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Case 3 Flashcards

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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?

24
Q

What is Hemianopia?

Study These Flashcards
A

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

25
What causes anopia?
Lesion in optic nerve
26
What causes hemianopia?
* 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
What is central scotome?
Degeneration of macular causing blind spot (scotoma)
28
What are the visual field tests?
Autonomated perimetry- head on chin rest, alert when you can see moving Object in peripheral vision
29
Which type of pituitary Tumor causes anopia before systemic symptoms?
Non-hormone secreting tumor
30
How long does it take for recovery of visual field after pituitary is removed?
1-2 months
31
What is refractive errors?
Light ray entering the eye doesn’t hit the retina causing diminished visual acuity
32
What is myopia?
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
What is hyperopia?
Long-sightedness - light ray doesn’t converge enough so focuses beyond Retina Solution is a converging / convex lens (plus)
34
What is presbyopia?
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
What is red desaturation?
Colour vision caused by optic nerve or tract lesion causing the colour red to appear dull, pink or washed out
36
What is astigmatism?
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
What is Amblyopia?
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
What causes amblyopia?
Strabismus, myopia or hyperopia, cataract
39
What is the treatment of amblyopia?
Spectacles is contact lenses / cataract removal / patching to strengthen weak eye
40
What is strabismus?
Squint caused by imbalance in extraocular muscles of the two eyes
41
What are the two types of strabismus?
Esotopia (convergent squint) - cross-eyed Expropria (divergent squint) - wall-eyed
42
What is the treatment of strabismus?
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
What is cataract?
Leading cause of blindness in the world Clouding of the lens common is people over 65
44
What is the treatment of cataract?
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
What is Glaucoma?
Progressive loss of vision associated with elevated intraoculaire pressure (aqueous humor) - compressing the optic nerve
46
What is the treatment of glaucoma?
* 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
How do we influence perception?
By paying attention to different aspects of our environment Stress and fatigue Brain damage
48
What is attention?
• attention - direction and focus of perception
49
What types of attention is there?
* 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
What is stigma?
Negative evaluation of and associated lowering of respect for individuals because of some personal characteristics, which may be physical or behavioural
51
What is enacted stigma?
Societal reaction produces discriminatory experience
52
What is felt stigma?
Expected societal reaction influences individuals self-identity
53
What is the model of disability?
Suggestion that disability occurred on a personal level due to: - personal tragedy - medical problem - individual adjustment
54
What is social model of disability?
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
What is medical model of disability?
Disability is caused by the disability/impairment of the person The solution is medical and other treatments
56
What is the psychological model of disability?
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
How is disability measured?
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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