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Low Vision Flashcards

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1
Q

Definition of low vision

A

The WHO defines low vision as visual acuity less than 6 / 18

and blindness as Visual acuity less than 3/60 or a visual field < 10 °

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2
Q

What is Disability Glare

Also known as veiling glare

A

Stray light which interferes with visual performance - normally this glare affects low vision Patients
Predominantly due to scatter and fluorescence in the Ocular media
helped by Suitable filter lenses which reduce shortwave radiation

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3
Q

what is discomfort Glare

A

Stray light which reduces visual comfort,not responsible forreduction in VA

Normally associated with differing levels of illuminance within the visual field
eg -Performing a visual task under bright direct lightening in a room with poor background illumination

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4
Q

Reflectance

A

A ratio comparing the lumens of flux leaving a Surface to the lumens of flux that were incident on the Surface

Symbol = P ( rho)

unit =none as a ratio - maybe given as a %( ratio → % X by 100)

optical Surface

P = ( n’ - n )2( Squared)
——–
n’ + n

non optical Surface

P= 0 leaving Surface
————————–
O incident on Surface

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5
Q

Albinism

2 forms

A

Congenital Condition - lach of pigment or body’s inability to Produce Pigmentation

2 forms
Ocolocutaneous - affect Skin,hair,eyes 1 In 20,000 - VA often worse

Ocular albinism - affects eyes 1 In 40,000 VA often less than 6/ 24
while eyelashes very Pale blue Iris look pink at times - light reflecting of blood vessels
Extreme photophobia,Pendular nystagmus,high refractive error,high with rule of Astigmatism full visual field
no treatment -Improve visual comfort with filters,tints,contact lens
Genetic counseling recommended

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6
Q

Photometry

Luminous Intensity

A

the Power /strength of a Source in a given direction
Symbol l
unit candela (cd)
I = lumens / w ( Solid angle )

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7
Q

photometry mean spherical intensity

A

The average intensity of a real world light Source considered to give out light equally in all directions
m. S.I = O (lumens) / 4 (Pie) solid angle Steridians around point)

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8
Q

luminous flux

A

the rate of light flow from the Source in a given direction

O = I x w

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9
Q

Illuminance

A

The amount of luminous flux falling on a Surface of unit are

Symbol = E unit lux

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10
Q

luminance

A

luminance Symbol L is the amount of light per unit area emitted by a surface in a given direction
luminance = illuminance X reflectance

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11
Q

Reflectance

A

A ratio comparing the lumens of flux leaving a surface to the lumens of flux that were Incident on the Surface
Symbol = P (rho )
unit = ratio= no unit maybe given as % ( x by 100)

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12
Q

luminous effectively

A

How many lumens of flux as Source produces per watt of electricity used

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13
Q

Inverse Square law

A

Illuminance at a Point on a surface perpendicular to a source is Inversely Proportional to the Square of the distance from the Source to the surface
E =I / d2 (Squared) (metres)

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14
Q

cosine law of illumination

A

E = I / d2 x COs O (angle)

the greater the angle between the light Source and the Surface

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15
Q

How many Steradians Surround a point

A

4 (Pie )

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16
Q

What is meant by the luminance of a Surface

A

How bright the surface is to the observer

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17
Q

A60 walt tungsten filament lamp has an efficiency of 12 lumens per watt
calculate
a) luminous flux
b) the mean Spherical intensity ofthe lamp

A

a) 12 lumens X 60 watts = 720 lumens

b) MSI = O / 4 (pie) 720 / 4 (pie) = 57. 30cd

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18
Q

Role of health care practitioner

A

is ( partially) to increase ‘activity and the participation of our patients

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19
Q

Impairments

A

problems in body function and structure Such as a significant deviation loss

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20
Q

functioning

A

an umbrella term for body function and structures it denotes the positive or neutral aspects of the interaction between a persons health conditions and that individuals Contextual factors

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21
Q

Activity limitations

A

Difficulties a person may have in executing activities

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22
Q

Participant restrictions

A

problems an individual may experience in involvement in life Situations

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23
Q

low vision definition

A

the who defines low Vision as visual acuity less than 6/ 18 and blindness as visual acuity less than 3/60 or a visual field < 10 degrees

