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OPTOM > OPTOM 216A > Flashcards

OPTOM 216A Flashcards

1
Q

Chart type in research

A

LogMAR

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2
Q

Most common chart type in clinics

A

Snellen

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3
Q

Snellen chart design advantage and disadvantage

A

Simple, cheap and small, most common in clinics but have non-uniform intervals, unequal crowding, different recognisability in letters and inconsistent fonts

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4
Q

Sloan font Design

A

5x5 px design, non-serif fonts with 10 letter sets, astigmatism detection.
Sloan + LogMAR = ETDRS chart

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5
Q

LogMAR chart design

A

Each line have same number of letters, 0.0 = 6/6 where lower decimal is better. Each letter scores 0.02 and each line scores 0.1.
Bailey lovie uses LogMAR with different optotype using 5x4 letter design.

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6
Q

LogMAR disadvantage

A

Mask distance information, Larger, Mesures in LogMAR but in clinics use Snellen fraction

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7
Q

What is VAR

A

Visual acuity rating

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8
Q

VAR equation

A

100 - 50LogMAR

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9
Q

What is VAR designed for

A

Used with BL charts where 6/6 = 100 score. Each letter worth 1 point, each line worth 5 points
Good for low vision patient

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10
Q

Visual efficiency ( % ) equation

A

0.836^( (1/decimal VA) - 1 )
Gives indication how different vision is to 6/6, 6/12 means a decimal VA of 0.5
Used to compare vision changes and always greater than 0

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11
Q

What chart to use if patient cant speak english

A

Tumbling E and Landolt C

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12
Q

Kids optotypes versions

A

Lea and Patti

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13
Q

Lea optotype

A

Only has 4 optotypes calibrated against landolt c

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14
Q

Patti optotype

A

Only has 5 symbols as ETDRS

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15
Q

How to measure Near vision

A

Same as measuring distant vision
Uses words and not letters at 40cm
Measures in M, N and J. Metric, point and Jaeger
N8 = M1.0 where M1.0 = optotype height of 5minarc at 1 meter

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16
Q

Near vision test disadvantages

A

Font details like upper/lower case, random words and size and crowding

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17
Q

Near vision chart design

A

LogMAR or Snellen, Can be single letter using ETDRS or BL
Or can use real world stuff like newspapers

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18
Q

What to consider when measuring VA

A

Can have partial lines ( 6/6+2 )
Metric or imperial
Latin or english
BE different to LE + RE
When to stop testing when errors are made

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19
Q

What is BSV

A

Binocular single vision, single unified perception of the world with both eyes without double vision that requires all parts of the visual system to function properly

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20
Q

BSV advantages

A

180 degree visual field, have stereopsis for depth, spatial perception and binocular summation. Also have one spare eye if one is damaged

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21
Q

BSV disadvantages

A

Entire visual system needs to properly function and can also cause Asthenopia with double or blurred vision

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22
Q

What are the 3 grades of normal BV

A

Simultaneous perception, Fusion and Stereopsis

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23
Q

Simultaneous perception

A

See two images fused together, otherwise diplopia

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24
Q

What is motor fusion

A

Bifoveal fixation on same object

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25
Q

What is sensory fusion

A

Unify two images into one in visual cortex

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26
Q

What is ocular deviation

A

When visual axis of each eye is not fixated on the same object

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27
Q

What is stereopsis

A

Ability to see depth, LE and RE see images differently known as Binocular disparity

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28
Q

What are eye movements for

A

Look around, locomotion and localisation

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29
Q

What is duction

A

Movement in one eye

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30
Q

What is a Version

A

Movement of both eyes in same direction

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31
Q

What is vergence

A

Opposite movement of both eyes

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32
Q

What is the 3 axis of rotation called

A

Axes of fick

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33
Q

What is a saccade

A

Rapid ballistic eye movement

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34
Q

What is smooth pursuit

A

Slow tracking movement of the eyes

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35
Q

Types of Ductions

A

Adduction, Abduction, Elevation, Depression, intorsion and extorsion

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36
Q

Types of versions

A

Laevoversion, Dextroversion, Elevation and depression

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37
Q

Types of vergence

A

Convergence, Divergence, Vertical vergence and Cyclo-vergence

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38
Q

How to assess eye movements

A

Double/Broad H or use Prisms

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39
Q

Prisms in optometry

A

Bend light toward base, measures eye movements, units are prism dioptres or degrees

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40
Q

What can prisms assess

A

See if pt can detect a change or see if they can move their eyes to the target

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41
Q

Equation for prism dioptres

A

Image displacement ( cm ) / Viewing distance

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42
Q

What type of vergence occurs with base out prisms

A

Convergence

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43
Q

Convergence measurement equation

A

In dioptres or degrees.
Equation = IPD(cm) / viewing distance(m)

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44
Q

What does the pupil do

A

Limit aberrations and control retinal illumination

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45
Q

What is the normal pupil size

A

2-9mm

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46
Q

What happens to pupils if they are not drugged

A

Always in motion, if drugged then no motion

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47
Q

What can observing pupils identify

A

State or arousal, Sleep state, if on drugs, sleepiness and stroke

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48
Q

What two muscles control pupil size

A

Radial dilator ( SNS ) and Circumferential sphincter ( PSNS )

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49
Q

Innervation of the pupil

A

Retina –> Pretectal nuclei –> Edinger westphal nuclei –> Ciliary ganglion –> Retina

