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Year 3 > Refractive management > Flashcards

Refractive management Flashcards

year 3 exam

1
Q

schematic eye

A

a basic or diagrammatic reprenstation of a real eye

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2
Q

Reduced eye

A

simplified versions of real eyes or previous models that will help us with calculation

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3
Q

optical axis

A

a line through the Centres at all refractive Surfaces - best Centration is given by this

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4
Q

visual Axis

A

a line from the Centre of the Macula through pupll Centre

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5
Q

the angle between the Visual + optical axes approx 5 Degrees horizontally

A

( Positive Vergence if the Visual axis in Space lies nasal to opic disc)

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6
Q

Axial length

A

the distance between the anterior corneal surface + the foveola - mean value 24mm ( adult)

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7
Q

Principal point

A

Position of a single equivalent lens which can replace a lens System

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8
Q

Nodal Point

A

point on a lens system to enable graphical construction light entering a System heading towards the first nodal Point exists Via the Second nodal Point

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9
Q

standard reduced emmetropic eye

A 
visual + optical axis coincide
pupil is at reduced Surface
The Macula (M' ) is at the second focal point ( fe') of the eye
the far point ( MR) is at Infinity 
the far point and macula are conjugate
P= Principal point
C= Centre of curvature 
N = Nodel point
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10
Q

light travels from left to right
Snells law applies n Sini = n’ Sin i ( light into denser medium is refracted towards the normal so light passing from air into the eye will be refracted towards the normal
Parallel light will Converge towards or appear to diverge from the Second Principle focus of a Surface

A

F= n / - f f = n’- n / r. L ‘ = L + F
in reduced eye. k’ = K + Fe
k = Vergence required at the eye to focus at M ‘
k’ = Vergence required leaving reduced Surface to focus on M ‘
k = for Point distance at ♾

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11
Q

k = Ocular refraction

A

k = n/ k = 1 / ♾ = + 0.00D

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12
Q

k’ = Axial length of eye

A

k’ = n’ / K’ = 4 / 3 / + 60 .OODx 1000 = + 22.22 mm

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13
Q

k’ = Dioptric length of eye

A

k’ = n’ / k ‘ = 4/3 / + 60.00 X 1000 =+ 22.22 mm

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14
Q

the Cornea

A

Transparent Medium - most of refraction Total Power = + 42.00D

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15
Q

the Aqueous

A

fills anterior and Posterior chamber n= 1. 336

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16
Q

The Iris

A

Contains pupil variable aperture 2-8mm

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17
Q

crystalline lens

A

Biconvex changes shape to become more Convex = Positive Power Increase = accomodation supplies the remaining balance of eyes refractive Power

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18
Q

Vitreous

A

largely homogenous gel like fluid - fills Space between lens + retina

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19
Q

Schematic and reduced eyes are used in optics to allow us to calculate

A

retinal image size
axial length
refractive Power
magnification

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20
Q

the Retina

A

.light sensitive neural layer containing rods and cones
Lies in contact with the vitreous and Vascular choroid
Rods -130 million Scotopic Achromatic ill defined
cones - 7 million Photopic full detailed Colour Vision
contains Macula and foveola - concentration of cones - highest Visual Acuity

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21
Q

Ametropia

A

An uncorrected ,unaccomodated ametropic eye will not focus distant light on the macula.
the eyes far point is not at infinity and there is Some degree of refractive error
The eyes Second Principal focus does not coincide with the macula

we can describe ametropia as either Myopia or hyperopia or value of refractive error

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22
Q

in the reduced eye

A

k’ = k + Fe

k = Vergence required at the eye to focus at M’
k ‘ = Vergence required leaving reduced surface to focus on M’

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23
Q

what is meant by the term emmetropia

A 
when light from a distant object is focused on the macula of an uncorrected unaccommodated eye
k = ♾  
K = 0.
K'= Fe
k' = fe'
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24
Q

vertex distance

A

the distance from the back Plane of the Spectacle lens to the Corneal apex
BS 2738 Any Rx over + / - 5.OOD must include a tested vertex distance

