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Year 2 > HNN Week 6 > Flashcards

HNN Week 6 Flashcards

1
Q

Name the three general layers of the eyeball and what they include:

A

1) outer fibrous layer = sclera and cornea
2) middle vascular layer = choroid, ciliary body and iris
3) inner retinal layer = retina

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2
Q

Describe anatomical drawing of the eye:

A
  • sclera and cornea make up outer eye layers
  • cornea covers the anterior of the eye
  • where sclera becomes cornea there is scleral venous sinus
  • ciliary body and iris come off the sclera anterior to the lens
  • choroid is the next layer in after the sclera and covers entire eye except the anterior part
  • retina is the next layer in and covers the entire inner eye except the anterior part and also covers the optic nerve
  • fovea centralis = central depression in retina below optic nerve entrance where light is focused
  • optic disc is area of the retina where the optic nerve leaves from and there are no light sensitive receptors here
  • optic nerve leaves the back of the eye
  • vitreous (postremal chamber) = from lens to retina
  • anterior chamber and posterior chamber make up anterior cavity
  • anterior chamber = between cornea and iris
  • posterior chamber = between iris and lens
  • ora serrata
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3
Q

Describe the structure and function of the sclera:

A
  • part of outer fibrous layer
  • opaque, dense connective tissue covering of the eye that covers entire eye except iris and pupil
  • has fibroblasts and collagen fibres
  • internal sclera surface is loosely attached to choroid
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4
Q

Describe the structure and function of the cornea and what type of epithelium it is made from:

A
  • continuous with sclera and covers anterior eye (iris and pupil)
  • non keratinised stratified squamous epithelium
  • receives O2 from the air by diffusion
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5
Q

Describe the structure and function of the scleral venous sinus:

A
  • opening at the junction of the cornea and sclera where aqueous humour drains
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6
Q

Describe the structure and function of the choroid:

A
  • thin pigmented vascular layer loosely attached to sclera and tightly attached to retina
  • contains melanocytes that produce melanin to absorb stray light rays and prevent light reflection/scattering
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7
Q

Describe the structure and function of the ciliary body:

A
  • anterior extension of choroid
  • triangular shaped and forms complete ring around eyeball
  • composed of ciliary muscle and ciliary processes
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8
Q

Describe ciliary muscle:

A
  • smooth muscle fibres under parasympathetic supply from CN3
  • alter lens shape
  • blood vessels secrete aqueous humour
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9
Q

Describe ciliary processes:

A
  • processes that leave the ciliary body called zonular fibres
  • zonular fibres collectively known as ‘suspensory ligament of the lens’ and hold it in place
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10
Q

Describe anatomy and function of the iris:

A
  • circular shaped structure extending from ciliary body
  • suspended between cornea and lens
  • circularly arranged smooth muscle fibres = sphincter pupillae muscle under parasympathetic control
  • radially arranged smooth muscle fibres = dilator pupillae muscle under sympathetic control
  • colour depends on melanin production being high (brown) or low (blue)
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11
Q

Describe the anatomy of the anterior and posterior chambers and their contents and how they are produced:

A
  • anterior chamber and posterior chamber collectively known as anterior cavity of eye
  • are continuous through pupillary opening in the iris
  • anterior chamber = between cornea and iris
  • posterior chamber = between iris and lens
  • ciliary body blood vessels secrete aqueous humour
  • passes into posterior chamber
  • passes from here though pupillary opening into the anterior chamber
  • absorbed through the scleral venous sinus
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12
Q

Describe the anatomy of the postremal (vitreous) chamber and its contents:

A
  • between lens and retina
  • contains gelatinous vitreous humour than cannot be replaced
  • vitreous humour contains phagocytes to destroy debris
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13
Q

Describe the function and anatomy of the lens:

A
  • divides anterior cavity and vitreous chamber
  • contains crystallins (proteins) that are arranged in layers
  • is attached to ciliary muscles so that it can change shape to maintain visual acuity
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14
Q

Describe the blood supply of the eye:

A

ARTERIES:

  • three branch types of the ophthalmic artery:
  • > short ciliary arteries
  • > long ciliary arteries
  • > anterior ciliary arteries (supply ciliary muscles)

VEINS:

  • 4 vorticose veins leave the sclera via 4 posterior quadrants of the eye
  • and enter superior and inferior ophthalmic veins

There is also a central retinal artery and vein which are below optic nerve but travel in same sheath

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15
Q

What is the ora serrata?

