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Gymnastics and tumbling > Chapter 27 (Monitoring Visual Function) > Flashcards

Chapter 27 (Monitoring Visual Function) Flashcards

1
Q

Function of Sclera?

A

Outer layer of the eye. Tough, strong white connective tissue, which protects and maintains shape of eyeball

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2
Q

Function of conjunctiva?

A

Thin layer or protective cells
Covered by layer of fluid secreted from tear ducts.

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3
Q

Function of cornea

A

Layer under conjunctiva and is continuous with sclera
Focuses light onto retina
Main structure responsible for the refraction of light rays onto the retina

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4
Q

Function of vitreous humour?

A

Helps maintain shape of eye by exerting outward pressure on sclera and surrounding tissue.
Help refract the light rays onto retina.
Supplies oxygen and nutrients to cornea and lens.

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5
Q

Function of choroid?

A

Richly supplied with blood vessels to supply oxygen and nutrients to retina.
A pigmented epithelium that absorbs any light that passes through rods and cones so it’s not reflected back into eye.

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6
Q

Function of iris?

A

Circular tissue - radial and circular muscles that control the size of the pupil.
Radial muscles stimulated by sympathetic nervous system
Circular muscles stimulated by parasympathetic nervous system.

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7
Q

Function of aqueous humour?

A

Helps maintain shape of eye by exerting outward pressure on sclera and surrounding tissue.
Help refract the light rays onto retina.
Supplies oxygen and nutrients to cornea and lens.

Less viscous than vitreous humour

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8
Q

Function of pupil?

A

Centre of iris which allows light to pass through

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9
Q

Function of retina?

A

Inner most layer of eye - sensory area.
Contains photoreceptors: cones, and rods.

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10
Q

Function of optic nerve?

A

Axons of cells in retina leave eyeball at this point. Carries action potentials to the brain.

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11
Q

Function of ciliary body?

A

Contains ciliary muscles which control the shape of the lens.
Controls diameter of suspensory ligaments, so therefore diameter of lens.

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12
Q

Function of lens?

A

Made of stacks of long, transparent cells
Make fine adjustments to the refraction of the light rays so they are sharply focused on retina.

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13
Q

Function of suspensory ligaments?

A

Holds lens in place and connects lens to ciliary muscles.

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14
Q

Function of fovea?

A

Most sensitive part of retina, contains highest conc. of cone cells.
Area with maximum visual acuity.

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15
Q

Function of blind spot?

A

Point at which optic nerve leaves eyeball, contains no photoreceptors to light hitting here isn’t interpreted.

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16
Q

Cornea, conjunctiva, lens info?

A

Don’t contain blood vessels as light has to pass these structures to reach the retina. If there was blood, it would absorb and reflect too much of the light.

17
Q

Definition of visual acuity?

A

Resolution of an image that is perceived by the brain.

18
Q

Visual acuity in rod cells info?

A

Low visual acuity

Many rod cells form synapses with the same bipolar cell. - the information is therefore combined.
This helps in the detection of dim light as small responses of many rod cells can be summated to produce a larger response in the brain.

‘The brain interprets an average response from a collection of rod cells not individual responses from individual cells’

19
Q

Visual acuity in cone cells info?

A

Each bipolar cell receives inputs from only one cell cone cell in the centre of the fovea.
The brain therefore receives information from each cone cell separately.
This produces a high resolution image, ie, high visual acuity.
This is further enhanced by the concentration of cone cells in the fovea where the image that is formed is sharpest and least distorted.

20
Q

What are eye tests?

A

Carried out to help detect eye diseases before there is any serious effect on sight, to prevent the condition getting worse by early treatment.
Carried out every 2 years by optometrists
Can detect diabetes, eye cancers etc..

21
Q

What do eye tests routinely test for?

A

Visual acuity, ie, ability to focus on objects
Colour vision
Pupil response to light intensity.

Other tests to be completed:
Eye pressure
field of vision

22
Q

Visual acuity test?