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25
Q

True far point

A

MR = a point conjugate with the macula in the uncorrected unaccommodated eye

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26
Q

Ocular refraction

A

K = Vergence required at the eye to focus rays of light from a distant object on the macula

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27
Q

Spectacle Correction fsp

A

Fsp = the placement of a thin Spectacle lens in front of the eye So that the lens’ Second Principle focus coincides with the eyes far point
( for thick lens the back Vertex focal length must coincide with the eyes far point

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28
Q

FSp=
fsp’ =
d=
k=

A

FSP = Power of spectacle lens
fsp ‘ = focal length of Spectacle lens
d= vertex distance
k = far point distance

fsp’ = k + d

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29
Q

FSP =K / 1 + dk

A

k = fsp / 1- d Fsp

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30
Q

explain the difference between subjective refraction and objective refraction

A 
Subjective = requires a response or input from patient
objective = does not require a response or Input from Patient
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31
Q

retinoscopy a subjective or objective method

A

objective

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32
Q

In subject refraction what is meant by the term best vision Sphere

A

the Sphere Power that achieves the best line on the snellan chart
BVS = Sph + 1 / 2 Cyl (Push plus onto Patient

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33
Q

if a cx has Rx -4.00 / -3.00 x45 What is best Vision Sphere would you expect for the subject

A

-5.50DS

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34
Q

Define spectacle magnification and state a formula which may be used to calculate it

A

SM =
Size of corrected retinal Image.
- - - - - - - - - - - - - - - - - - - - - - - - - -
Size of uncorrected retinal image.

h’ k
- - - - - -
hu’ fsp

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35
Q

Define relative Spectacle magnification and state a formula which may be used to calculate it

A 
RSM = 
Size of corrected retinal image.       
 - - - - - - - - - - - - - - - - - - - - - - - - -       
Size of retinal Image in Standard.      
                reduced eye

k. x ke’
fSp k ‘

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36
Q

Heterophoria and Heterotropia

eyes associated

A

the eyes are both Viewing in the primary Position and appear to have taken up the primary Position of gaze

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37
Q

Heterophoria and Heterotropia

eyes disassociated

A

one eye occluded therefore the fusion reflex is prevented

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38
Q

Heterophoria and Heterotropia

Active and passive Positions

A

when both eyes are uncovered they are associated and are in the Active Position

If only one eye fixates and the other is occluded then the occluded eye is in the passive Position - No fusion reflex for binocular Vision

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39
Q

Orthophoria

Ortho = straight
phoria = state
A

Ideal state for distance and near objects
the visual axes always remain directed towards the fixation object- even when the eyes are dissociated
typical values are less than 1Prism horizontally and less than 0.25
Prism vertically
Some patients can be orthophoric for distance but not for near vision

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40
Q

Heterophoria

Heter - other
phoria - State
or latent strabismus (dormant Squint)

A

the visual axis are directed towards the fixation object when the eyes are associated but deviate when dissociated

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41
Q

Heterophoria classification

A

classified according to the movement of the eye under Cover from it’s active to its Passive position by observing the recovery Movement

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42
Q 
classification
Orthophoria
Exophoria 
Esophoria 
Hyperphoria 
Hypophoria 
in- cyclophoria
EX-cyclophoria
A 
NO Movement
Temporalwards abduction
Nasalwards - adduction
Turns up
Turns Down
upper pole - nasal
upper Pole temporal
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43
Q

Direction of prism in Heterophoria

A

exo - Base in
eso - Base out
R. Hyper- base down
L. Hyper. Base down

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44
Q

Maddox Rod

A

a Series of Parallel glass rods/ cyls that creates an image of light Source into a streak of light Perpendicular to its axis

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45
Q

Compensated Heterophoria

A

Dissociated phoria which usually not corrected no Symptoms or binocular discomfort
Subjective amount depending on the patients fusional reserves
not usually Prescribed

