote spot. Once the void in the bottom figure falls on the blind spot, the visual device "fills in" the line. So why don"t we notification the remote spot in regular vision? for one, we have actually two eyes and the blind spots room in non-corresponding areas (they room nasally located (towards the nose) top top the retina for this reason the blind spots room temporal (towards the temple) in the visual field). In addition, the filling in procedure makes the blind spot less noticeable especially in a peripheral area of vision that has less visual acuity (the capability to check out detail).

As discussed above, in prior of the receptors room layers the cells through which the light must pass. In enhancement there is vasculature on the front surface of the retina.

You deserve to see this vasculature (or much more correctly its shadow) by pushing a pen light to the next of your eyeball and gently wiggling it. What you will see looks like the number below.


Why don"t we see this regularly? As stated previously, the visual mechanism is perceptible to readjust and as soon as the irradiate enters usually through the pupil, the vessels room stable. They space also small and small so they perform not block lot light yet when illuminated from the side they actors a broader shadow.

If you look in ~ a deep blue field or up in ~ the skies (not the sun) top top a clear day, girlfriend may notification pulsations or squiggles relocating around. These are the shadows the the red corpuscles in the blood in these vessels.

The Fovea

The fovea is the place on the retina of central gaze. As soon as you look at directly, or fixate, at a stimulus you the retinal locus that this main fixation is the fovea. Over there are only cones in the human being fovea (no rods). They space thinner, elongated, any very tightly packed. Due to the fact that of this, the fovea is the location of highest visual acuity and best color vision.

In the diagram listed below you can see that the retinal layers space pulled aside (the axons the the receptors are elongated) leaving a clearer course for the irradiate to reach the receptors. Over there is in reality a little indentation or pit in ~ the location of the fovea because of this and it is a clear landmark in the retina during an ophthalmic examination. The elongated external segments the the hat (where the photopigment is and where the transduction occurs) boost the sensitivity by raising the amount of photopigment. There is no vasculature in the central fovea.


The Macula

Covering the fovea is a pigment referred to as the macula. It is assumed that the macula serves as a safety filter end the foviea that absorbs blue and ultraviolet radiation. This pigment varies from observer to oberver and is a source of separation, personal, instance variation in shade vision. Typically we do not an alert the filtering of the macula but under special conditions we can notification its presence bring about what is well-known as Maxwell"s spot.

Here is a plot the the thickness of the macula together a duty of wavelength:


To view Maxwell"s spot shot alternately viewing v a blue and also yellow filter. Once looking at v the blue filter after adapting with the yellow filter you may see a dark an ar covering around the central 3° of intuitive angle. Try it by clicking here. No guarantees.


The middle- and also long- wavelength sensitive cones room selectively adjusted to the yellow so that their an answer is attenuated while subsequently looking with the blue, thereby boosting the visual result of the macula.

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Another demonstration of the macula is referred to as Haidinger"s Brushes.

Look in ~ a uniform blue ar (again the clear skies works well because that this) through a direct polarizer. Friend may be able to see a little yellow hourglass in the main 3° area. As you readjust the orientation of the polarizer, the orientation the the hour glass changes.