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clinical skills > Optical Instruments 1 > Flashcards

Optical Instruments 1 Flashcards

1
Q

What instruments are used in a typical routine eye examination?

A 
Letter chart e.g logMAR, Snellen
Retinoscope 
Autorefractor
Slit-lamp
Opthalmoscope
Fundus camera
Non-contact Tonometer
Keratometer
Optical coherence tonography
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2
Q

What is the examination when using slit-lamp?

A

external eye health check

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3
Q

What is the examination when using a opthalmoscope and fundus camera?

A

internal eye health check

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4
Q

What examination when using keratometer?

A

Corneal curvature (K readings)

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5
Q

What is the examination when using a Non-contact Tonometer?

A

intraocular pressure

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6
Q

What is the examination when using Letter chart?

A

measure vision/visual acuity

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7
Q

What is the examination when using a retinoscope and autorefractor?

A

objective refraction

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8
Q

What is the examination when using a Humphreys or Henson?

A

visual fields (peripheral vision)

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9
Q

What is objective refraction?

A

when tests are carried out without opinion from patient

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10
Q

What is the the objective refraction testing for?

A

measuring if patient is short sighted or long sighted.

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11
Q

Who carries out a screening test?

A

optical assistant before the patient sees an optometrist

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12
Q

What does the screening test include?

A 
Autorefractor- objective refraction
Non-contact tonometry- intraocular pressure
Visual fields-  
Pachmetry- corneal curvature
fundus camera- fundus image
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13
Q

What is the opthalmoscope used for?

A

look back of eye

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14
Q

What is the perimetry used for?

A

used to measure visual fields which is peripheral vision

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15
Q

What is an autorefractor?

A

an instrument used to determine a patients prescription i.e refractive error

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16
Q

When is a autorefractor used?

A

used in pre-screening

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17
Q

What is a problem with an autorefractor?

A

reading may not be accurate prescription

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18
Q

What is the reason why we cant have an autorefractor reading?

A

if pupil is too small- therefore cant give proximal accomodation

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19
Q

What is proximal accomodation?

A

is when the eye id being tricked into thinking its looking at a distance by using the autorefractor.
The autorefractor machine goes in a out of focus to trick the brain into thinking its looking at a distance
this is to counteract the proximal accomodation

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20
Q

What is the advantage of using an autorefractor?

A

ojective- so therefoere requires minimal input from patient

quick

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21
Q

What is the disadvantage of using an autorefractor?

A
  • affected by proximal accomodation
  • expensive
  • non-portable
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22
Q

What sort of prescriptions does the autorefractor measure?

A

up to 25DS

up to 10DS

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23
Q

What is the minimal pupil diameter which can be measured from the autorefractor?

A

2.0mm

24
Q

How can we relax accomodation

A

autofogging - when image keeps on focusing and non-focusing so this prevents it

25
Q

What is a TOPCON TRK- 1P?

A

4 in one instrument encompassing autorefraction, tonometry, keratometry, and pachymetry

26
Q

how is intraocular pressure maintained?

A

by the balance between the aqueous production and outflow

27
Q

What is positive intraocular pressure required?

A

to maintain the shape of the eye

28
Q

How does the balance of pressure occur?

A

the aqeuous humour flows out through the drainage angle, infront of the iris. This equal flow maintains stable pressure

29
Q

So what would happen if the outflow was reduced?

A

pressure would build up in eye

30
Q

How can the iincrease in pressure affect the eye?

A

risk of glaucoma

31
Q

What is glaucoma?

A

causes optic nerve fibres to die (atrophy) which leads to visual field defects and possible blindness

32
Q

Why do we measure IOP?

A

to detect the risk factor of glaucoma

33
Q

What can reducing IOP do?

A

can slow down the progression of optic neuropathy

34
Q

Why is early detection beneficial?

A

so can be acted on by e.g prescribing eye drops to reduce aqueous humour flowing to balance pressure or allow the flow

35
Q

What is normal IOP?

A

patients IOP should be 15mmHG (mercury)

36
Q

What are the 3 main factors which affect IOP?

A
  • The amount of fluid within the eye
  • external forces acting upon the eye, including the tension within the ocular walls (what gives eye shape)
  • intraocular volume
37
Q

What other factors affect IOP?

A
  • Age- older more at risk
  • Also pulsates with cardiac cycle- as choroid fills with blood and is emptied
  • gender- higher in older women (2mmHG higher)
  • Being short sighted (myopia)- risk of higher IOP
  • Genetics
  • Race- black population higher
38
Q

What affects IOP?

A

Time of day- higher in mornings with afternoon dip esp males

39
Q

Why do we repeat IOP measures?

A

so record at different times of day due to it being different at certain times of day

40
Q

How do we measure IOP?

A

Tonometry - 2 methods

  • applanation
  • non-contact tonometry
41
Q

Why is it important to repeat IOP measurements at different times of day?

A

if you think your patient is at risk or you see that pressure is high

42
Q

What is applanation tonometry?

A

its the amount of corneal flattening produced by a known weight that is then measured.

43
Q

What is non-contact tonometryy?

A

measure the IOP in the eye

44
Q

How does non-contact tonometry work?

A

Puff air into the eye and measure how much air pressure is required to flatten the cornea .

45
Q

How can you detect how much the cornea has flattened in non-contact tonometry?

A

by the IR emitter and detector

46
Q

How many measurements do you take on the non-contact tonometry?

A

3 as it is very fast

47
Q

Why are 3 readings taken from the Non-contact tonometry?

A

IOP varies with the cardiac cycle

Take 3 readings and average as reading could be taken at the trough or at the peak in the cardiac cycle

48
Q

What is the average corneal thickness?

A

0.54mm

but can range from 0.44-0.64mm

49
Q

What else can affect IOP?

A

corneal thickness

corneal curvature

50
Q

Why will the reading be less from thin cornea?

A

less force to flatten

51
Q

Why will the reading be more from thick cornea?

A

more force to flatten

52
Q

How do you measure corneal thickness?

A

Pachymetry via the instrument Topcon

53
Q

What are the 3 main things which IOP is affected by?

A

Family history
Refractive error
Time of day

54
Q

What is the percentage of the population which have IOP less than 22mmHg?

A

95%

55
Q

What do you use a tonometry for?

A

to measure eye pressure

clinical skills (13 decks)

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