46
Q

uncompensated Heterophoria

De compensated

A

A phoria becomes uncompensated when BV is under Stress
Cx who attempt to maintain binocular vision by straining will have symptoms which include headaches,blurred vision diplopia and vertigo
caused by eye fatigue age,bad light
Prisms prescribed to decompensated
uncompensated phoria checked using a fixation technique : Mallet unit

47
Q

Mallet unit

A

O X O target viewed through polarising filter
2 bars are plane polarised So each eye See’s one of the lightbars
light increased
Any Misalignment of nonios lines is Compared to the ‘ X ‘ fixation letter
Prism added to realign lines
Detects weakest prism needed

48
Q

causes of heterophoria

A 
refractive
under corrected Hypermetropia for distance- need to accommodate
under corrected myope- need to Converge
Dissociation with eyes - Pro longed use 
abnormality of the orbits
exophthalmos Iarge PD- prone exo
Endothalmos Narrow PD - prone eso
49
Q

Concomitant Squint -

A

The angle between the visual axis is the same for all distances + directions of gaze

50
Q

InConmitant Squint

A

the angle between the visual axis varis with direction of case

51
Q

Amblyopia

A

A unilateral or bilateral decrease in vision for which there is no obvious cause found on physical examination of the eye

52
Q

Retinoscopy

A 
key technique
it allows an objective measure of the patients prescription where barriers such as language,mental Capacity and compliance do not allow fora subjective examination
need a visible light reflex
Spot /Streak 
collar up: Convergent bean
Collar down -Divergent beam
53
Q

Reflex

A

Fsp = Frev - WD

fsp= final Rx
frev =the lens used to get reversal
WD= working Distance

54
Q

Your final RX is +4.00 / -3.50 x180
WD= 1 / 2 a metre
What lens did you use to find reversal

A

fsp = frev - WD
100/ 50 =+ 2.00 D

frev = fsp + WD = +4.00 + +2.00 = +6.00

final = +6.00 / -3.50 x180

55
Q

Mohandria Technique

A

Alternative to cycloplegia instead of drops the room is made dark child expected to look at light of the retinoscope
accomodation assumed to be relaxed
Working distance reduced to 50cm (lens is 2.00D)
-1:25 adjustment may be made to compensate

56
Q

Accommodation + Convergence
Binocular movements

versions
vergences

A

versions - conjugate Movements. eyes move together binocularly and the angles between the Visual axes is constant

Vergences - Disjunctive Movements .eyes move In opposite Directions

57
Q 
Binocular Movements
version and movement
Dextroversion
Laevoversion 
Superversion
infraversion
A

looking Right
looking Left
looking up
looking down

58
Q 
Binocular Vision
vergence and Movement
convergence
Divergence
Right Supra vergence
Right in fra vergence
In- cyclo Vergence
Ex. cyclo vergence
A 
Eye turns Inwards
Divergence eye turn out
RE turns up + left 
RE turns down I left
upper poles of eyes + Inwards
upper poles of eyes rotate out
59
Q

what 3 ocular movements occur when viewing a near object

A 
Convergence- Aligns Visual Axes with object, 2 Images will fall on corresponding retinal points
Accomodation -the Power of the crystalline lens Increases to create a Sharp Image of the near object on the retina
Pupil miosis (constriction) -reduces blur + increases Depth of field (ocular motor nerve CNIII )
60
Q

Binocular vision Problems can therefore be the result of an excess of deficiency of

A
  1. vergence or control problem (Prism dioptres)

2. Power or focusing (dioptres)

61
Q

Examples of everyday tasks that could lead to binocular vision problems

A

Reading
VDu use
Driving ( distance to dash board+ back)
TV

62
Q

accommodative Convergence

A

the amount of convergence Stimulated by the act of accommodation

63
Q

AC /A ratio

A

the amount of accommodative Convergence per 1.00D of accommodation

Accommodative convergence
- - - - - - - - - - - - - - - - - - - - - - -
Accomodation

an average 1.00D of Accommodation = 4.00Prism of Convergence

64
Q

accomodation

Hyperopes

A

uncorrected hyperopes need to accomodate to see a distant object but most not converge