Upper thoracic segments of the spinal cord –> Superior cervical sympathetic ganglion –> Carotid plexus –> Retina

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50
Q

Pupil light reflex test

A

Dont have other light sources
Shine light in eye, look at Direct and consensual for BE as pupil light reflex is bilateral. Then swinging test to check for RAPD then near target response to check near target pupil constriction

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51
Q

How to note a normal pupil light reflex

A

PERRLA, No RAPD

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52
Q

If anisocoria then how to note

A

PRRLA, R>L Aniso +0.5mm dim + Light

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53
Q

What can the pupil light reflex also check for

A

Iridodialysis, corectopia and polycoria

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54
Q

What are 4 pupil abnormalities

A

Physiological anisocoria, Horners syndrome, Adies tonic pupil and Argyll robertson pupil

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55
Q

What is physiological anisocoria

A

in 40% of healthy population, No RAPD, no management needed and can spontaneously resolve

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56
Q

Horners syndrome

A

Sympathetic Efferent Defect with triad symptoms ( Miosis, Ptosis and Anhidrosis ).
No RAPD but direct and consensual effected, defect can be in any of the 3 order of neurons. Syndrome can be isolated using drugs

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57
Q

Adies tonic pupil

A

PSNS Efferent defect with pupils dilated on presentation. Poor light response. No RAPD but Direct and consensual effected. This is idiopathic and self resolves. Can test for this using pilocarpine

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58
Q

Argyll Robertson syndrome

A

Bilateral miotic pupils then constrict to near and not to light. Associated with neurological syphylis. Sexual syphilis untreated causes death. This is a lesion in the dorsal midbrain, can be diabetic neuropathy so check eyes for atrophy

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59
Q

What tests do both screening and diagnosis

A

Cover test and Ocular motility

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60
Q

What is ocular deviation

A

Unaligned visual axis like Phoria or tropia

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61
Q

What is a phoria

A

Aligned in normal viewing conditions

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62
Q

What is a tropia

A

Misaligned axis in normal conditions where pt has no motor fusion

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63
Q

Causes of tropia

A

Idiopathic, EOM abnormality, Cranial nerve palsy and Head injury

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64
Q

What to record if pt has tropia

A

Laterality, Direction, Frequency and Magnitude

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65
Q

How to check for a phoria

A

Remove stimulus in BE and covering one eye

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66
Q

How to record a normal pt if they dont have tropia or phoria

A

NS, Orthophoria

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67
Q

Hirschberg test

A

Use a penlight 40cm away, look at the corneal light location and see if it is symmetrical, every 1mm difference is 15 dioptres. This can only check for large tropias.

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68
Q

When to use the hirschberg test

A

When cover test cant be done like in children

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69
Q

Requirements for cover test

A

Both eyes need to fixate

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70
Q

Setting up cover test

A

1 VA line better than patients worse eye but ENSURE they can see the letters with each eye and ask patient to keep their head still

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71
Q

Steps for a cover test

A

Unilateral, alternating and Phoria recovery ( If they have a phoria )

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72
Q

What can Unilateral cover test check for

A

Only detect for Tropia or NO tropia

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73
Q

What does the alternating cover test check for

A

Measures the size of the deviation

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74
Q

What is phoria recovery

A

Assess patients ability to gain bifoveal fixation on target after dissociation

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75
Q

How to assess ocular motility

A

Use Broad/Double H test and requires at least 1 eye to see light

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76
Q

What does the H test check for

A

Restrictions, Jerky or inaccurate movements, Pupil size in eyes and Diplopia

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77
Q

Broad/Double H test instructions

A

Ask patient to tell if there is any pain and discomfort and also to keep head still

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78
Q

What to record if H test is normal

A

Motility full + smooth, no diplopia or pain

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79
Q

How to assess vergence

A

Using NPC ( Near point convergence )

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80
Q

How to perform NPC

A

Patient needs BSV and ask patient if they get diplopia during the test
Break = Diplopia during the test
Recovery = When BSV is regained\
A break of more than 10cm means convergence problems

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81
Q

How to record NPC results

A

NPC with RAF rule : 5/7cm, 5/7cm, 5/7cm

IF to nose then record as NPC with RAF rule : To nose

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82
Q

What is accommodation

A

Far to near focus where there is no accommodation when viewing at optical infinity in emmetropic eye

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83
Q

How does the eye accommodate

A

Retina detects blur and information send to visual cortex causing ciliary muscles to work inducing a change in lens curvature via Helmholts theory

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84
Q

What is the ciliary muscles main innveration

A

PSNS and accommodation decreases with age

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85
Q

What is the near triad

A

Accommodation, Convergence and Miosis when looking at near objects

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86
Q

How to calculate the stimulus to accommodation ( STA )

A

1/viewing distance with units as Dioptres

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87
Q

How to calculate amplitude of accommodation

A

1/near point - 1/far point

Pt with refractive error correction has their far point at infinity

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88
Q

How to measure amplitude of accommodation

A

Use RAF rule –> Bring target closer from clear to blur until first sustained blur and repeat 3 times for RE, LE and BE
Units in dioptres

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89
Q

How to record result for amplitude of accommodation

A

Amplitude of accommodation with RAF rule push up method : 12D, 12D, 12D

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90
Q

Duane-Hoffstetter equation

A

Max amplitude = 25 - 0.4 x age
Average amplitude = 18.5 - 0.3 x age
Min amplitude = 15 - 0.25 x age

