Vision Physiology Flashcards Preview

Opthamology > Vision Physiology > Flashcards

Flashcards in Vision Physiology Deck (50):
1

What is the function of the eye?

-to transform light energy into nerve signals that can be transmitted to the cerebral cortex for interpretation

2

Eye sits on the roof of what?

Maxillary sinus

3

Sphincter pupillae
-use for what type of vision

-close vision and bright light, constricts and makes pupil smaller
-circular muscle

4

Dilator Pupillae
-used for what type of vision?

-distant vision and dim light, pupil dilates
-radial muscle

5

Stimulation of the _____ EXCITES the pupillary sphincter muscle, thereby ______ the pupillary aperture.

1.) parasympathetic nerves
2.) decreasing (constricting)

6

Stimulation of ______ excites the dilator pupillae muscle, thereby ____ the pupil.

1.) Sympathetic nerves
2.)dilating

7

What are the fancy words for dilation and constriction of the pupils?

dilation- mydriasis

constriction- miosis

8

What is an afferent pupillary defect?
-cause
-how can this be demonstrated?

- decreased direct response caused by decreased visual function in one eye

-swinging flashlight test; the light is moved back and forth between the eyes every two to three seconds.

-afferent pupillary defects is when the flashlight is moved from the normal to the affected eye and the affected pupil DILATES in response to LIGHT.

9

What is hippus?

-normal, brief oscillations to the pupillary size in response to light.

10

Direct Response (pupil illuminated)
-explain this
-when would this be impaired?

-direct response is the change in pupil size in the eye to which the light is directed.

-impaired when lesion in the ipsilateral optic nerve, pretectal area, ipsilateral parasympathetics traveling to CN III, or lesion in pupillary constrictor muscle of iris/

11

Consensual Response (Contralateral pupil illuminated)
-explain this
-when would this be impaired?

- the change in pupil size in the eye opposite to the eye to which the light is directed.
**normally light that is directed in one eye produces pupil constriction in both eyes.

-lesions of the contralateral optic nerve, pretectal area, ipsilateral parasympathetics traveling to CN III, or the pupillary constrictor muscle.

12

Accommodation (response to looking at something moving towards the eye)
-explain this
-when would this be impaired?

- elicited when the viewer directs their eyes from a distance object to a nearby object.

-impaired in lesions of the ipsilateral optic nerve, the ipsilateral parasympathetics traveling in CN III, pupillary constrictor muscle, bil. lesion of the pathways from the optic tract to the visual cortex.
*accommodation is spared in lesion tof the pretectal

13

Examples of disease states that block pupillary reflex

*these include but are not limited to...
alcoholism

encephalitis

CNS syphalis

14

Binocular vision

-ocular reflex mechanism that adjusts the orientation of each eye to produce a single image.

15

Conjugate Gaze

refers to the use of both eyes to look steadily in one direction

16

Saccadic eye movements defintion

small jumping movements that represent rapid shift in conjugate gaze orientation

17

Nystagmus def

sequence of SLOW ocular rotation d/t muscle fatiguing can get this with cerebellar dysfunction

18

Lens
-describe its structure
-what holds it in place?

avascular transparent biconvex body

-posterior side is more convex

-elastic capsule holds the lens in place, allows lens to change shape

19

Talk about how the lens changes.

-sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens.
This is for distant vision

-parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge

- under normal conditions the lens remains relatively flat.

20

Refraction of light: When light rays strike an interface that is perpendicular to the beam the rays _______. What happens to the rays when they strike an interface that is angulated?

- rays do not deviate from course

-rays bend, the amount they bend depend on the difference between the refractive indices of the respective mediums, the greater the difference in refractive index the more the rays will bend.

Ex.- look through window the light rays strike the interface and do not deviate from their course.

Look at fish in river through water the light rays strike the interface and become angulated and bend.

21

What happen to the light rays as they hit the convex lens? Bending of ray occurs?

-if they hit at the center the light ray will strike perpendicular and NOT diverge
-the further from the center, the more angulation and bend of the rays
*with a perfect convex lens all of the rays can be focused (convergence) on one spot (focal point)

-bending occurs both when rays ENTER and EXIT the lens

22

Focal length def

the distance from the lens to the focal point

23

Focal point def

the point where all of the light rays meet.

24

What happen to the light rays as they hit the convex lens? Bending of ray occurs?

