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Opthalmology > vision physiology > Flashcards

vision physiology Flashcards

1
Q

Pupillary reflex

A

Automonic nervous sytems

Cranial nerve II AND III

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2
Q

What causes miosis (decreasing the pupillary aperture?

A

Stimulation of the parasympathetic nerves EXCITES the pupillary sphincter muscle

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3
Q

What causes mydriasis (dilation of the pupil)

A

Sympathetic stimulation

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4
Q

Direct response (pupil illuminated)

A

The direct response is impaired in lesions of the ipsilateral optic nerve, the pretectal area, the ipsilateral parasympathetics traveling in CN III, or the pupillary constrictor muscle of the iris.

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5
Q

Extraocular Muscles

A 
Medial and lateral recti
Move the eye from side to side
Superior and inferior recti
Move the eye up and down
Superior and inferior obliques
Rotate the eye around its optical axis
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6
Q

Oculomotor nerve (CN III)

A 
Innervates the medical rectus
Turns the eye medially
Innervates the superior rectus
Elevates the eye and rolls it upward
Innervates the inferior rectus
Depresses the eye and rolls it downward
Innervates the inferior oblique
Elevates the eye and turns it laterall
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7
Q

Trochlear nerve (CN IV)

A

Innervates the superior oblique and turns the eye downward and laterally

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8
Q

Abducens nerve (CN VI)

A

Innervates the lateral rectus and moves the eye laterally

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9
Q

LENS

A

An avascular transparent biconvex body.

Posterior side is more convex than the anterior side.

Elastic capsule holds lens in place, allows lens to change shape

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10
Q

Refraction of Light

A

When light rays strike an interface that is perpendicular to the beam, rays do not deviate from course
When light rays strike an interface that is angulated, the rays bend
The amount the rays bend depend the difference between the refractive indices of the respective mediums
The greater the difference in refractive index, the more the ray will bend

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11
Q

Convex Lens:

A

At the center, the light ray will strike perpendicular and therefore will NOT diverge
The further from the center, the more the angulation… and therefore with a perfect convex lens all of the rays can be focused (convergence) on one spot (focal point)
Bending occurs both:
As the rays enter the lens
As the rays exit the lens

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12
Q

Concave Lens:

A

At the center, the light ray will strike perpendicular and therefore will NOT diverge
The further from the center, the more the angulation… and therefore the more the rays spread apart (divergence)

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13
Q

Is Focal length the same thing as Focal point?

A

No

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14
Q

Accomodation of Lens

A

Accommodation is the process by which a clear image is maintained as gaze is shifted from afar to a near object.
Requires convergence of the eyes. Pupillary constriction and thickening of the lens through contraction of the ciliary muscle.
Parasympathetic portion of CNIII is in control.
Accommodation does not occur in the totally blind, during sleep or in the comatose person because visual function must be present to evaluate and adjust the clarity of the image.

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15
Q

Accommodation

A

The focusing surface of the eye is the retina
It is at a fixed distance from the lens
The ability to adjust the refractive power of the lens is… ACCOMMODATION.

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16
Q

Emmetropia

A

normal vision

17
Q

Presbyopia

A

As a person grows older
Lens grows larger and thicker
Lens becomes far less elastic
Ability of the lens to change shape decreases
Power of accomodation decreases to almost 0 diopters by the age of 70

18
Q

Hyperopia

A

Eyeball is too short so focal point is behind the retina

By using the mechanism of accommodation, these folks are capable of focusing distant objects on the retina

19
Q

Myopia

A

Eyeball is too long so focal point in front of retina

YOU CAN’T RELAX THE CILIARY MUSCLE ANY MORE TO EXTEND THE FOCAL POINT BACK ANY FURTHER!!

20
Q

Astigmatism

A

Well, all astigmatism is is when the image in one plane focuses at a different distance from that of the plane at right angles
Basically, it’s the golfball (normal lens) versus the egg (astigmatic lens)
***Because accomodation manipulates the entire egg, no degree of accomodation can correct for the refractive error

21
Q

Rods and Cones

A

Rods: black and white
Cones: color

22
Q

Cones and Color Sensitivity

A

Cone receptors that are selectively sensitive to different wavelengths of light provide the basis for color vision.
Three types of cones or cone color systems, respond to the blue, green and red portions of the visible electromagnetic spectrum

23
Q

Depth Perception

A

Sizes of the images of known objects
Phenomenon of moving parallax
Phenomenon of stereopsis (binocular vision)

24
Q

Two portions

A

Aqueous humor: lies in front of the lens
Freely flowing fluid
Vitreous humor: lies between posterior surface of the lens and the retina
Gelatinous mass (water and dissolved substances can diffuse very slowly in the vitreous humor, but there is little flow of fluid)

25
Q

Aqueous Humor

A

Continually being formed and reabsorbed
***Balance between formation and reabsorption of aqueous humor regulates the total volume and pressure of the intraocular fluid

26
Q

Aqueous Humor

A 
Formation
Ciliary body forms aqueous humor
2-3 microliters per minute
Outflow
Flows through pupil into anterior chamber
Then into the angle between the cornea and iris
Through meshwork of trabeculae
Enters Canal of Schlemm
Empties into extraocular veins
27
Q

Intraocular Pressure

A

Average normal intraocular pressure is about 12-20mm Hg

Pressure remains constant in the normal eye

28
Q

Glaucoma

A

One of the most common causes of blindness
Disease in which the intraocular pressure becomes pathologically high (sometimes rising to 60-70 mm Hg)
Pressures of 25-30 mm Hg for long periods can lead to loss of vision however

29
Q

Optic Chiasm

A

The two optic nerves meet and fuse at the optic chiasm.

Axons from the nasal retina of each eye cross to the opposite side and join the axons of the temporal retina of the contralateral eye to form the optic tracts.

One tract contains fibers from both eyes that transmit info from the same visual field.

30
Q

Visual cortex

A

Located in the occipital lobe

How is this information disseminated?
Physical separation of the info from the left and right visual fields is maintained in the visual cortex

Opthalmology (6 decks)

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