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91
Q

Factors to consider for accommodation measurements

A

Uncorrected refractive errors, test conditions, patients motivation to exert effort and their criteria for blur

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92
Q

What is lag of accommodation

A

When accommodation is less than STA where large lag = blurry vision

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93
Q

What is lead of accommodation

A

When accommodation is more than STA where accommodation is closer than STA

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94
Q

Presbyopia

A

40-50 years old and is a natural loss of AoA with age

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95
Q

What is presbyopia caused by

A

UV, Lens sclerosis and lens hardening

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96
Q

How is Assessment of accommodative facility measured

A

Measured free space or with lens flippers and patient needs to be fully corrected for refractive error

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97
Q

Lens flipper vs free space

A

Free space have higher CPM than lens flipper due to less accommodative change and binocular testing helps with free space

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98
Q

Assessment of accommodative facility requirements

A

Patients accommodative range must be greater than the lens flipper power
Both tests have to be 1-2 lines better than their VA

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99
Q

Using Free space to test for accommodative facility

A

Distance correction on, the test uses both near and far object at 40cm and 6m. Ask patient to focus on distant until clear and jump to near target until clear. Repeat for 1 min and units in CPM

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100
Q

How to use lens flippers for accommodative facility

A

Distance correction on and covering the eye not tested. Use default lens flippers at +/-2.00D flippers. If pt cannot focus with it then use lower power flippers

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101
Q

Lens flipper instructions

A

As pt to focus until clear starting with the plus lens, when clear flip the lens and the focus until clear. Everytime patient clears the image they must say clear.
Also timed for a minute and units in CPM

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102
Q

Recording results for lens flipper

A

Can write “Showed fatigue”, “Diplopia on minus” or “Slower on plus than minus”

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103
Q

What does perimetry do

A

Assess the visual field

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104
Q

What is perimetry used for

A

Diagnosing visual pathway damage, monitor disease/treatment progress. Also a direct measure of visual function

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105
Q

Perimetry advantages

A

Quantitative, simple and automated

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106
Q

The central visual field

A

30 degrees out

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107
Q

What measures the central visual field

A

Visual field analyser

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108
Q

What measured the peripheral visual field

A

Arc Perimeter

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109
Q

What is the island of vision

A

3D sensitivity profile across the visual field

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110
Q

What happens if a stimulus is outside of the island of vision

A

It is not seen

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111
Q

Ways to assess the island of vision

A

Kinetic and Static strategy

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112
Q

What is the Kinetic strategy

A

Stimulus moved from periphery to centre and patients reports detection

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113
Q

What machine is used for the kinetic strategy

A

Goldmann bowl perimeter, different light intensities plots isopters

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114
Q

Disadvantages of the Goldmann bowl perimeter

A

Time consuming, not automated, rarely used in modern practice

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115
Q

What is the static strategy

A

Stimulus shown randomly shown 1 at a time, the brightness is increased until detection where the sensitivity is the inverse of the detection luminance

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116
Q

What are the two types of the static strategy

A

Full threshold and Supra-threshold strategy

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117
Q

What is the full threshold

A

Threshold determined at all points in the visual field but it is the very time consuming but the MOST accurate

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118
Q

Advantage of full threshold strategy

A

Monitors change over time

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119
Q

What is the supra-threshold strategy

A

Stimuli is set at a set just above the expected threshold in their visual field. This means that no further testing is done if stimulus is seen.
If the stimulus is not seen then use staircase method to determine threshold

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120
Q

Advantage of Supra-threshold strategy

A

Very fast to do

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121
Q

Decibel scale graph for perimetry

A

0 decibel = 0 log scale = 1000 intensity
10 decibel = 1 log scale = 100 intensity
20 decibel = 2 log scale = 10 intensity

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122
Q

What does Humphrey visual field analyser measure ( HFA )

A

Measure Centre island of vision

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123
Q

How to use the HFA

A

One eye is covered and the patient presses a button when they see a light flashing

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124
Q

HFA advantages

A

Automated, full threshold, most used, gold standard for glaucoma patients, it is a short wavelength automated perimetry ( SWAP )

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125
Q

What is a scotoma

A

Area of reduced sensitivity

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126
Q

What is diffuse depression

A

reduced sensitivity is constant on all parts of the retina, can be due to cataracts

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127
Q

Sensitivity profile parameters

A

Either stimulus or patient parameters

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128
Q

Stimulus parameters to consider

A

Size, duration, colour and background luminance

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129
Q

How is stimulus size determined

A

Using Riccos law ; Luminance at threshold x Area = Constant

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130
Q

What is the normal size used in perimetry

A

26 arcmin

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131
Q

How is stimulus duration determined

A

Using Bloch’s law ; Luminance at threshold x Duration = Constant

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132
Q

What is the critical duration

A

0.1s

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133
Q

What is the saccadic reaction time

A

0.25s

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134
Q

What is the duration of stimulus in perimetry

A

0.2s

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135
Q

Patient parameters to consider

A

Dark adaptation level, age and uncorrected refractive error

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136
Q

What should the normal background luminance be

A

In the low photopic range of 31.5asb

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137
Q

What is asb

A

Apostilb

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138
Q

Why should background luminance be in the lower photopic range

A

Shorter adaptation time for the patient and also reduces sensitivity to fluctuations in ambient luminance. Dark adaptation affects island of vision and pt should adapt to background level of the test machine therefore testing with bright lights are not done before visual field testing