- at the center the light ray will strike perpendicular and will NOT diverge

-the further from the center the more angulation and therefore the more rays spread apart (divergence)

-bending occurs at both at ENTRY and EXIT

25

The retina doesnt move and therfoer the _____ must change in order to focus the image with change of distance.

lens

26

Accomodation def

-the process by which clear image is maintained as gaze is shifted from afar to a near object.
- also the ability to adjust the refractive power of the lens.

* 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.

27

Does accommodation occur in the blind, during sleep, or in the comatose person?

No, visual function must be present to evaluate and adjust the clarity of the image.

28

What influence does a greater refractive power have on focal length and lens?

the stronger the lens is, the nearer to the lens, the focal point is. (much shorter focal length)

29

Ciliary muscle is made up of which two seperate sets of smooth muscle fibers?

-meridonial fibers
- circular fibers

30

Light rays from _____ objects are nearly _____ and dont need as much refraction to bring them to focus.

- distant
-parallel

31

Light rays from ____ objects _____ and require more refraction for focusing.

-close
-diverge

32

What controls the ciliary muscle?

Parasympathetic stimulation of Cranial Nerve III

33

Accomodation process of the lens

1. parasympathetic nerve signal
2. contraction of ciliary muscle fibers
3. relaxation of lens ligaments
4. lens assumes more spherical shape
5. INCREASED refractive power
6. ability to focus on NEARER objects.

34

Emmatropia def

normal vision
-is when parallel light rays from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed.

*eye must contract ciliary muscle to accommoadte from objects at close range.

35

Presbyopia def

as person grows older;
-lens grows larger and thicker
-lens becomes far less elastic
-ability of lens to change shape decreases
-power of accommodation decreases to almost zero diopters by age of 70.

*gramps can neither see far or near.

36

Hyperopia def

-aka- farsightedness
-when the eyeball is too short so the focal point is behind the retina

-capable of focusing on distant objects on the retina.

- corrected w/ a biconvex lens, shortening the focal length thereby moving focal point from behind the retina closer to the lens.

37

Myopia def

-aka- nearsightedness
-eyeball is too long so focal point is in front of retina.

*this person requires a biconcave lends which moves focal distance further back.
*convex only makes myopia worse.

38

What is an Astigmatism?
Can accommodation correct this refractive error?

abnormal shape of the lens, it
- is when the image in one plane focuses at a different distance from that of the plane at right angles.

-is not golfball (normal lens) shape, rather it is egg (astigmatic lens) shaped.

-NO! accommodation manipulates the entire egg, no degree of accommodation can correct for the refractive error.

39

Where will you find the majority of rods and cones? What are their functions?

-find rods in the periphery, detect under dim light, white & black

-find cones in fovea/macula, takes care of color vision (blue green and red.)

40

Color Blindness
-describe this
-cause
-male or female more affected?
-what colors are affected in the periphery vs central retina?

-confuse/mismatch colors or experience reduced acuity for color discrimination.

-caused by genetic defect in one or more of the three color cone mechanisms.

-Males more often affected

- disease of peripheral retina affects blue
-disease of central retina affects red and green (blue are not in central fovea)

41

How is depth perception determined?

-size of images of known objects
-phenomenon of moving parallax (further things appear to move slower)
-phenomonon of stereopsis(binocular vision)

42

Describe the fluid system of the eye

Aqueous humor lies in front of the lens (freely flowing). continually being formed by ciliary body and reabsorbed.

Vitreous humor lies between the posterior surface of the lens and the retina. (gelatinous mass, little flow of fluid)

43

Whats another name of the scleral venous sinus?

Canal of Schlemm

44

What is normal intraocular pressure and what is it determined by?

-12-20mmgh
- pressure determined by resisitance to outflow of aqueous humor from anterior chamber into the canal of Schlemm. [In]=[out]

45

What is glaucoma? Treatement?

-one of most common cuases of blindness

-disease in which the intraocular pressure becomes pathologically high, sometimes 60-70mmhg
- decrease secretion of increase absorption, if this fails surgical intervention.

46

Describe how vision info gets to the visual cortex

optic nerve travels to optic chiasm located near the pituitary gland.

At the chiasm optic nerve fibers from the nasal half of each retina cross over to the other side.

Nerve fibers originating from the temporal retina do not cross over.

47

Optic nerve represents...?

an outgrowth of the brain rather than a peripheral nerve.

48

What would a patients visual disturbance be if you severed their left optic tract?

- you would lose both right sided vision in both eyes.
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49

What would a patients visual disturbance be if you severed their right optic nerve?

- they would lose full vision in their right eye.
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50

What would a patients visual disturbane be if you severed their optic chiasm?

-they would lose their peripheral vision.
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