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Sem3 > Case 3 > Flashcards

Case 3 Flashcards

1
Q

What is the function of the cornea and the lens?

A

To refract the light

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2
Q

How is accommodation accomplished?

A

The lens changes shape by the contraction of the cilliary muscles or relaxation to allow you a sharp focus on near or far objects (respectively)

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3
Q

What is aberration?

A

Chromatic = refraction of different wavelengths on the retina at different angles

Spherical= increases refraction of light as they hit the lens

In both there is a failure to focus

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4
Q

What is the function of the pupillary light reflex?

A

Changes the pupil size to reduce aberration and increase focus and depth of field i.e. distance within which objects are seen without blurring

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5
Q

What is visual field?

A

What you are able to see when your eyes are fixed straight ahead

Binocular = both eyes
Uniocular = one eye
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6
Q

What is visual acuity?

A

Ability to distinguish 2 nearby points (sharpness of our vision)

It is dependent on the spacing of photoreceptors and precision of the eye’s refraction

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7
Q

What are the cells of the retina?

A
  • Photoreceptors: cones and rods which contain photopigments
  • horizontal: allow lateral interactions between photoreceptors and bipolar cells
  • amacrine: they are between the bipolar and ganglion cells
  • Retinal Pigment Epithelium: phagocytose dead membranous disks and produce new photo pigment molecules after they are exposed to light
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8
Q

What is the function of Rods and Cones?

A
  • Rods: sensitive to light; low spatial resolution; night vision
  • Cones: relatively insensitive to light; high spatial resolution; acuity and colour vision

As light intensity increases you use more cones than rods because the rods cells membrane channels becomes saturated

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9
Q

What is the result of loss of rods or cones?

A

Loss of cones = blindness

Loss of Rods= night blindness

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10
Q

How is acuity achieved in cone cells?

A

One-to-one relationship to bipolar cells

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11
Q

Where is the highest distribution of cones?

A

In the avascular foveola in the fovea

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12
Q

How does phototransduction occur?

A

Light ray hits photoreceptors > cis retinal is converted to all-trans retinal and Opsin is released > G-protein transducin activates phosphodiesterase enzyme via GTPase activity > PDE breaks down cGMP into GMP > calcium and sodium fated channels are closed > hyperpolarisation in photoreceptor > reduction in release of Glutamate > bipolar cell is depolarised > increased release of glutamate to ganglion cell > AP generated to Optic nerve

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13
Q

What is the pigments in each G-protein coupled photoreceptors?

A

Rods: Retinal and Opsin

Cones: Iodine and Opsin (the Opsin has different amino acids so you have blue, green and red cones)

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14
Q

What is the Dark to Light Adaptation?

A

Pupils constrict > increase focus to fovea > photopigment is bleached > rods turn off > night vision and sensitivity decreases > cones turn on > increased acuity and colour vision

This takes 5-10mins

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15
Q

What is bleaching of photopigments?

A

This is where all trans retinal reduces to all-trans retinol

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16
Q

How is retinal restored?

A

Transducin moves into inner segment to allow regeneration of photopigment (makes Opsin available)

All-trans retinol enters Retinal Pigment Epithelium and is converted to 11-cis retinal which then goes back into outer segment of photoreceptor to bind with Opsin to form the photopigment

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17
Q

What is the light to dark adaptation?

A

Pupils dilate to increase spread of light ray > rods activated > rhodopsin accumulates again so transducin returns > increased retinal sensitivity and decreased colour vision and acuity

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18
Q

What are the different receptors on Off and On centre bipolar cells?

A

Off: ionitropic receptors (AMPA and Kainate)

On: G-protein-coupled metabotropic glutamate receptors (mGluR6)

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19
Q

What is the primary visual pathway?

A

Optic nerve to optic chiasm > decussation of nasal retinal fibres > optic tract > lateral Geniculate Nucleus (Ipsilateral - layers 2.3.5;contralateral - layers 1.4.6) > some fibres go to superior colliculus and pretextal nucleus while others go to striate cortex (primary visual cortex via temporal lobe (inferior retinal fibres - Meyer’s loop) or parietal lobe (superior retinal fibres - Baum’s loop) in the optic radiation

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20
Q

What is the primary and secondary visual pathways?

A

Primary is to LGN

Secondary is go Pretectum (pupil response), Superior Colliculus (Eye movement) and Hypothalamus (circadian rhythm)

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21
Q

What is the pupil response?

A

Light into one eye > ganglionic cells melanopsin cascade > optic nerve to optic chiasm > optic tract to LGN > PTN bilaterally innervates EW Nuclei > ciliary ganglion of the eye > short ciliary nerves supply ciliary muscles and iris sphincter > both pupil constrict/dilate = direct and consensual response

If this doesn’t occur = Marcus Gunn sign

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22
Q

What is the accommodation reflex?

A
  • Parasympathetic: ciliary muscles contract, relaxing suspensory ligaments, lend bulges and decrease focal length; iris sphincter pupilles contract, reducing pupil size and increasing light focus
  • sympathetic: (long ciliary nerve travels with CN VI from superior Carotid ganglion) ciliary muscle relaxes, contracts suspensory ligament and lens flattens to increase focal length; iris dilator pupilles constrict - pupils dilate
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23
Q

What is the name of visual field defects?