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24
Q

low vision consensus group 1999

A

A person with low vision is someone who has impairment of visual function for whom full remediation is not possible by conventional Spectacles contact lenses or medical intervention and which causes restrictions in that persons everyday life

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25
Blind
So blind as to be unable to perform any work for which eye sight is essential
26
* SSl registrants Can be classified into 3 groups
Groups 1 visual acuity below 3/60 A Cx who is 1/18 cannot be Certified in group 1 Group 2 Visual acuity between 3/60 and 6/60 and is Significantly contracted field of Vision Group 3 visual Acuity better than 6/60 and have a Severely contracted field of view especially if in the inferior field
27
Community care act
1948
28
referral of visual Impairment
``` RVI form can be sent from a hospital clinic informs Social Services Request assessment states Urgency ```
29
benefits of registration
``` personal independance Payment (pip) free or reduced bus fare free NHS eye exam Assesment by Social Services SI -don't get tax allowance TV license reduction blue badge ```
30
Services available multidisciplinary team
``` low vision Clinic rehab officers mobility officer ECLO G.P occupational therapist audiology education officer ```
31
role of dispensing optician
``` Assist in devices - LVA non optical aid correct addition illumination advice Discuss pathologies refer to multidisciplinary contrast advice local charities ```
32
How do we measure contrast sensitivity
Allows us to gauge visual Performance under real world conditions Allows us to predictthe likely success of LvA'S consider weather contrast advice + support needed calculate contrast reserve+ feeds into our prescribing strategies
33
Pelli robson- chart
All letters same size (2.8 degrees at 1m) use at 1m 8 rows comprising of 2 triplets of letters each triplet has Some contrast Contrast reduces across and down range 89% to 0.5%
34
Baily lovie chart
``` one panel distance acuity one panel low Contrast difference in lines gives low contrast sensitivity value externally illuminated 100% contrast one side 10% contrast other side logmar progression 5x4 grid 6 metre 14 lines of 5 lettersper line ranging from 0.8 logmar to - 0.5 logmar 53x61mm ```
35
vistech chat
``` Five rows Nine columns Sine wave grating/ circular grating Decrease in contrast left to right increase in Spatial frequency top to bottom used at 3m ```
36
Rods
``` Rhodopsin Scotopic low acuity Achromatic High density away from macula ```
37
Cones
``` 3 types Red blue green photopic High Acuity Trichromatic Central retina / fovea most dense ```
38
Visual field
the extent of the area In space in which object are visible to an eye in a given Position
39
Scotoma
An area of reduced / no visual acuity Surrounded by an area of relatively normal vision
40
Absolute Scotoma
Blind spot - no photoreceptors | a defect that is present during all Stimulus
41
relative scotoma
a defect that Presents when stimulus is weaker | eg reduced contrast Sensitivity
42
negative scotoma
A Scotoma that's not generally percieved by Cx | eg blind spot
43
Positive Scotoma
Percieved by the Patient . Such as black spot in vision
44
Hemianopia
loss of one 1/2 of your visual field
45
eccentric fixation
is the process of rotating the eye so light falls on a different less damaged part ( close to macula) called PRL Preffered retinal location
46
Steady eye strategy
employed by the patient achieving their PRL keeping eye still and moving print 6 weeks training
47
AmsIer chart
``` Gid of lines making Squares Central fixation point Some have diagonal lines to and fixation designed to measure Central10 degrees of visual field well light room held at 30cm wear SVN each eye occluded stare at central fixation Spot report any lines distarted or missing ( emergency referral optom) ```
48
Disadvantages of Snellen chart in LV
``` Too few letters at lower acities non logarithmic design no contrast ratio between letter size non consistant Spacing measures high contrast acuity only designed at 6m ```
49
advantages baIie lovie chart in LV
``` logarithmic design constant ratio of letter size line + letter spacing same any appropriate WD 5 letters per line ```
50
magnification
New RIS / Old RIS
51
BS EN iso 15253
British standard which covers Optical devices for low Vision aids
52
estimating mag
= Acuity Achieved / Acuity required. | AA / AR
53
Threshold acuity
the smallest possible size they can read .
54
fluency
As a print Size reduces towards a patients threshold acuity their reading rate reduces