139
Q

Sensitivity decreases with what and at what rate

A

Decreases with age, after 40 years of age sensitivity decreases at 1dB/decade

140
Q

What does uncorrected refractive error do to the contrast sensitivity of the fovea, and why

A

It decreases the contrast sensitivity because defocus raises threshold near the fovea distorting the island of vision reducing the central peak

141
Q

What is a problem with corrective refractive error during visual field testing

A

Lens-rim artefacts

142
Q

Lesions in the visual pathway

A

Monocular, Binocular lesions and pituitary tumors

143
Q

Where is Monocular lesion located

A

Pre-chiasmal

144
Q

Where is Binocular Lesion

A

Post chiasmal or symmetrical pre-chiasmal

145
Q

What is hemianopia

A

Loss of half of their visual field in ONE eye

146
Q

What is homonymous

A

Same side of each eye affected

147
Q

What is heteronymous

A

Opposite side of each eye affected

148
Q

What is Quadrantonopia

A

1/4 loss of visual field in each eye

149
Q

What is congruous / Incongruous

A

Same/Different shape in each eye of visual field loss

150
Q

Optic fibres crossing patterns

A

Temporal fibres do not cross but nasal fibres do.
Nasal fibres have an anterior knee of willbrand and posterior knee of willbrand

151
Q

What is the sella turcica

A

Houses the pituitary gland

152
Q

What is macular sparing

A

Posterior cerebral artery obstructed gives homonymous hemianopia. During SPARING, area 17 is supplied by both the posterior and middle cerebral artery so still receives blood if posterior cerebral artery is blocked.

153
Q

What part of the retina is affected if the inferior vision has a defect

A

The Superior retina

154
Q

How many types of confrontation is there

A

3

155
Q

What is confrontation 1

A

Rapid check for gross field loss in the periphery using confrontation wand in dim illumination

156
Q

What is confrontation 2

A

Patients can identify differences in hue, this is done monocularly. Two red targets on either side of fixation and is patient tries to identify if one target is less saturated than the other. If different then visual field defect indicating cone-dominated pathway

157
Q

What is confrontation 3

A

Count fingers

158
Q

What is used to assess the central macular function

A

Black or white Amsler grid

159
Q

Amsler grid advantages

A

Simple, fast and sensitive for little macular defects

160
Q

How to use the Amsler grid

A

Used at 30cm where each square is 1 degree on the retina.
If patient describes any distortion, missing or blurry areas then macular defect
Also checks for macular sparing

161
Q

What is the Friedmann Visual field analyser

A

Gradient adapted using the supra-threshold strategy and uses multiple stimuli at the same time and pt reports amount of stimuli seen

162
Q

What is the problem with the Friedmann visual field analyser

A

Makes process faster, but if the pt gives wrong answer, you dont know which stimulus is not seen

163
Q

What are the 2 types of test patterns in visual field analysers

A

24-2 and 30-2

164
Q

What is 24-2

A

54 Black dots

165
Q

What is 30-2

A

Black and red dots = 76 dots total

166
Q

What does the blue dot represent

A

Blind spot

167
Q

How to maintain patients fixation onto targets during visual field testing

A

Need a fixation target that is short and random

168
Q

How to monitor patients fixation onto target

A

Show stimulus at the blindspot, if seen then the fixation is lost or use the automated gaze tracker

169
Q

HFA plot graphs

A

Varies in numbers around visual field in decibels that represent sensitivity

170
Q

How is data from HFA plotted

A

Using variable number of flashes to determine threshold at each point

171
Q

False positives and Negative errors in HFA

A

False positives = Seeing a non-existent stimuli
False negative = Failing to see repeated stimuli above threshold

172
Q

Factors for errors in HFA

A

Patient reliability and attentiveness

173
Q

What is total deviation in HFA

A

Point by point difference from expected age-corrected normal values and shows a general depression

174
Q

Disadvantage of total deviation in HFA

A

Scotomas may be masked if overall sensitivity is pressured from cataracts

175
Q

What is the pattern deviation plot in HFA

A

Most useful plot, defects may not be apparent in total deviation plot but shows up in pattern deviation plot exposing abnormal patterns in the island of vision

176
Q

Advantage of Pattern deviation in HFA

A

Confirms scotoma after adjusting for overall depression of island of vision

177
Q

How many global indices are there

A

2

178
Q

What is global indices 1

A

Has a Mean deviation and pattern standard deviation
Mean deviation is the mean elevation of depression of overall sensitivity compared to the age-corrected normal
Pattern standard deviation measures the amount which the island of vision shape varies from the age-corrected normal where a low PSD = smooth island

179
Q

What is global indices 2

A

Has a Short term fluctuation and a corrected pattern standard deviation
Short term fluctuation tests for consistency of patient responses where 10 points in the field are tested twice allows consistency
Corrected pattern standard deviation is the pattern standard deviation minus the estimated scatter shown by the short term fluctuation in patient response

180
Q

What is the Glaucoma Hemifield test ( GHT )

A

Compares 5 zones in the upper field with mirror images in the lower field

181
Q

Disadvantage of GHT

A

Does not analyse nerve fibre defects serving temporal visual field

182
Q

How to assess screening results

A

Study the raw data
Normal points are 6db suprathreshold
Comparing fields of BE to look for asymmetry
Suspicious if there is a cluster of more than 3 points with more than 8dB loss
Results is a FAIL is 15% points are abnormal or if there more than 50% of the points abnormal in any quadrant

183
Q

How many tests needed to confirm glaucoma

A

3 needed`

184
Q

Detecting glaucoma using SWAP

A

Detects glaucoma 3-5 years earlier than white on white due to having less blue cones in the retina hence less ganglion cells activated. Not that effective though

185
Q

Detecting glaucoma using FDT ( Frequency doubling technique )

A

High temporal frequency information carried by the magno-cellular ganglion cells hence Glaucoma indicates magno-cellular cells loss.

