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Investigations > Refraction outline > Flashcards

Refraction outline Flashcards

1
Q

What are 7 points of the essential history for performing refraction?

A
  1. reason for visit/rationale for refraction e.g. symptoms
  2. demographics including age
  3. POH, including previous surgery, allergies, and use of refractive corrections such as spectacles and CL
  4. family ophthalmic history
  5. PMH
  6. medication
  7. visual requirement such as occupation, VDU use, driving, hobbies
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2
Q

What are 6 parts of the preparation for refraction?

A
  1. focimetry on current spectacles
  2. room lights on
  3. visual acuity - unaided and with current prescription + with pinhole if <6/9
  4. cover/uncover test at distance and near
  5. motility and pupil examination
  6. measure IPD - set up trial frame
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3
Q

At what visual acuity should you perform pinhole acuity?

A

<6/9

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4
Q

Should room lights be on or off for retinoscopy?

A

off

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5
Q

What should the patient focus on to perform retinoscopy?

A

non-accommodative target distance e.g. green duochrome

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6
Q

Prior to commencing retinoscopy, how can refractive error be estimated? 2 factors

A
  • previous prescription
  • visual acuity: 1.0 D of blur reduces VA by about 4 LogMAR lines if no accommodation exerted
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7
Q

What should be your starting lens for retinoscopy be?

A

estimated from previous prescription and VA, compensated for by your working distance (e.g. +1.5D for 2/3m)

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8
Q

What effect does 1.0D of blur have on VA in terms of LogMAR lines?

A

1.0D of blur reduces VA by 4 LogMAR lines if no accommodation exerted

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9
Q

How is accommodation prevented when performing retinoscopy?

A

fog fellow eye with a high plus powered lens

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9
Q

How is accommodation prevented when performing retinoscopy?

A

fog fellow eye with a high plus powered lens

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10
Q

At what point should you aim to be when performing retinoscopy?

A

as close to patient’s visual axis without obscuring their fixation target

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11
Q

Why is it important your head doesn’t get in the way in retinoscopy?

A

pt likely to look at head and start accommodating

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12
Q

How can you reduce accommodation in retinoscopy from your head getting in the way?

A

ask pt to tell you if this happens

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13
Q

How can you identify the axis of astigmatism with retinoscopy?

A

from movement of retinoscopy light as sweep across the eye

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14
Q

How is the reflex of retinoscopy neutralised?

A

neutralise reflex in one meridian with DS lenses; if reflex is ‘with’, add plus; if against, add minus
when point of reversal is reached in one meridian, add cylindrical lenses to neutralise in the other meridian

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15
Q

What does it mean to be consistent with cylindrical lenses and why is this important?

A

either work with minus or plus cylindrical lenses; in optometry it is commoner to use minus cylinders

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16
Q

Which sign of cylinder (plus or minus) is most commonly used in optometry?

A

minus

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17
Q

If using minus cylinders, which meridian should you correct first in retinoscopy?

A

the most plus meridian - if both reflexes are against, it is the faster reflex. if both reflexes are with it is the slower reflex. if one is with and one against, it is the with reflex

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18
Q

If using plus cylinders, which meridian should you correct first in retinoscopy?

A

most minus meridian; if both reflexes are against, it is the slower reflex; if both are with, it is the quicker reflex. if one is with and one against, it is the against reflex

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19
Q

What are 3 things to consider that could cause a poor reflex with retinoscopy?

A
  1. media opacity
  2. high refractive error
  3. keratoconus
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20
Q

What are 2 things to do to reduce media opacity causing poor retinoscopy reflex?

A
  1. optimise illumination
  2. check they are not accommodating on your head
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21
Q

What is a measure to take to reduce the effect of high refractive error causing poor retinoscopy reflex?

A

use large steps e.g. +- 5DS or +-10DS

22
Q

What are 2 things that may suggest keratoconus causing poor retinoscopy reflex?

A

swirling reflex or oil drop sign

23
Q

Should room lights be on or off for subjective refraction?

A

on

24
Q

What are 3 initial steps to take for subjective refraction?

A
  1. remove ‘working distance’ lenses
  2. occlude eye not being tested
  3. check VA
25
Q

What is the overall order for subjective refraction after the initial steps?

A
  1. verify sphere
  2. verify cylinder axis
  3. verify cylinder power
  4. refine best sphere
26
Q

What are the 5 steps to take to verify the sphere?

A
  1. ask patient to look at the smallest line they can see clearly
    2.verify sphere by offering +- DS (usually +- 0.25DS to fine-tune, may need +-0.5DS if poor vA)
    3.ask is line clearer and easier to read with lens 1 or 2?
    4.do not make prescription more minus if lens doesn’t improve number of letters that can be read + just makes it look ‘darker’. put high power lenses at back of trial frame
    5.measure and document back vertex distance, especially if >4.0DS
27
Q

At what spherical correction is it very important to measure BVD?