A

Measured using the Snellen scale
No. rows of letter that get smaller (or pictures for the young)
Quantitative measure of ability to see an in-focus image at certain distance.

  1. Cover one eye
  2. Read chart top to bottom at distance of 6m/20ft.
  3. Then repeat with other eye.

if 20/20 vision, patient can read letters under 1cm in height, at a distance of 20ft.

Appropriate corrective measures, eg, glasses, contact lenses, surgery.

23
Q

Colour vision test info?

A

(arise from altercations in gene located on X chromosome and is recessive, so males are more likely to be colour blind)

Two types:
Ishihara pseudo-isochromatic colour plate exam
Farnsworth-Munsell 100 hue test.

24
Q

Ishihara pseudo-pseudo-isochromatic colour plate exam info?

A

Most common
Series of test plates where a matrix of coloured dots are arranged with a number visible on the page.
Usually to test for red-green blindness.

25
Q

Farnsworth-Munsell 100 hue test info?

A

Involves asking patient to arrange a coloured set of caps in sequence to form a gradual transition of colour between two points.
Caps show 4 times 25 hues of different colours
Each colour hue at each end is fixed.
Use to grade colour discrimination.

26
Q

Optical coherence tomography (OCT) scan info?

A

Capture image reflections from within eye tissue
Produce cross-sectional images at very high resolutions
Used to diagnose:
AMRD
Diabetic retinopathy
Macular holes
Macular oedema

27
Q

OCT scan procedure

A

Optical beam of near infra-red light detected at tissue
Small proportions of light reflected by retina are captured

Limitations:

  • Most light scatters off at large angles which causes background noise and obscured image - interferometry can reject background noise and build up clear 3D images.
  • Eyes may be sensitive to bright light for several hours after exam
  • Can only image tissue to max depth of ~ 1-2mm below surface (but retina is ~ 0.5mm, so ok)
28
Q

Advantages of OCT scan?

A

Non-invasive
Totally painless
Only takes ~10-15 minutes
Results available instantly.

29
Q

Definition of accommodation

A

The change in shape of the lens to focus objects from a particular distance
Achieved by varying tension on suspensory ligaments which makes the lens more or less convex.

30
Q

How are the light rays bent?

A

They are focused on the retina by cornea, aqueous humour, lens, and vitreous humour. Majority of refraction occurs at surface of cornea.

31
Q

Focusing on distant object

A

Light rays enter eyes parallel.
Cornea bends light rays
Ciliary muscle relaxes, diameter is wider
This pulls on suspensory ligaments so they are under tension, pulled taut.
Lens is stretched, becomes thinner and less convex.
Bends light rays slightly.

32
Q

Focusing on nearby object?

A

Light rays enter eye widely diverging
Cornea bends light rays
Ciliary muscle contacts, diameter reduces
This loosens tension on SL so they slacken.
Lens is under pressure so becomes fatter and more convex
Bends light rays strongly

33
Q

Myopia info?

A

Short sightedness
Light focused in front of retina.
Can’t see distant objects clearly.

Causes
Eye ball is too long
Cornea is too curved
Lens is too thick

Concave lenses to correct.

34
Q

Hyperopia info?

A

Long sightedness
Light focused behind retina
Can’t see close up objects clearly

Causes
Eye ball too short
Cornea not curved enough
Lens too thin
Can be caused by diabetes

Convex lenses to correct.

35
Q

Similarities between rod and cone cells?

A
  • Both are photoreceptors
  • Both detect and respond to light
  • Both contain molecules that change shape when light hits them
  • Both contain opsins (specialised proteins)
  • Both have similar structures

NOT FINISHED!!!!

36
Q

Info on bipolar and ganglion cells?

A
  • Specialised neurones
  • Carry action potential from rod and cone cells to optic nerve
  • Are unmyelinated (so are transparent) to allow light to pass through them to the rod and cone cells.
  • Cell bodies of the bipolar and ganglion cells in the fovea are pushed to the side so light hits the photoreceptors without having to pass through other cells first

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