Sinusoidal grating flickers at 25hz for 7.2s, Pt sees flicker = normal. In glaucoma the stimulus is not seen

FDT not useful to monitor progression but good to detect glaucoma

186
Q

What is contrast sensitivity ( CS )

A

Difference between the brightest and dimmest part of a target

187
Q

Contrast sensitivity equation

A

1/contrast

188
Q

How to convert contrast into a linear scale

A

Log(1/contrast) via LogCS

189
Q

Contrast sensitivity table

A

100% contrast = 1 contrast ratio = 1 contrast sensitivity = 0 LogCS

90% contrast = 0.9 Contrast ratio = 1.11 Contract sensitivity = 0.05 LogCS

190
Q

Weber contrast ( Luminance )

A

For Non-repetitive patterns and calculated as background difference / Background brightness
(Lmax - Lmin) / Lmin

191
Q

What is the weber contrast best for

A

Optotypes

192
Q

Michelson contrast ( Modulation )

A

For repetitive patterns and calculated background difference / Total brightness
(Lmax - Lmin) / (Lmax + Lmin)

193
Q

Similarity in both contrasts

A

0% means no contrast and a minimum of 90% contrast required by british standard for high contrast letter acuity charts

194
Q

Why do we measure contrast sensitivity

A

VA measures ability to see small and high contrast objects however everyday objects have more contrast than small size

195
Q

What is contrast sensitivity affected by

A

Optical Blur, optical media disorders, retina and neural processing

196
Q

What relationship does contrast and VA have

A

A proportional relationship where contrast sensitivity function is the area under the functions curve is the functional vision

197
Q

3 points of contrast sensitivity function are

A

A, B and C
A is the Peak contract sensitivity of 1% at the peak of the graph
B is the visual acuity at 30CPD at the end of the graph
C is the difference between points B and A that determines the slope in between points A and B

198
Q

Charts with variable size and contrast

A

Vistech chart and FACT ( Functional acuity contrast test )

199
Q

Charts with Fixed contrast and a variable size

A

BL low contrast chart

200
Q

Charts with a fixed size and variable contrast

A

Pelli-robson chart and the Melbourne edge test

201
Q

VISTECH chart

A

6 rows and 9 sine wave grating columns
Each row has different spatial frequency of 1-24 PD
Gratings are tilted in three directions or is blank
Patient will indicate is the patch is blank or which direction grating is tilted in
No longer commercially produced

202
Q

FACT ( Functional acuity contrast test )

A

Aks VISTECH V2
Has 5 rows and 9 grating patch columns where each row increases with spatial frequency from 1.5-18cpd
Each row decreases in contrast in 0.15 log steps and edges of the patches blend into the grey background

203
Q

What are the benefits of grating charts

A

Assess CSF from low to high spatial frequencies used on illiterate children or patients usings hands or pencil to demonstrate orientation of grating

204
Q

High and Low contrast Bailey lovie charts

A

Not just a contrast sensitivity chart
Has fixed number of letters per line, log progression of letter size and spacing and has standardised letter set and a standard scoring system
Produced in low contrast 18% weber contrast for clinics and proposes that low contract acuity charts gives same information as contrast sensitivity function testing
The difference in HC and LC VA is constant in all acuity ranges of about 2 lines.
LC BL chart useful as screening tool

205
Q

Pelli-robson chart

A

8 lines of letters where each subtends 3 degrees to the patient at 1 metre
2 groups of 3 letter letters per line where letters in each group have the same contrast
Contrast decreases by 0.707

This uses letter rather than sine wave gratings and is a recognition task hence more cortical processing needed compared to a direction detection of sine wave grating

206
Q

Melbourne edge test advantage

A

Compact and portable non grating contrast sensitivity test

207
Q

Melbourne edge test

A

It is small, has 20 disks each 25mm in diameter
The test is in 4 rows and 5 columns where each disk has an edge that decreases in contrast from the top to the bottom of the chart

Patient indicates direction of edge in each disk

208
Q

Why is contrast sensitivity used in clinics

A

Explains poor vision symptoms of poor vision even though they have good VA. Also used after cataract assessments and post-lasik surgery
Also looks for glaucoma, macular degeneration and diabetic maculopathy

209
Q

What is glare sensitivity

A

Measure effect of glare on patients visual function

210
Q

What is the 2 types of glare

A

Disability and Discomfort glare

211
Q

What is disability glare

A

Glare that reduces visual function

212
Q

What is discomfort glare

A

Glare that causes discomfort but does not reduce visual function

213
Q

What type of glare is do we get in everyday life

A

Both disability and discomfort

214
Q

Glares effects on vision

A

Alot of patients with media haze retains good VA but bad visual problems.