A

Anopia

24
Q

What is Hemianopia?

A

decreased vision/blindness in half of the visual field of one or both eyes

25
Q

What causes anopia?

A

Lesion in optic nerve

26
Q

What causes hemianopia?

A
  • Bitemporal = lesion in chiasm
  • Homonymous =lesion in optic tract
  • Quadrantic = temporal or parietal lesions in MCA
  • Hemianopia w/ macular sparing = lesion in bilateral projections to occiput (PCA)
27
Q

What is central scotome?

A

Degeneration of macular causing blind spot (scotoma)

28
Q

What are the visual field tests?

A

Autonomated perimetry- head on chin rest, alert when you can see moving Object in peripheral vision

29
Q

Which type of pituitary Tumor causes anopia before systemic symptoms?

A

Non-hormone secreting tumor

30
Q

How long does it take for recovery of visual field after pituitary is removed?

A

1-2 months

31
Q

What is refractive errors?

A

Light ray entering the eye doesn’t hit the retina causing diminished visual acuity

32
Q

What is myopia?

A

Short-sightedness - light ray is too converged so focuses before retina

Solution is a diverging/concave (minus) lens

Refractive error: 0.5-8D if physiologic and >8D if pathological

33
Q

What is hyperopia?

A

Long-sightedness - light ray doesn’t converge enough so focuses beyond Retina

Solution is a converging / convex lens (plus)

34
Q

What is presbyopia?

A

Normal aging of the lens that leads to change in refractive state of the eye

As the lens ages it becomes less able to alter curvature - hard to see near objects

35
Q

What is red desaturation?

A

Colour vision caused by optic nerve or tract lesion causing the colour red to appear dull, pink or washed out

36
Q

What is astigmatism?

A

Asymmetrical corneal surface - light is refracted to multiple areas of the retina

Regular astigmatism is resolved w/ cylindrical and spherical lenses or rigid contact lenses

Irregular astigmatism is only resolved with rigid contact lenses

37
Q

What is Amblyopia?

A

Develops before age 2

Suppression of image by visual cortex from the eye that has an interference with image

If it consist beyond 8 without treatment it can cause blindness

38
Q

What causes amblyopia?

A

Strabismus, myopia or hyperopia, cataract

39
Q

What is the treatment of amblyopia?

A

Spectacles is contact lenses / cataract removal / patching to strengthen weak eye

40
Q

What is strabismus?

A

Squint caused by imbalance in extraocular muscles of the two eyes

41
Q

What are the two types of strabismus?

A

Esotopia (convergent squint) - cross-eyed

Expropria (divergent squint) - wall-eyed

42
Q

What is the treatment of strabismus?

A

Prismatic glasses

Surgery to extraocular muscles to realign the eyes

If not treated you end up with poor stereoacuity (depth of perception) leading to suppression of image from one eye - suppressed eye becomes amblyopic

43
Q

What is cataract?

A

Leading cause of blindness in the world

Clouding of the lens common is people over 65

44
Q

What is the treatment of cataract?

A

Surgery - replacement of lens for artificial one

Con: plastic lens can’t adjust curvature so clear image but poor focal length therefore glasses needed

45
Q

What is Glaucoma?

A

Progressive loss of vision associated with elevated intraoculaire pressure (aqueous humor) - compressing the optic nerve

46
Q

What is the treatment of glaucoma?

A
  • Prostaglandin analogue - reduce intraocular pressure by increasing outflow of aqueous humor
  • Beta-blocker (timolol) - reduce intraocular pressure by my decreasing production of aqueous humor
  • Carbonicanhydrase inhibitor (brinzolamide) - reduce intraocular pressure by decreasing aqueous humor production/secretion
47
Q

How do we influence perception?

A

By paying attention to different aspects of our environment

Stress and fatigue

Brain damage

48
Q

What is attention?

A

• attention - direction and focus of perception

49
Q

What types of attention is there?

A
  • Selective - paying attention to stimuli that are changing, repeated, intense and personally meaningful
  • divided/focus - we can divide attention (but this is limited but with practice can be improved)
50
Q

What is stigma?

A

Negative evaluation of and associated lowering of respect for individuals because of some personal characteristics, which may be physical or behavioural

51
Q

What is enacted stigma?

A

Societal reaction produces discriminatory experience

52
Q

What is felt stigma?

A

Expected societal reaction influences individuals self-identity

53
Q

What is the model of disability?

A

Suggestion that disability occurred on a personal level due to:

  • personal tragedy
  • medical problem
  • individual adjustment
54
Q

What is social model of disability?

A

Disability is caused by way society is organised, rather than by a person’s impairment or difference - discrimination

It is resolved by removal of environmental barriers that restrict life choices for disabled people

55
Q

What is medical model of disability?

A

Disability is caused by the disability/impairment of the person

The solution is medical and other treatments

56
Q

What is the psychological model of disability?

A

Activities performed (or not performed) by someone with a “health condition” are influenced by the same psychological processes that affect the performance of these behaviours by non-disabled people.

57
Q

How is disability measured?

A

Activities of Daily Living (ADL) - assesses thé person’s ability to perform everyday self-care or mobility activities via self-report or observation

Sem3 (10 decks)

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