A

> 4.0DS

28
Q

What are 5 steps to verify the cylinder axis in subjective refraction?

A
  1. ask patient to look at round target/ easily readable such as ‘O’ or dots
  2. use cross-cylinder (+- 0.25 cross-cylinder or +- 0.50 or +- 1.00 if VA poor)
  3. align handle with axis or trial cylinder
  4. ask ‘is the circle rounder and clearer with lens 1 or 2’?
  5. rotate cylinder towards the preferred cross cylinder respecting its sign - i.e. plus trial cylinder rotated towards plus sign of cross cylinder
29
Q

What are 2 things you should do as good practice when rotating the cross cylinder for subjective refraction - verifying cylinder axis?

A
  1. Try not to remove the cross-cylinder from in front of the eyes
  2. explain to the patient it will be clearer without this lesn
30
Q

Waht are 3 steps for verifying cylinder power?

A
  1. once no difference in two positions with cross-cylinder handle along axis of cylinder, repeat but with handle at 45 degrees to axis of trial cylinder - offers +- 0.25D cyl if using 0.50 cross-cylinder
  2. add sign of the cylinder preferred in 0.25D steps until there is a reversal
  3. add 0.25DS for every 0.5DC lost
31
Q

How should you correct the spherical power when verifying the cylinder power?

A

add 0.25DS for every 0.5DC lost

32
Q

What are 4 tests for refining the best sphere in subjective refraction?

A
  1. plus 1 blur test
  2. duochrome test
  3. measure and record BVD
  4. check near requirement
33
Q

What effect should the plus 1 blur test have and what should be done if this is not the outcome?

A
  • should reduce VA of 6/5 or 6/6 to about 6/12
  • if not, add more plus
34
Q

What are 2 ways the duochrome test should be done and what is the desired outcome?

A
  • monocular and binocular
  • aim for no preference or slight red preference
35
Q

At what distance should near requirement be checked?

A

at usual reading/working distance

36
Q

What are 4 steps for checking near requirement?

A
  1. perform at usual reading/working distance
  2. if presbyopic (usually age >45) add near addition for patient’s age and refine for preferred working distance and range
  3. calculate residual accommodation with RAF rule (perform 3x for each test) or rule and near target
37
Q

What are 2 ways that residual accommodation remaining can be tested for when checking near requirement in subjective refraction?

A
  1. RAF rule
  2. rule and near target
38
Q

What does the residual accommodation tell you?

A

determines the closest distance the text can be moved towards the eyes before the letters blur and cannot be made clear with effort

39
Q

How many times should the RAF rule be performed for each test in subjective refraction?

A

3x

40
Q

What is the estimated near correction for age 45-50y?

A

+1.0DS

41
Q

What is the estimated near correction for age 50-55y?

A

+1.5DS

42
Q

What is the estimated near correction for age 55-60y?

A

+2.0DS

43
Q

What is the estimated near correction for age >60 or pseudophake?

A

+2.5DS

44
Q

What are 2 general types of autorefractors?

A

stand-mounted

45
Q

How do autorefractors work for objective refraction?

A

reflect light off the retina and analyse its deviation or distance of peak focus in multiple locations across the pupil once it has returned through the eye’s optical path

46
Q

What are autorefractors for objective refraction useful for?

A

estbalishing a starting point for subjective refinement, or may suffice where specialist subjective refraction skills are not available

47
Q

What are 3 types of measures of oculomotor balance between the eyes that should eb performed for refraction?

A
  1. cover test
  2. fixation disparity at distance and near
  3. dissociative tests (no fusional lock) e.g. Maddox rod and wing
48
Q

What is the only instance when you should prescribe prisms for muscle imbalance?

A

if symptomatic

49
Q

What should be done before prescribing prisms for muscle imbalance?

A

consider whether further investigation (including orthoptic referral) is necessary

50
Q

What is asthenopia?

A

refractive discomfort or ‘eye strain’

51
Q

What is asthenopia?

A

refractive discomfort or ‘eye strain’

52
Q

What are 5 possible causes of asthenopia causing spectacle intolerance?

A
  1. significant change in axis or size of cylinder
  2. change of lens form
  3. overcorrection, especially of myopes who will end up permanently accommodating
  4. excessive near correction resulting in an uncomfortably near and narrow reading distance
  5. unsuitable bifocal or progressive lenses - consider occupation, requirements, and general faculties of the patient

Investigations (29 decks)

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