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MD4001 Physiology > The eye and seeing > Flashcards

The eye and seeing Flashcards

1
Q

what are the 3 stages in seeing

A

optical part
conversion of light into visual code
cognition of the optical code

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2
Q

what is the anterior chamber

A

the fluid filled space between the iris and the cornea

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3
Q

what is the central retinal artery and vein

A

blood supply for inner layers of the retina

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4
Q

what is the choroid

A

vascularised nutritice layer between the sclera and the retina

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5
Q

what is the ciliary body

A

ring of ciliary epithelium that produces aqueous humour and the ciliary muscle which alters the shape of the lens for focussing

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6
Q

what is the cornea

A

tranparent tissue forming the anterior wall of the anterior chamber

important for refraction of light entering the eye

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7
Q

what is the fovea

A

centra part of the macula with the highest visual acuity

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8
Q

what is the fundus

A

posterior aspect of the interior of the eye, viewed with the opthalamoscope

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9
Q

what is the iris

A

diaphragm which regulates the amount of light entering the eye

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10
Q

what is the lens

A

adjustable element that allows focussing of light

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11
Q

what is the macula

A

central area of retina with the highest visual acuity

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12
Q

what is the optic disc

A

area with no photoreceptors so a blind spot

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13
Q

what is the retinal pigment epithelium

A

pigmented monolayer located betwen the inner choroid and outer photoreptor layer of the retina.
the RPE interacts with photoreceptors in the maintenance of visual function

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14
Q

what is the pupil

A

opening in the centre of the iris through which light passes

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15
Q

what is the retina

A

part of the CNS which contains light sensitive cells and other neurons which detect light and process light images

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16
Q

what is the sclera

A

tough outer covering of the eye

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17
Q

what is the vitreous cavity

A

space between the lens and the retina filled with clear gel

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18
Q

what is the suspensory ligament

A

Zonular fibres that transmit tension from the ciliary body to the lens to enable focussing of light passing through the lens

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19
Q

what is the conjunctiva

A

lines the inside of the eyelid and joins the cornea at the limbus
secretes mucin onto the cornea

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20
Q

what is bullous keratopathy

A

endothelial pump failure, e.g. secondary to complicated cataract surgery or degenerative

fluid is retained in the cornea- so a loss of transparency

painful eye with poor vision

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21
Q

what are the 3 layers of the tear film

A

oily lipid outer layer to reduce evaporation

aqueous middle layer containing lysozymes and antibodies

mucin layer containing glycoprotein, wets the cornea and allows good coverage

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22
Q

what is the function of the tear layer

A

wash the eye of debris
provide dissolved O2 to the cornea external epithelium
lubrication of the cornea

23
Q

what is dry eye syndrome

A

dysfunction of either the lids and conjunctiva, lacrimal gland, or vit A deficiency

24
Q

what structure is most responsible for refracting light so it focuses on the back of the eye

A

cornea because the greatest difference in refractive index is between the air and the cornea

the lens also refracts but to a lesser extent - fine tunes

25
Q

what does the amount of difraction depend on

A

the difference between the two substances with
the refractive or focal power (diopters) given by

(n2 – n1)/r

where n1 and n2 are the refractive indices of the respective media and r is the radius
of the radius of the lens curvature (in meters)

26
Q

how does the lens change when veiwing an object close up

A

lens bulges

(flattens for distant vision)

cilliary muscles contract which removes some of the radial tension on the lens provided by the elastic zonal fibres

27
Q

what part of the nervous system is responsible for flattening the lens

A

sympathetic (distant viewing) cilliary muscles relax

28
Q

describe the lens at rest

A

held in a flattened shape by elastic zonal fibres around the edge

29
Q

what is presbyopia

A

with age, lenses lose their elasticity which makes it harder to focus an image on the retina (accomodation)

30
Q

what is the other word for short sightedness

A

myopia

image focuses slightly anterior to the retina

31
Q

what is the word for normal vision, neither long or short sighted

A

emmetropia

32
Q

what is the other name for long sightedness

A

hyperopia

the image falls behind the retina

33
Q

how is depth of field altered

A

altering the diameter of the pupil

34
Q

how is myopia corrected

A

concave lens

35
Q

how is hyperopia corrected

A

convex lens

36
Q

what is astigmatism

A

a defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus.

37
Q

what are cataracts

A

clouding of the lens usually due to the lens thickening with time

the lens epithelia differentiates into lens fibres which form the rest of the lens along with crystalin proteins
the lens becomes less elastic and the central portion clouds over due to being nutritionally deprived

corrective surgery is fairly straightforward

38
Q

what structure produces aqueous humour

A

ciliary processes

39
Q

what is normal intraocular pressure

A

10- 20 mmhg

40
Q

what can lead to a rise in intraocular pressure

A

blockage in drainage (scleral venous drainage via canal of schlemm)

41
Q

what are the possible consequences of glaucoma

A

severe optic nerve atrophy and irreversible loss of sight

42
Q

what are the layers of the retina

A 
outer nuclear layer
ganglion cell layer
plexiform layer
outer nucleur layer 
pigmented epithelium
43
Q

what is the ratio of rods to cones

A

20x as many rods

44
Q

where are cones concentrated

A

in the macula

45
Q

what is the convergence ratio

A

the number of rods or cones that synapse onto ganglion cells

46
Q

what is the convergence ratio in the central retina of ganglion cells to rods or cones

A

1: 1
1: many

47
Q

what protein derived from vitamin A is found in all rods and cones

A

retinal

48
Q

what protein is retinal bound to under unstimulated conditions

A

opsin

49
Q

what is the cause of colour blindness

A

inability to produce different forms of opsin

50
Q

what happens when purple coloured retinal-opsin is hit by light

A

changes conformation and becomes detached- retinal appears bleached/ clear

51
Q

what type of opsin is found in rods

A

rhodopsin

52
Q

what form are photoreceptors in when in the dark

A

depolarised

hyperpolarised in the light

53
Q

how do our eyes adapt to differering light levels

A

pupil constriction

difference in sensitivity of rods and cones

photoreceptors adapt to high levels of stimulation

levels of light are relative rather than absolute

MD4001 Physiology (19 decks)

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