Glare also depends on media clarity

215
Q

How to measure glare

A

Standard high contrast acuity does not assess glare effect on vision. Disability glare is assessed using a contact threshold value

216
Q

What is the contact threshold value

A

When the test target is JUST detectable with and without glare source

217
Q

What is the Brightness acuity tester ( BAT )

A

Hand held device that performs Brightness acuity test and the Macular photostress test

218
Q

How many conditions can the BAT simulate and what are they

A

3, High direct overhead sunlight, partly cloudy day and a low-bright overhead commercial light

219
Q

How is the brightness acuity tester used

A

Tests monocularly using all three settings with the patient at the standard distance from the letter chart, undilated pupils in a dark examination room

Test and record VA at each of the three settings.

220
Q

What are the possible results that can be recorded for each test with the BAT

A

No change in acuity, reduction in acuity and improvement in acuity

221
Q

What is the Berkeley Glare Acuity tester ( BGAT )

A

A reduced HC and LC Bailey lovie letter chart on an opaque panel in the centre of a plexiglass screen.
The chart is front illuminated with the glare source from trans-illumination of plexiglass panel

222
Q

BGAT test conditions

A

High and Low contrast VA measured at 1 metre with and wihtout glare source

223
Q

The Macular photostress test using the BAT

A

Not a measure of glare sensitivity. Here the BAT provides the hemispherical lighting to stress the macular region. This test is to detect patients with macular diseases

224
Q

How is the Macular photostress test done with the BAT

A

Light is shone for 10s, then measure time taken for VA recovery within 3 letters

225
Q

How long does it take to recover from the macular photostress test

A

20-30s, macular diseases takes longer to recover

226
Q

What is colour vision

A

Ability to see HSL, Saturation, Brightness, Hue, CMYK and Chroma

227
Q

Why is evolution an evolutionary advantage

A

For us to see ripeness of fruit, spot predator or prey and to attract mates

228
Q

What is young helmholtz theory on colour

A

There 3 primary colours in vision, originally thought to be RYB but its actually RGB. A combination of these colours can make other colours

229
Q

Which photoreceptor is for colour

A

Cones

230
Q

What are the three types of cones

A

Long, Medium and Short wavelength cones

231
Q

What is Herings theory on colour

A

This theory proposed 4 primary colours of R/G and Y/B in opponent colours. A third pair is the luminance mechanism

232
Q

What is the luminance mechanism

A

This mechanism explains no reddish green or bluish yellow colours and explains afterimages

233
Q

What is the current theory on colour

A

Both Herings and Helmholtz theory

234
Q

What does the current theory for colour say

A

Trichromatic at receptor levels, opponent colours at ganglion cell level onwards and Munsell colours in the Cortexx

235
Q

What is the chromativity diagram

A

2D representation of 3D colour space giving a brightness constant

236
Q

Features of the chromativity diagram

A

Centre of the diagram is the location of equal energy
the Black line is the colour of blackbody emitters
Can use diagram to find dominant wavelength
Has MacAdam eclipses

237
Q

What are MacAdam eclipses ( Ovals )

A

These show the colours the look the same to a normal observer

238
Q

How many colours are luminance controlled

A

17000

239
Q

How many colours are there overall

A

3 million

240
Q

What is a Protan defect

A

Red cone defect so sees more green

241
Q

What is a Deutan defect

A

Green cone defect so sees more red

242
Q

What is a Tritan defect

A

Blue cone defect

243
Q

Who are monochromats

A

People that see in black and white

244
Q

Problems with monochromats

A

If no Long or medium cones the VA decreases resulting in photophobia and Nystagmus

245
Q

Who are Dichromats

A

People with two types of photopigments with one missing. This condition is luminance controlled and has a confusion loci where different colours appearing the same

246
Q

What is a trichromat

A

Have all photopigments aka Normal

247
Q

What is an Anomalous Trichromat

A

1 photopigment has a different sensitivity to normal. The most common type of colour deficiency with different levels of severity `

248
Q

What is a Tetrachromat

A

Having 4 photopigments like in some animals

249
Q

What is a confusion loci

A

This is plotted on a CIE diagram where the isochromatic lines show the colours that look the same
Isochromatic lines are shorter for anomalous trichromats as they dont have a full range of colour compared to a drichromat

250
Q

What is an inherited CVD

A

From birth where the type and severity is the same throughout life where VA and VF is normal with mainly red and green defects.

251
Q

Deutan

A

Green cone defect, this is the most common followed by protan and tritan

252
Q

Which colour vision defect is more common than dichromats

A

Anomalous trichromat, this has a large variation in different ethnic groups

253
Q

What is the male deutan prevalence in descending order

A

Europeans, Asians, Africans, Indigenous americans and polynesians

254
Q

What type of genetic defect are Protan and Deutan

A

X-linked recessive ; Sons inherit from mother who was a carrier and all daughters inherit recessive gene from a red/green deficient father

255
Q

What type of genetic defect is tritan

A

Autosomal dominant with incomplete expression and affects males and females equally

256
Q

What is a factor that can change colour appearance

A

Illumination source

257
Q

Why is illumination during colour vision tests important

A

Illumination changes perception of colour vision defect tests where people with CVD could pass and people with good colour discrimination make errors

258
Q

Are cooler colours higher or lower temperature

A

Higher temperature

259
Q

What can we use for illumination

A

Illuminate C for tests needing pigment colours and Macbeth lamp for tungesten illumation