55
Hand magnifiers | advantages
``` Inexpensive cosmetically acceptable can be internally illuminated Portable lightweight trained to be used with Spectacles flexible working distances ```
56
Hand magnifiers | Disadvantages
``` requires steady hand not both hands free Poor Image quality effective magnification less than described needs training due to dynamic System difficult to change batteries for LV Cx ```
57
Stand magnification | advantages
``` very high magnification can be internally illuminated Some can tilt Hands free adjustable ```
58
Stand magnifiers | disadvantages
``` Poor fOv Increased aberrations more conspicuous most require near correction requires flat surface may struggle with body position ```
59
Bar devices
``` reading addition flat Surface tasks place device directly on task good FOV Reducing eye to lens does not effect FoV ``` Inexpensive ease of use cosmetically acceptable Good FoV Very limited magnification range one meridian only - distorts Image
60
stale the formula for and Conditions under which nominal magnification is Created
Mnom = Fe / 4 object is @ F 1st principal focus Image@ infinity
61
state formula for and Conditions under which maximum magnification is created
Mnom = Fe / 4 + 1 Vertex distance = O Image formed RSD - 25 CM ( reference Seeing distance)
62
Contrast
is measured of the difference between brightest and darkest Point
63
Distance Telescope | objective lens
the lens nearer the object it is the entrance pupil for telescopes its diameter controls field of Vlew
64
Distance Telescope | eyepiece lens System
the lens nearer the patient always the highest power lens Sometimes a Series of lenses which help control aberrations Position controls field of View
65
afocal
A telescope where parallel light enters and leaves the System is referred to as afocal
66
Distance object | Benefits
``` only realistic option for Dv mag where object cannot be Moved or changed Good depth of field hands free can be Mono /binocular can be variable focus ```
67
Distance telescope | limitations
``` High cost difficult to use extensive training Very poor Fov Heavy conspicuous Require Very accurate Centration ```
68
Types of telescopes
Spotter handheld monocular - hand held non adjustable afocal easier to use,Small Adjustable handheld Monocular - adjustable tube Binoculars - wide FOV cheap Bl optics - Spec mounted on different plane Spec mounted telescopes
69
calculating magnification
``` M = - Fe / Fo. fe = eyepiece fo = objective ```
70
Markings
8 X 20 X 7. 5 8: magnification 20: objective Diameter 7. 5: field of View In degrees
71
field of Vlew
This is Significantly restricted in telescopes binocularity Is Important to Improve foV Improves mobility or fluency and visual Comfort
72
terrestrial telescope
astronomical telescope been modified to produce upright Image
73
Distance cap
a negative (Concave ) Mounted on the front of a telescope to modify it from near to distance vision
74
Reading cap
a positive lens mounted on front of a distance vision telescope to modify for near
75
tele microscope
A distance vision telescope being modified for near with use of reading cap
76
free working distance
Distance between the most anterior part of System ( front) + object being viewed
77
Exit image Vergence
Power of light leaving back of System
78
Explain the stage depression of loss model | Include a minimum of 4 facts
lack of engagement with professional feeling of worthlessness poor memory fee lings of hopelessness at outcome
79
How will the patients age in f luence the successful use of low vision aids ( 4 facts)
less likely to accept Dexterity issues more likely to have additional needs / health issues difficult to learn new Skills
80
name a non optical aid that may assist Mrs D Seeing the dials on her Cooker
Stickers or labels @ N18
81
what is the benefit of testing contrast Sensitivity
15 Mark answer- Allows use to Predict the Likely Success of LVAs Allows us to gauge weather contrast advice Is warrented 5 mark - gauges visual performance in real world.
82
state Criteria for registration as Sight Impaired
3/60 → 6/60 full visual field 6/60→ 6/24 moderate field loss 6/18 or better + gross field defect
83
Symbol cane
symbol cane - foldable White cane Indicates Visually Impaired -extends Cane and holds diagonally across body or keeps folded and holds across chest low
84
guide Cane
to find obstacles be .. holds guide cane diagonally across your body.and use it to find Sstacks
85
long cane
To avoid obstacles you roll or tap It from Side to side as you Walk
86
Red + white Cane
low hearing and Vision

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