A
  • serrated junction between retina and ciliary body where there is transition from simple non-photosensitive area to multilayered photosensitive layer
  • i.e. the junction between the neural and pigmented parts of the retina
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16
Q

Describe the anatomy of the retina and all its layers:

A
  • has two parts:
  • > neural layer = photosensitive and found posteriorly
  • > pigmented layer = covers internal surface of ciliary body and iris and is not photosensitive
  • -> the ora serrata is the junction between these two layers

Cell layers from deep to superficial:

  • pigmented layer with epithelial cells and melanocytes
  • photoreceptors = rods and cones
  • then there is outer synaptic layer
  • bipolar cell layer = bipolar cells, horizontal cells and amacrine cells
  • then there is inner synaptic layer
  • ganglion cell layer
  • optic nerve axons
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17
Q

Describe rods:

A
  • provide black and white vision and function in dim light
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18
Q

Describe cones:

A
  • provide colour vision and there are blue/red/green cones that work together to produce various cell combinations
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19
Q

Describe bipolar cells:

A

transmit signals from photoreceptors to ganglion cells and function by GRADED potentials not action potentials

20
Q

Describe amacrine cells:

A
  • receive information and are excited by bipolar cells

- pass info onto ganglion cells about illumination on the retina

21
Q

Describe horizontal cells:

A
  • send lateral inhibitory signals to bipolar cells, this enhances contrast and colour differentiation
22
Q

Describe ganglion cells:

A
  • fire action potentials which travel along the optic nerve
23
Q

What is the optic disc?

A
  • blind spot

- area on retina where optic nerve leaves and there are no light receptors

24
Q

What is the fovea centralis?

A
  • central area of macular lutea where light is focused and the bipolar and ganglion cells are displaced
25
Q

What is the macula lutea?

A
  • area of greatest visual acuity where there are few rods and many cones, found lateral to optic disc
26
Q

What is the ratio of rods to bipolar cells in terms of synapses? What does this mean in terms of vision?

A

6-600 rods : 1 bipolar cell

Vision is more sensitive to light but less accurate/focused due to high synapse rate

27
Q

What is the ratio of cones to bipolar cells in terms of synapses? What does this mean in terms of vision?

A

1 cone : 1 bipolar cell

Vision is more accurate due to low synapse ratio

28
Q

Describe the pressure in the eye and how it is maintained:

A
  • intraoccular pressure is normally ~16mmHg
  • this pressure maintains eyeball shape and prevents the eyeball collapsing
  • the pressure is created mainly by aqueous humour and partly by vitreous humour
29
Q

What are the components anatomically of the visual pathway?

A
  • optic nerves
  • optic chiasm
  • optic tracts
  • lateral geniculate nucleus in the thalamus
  • optic radiation
  • visual cortex in the brain
30
Q

Where does fibre decussation occur and what fibres decussate?

A
  • Fibres decussate in the optic chiasm and fibres from the nasal parts of the retina decussate
31
Q

What is the function of the lateral geniculate nucleus?

A
  • relays info from the optic tract to the optic radiation which passes to the primary visual cortex in the medial occipital lobe
  • it gates information that reaches the visual cortex in 2 ways:
  • > corticofugal fibres that run back from the visual cortex to the LGN
  • > other reticular midbrain areas
  • these -> mechanisms are inhibitory and turn off transmission through certain areas of the LGN so that only certain important visual information can pass
32
Q

What features of objects are highlighted by visual processing?

A
  • colour
  • shape
  • size
  • movement
  • location
33
Q

Describe the anatomy of an individual rod/cone cell:

A
  • has outer segment, inner segment, nucleus and synaptic body
  • outer segment is where light-sensitive photochemicals are found
  • inner segment is where mitochondria and organelles are found
34
Q

What photochemicals are found in rods and cones and where are they found?

A
  • RODS: rhadopsin
  • CONES: 3 different photopigments with spectral sensitivity
  • the cell membrane on the outer segment of rods and cones is folded into discs and the photopigments are found bound to transmembrane proteins on this folded membrane
35
Q

Describe the breakdown of rhadopsin when it is exposed to light:

A
  • rhadopsin is converted (when exposed to light) into bathorhodopsin
  • there is then a chain of reactions:
  • bathorhodopsin -> lumirhodopsin -> metarhodopsin 1 - metarhodopsin 2
  • when metarhodopsin 2 is formed this produces electrical signals that are sent to the brain via optic nerves
  • the 11-CIS RETINAL in rhadopsin is broken down into ALL TRANS RETINAL
36
Q

How rhadopsin can be reformed after it has been broken down?

