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Y2 LCRS Neuroscience and Mental Health > vision > Flashcards

vision Flashcards

optics: explain the basis of physiological optics and the common defects of refraction

1
Q

what is the index of refraction (n)

A

speed of light in vacuum/speed of light in medium (as denominator always smaller, value is unitless and greater or equal to 1)

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2
Q

what 2 things change when light goes from one medium to another

A

velocity and direction

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3
Q

what 2 things happen when light reaches a new medium

A

some reflects off boundary, and some refracts through boundary

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4
Q

what is the angle of incidence equal to

A

angle of reflection

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5
Q

what is angle of incidence > or < angle of refraction depending on

A

direction of light

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6
Q

2 types of lenses, shape and what they do

A

converging (convex) brings light rays to a focal point (distance from lens to focal point is focal length); diverging (concave) spreads light rays from source (focal point) outwards (distance from focal point to lens is focal length)

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7
Q

function of converging lens

A

focus an image

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8
Q

what is emmetropia

A

adequate correlation between axial length and reflective power, so parallel light rays fall on retina with no accomodation

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9
Q

what is ametropia

A

refractive error where there is a mismatch between axial length and refractive power, meaning light rays don’t fall on retina (no accomodation)

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10
Q

4 types of ametropia

A

nearsightedness (myopia), farsightedness (hyperopia), astigmatism, presbyopia

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11
Q

what happens in myopia

A

parallel rays converge at focal point anterior to retina

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12
Q

2 causes of myopia

A

genetic factor: excessive long globe (axial; more common), excessive refractive power (refractive; lens is too convex)

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13
Q

3 symptoms of myopia

A

blurred distance vision, squint in attempt to improve uncorrected visual acuity when gazing into distance (only get light that is straight so no need for refractive power), headache

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14
Q

3 ways myopia is corrected

A

diverging lens, by making retina more convex, or by removing lens to reduce refractive power of eye (no longer done as many other issues)

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15
Q

what happens in hyperopia

A

parallel rays converge at focal point posterior to retina

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16
Q

2 causes of hyperopia

A

inherited: excessive short globe (axial; more common), insufficient refractive power (refractive)

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17
Q

2 symptoms of hyperopia

A

visual acuity at near tends to blur relatively early, asthenopic symptoms

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18
Q

when is blurred vision more noticeable

A

when tired, weak printing, or inadequate lighting

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19
Q

asthenopic symptoms of hyperopia

A

eyepain, headache in frontal region, burning sensation in eyes, blepharoconjunctivitis

20
Q

what is ambylopia

A

uncorrected hyperopia > 5D, so vision is always blurry regardless of distance; lazy eye ir not corrected at childhood as brain doesn’t use that eye as blurred

21
Q

how is hyperopia corrected

A

converging lens, anterior chamber intraocular lens, posterior chamber intraocular lens

22
Q

what happens in astigmatism

A

parralel rays come to focus in 2 focal lines rather than one, as cornea dome different shape

23
Q

cause of astigmatism

A

hereditary; refractive media is not spherical so refracts differently along one meridian than along meridian perpendicular to it, creating 2 focal points on retina (punctiform object represented as 2 sharply defined lines)

24
Q

4 symptoms of astigmatism

A

asthenopic symptoms (eyepain, headache), blurred vision, distorted vision, head tilting and turning

25
Q

treatment of regular astigmatism

A

cylinder lenses with/without spherical lenses (convex or concave), so light pasing through vertical part will go straight, but light passing through side will hit convex/concave structure, creating joint focal point

26
Q

treatment of irregular astigmatism

A

rigid cylinder lenses, surgery

27
Q

what is the near response triad for

A

adaption for near vision

28
Q

3 things responsible for near response triad

A

pupillary miosis, convergence, accomodation

29
Q

what causes pupillary miosis and effect

A

sphincter pupillae to increase depth of field

30
Q

what causes convergence and effect

A

medial recti from both eyes to align both eyes towards a near object

31
Q

what causes accomodation and effect

A

circular ciliary muscle to increase refractive power of lens for near vision

32
Q

what is presbyopia

A

naturally occuring loss of accomodation (focus for near objects) after 40 years, with distant vision intact

33
Q

how is presbyopia corrected

A

reading glasses with convex lenses to increase refractive power of eye; also bi/tri focal glasses or progressive power glasses

34
Q

4 types of optical correction

A

spectacle lenses, contact lenses, intraocular lenses, surgical

35
Q

types of spectacle lenses

A

monofocal: spherical, cylindrical; multifocal

36
Q

contact lenses vs spectacle lenses

A

contact lenses have higher quality of optical image and less influence on size of retinal image

37
Q

indication for contact lenses

A

cosmetic, athletic activities, occupational, irregular corneal astigmatism, high anisometropia, corneal disease

38
Q

disadvantages of contact lenses

A

careful daily cleaning and disinfection, expense

39
Q

complication of contact lenses

A

infectious keratitis, giant papillary conjunctivitis, corneal vascularisation, severe chronic conjunctivitis

40
Q

what is intraocular lenses

A

replacement of cataract crystalline lens

41
Q

when are intraocular lenses used

A

best optical correction for aphakia, and avoid significant magnification and distortion caused by spectacle lenses

42
Q

2 types of surgical correction

A

keratorefractive, intraocular

43
Q

what is clear lens extraction with intraocular lens; what is lost and correction

A

same as cataract extraction, with implantation of artifical lens; lose accomodation so needs reading glasses

44
Q

accomodation mechanism for near vision

A

circular ciliary muscle in ciliary body contracts -> zonules between ciliary body and lens capsule attachment passively relax -> lens returns to natural convex shape due to innate elasticity -> refractive power of lens increases

45
Q

what mediates accomodation

A

efferent oculomotor nerve

Y2 LCRS Neuroscience and Mental Health (79 decks)

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