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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?

24
Q

How can we relax accomodation

A

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

25
What is a TOPCON TRK- 1P?
4 in one instrument encompassing autorefraction, tonometry, keratometry, and pachymetry
26
how is intraocular pressure maintained?
by the balance between the aqueous production and outflow
27
What is positive intraocular pressure required?
to maintain the shape of the eye
28
How does the balance of pressure occur?
the aqeuous humour flows out through the drainage angle, infront of the iris. This equal flow maintains stable pressure
29
So what would happen if the outflow was reduced?
pressure would build up in eye
30
How can the iincrease in pressure affect the eye?
risk of glaucoma
31
What is glaucoma?
causes optic nerve fibres to die (atrophy) which leads to visual field defects and possible blindness
32
Why do we measure IOP?
to detect the risk factor of glaucoma
33
What can reducing IOP do?
can slow down the progression of optic neuropathy
34
Why is early detection beneficial?
so can be acted on by e.g prescribing eye drops to reduce aqueous humour flowing to balance pressure or allow the flow
35
What is normal IOP?
patients IOP should be 15mmHG (mercury)
36
What are the 3 main factors which affect IOP?
- 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
What other factors affect IOP?
- 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
What affects IOP?
Time of day- higher in mornings with afternoon dip esp males
39
Why do we repeat IOP measures?
so record at different times of day due to it being different at certain times of day
40
How do we measure IOP?
Tonometry - 2 methods - applanation - non-contact tonometry
41
Why is it important to repeat IOP measurements at different times of day?
if you think your patient is at risk or you see that pressure is high
42
What is applanation tonometry?
its the amount of corneal flattening produced by a known weight that is then measured.
43
What is non-contact tonometryy?
measure the IOP in the eye
44
How does non-contact tonometry work?
Puff air into the eye and measure how much air pressure is required to flatten the cornea .
45
How can you detect how much the cornea has flattened in non-contact tonometry?
by the IR emitter and detector
46
How many measurements do you take on the non-contact tonometry?
3 as it is very fast
47
Why are 3 readings taken from the Non-contact tonometry?
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
What is the average corneal thickness?
0.54mm | but can range from 0.44-0.64mm
49
What else can affect IOP?
corneal thickness | corneal curvature
50
Why will the reading be less from thin cornea?
less force to flatten
51
Why will the reading be more from thick cornea?
more force to flatten
52
How do you measure corneal thickness?
Pachymetry via the instrument Topcon
53
What are the 3 main things which IOP is affected by?
Family history Refractive error Time of day
54
What is the percentage of the population which have IOP less than 22mmHg?
95%
55
What do you use a tonometry for?
to measure eye pressure

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