AREA 2: Fitting single-vision lenses
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AREA 2: Fitting single-vision lenses • Topic 4: Alignment, decentration, and minimum diameter • Topic 5: Calculating thickness in spherical lenses • Topic 6: Calculating thickness in astigmatic lenses • Topic 7: How lenses affect vision • Topic 8: Prismatic effects • Topic 9: Base rules • Topic 10: How alignment affects binocular vision
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AREA 2: Fitting single-vision lenses. Topic 4: Alignment, decentration, and minimum diameter Topic 5: Calculating thickness in spherical lenses Topic 6: Calculating thickness in astigmatic lenses Topic 7: How lenses affect vision Topic 8: Prismatic effects Topic 9: Base rules - PowerPoint PPT Presentation
Transcript of AREA 2: Fitting single-vision lenses
AREA 2: Fitting single-vision lenses
• Topic 4: Alignment, decentration, and minimum diameter• Topic 5: Calculating thickness in spherical lenses• Topic 6: Calculating thickness in astigmatic lenses• Topic 7: How lenses affect vision• Topic 8: Prismatic effects• Topic 9: Base rules• Topic 10: How alignment affects binocular vision
Topic 7: How lenses affect vision
• Changes in visual fieldChanges in visual field
• Changes in retinal image sizeChanges in retinal image size
• Effect of vertex distanceEffect of vertex distance
Peripheral visual field Central visual field
PE z’
Changes in visual field
60º
75º
95ºT N
S
I
60º
95º
75º
T
S
I
OD OS
Changes in visual field
60ºN
60º
Reduction of visual field by frame
z’ ‘
'2l
C A
Changes in visual field
Apparent visual field
'' Ltg2
Reduction of visual field by lens vergence
Plus lens Minus lens
z’ z‘
'2l
2l
C R
C A
z’z ‘
'2l
2l
C R
C A
Changes in visual field
Real visual field
BVPLtg '2
Calculation of real visual field (2)
Changes in visual field
Changes in visual field
Scotoma in plus lenses
Spectacle magnification
Changes in retinal image size
Spectacle magnification:
’
’
H H ’
f ’- x
f ’ x
h ’
R = F’
'lens WITHsize image Retinal
lens WITHOUTsize image Retinal
tg
tgSM
Changes in retinal image size
F´ = RE
f´ v p
d v
de c
3 m m
Reverse afocal Galilean viewfinder
Thin lens
Changes in retinal image size
1F
2F
ce 2f
1f
nP
T
Ms
c11
1
Afocal Galilean viewfinder
Changes in retinal image size
F´ = RE
3 m m
v pf
xd
vd
H H
BVPdMp
1
1
Thin lens
Changes in retinal image size
11
1
1
1
Pn
TBVPdSM
c
MpMp
MsMs
Spectacle magnification:
Changes in retinal image size
BVP (D) Tc (mm) P1 (D) Ms Mp SM % SM
-20.00 0.70 0.00 1.000 0.758 0.758 -24.2%
-15.00 0.70 0.00 1.000 0.806 0.806 -19.4%
-10.00 0.80 +3.00 1.002 0.862 0.864 -13.6%
-5.00 0.80 +4.49 1.002 0.926 0.928 -7.0%
0 1.80 +5.96 1.007 1.000 1.007 0.7%
+5.00 4.50 +10.19 1.031 1.087 1.121 12.1%
+10.00 7.00 +12.27 1.060 1.190 1.216 26.1%
+15.00 8.50 +13.84 1.084 1.316 1.426 42.6%
Changes in retinal image size
Changes in retinal image size
Spectacle magnification
Anisometropia and aniseikonia
Changes in retinal image size
Anisometropia and aniseikonia
Changes in retinal image size
Aniseikonia
• <3% No symptoms
• 3-5% Asthenopia
• >5% Problems with binocular
vision
Changes in retinal image size
Tc P1 P2 BVP SM
n = 1.523vd = 15
mmØ = 65 mm
OD 2.04 +5.21 -4.25 +1.00
7.1%OS 5.28 +7.78 -4.00 +4.00
n = 1.8vd = 12
mmØ = 65 mm
OD 1.66 +5.22 -4.25 +1.00
5%OS 3.68 +7.87 -4.00 +4.00
n = 1.8vd = 12
mmØ = 55 mm
OD 1.9 +5.22 -4.25 +1.00
3.8%OS 1.9 +5.22 -1.25 +4.00
Aniseikonia caused by anisometropia
Changes in retinal image size
Aniseikonia greater than 5%
• Myopia, anisometropia > 3.00 D
• Hyperopia, anisometropia > 2.00 D
Changes in retinal image size
Distortion in astigmatic lenses:Distortion in astigmatic lenses:
90º+ 2.00+ 4.00
+ 6.00
+ 4.00
+ 4.00
+ 6.00O BJ EC TE
Changes in retinal image size
min
max
SM
SM
max
minmax100SM
SMSMFAA
Changes in retinal image size
Angular distortion
O BJ EC TE
+ 6.00
+ 4.00
120º-2.00+6.00 D
Changes in retinal image size
Object
Image
Cylinder axis expressed as plus cylinder
Changes in retinal image size
Effect of angular distortion
+ 6 .0 0 D+ 4 .0 0 D
+ 6 .0 0 D+ 4 .0 0 D
Object 50º +2.00 +4.00 D lens
Changes in retinal image size
eff LL 212
2
22
1 1111
L
L
LL
L Pe
P
ePef
P
R= F’
2Lf
1Lf
e
Effect of vertex distance
Myope: Glasses prescription with vd of 12 mm, -9.00 D
Glasses prescription with vd of 15 mm, -9.25 D
1
12 1 Lo
LoLo Pe
PP
123
1215 1031 L
LL P
PP
Example:Example: New frameNew frame
Effect of vertex distance
12 dde
R=F’
LCf
1Lof
2Lof
dve
Effect of vertex distance
Example:Example: Fitting a contact lens (above 5.00 D)Fitting a contact lens (above 5.00 D)
Lo
LoLC Pdv
PP
·1
Movement of glasses to see
betterHyperopia Myopia
Closer to the eyes Overcorrected Undercorrected
Away from the eyes Undercorrected Overcorrected
Effect of vertex distance
Example:Example: SignsSigns
Example:
Signs
Effect of vertex distance
