Vision I Flashcards Preview

A. White- Human Physiology > Vision I > Flashcards

Flashcards in Vision I Deck (33):

What does the degree of refraction (amount of bending) depend on?

The ratio of the two refractive indices of the two transparent media.

The degree of angulation between the interface and the entering wave front of the light waves.


What is a refractive index?

The ratio of the velocity of light in the air to the velocity of light traveling in the substance.

RI of air = 1.00


What is refractive power?

A measure of how much a lens bends light waves. It is measured in diopters.


What is the focal point?

The point through which all parallel rays of light will pass after passing through each part of the lens.


What is focal length?

The distance from the center of the lens to the focal point.


What is the function of the iris?

It functions in a similar manner to the iris disphragm of a camera. It controls the amount of light entering the eye from darkness to light conditions.


How does an object look when it is projected onto the retina?

It is reversed and inverted.


As the depth of focus of the lens increases, ___ decreases.

Pupillary diameter.


What is emmetropia?

The normal eye with regard to depth of focus.

Parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed.

All distant objects can be seen clearly.


What is hyperopia?


Usually due to an eyeball that is too short or, occasionally a lens system that is too weak.

All distant objects can be seen clearly.


What is myopia?


When ciliary muscle is completely relaxed, light rays coming from distant objects are focused in front of the retina.

It is usually due to too long of an eyeball.


What is visual acuity?

A measure of the resolving power of the eye.

Light from a distant point source will normally create a spot with a diameter of about 11 micrometers and a center that is brighter than the periphery.

The maximum visual acuity for two-poitn sources of light is 1.5 to 2 mm.


What is aqueous humor formed by?

Ciliary processes.


What does the ciliary apparatus consist of?

Two opposing layers of epithelial cells with a space between them.

Sodium ions are actively transported into this space and are accompanied by chloride and bicarbonate ions.


How is water draw into the ciliary space?

By sodium, chloride and bicarbonate ions. They draw water into the space and the aqueous solution is then passed into the anterior chamber.


What is the movement of the fluid from the eye?

Fluid flows from the anterior chamber into the canal of Schlemm and from there into aqueous veins in the sclera.


What is used to measure intraocular pressure?

A tonometer


What is the term for the color pigment found in rods?



How many different color pigments are in the eye?


These pigments are transmembrane conjugated proteins.


What are the major functional segments of rods and cones?

Outer segment (light sensitive photochemicals)

Inner segment (organelles, such as mitochondria)


Synaptic body (connects with horizontal and bipolar cells)


What is rhodopsin formed from?

Rhodopsin = scotopsin + 11-cis retinal


What are the products of rhodopsin + light?

Rhodopsin + light -> scotopsin + all-trans retinal

11-cis retinal is converted to all-trans retinal and dissociates from scotopsin.


What is metarhodopsin II?

An intermediate in the rhodopsin pathway that excites electrical changes in the rods.


What is needed to convert all-trans retinal into 11-cis retinal?

Isomerase and metabolic energy.


What does 11-cis retinal recombine with in order to make rhodopsin?



What is the alternate pathway of the rhodopsin-retinal visual cycle?

All-trans retinal -> all-trans retinol (vitamin A)

All-trans-retinol -> 11-cis retinol -> 11-cis retinal


What is the effect of excitation of rods?

It causes increased negativity of the intrarod membrane potential (hyperpolarization)

Decomposition of rhodopsin decreases rod membrane and conductance for sodium ions in the outer segment.

Results in hyperpolarization of entire rod membrane.


What is the movement of ions in the inner segment of the rod?

It continusally pumps sodium from inside the rod to outside and potassium in the opposite direction.

Potassium ions leak out of the cell via non-gated channels.

A negative potential is created on the inside of the cell.


How does the outer segment of a rod react to darkness?

There is reduced electronegativity inside the membrane.

The membrane is leaky to sodium ions that flow through cGMP-gated channels.

Sodium ions leaks into the cell and neutralize much of the negativity on the inside of the entire cell.


Who does the outer segment of a rod react to exposure to light?

Rhodopsin decomposes, which activates the rhodopsin complex.

The retinal portion of the rhodopsin complex is activated and stimulates transducin, which eventually causes closure of sodium channels.

Photoreceptors become hyperpolirzed.


When rhodopsin is activated, several ___ channels close for each rhodopsin molecule activated.



How do rods and cones differ?

Cones are similar to rods except that the protein portions (opsins) of the photochemicals are different from the scotopsin of the rod photochemicals.

Retinal portions are the same in both rods and cones. Cones are blue, green and red sensiive


What is refraction?

The bending of light waves at an angulated surface of a transparent material.