Refractive management Flashcards
year 3 exam
1
Q
schematic eye
A
a basic or diagrammatic reprenstation of a real eye
2
Q
Reduced eye
A
simplified versions of real eyes or previous models that will help us with calculation
3
Q
optical axis
A
a line through the Centres at all refractive Surfaces - best Centration is given by this
4
Q
visual Axis
A
a line from the Centre of the Macula through pupll Centre
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)
6
Q
Axial length
A
the distance between the anterior corneal surface + the foveola - mean value 24mm ( adult)
7
Q
Principal point
A
Position of a single equivalent lens which can replace a lens System
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
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
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 ♾
11
Q
k = Ocular refraction
A
k = n/ k = 1 / ♾ = + 0.00D
12
Q
k’ = Axial length of eye
A
k’ = n’ / K’ = 4 / 3 / + 60 .OODx 1000 = + 22.22 mm
13
Q
k’ = Dioptric length of eye
A
k’ = n’ / k ‘ = 4/3 / + 60.00 X 1000 =+ 22.22 mm
14
Q
the Cornea
A
Transparent Medium - most of refraction Total Power = + 42.00D
15
Q
the Aqueous
A
fills anterior and Posterior chamber n= 1. 336
16
Q
The Iris
A
Contains pupil variable aperture 2-8mm
17
Q
crystalline lens
A
Biconvex changes shape to become more Convex = Positive Power Increase = accomodation supplies the remaining balance of eyes refractive Power
18
Q
Vitreous
A
largely homogenous gel like fluid - fills Space between lens + retina
19
Q
Schematic and reduced eyes are used in optics to allow us to calculate
A
retinal image size
axial length
refractive Power
magnification
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
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
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’
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'
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
25
True far point
MR = a point conjugate with the macula in the uncorrected unaccommodated eye
26
Ocular refraction
K = Vergence required at the eye to focus rays of light from a distant object on the macula
27
Spectacle Correction fsp
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
28
FSp=
fsp' =
d=
k=
FSP = Power of spectacle lens
fsp ' = focal length of Spectacle lens
d= vertex distance
k = far point distance
fsp' = k + d
29
FSP =K / 1 + dk
k = fsp / 1- d Fsp
30
explain the difference between subjective refraction and objective refraction
```
Subjective = requires a response or input from patient
objective = does not require a response or Input from Patient
```
31
retinoscopy a subjective or objective method
objective
32
In subject refraction what is meant by the term best vision Sphere
the Sphere Power that achieves the best line on the snellan chart
BVS = Sph + 1 / 2 Cyl (Push plus onto Patient
33
if a cx has Rx -4.00 / -3.00 x45 What is best Vision Sphere would you expect for the subject
-5.50DS
34
Define spectacle magnification and state a formula which may be used to calculate it
SM =
Size of corrected retinal Image.
- - - - - - - - - - - - - - - - - - - - - - - - - -
Size of uncorrected retinal image.
h' k
- - - - - -
hu' fsp
35
Define relative Spectacle magnification and state a formula which may be used to calculate it
```
RSM =
Size of corrected retinal image.
- - - - - - - - - - - - - - - - - - - - - - - - -
Size of retinal Image in Standard.
reduced eye
```
k. x ke'
fSp k '
36
Heterophoria and Heterotropia
eyes associated
the eyes are both Viewing in the primary Position and appear to have taken up the primary Position of gaze
37
Heterophoria and Heterotropia
eyes disassociated
one eye occluded therefore the fusion reflex is prevented
38
Heterophoria and Heterotropia
Active and passive Positions
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
39
Orthophoria
```
Ortho = straight
phoria = state
```
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
40
Heterophoria
Heter - other
phoria - State
or latent strabismus (dormant Squint)
the visual axis are directed towards the fixation object when the eyes are associated but deviate when dissociated
41
Heterophoria classification
classified according to the movement of the eye under Cover from it's active to its Passive position by observing the recovery Movement
42
```
classification
Orthophoria
Exophoria
Esophoria
Hyperphoria
Hypophoria
in- cyclophoria
EX-cyclophoria
```
```
NO Movement
Temporalwards abduction
Nasalwards - adduction
Turns up
Turns Down
upper pole - nasal
upper Pole temporal
```
43
Direction of prism in Heterophoria
exo - Base in
eso - Base out
R. Hyper- base down
L. Hyper. Base down
44
Maddox Rod
a Series of Parallel glass rods/ cyls that creates an image of light Source into a streak of light Perpendicular to its axis
45
Compensated Heterophoria
Dissociated phoria which usually not corrected no Symptoms or binocular discomfort
Subjective amount depending on the patients fusional reserves
not usually Prescribed
46
uncompensated Heterophoria
| De compensated
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
Mallet unit
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
causes of heterophoria
```
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
Concomitant Squint -
The angle between the visual axis is the same for all distances + directions of gaze
50
InConmitant Squint
the angle between the visual axis varis with direction of case
51
Amblyopia
A unilateral or bilateral decrease in vision for which there is no obvious cause found on physical examination of the eye
52
Retinoscopy
```
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
Reflex
Fsp = Frev - WD
fsp= final Rx
frev =the lens used to get reversal
WD= working Distance
54
Your final RX is +4.00 / -3.50 x180
WD= 1 / 2 a metre
What lens did you use to find reversal
fsp = frev - WD
100/ 50 =+ 2.00 D
frev = fsp + WD = +4.00 + +2.00 = +6.00
final = +6.00 / -3.50 x180
55
Mohandria Technique
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
Accommodation + Convergence
Binocular movements
versions
vergences
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
```
Binocular Movements
version and movement
Dextroversion