A
  • 11-cis retinal can be reformed by converting the all trans retinal back into 11-cis retinal using isomerase enzyme and metabolic energy
  • another way to reform 11-cis retinal is to convert the all trans retinal into all trans retinol
  • al trans retinol is a form of vitamin A that is always present in the retina and can be used to renew retinal when needed
  • if there is XS retinal it can be converted into retinol to be stored
37
Q

Describe normal ion movement in the rod cells when rhadopsin is decomposed:

A
  • activation of rhadopsin causes hyperpolarisation of the rods membrane and decreases Na+ conduction
  • on the inner segment of the rod there is Na/K ATP-ases where Na moves out of the cell and K+ into the cell
  • the K+ can leak out of the cell again through non-gated K+ channels and this creates a negative potential within the cell
38
Q

Describe ion movement and what happens in a rod cell when it is dark:

A
  • the membrane of the rod outer segment is permeable to Na ions which enter the rod through cGMP- gated-channels
  • cGMP levels are high when it is dark
  • this causes Na to leak into the cell
  • this neutralises the integrity of the cell and the RMP changes from -70/80mV and rises to -40mV
39
Q

Describe ion movement and what happens in a rod cell when it is light:

A
  • cGMP levels are low when there is a lot of light on the retina and cGMP channels are shut
  • the outer segment of the rod membrane lets in LESS Na BY THREE STEP MECHANISM:
    1) light is absorbed by the retina and causes photo-activation of rhadopsin in the retina
    2) active rhadopsin activates a G-protein called transducin which activates the enzyme cGMP phosphodiesterase to break down cGMP
    3) the reduction in cGMP closes the cGMP-gated channels and this means there is less Na inward movement into the rod cell
  • overall more Na leaves the rod than enters
  • the internal environment of the cell becomes more negative and there is hyper-polarisation and action potentials are fired
  • at maximum light intensity, the RMP of the rod is ~-70-80mV
40
Q

Define macular degeneration and describe the two types:

A
  • progressive disease involving damage to the macula of the retina that is associated with distortion, reduced visual acuity and may result in blindness
    1) Dry/geographic/atrophic = atrophy of the outer retina, has slow progression and is associated with visual blurring
    2) Exudative/wet/neo-vascular = rapid progression, associated with growth of new blood vessels out from the choroid under the retina and can cause metamorphopsia (distortion)
41
Q

Describe the aetiology of macular degeneration:

A
  • drusen form -> photoreceptor cells continually produce pigment throughout their life and the ends of the photoreceptive cells decay and are removed by RPE cells (retinal pigment epithelial cells) and the breakdown products of photoreceptive cells accumulate forming drusen which are yellow lipid deposits under the retina

Risk factors:
- drusen, smoking, increasing age, diet (fruit and vitamin A/C protective), FH, previous cataract surgery, CVD and hypertension

Genetic changes:

  • complement factor H changes (complement factor H normally involved in regulating inflammation and stopping inflammatory cells attacking self cells) associated with 7.4x increased risk of developing AMD
  • HDL or LDL changes
  • changes in complement genes C2, C3, and CB1
  • may also be caused by oxidative stress
42
Q

Describe the pathophysiology of macular degeneration:

A
  • changes in structure of the retinal layers
  • initiating process unknown but Fe accumulates in the RPE cells causing oxidative stress
  • ischaemia of RPE cells = increased VEGF production = neovascularisation = disrupted Bruch’s membrane and disruption of photoreceptive cells in the macula and fovea
  • blood vessels leak causing retinal oedema and scar tissue grows under the retina
  • normally macula receives nutrients and O2 by diffusion from the choroid by diffusion so when there is O2 stress in the cells this is another trigger for neovascularisation
43
Q

How can you investigate and diagnose AMD?

A
  • history (presence of risk factors)
  • examination with ophthalmoscope with tropicamide (an anticholinergic) used to dilate pupil first
  • > pigment changes of macula
  • > scars
  • > new vessel formation
  • amsler grid (look for line distortion, measures progression of AMD)
  • optical coherence tomography (electromagnetic waves used to produce subsurface retinal images)
  • genotyping (for research only to identify predisposing genes)
  • visual acuity tests
  • fundus fluroscein angiogram (fluroscein injected IV and normally is bound to albumin so if there is leakage of vessels and albumin, fluroscein conglomerates will be seen)
44
Q

At what level are you considered legally blind?

A

3/60

45
Q

Describe some of the psychological and social implications of blindness:

A
  • psychological = isolation, depression, anxiety
  • social = domestic difficulties (cooking, cleaning, dressing)
  • finances, bills, bank statements
  • navigation and safety
  • work and loss of income
  • requiring residential care
  • health risks (falls, fractures)
  • additional disability (hearing impairment)
  • affects education
46
Q

What drugs are used to treat AMD and how do they work?

What are the financial and logistical issues with these drugs?

A
  • Anti-VEGF drugs
    1) Bevacizumab
    2) Ranibizumab
  • both are monoclonal antibodies that bind to VEGF and neutralise it, stopping it having its effect
  • both are equally effective
  • bevacizumab is cheaper but unliscenced
  • ranibizumab us more expensive but liscenced

Year 2 (22 decks)

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