65
Q

myopes

A

uncorrected myopes must converge to see a near object but will not need to accommodate

66
Q

optometers

A

Opthalmic devices used to measure ametropia

67
Q

Subjective

Objective

A

subjective - refractive error - needs response from patient( Snellen)
objective -no response ( Auto refractor)

68
Q

Scheiner Disc

A

an opaque disc 38mm in diameter can be used to distinguish Spherical ametropia
2 pin holes around 0.75 mm - 1mm in diameter and 2-3mm apart

69
Q

Badal optometer

A

optameter comprises of a linear Scale,Produces an Image size that is nearly constant
consists of Single lens( + 16.00D )
lens positioned so 2nd focal Point coincides with Spec lens plane = Spec Rx
one eye occluded -target Moved closer to cx until clear
xx’ = ff’

70
Q

Telescope optometer page 248-252

A

Galilean telescope used to determine the Spectacle refraction.when retinalImage is clear the Position of the objective lens Indicates the refractive error

71
Q

young Porterfield optometer page 248-252

A

consists of a black Rule with a white line down the centre.
A + 10D lens and 2 Parallel Slits are mounted at the end.Each SIit form an Image of a white line Cursor Can be moved by CX to indicate the Intersection of the white line

72
Q

grades of binocular vision

A

1 simultaneous
2 fusion
3 Stereopsis

73
Q

Simultaneous

A

lowest grade

the abilly to perceive two Seperate Images and then to Superimpose them

74
Q

fusion

A

The ability to fuse two images into a single Image (percept)
Sensory - neurological ability to percieve 2 Similar Images
motor extraocular muscles work during vergence to maintain Single image

75
Q

why is fusion Important
who doesn’t have fusion?
What happens if lost

A

if 2 eyes cannot produce 2 Similar Images which can be fused diplopia will result
Someone with Squint
anisometropic Rx
Someone with one eye

poor depth perception
Reduced Fov
clumsy

76
Q

Supression

A

Squints when young
Suppression rarely Possible if diplopia occurs as adult ( brain can’t cope)
can occur in adults If VA Poor In one eye or one eye occluded due by cataract

77
Q

3 types of Diplopia

A

Pathological - ( muscles affected)
Physiological - ( most common ) crossed + uncrossed
Prism induced

78
Q

Exam Question
A patient Views a Spotlight at a distance of 6m through a 3 prism base down in front of the left eye . Explain what the Patient will see

A

which eye has Image on macula - Right eye
Image of the spotlight will be seen on RE Macula but the Image of Spotlight is displaced down due to prism base in LE
Image is seen double
Px will see the image in the LE as being above the image Seen by RE

79
Q

exam Questions Monocular cues

overlapping

A

objects in the foreground are percievedto be closer to us compared to those behind that are obsecured by objects in foreground

80
Q

Exam Q

Geometric perspective

A

Straight lines - narrowing into the distance giving them perception of distance away from you

81
Q

Exam Q

Relative Size

A

your understanding of the size of an object when smaller than normal you Percieve it to be further away

82
Q

Exam Q

Light and shading

A

the change of light or shading of a object is different when nearer to us Compared to when further away we can use that detail like shadow to See as 3 D

83
Q

Exam Q

Aerial Perspective

A

the lower the contrast of an object denotes how far it may be away in the distance

84
Q

Exam Q Monocular cues

Parallax

A

is the ability to judge distance based On the percieved Speed of the object if further away will Seem like going slower

85
Q

Explain how astigmatism may be classified according to the position relative to the retina of the focal lines formed by a distant point object

A

Simple myopia . 1 focal line in front other on retina
Compound =both focal lines in front- myopia
Simple Hypermetropia 1 line on retina are behind
Compound Hyperemetrope both behind retina
Mixed lines either side of retina

86
Q

the cross cyl method is often used to refine the Astigmatic Component during Subjective refraction with aid of diagram describe the Cross cylinder lens

A

2 plano cyls Perpendicular to each other

most common + / - 0.25 and + / - 0.50

87
Q

an astigmatic Subject re quires a negative Cylinder with its axis at 90 if cross cyl used what would the orientation of the cross cyl handle