Laevoversion
Superversion
infraversion
```
looking Right
looking Left
looking up
looking down
58
```
Binocular Vision
vergence and Movement
convergence
Divergence
Right Supra vergence
Right in fra vergence
In- cyclo Vergence
Ex. cyclo vergence
```
```
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
what 3 ocular movements occur when viewing a near object
```
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
Binocular vision Problems can therefore be the result of an excess of deficiency of
1. vergence or control problem (Prism dioptres)
| 2. Power or focusing (dioptres)
61
Examples of everyday tasks that could lead to binocular vision problems
Reading
VDu use
Driving ( distance to dash board+ back)
TV
62
accommodative Convergence
the amount of convergence Stimulated by the act of accommodation
63
AC /A ratio
the amount of accommodative Convergence per 1.00D of accommodation
Accommodative convergence
- - - - - - - - - - - - - - - - - - - - - - -
Accomodation
an average 1.00D of Accommodation = 4.00Prism of Convergence
64
accomodation
| Hyperopes
uncorrected hyperopes need to accomodate to see a distant object but most not converge
65
myopes
uncorrected myopes must converge to see a near object but will not need to accommodate
66
optometers
Opthalmic devices used to measure ametropia
67
Subjective
| Objective
subjective - refractive error - needs response from patient( Snellen)
objective -no response ( Auto refractor)
68
Scheiner Disc
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
Badal optometer
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
Telescope optometer page 248-252
Galilean telescope used to determine the Spectacle refraction.when retinalImage is clear the Position of the objective lens Indicates the refractive error
71
young Porterfield optometer page 248-252
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
grades of binocular vision
1 simultaneous
2 fusion
3 Stereopsis
73
Simultaneous
lowest grade
| the abilly to perceive two Seperate Images and then to Superimpose them
74
fusion
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
why is fusion Important
who doesn't have fusion?
What happens if lost
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
Supression
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
3 types of Diplopia
Pathological - ( muscles affected)
Physiological - ( most common ) crossed + uncrossed
Prism induced
78
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
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
exam Questions Monocular cues
| overlapping
objects in the foreground are percievedto be closer to us compared to those behind that are obsecured by objects in foreground
80
Exam Q
| Geometric perspective
Straight lines - narrowing into the distance giving them perception of distance away from you
81
Exam Q
| Relative Size
your understanding of the size of an object when smaller than normal you Percieve it to be further away
82
Exam Q
| Light and shading
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
Exam Q
| Aerial Perspective
the lower the contrast of an object denotes how far it may be away in the distance
84
Exam Q Monocular cues
| Parallax
is the ability to judge distance based On the percieved Speed of the object if further away will Seem like going slower
85
Explain how astigmatism may be classified according to the position relative to the retina of the focal lines formed by a distant point object
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
the cross cyl method is often used to refine the Astigmatic Component during Subjective refraction with aid of diagram describe the Cross cylinder lens
2 plano cyls Perpendicular to each other
| most common + / - 0.25 and + / - 0.50
87
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
45 degrees to axis Or @ 135
| Handle will be at 45/135 axis will be alinged with 90/180 medians
88
Keratometry
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
4 Purkinje Images
| formed
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
Purkinje Image 1
```
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
Purkinje Image 2
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
Purkinje Image 3
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
' Purkinje Image 4
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
Keratometry
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
Keratometry Exam Q
| However the eye is constantly making Small tremor,Microsaccadic and drift Movements while trying to hold fixation
Because of these constant Movements the Image size cannot be measured against a fixed Scale
96
```
Image doubling
( formula 2)
```
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
Keratometry formula 3
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
one position instrument
has single mire and uses 2 doubling Prisms@ 90degrees opposed to one another This allows it to readboth principal meridians of the Cornea
99
Two position
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
Why is doubling necessary
Indirect method of Measuring the image size of the Cornea that's not affected by these constant Movement
101
Exam Q
| Heterophoria
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
Exam Q
| Heterotropia
one eye will always deviate. the 2 visual axis are never directed in the same place
103
What is Keratoscopy
overall shape of the cornea
104
what is the main use of Keratoscopes and Keratometers in practice
fitting of CL
105
what is entoptic ehenomena
happens within the eye itself visual disturbances
106
Give are example of an entopic phenomenon Caused by ocular media
floaters casting Shadows on the retina
107
Exam Q
| what lightening should be used to Illuminate the Ishihara test ? (5)
108
Exam Q
| Ishihara colour Vision test what is recommended working distance
75mm
109
what is most common type of congenital Colour vision defect
110
```
Exam Q
explain meaning - Colour vision for
Deuteranomaly
Protanopia
Rod monochromacy
```
111
exam Q
| state 2 causes acquired Colour vision defects
112
Exam Q
| state 2 ways in which acquired Colour vision de fects may differ from congenital Defects