260
Q

What are the types of colour tests

A

Pseudoisochromatic plates, Hue discrimination or sorting tests, Colour matching ( Anomaloscope aka Medmont C100 ) and Colour naming ( Falant Lantern )

261
Q

What can be used to detect colour vision defect

A

Ishihara test, city university colour vision test, lanthonys trion album and the Farnsworth D15 test

262
Q

Which colour vision test is the most common in NZ

A

Ishihara plates

263
Q

How does the Ishihara test work

A

Screens for protan and deutan defects only, has a diagnosis plate but not always accurate
Count the number of errors, allowing 3s for response for each plate. Number of errors does not give severity

264
Q

How many types of plates are there in the Ishihara test

A

5 –> Demo, Transforming, Disappearing, Appearing and the Diagnostic plates

265
Q

How far away is the ishihara test done and at what VA

A

75cm with VA at least VA of 6/60 with Rx

266
Q

Who can see disappearing plates

A

People with Protan defects

267
Q

Who can see appearing plates

A

People with Deutan defects

268
Q

What happens if the Ishihara test is failed

A

Move onto Medmont C100 ( Anomaloscope )

269
Q

How does the Medmont C100 work

A

This test separates Protan and deutan, patient will adjust amount of red and green in the mixuture until there is no flicker. 7 readings are taken and then averaged

270
Q

When is the medmont C100 used

A

Not a screening tool so used after a colour vision defect is picked up

271
Q

How does the medmont c100 separate Protan and Deutan defects

A

Protan defects adds more red due to reduced red sensitivity, Deutan adds more green

272
Q

What is the gold standard to measure CVD severity

A

Anomaloscope

273
Q

Which CVD tests do not give severity

A

Ishiharam Medmont C100, D15 and the F2 plate

274
Q

Which CVD tests claim to give severity

A

City university and Lanthonys tritan album but are inaccurate

275
Q

What are the problems with the city university colour vision test

A

1st and 2nd editions found fewer protans failing but more deutan failing compared to the D15
This test is also a forced choice

276
Q

How does the City university 3rd edition work

A

First part is screening there you look at a row of 3 spots and identify which spot is different to the other two is any
Second part is detection where you identify which spot is the closest in colour to the centre spot

277
Q

What does the Lanthonys tritan album detect

A

Detects tritan defects only

278
Q

How does the lanthonys tritan album work

A

There is a demo and 5 test plates with a combo of grey and blue-purple dots of different luminance. The patient indicates if there is a coloured square in one corner

279
Q

What is the Farnsworth F2 plates

A

Asks for how many squares are seen and if seen, which is more obvious and indicate where on the plate it is seen. This test does not use colour names and is also no longer produced

280
Q

What is the D15 test

A

A sorting test where you arrange caps in their colour sequence starting with the reference cap

281
Q

What does the D15 test identify

A

The confusion loci if the test is failed

282
Q

What is the advantage of this test

A

Separates mild and moderate defect from a severe defect when results are combined with other test results

283
Q

How to graph the data for the D15 test

A

15 colours in a rough circle around a point and connect the dots according to the patients arranged sequence

284
Q

How to pass the D15 test

A

Max of 2 transpositions of adjacent caps or one major dirchromatic crossing. Much more Anomalous trichromats pass compared to dichromats

285
Q

Difference between D15 and D15 desaturated

A

Desaturated D15 has similar colours but paler using an illumination of 1000 lux

286
Q

What is the H16 test

A

Detects only protan and deutan, similar to D15 but different hues are chosen and are more saturated

287
Q

What is the munsell system

A

Defines colour by hue, value and chroma

288
Q

How is hue defined as

A

There are 10 hues, Red, yellow, green, blue and purple. Hues have 10 steps ( 1RY to 10RY )

289
Q

What is Value in the munsell system

A

The amount of light reflected where black is 0 and white is 10

290
Q

What is chroma in the munsell system

A

Amount of colour present similar to saturation

291
Q

What is the Farnswoth-Munsell 100 Hue

A

A sorting test for hue discrimination, this is not a screening test and used to assess/monitor CVD and identify colour normals with very good colour discrimination

292
Q

How does the farnswoth-Munsell 100 hue work

A

4 boxes of colours caps. Each box has 21 caps, first box has 22 caps with colours varied by hue and not chroma

293
Q

Performance Factors when doing the Farnsworth-Munsell 100 hue

A

Performance factor is age, learning effects have a 30% improvement in their score

294
Q

How to calculate Error score in the Farnsworth-Munsell 100 hue

A

Record order with the patient arranged the caps, compare adjacent caps and find the different between the adjacent caps where normal is a value of 2. Subtract 2 from all results and add the scores together to get a total error score

295
Q

Total error score for the farnsworth-munsell 100 hue

A

less than 20 is superior and 20-1– score is average, more than 100 score is a problem

296
Q

What is the Z score

A

Relates error score to the population normal

297
Q

How to calculate Z score

A

Mean / standard deviation

298
Q

What does a Z score of 0 mean

A

The mean for the population

299
Q

What does a negative Z score mean

A

Better than population mean

300
Q

What does a positive Z score mean

A

Worse than population mean

301
Q

Computer analysis of sorting tests

A

Helpful when error score is very large to tell the axis of confusion. This uses vector analysis