A

45 degrees to axis Or @ 135

Handle will be at 45/135 axis will be alinged with 90/180 medians

88
Q

Keratometry

A

Keratometry measures the radius of Curvature of the Central anterior surface of the cornea over a 3-4mm diameter ( optic cap)

the practioner can then select the most appropriate back optic Zone Radius ( BOZR) when fitting CL

89
Q

4 Purkinje Images

formed

A

Image 1 - Corneal reflex
Image 2 - formed by refraction and reflection( Posterior corneal Surface)
Image 3 - formed by refraction and reflection (anterior lens)
Image 4 - formed by refraction and reflection ( Posterior lens)

90
Q

Purkinje Image 1

A 
Corneal reflex 
reflection at the anterior Corneal Surface
Virtual upright
falls inside crystalline lens
Brightest of all
used in beratemetry and to measure PD
91
Q

Purkinje Image 2

A

formed by refraction and reflection at the Posterior corneal Surface
virtual and upright
falls inside the crystalline lens just behind Image 1
1 / 100th the brightness of Image 1

92
Q

Purkinje Image 3

A

formed by refraction and reflection at the anterior Surface of the crystalone lens
Virtual and upright
falls inside the vitreous
1 / 100th of brightres of image 1

93
Q

’ Purkinje Image 4

A

formed by refraction and reflection at the posterior Surface of the Crystalline lens
Real and inverted
falls inside crystanline lens
1 /100th the brightness of Image 1

94
Q

Keratometry

A

uses Purkinje Image 1 and by treating the cornea as a curved mirror makes use of the relationship between focal length and radius of Curvature

95
Q

Keratometry Exam Q

However the eye is constantly making Small tremor,Microsaccadic and drift Movements while trying to hold fixation

A

Because of these constant Movements the Image size cannot be measured against a fixed Scale

96
Q 
Image doubling
( formula 2)
A

fixed doubling System power and Position of Prism= fixed
size of corneal Image calculated by
h’ = Pd / 100
Power of Prism x distance

use this then r= 2 h’ / h xd

97
Q

Keratometry formula 3

A

using variable doubling System there is only one fixed object
no calculate the sizeof the corneal Image
h’ = - P S / 100 Mo
Mo -magnification observation System
P. Power of Prism
s = Distance of object to Image

98
Q

one position instrument

A

has single mire and uses 2 doubling Prisms@ 90degrees opposed to one another This allows it to readboth principal meridians of the Cornea

99
Q

Two position

A

can only take reading from are Corneal meridian at a time

instrument must be rotated through 90 to a Second Position to measure Second principal meridian

100
Q

Why is doubling necessary

A

Indirect method of Measuring the image size of the Cornea that’s not affected by these constant Movement

101
Q

Exam Q

Heterophoria

A

in normal binocular vision with both eyes fixating there is no deviation.If one eye occluded or binocular Vision prevented then one eye will deviate

102
Q

Exam Q

Heterotropia

A

one eye will always deviate. the 2 visual axis are never directed in the same place

103
Q

What is Keratoscopy

A

overall shape of the cornea

104
Q

what is the main use of Keratoscopes and Keratometers in practice

A

fitting of CL

105
Q

what is entoptic ehenomena

A

happens within the eye itself visual disturbances

106
Q

Give are example of an entopic phenomenon Caused by ocular media

A

floaters casting Shadows on the retina

107
Q

Exam Q

what lightening should be used to Illuminate the Ishihara test ? (5)

A
108
Q

Exam Q

Ishihara colour Vision test what is recommended working distance

A

75mm

109
Q

what is most common type of congenital Colour vision defect

A
110
Q 
Exam Q
explain meaning - Colour vision for
Deuteranomaly 
Protanopia 
Rod monochromacy
A
111
Q

exam Q

state 2 causes acquired Colour vision defects

A
112
Q

Exam Q

state 2 ways in which acquired Colour vision de fects may differ from congenital Defects

A

Year 3 (8 decks)

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