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MD4001 Physiology > The eye and seeing > Flashcards

The eye and seeing Flashcards

(53 cards)

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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

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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

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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

Study These Flashcards
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
what does the amount of difraction depend on
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
how does the lens change when veiwing an object close up
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
what part of the nervous system is responsible for flattening the lens
sympathetic (distant viewing) cilliary muscles relax
28
describe the lens at rest
held in a flattened shape by elastic zonal fibres around the edge
29
what is presbyopia
with age, lenses lose their elasticity which makes it harder to focus an image on the retina (accomodation)
30
what is the other word for short sightedness
myopia image focuses slightly anterior to the retina
31
what is the word for normal vision, neither long or short sighted
emmetropia
32
what is the other name for long sightedness
hyperopia the image falls behind the retina
33
how is depth of field altered
altering the diameter of the pupil
34
how is myopia corrected
concave lens
35
how is hyperopia corrected
convex lens
36
what is astigmatism
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
what are cataracts
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
what structure produces aqueous humour
ciliary processes
39
what is normal intraocular pressure
10- 20 mmhg
40
what can lead to a rise in intraocular pressure
blockage in drainage (scleral venous drainage via canal of schlemm)
41
what are the possible consequences of glaucoma
severe optic nerve atrophy and irreversible loss of sight
42
what are the layers of the retina
``` outer nuclear layer ganglion cell layer plexiform layer outer nucleur layer pigmented epithelium ```
43
what is the ratio of rods to cones
20x as many rods
44
where are cones concentrated
in the macula
45
what is the convergence ratio
the number of rods or cones that synapse onto ganglion cells
46
what is the convergence ratio in the central retina of ganglion cells to rods or cones
1: 1 1: many
47
what protein derived from vitamin A is found in all rods and cones
retinal
48
what protein is retinal bound to under unstimulated conditions
opsin
49
what is the cause of colour blindness
inability to produce different forms of opsin
50
what happens when purple coloured retinal-opsin is hit by light
changes conformation and becomes detached- retinal appears bleached/ clear
51
what type of opsin is found in rods
rhodopsin
52
what form are photoreceptors in when in the dark
depolarised hyperpolarised in the light
53
how do our eyes adapt to differering light levels
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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