302
Q

What is the angle for major axis of confusion

A

Horizontal for protan and deutan and Vertical for Tritan

303
Q

What does the S index measure

A

Randomness

304
Q

What does the C index measure

A

Severity

305
Q

What is Retinoscopy

A

An objective refraction, objective because patient does not need to respond

306
Q

How does the retinoscope work

A

Has a bulb and a lens system where the lens is moveable and changes the position of the light source where the beam is either convergent or divergent depending on the type of mirror

307
Q

What are the two types of retinoscopes

A

Spot and Streak retinoscopes

308
Q

Spot retinoscope

A

Patch of light is round with the bulb is a small coiled filament 1-2mm in size

309
Q

Streak retinoscope

A

Patch of light is rectangular with the bukb is uncoiled linear filament, bulb is rotated to change the orientation of the projected beam which is helpful to find axis of astigmatism

310
Q

What are the two types of Retinoscope mirror types

A

Plane and Concave

311
Q

Is light convergent of divergent in plane mirror

A

Divergent

312
Q

What is the secondary source and how is it made

A

In the retinoscope the bulb is fixed but the lens distance changes which changes the beams vergence when leaving the mirror producing a secondary source ( S’ ) either behind or infront of the retinoscope

313
Q

What influences the movement of light on the retina when the retinoscope is tilted

A

The position of the secondary source

314
Q

Plane mirror retinoscopy

A

Sleeve is down decreasing bulb-lens distance decreasing the effective power causing the light to diverge from the retinoscope. Here the secondary source is behind the retinoscope.
A with movement is Hyperopia
An Against movement Myopia

315
Q

Concave mirror retinoscope

A

Sleeve is up increasing bulb-lens distance increasing the effective power causing the light to converge from the retinoscope. Here the secondary source is between the retinoscope and the patient.
With movment = Myopia
Against movement is Hyperopia

316
Q

Which type of retinoscope is recommended to use

A

Plane mirror retinoscope

317
Q

Advantages of the plane mirror retinoscope

A

With movements are easier to see and the sleeve is easier to reach with the thumb to change from plane mirror to concave mirror to confirm

318
Q

Retinal reflex observations

A

Observe movement of image from the patch of light where the movement direction of the image depends on the refractive state

319
Q

What is neutralisation in retinoscopy

A

Aligning the retina plane with the retinoscope plane

320
Q

Reflexes to observe in retinoscopy

A

Direction, Speed, Brightness and Width

Faster the speed the closer to neutral
Width from meridional direction either large or small refractive correction

321
Q

Observation of Hyperopia

A

This is with movement
The image patch on the retina is virtual and behind the pt so when face beam is tilted u then the reflex also goes up

322
Q

Neutralising Hyperopia

A

Add positive lens toward retinoscope from behind it, when neutral the reflex will flash instantaneously in and out of view

Adding more positive power after neutralisation will have a reversal in movement of reflex so an against movement is seen

323
Q

Observation of Myopia

A

This is against movement
Image patch on retina is real and between the pt and the observer where face beam is up and the reflex moves down

324
Q

Neutralising Myopia

A

Add negative lens of increasing power, the reflex image will move towards the retinoscope. At neutral the reflex flashes instantaneously in and our of view

Adding more negative power after neutral will reverse reflex movement so a with movement is seen

325
Q

What does a speed of a reflex tell you

A

Slower speed means more ametropia
Infinitely fast speed of reflex means neutral

326
Q

On-Off phenomenon

A

If the retinoscope is placed in the far point there will not be a with or against motion as the retinoscope is placed at neutrality. This phenomenon is known as the end point when trying to neutralise

327
Q

What does the brightness of a reflex tell you

A

Closer to emmetropia has a brighter reflex
In hyperopia the retina is closer to the retinoscope and in myopia the retina is further from the retinoscope

328
Q

What does the reflex look like in the plane mirror

A

Reflex smaller and brighter for hyperopia than myopia where the S’ is closer to the hyperopic far point

329
Q

What does the reflex look like in concave

A

Reflex is smaller and brighter for myopia than hyperopia where S’ is closer to the myopic far point

330
Q

Controlling accommodation methods

A

cycloplegia, Controlling fixation distance, Inserting working distant lens and Checking BE for against movement

331
Q

How does cycloplegia work

A

Using drugs to relax ciliary body

332
Q

How to control fixation distance

A

Asking patient to look at target at 6m with BE open using a large letter with duochrome overlay. Ask pt to look at the green background. Then scope the RE while the patient observes with their left eye.

Ask pt to indicate if your head is blocking their LE view
Important to keep close to their line of sight you are scoping

333
Q

How does a working distant lens work

A

Working distant lens will relax their accommodation and will move their far point to the retinoscope and has their distant vision blurred in an emmetropic eye
In a myopic eye the WD lens moves their far point in front of the retinoscope so their vision is more blurred
In a hyperopic eye the WD lens moves their far point behind the retinoscope and +2 or +1.5 lens may not be enough to cause blur

334
Q

Checking both eyes for against movement in retinoscopy

A

If movement is with, add plus lens until BE are blurred making the eye myopic eith their focal plane in front of the retinoscope

335
Q

What is a working distant lens

A

Not possible to do retinoscopy from infinite distance so we adapt a working distant of 67cm at +1.50D. The working distance lens adjusts for vergence from near position and helps to relax accommodation

336
Q
A
337
Q
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338
Q
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338
Q
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339
Q
A
340
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341
Q
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341
Q
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OPTOM (6 decks)

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