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14 Cards in this Set
- Front
- Back
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Stokes Sphere Formula |
S = F1 + F2 - FC/ 2 |
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Stokes Angle a formula |
a = (F2 axis - F1 axis) |
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Bifocal Terms |
OD = Optical Centre of main seg HCL or Box Centre = Centre of frame Segment Top Position = From HCL to top of seg |
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Aspheric Sag Formula |
S = r/p + Square root of (r/p)2 - y2/p |
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h' formula |
-f tan w |
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Calculate angle which eye must rotate from primary position to view image |
tan° = h'/ l' - s tan -1 |
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Ocular rotation measurements |
s = lens to eyes centre of rotation r = cornea to eyes Centre of rotation d = vertex distance w = angle that subtends Theta = Angle the eye rotates |
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Ring Scotoma |
Produced in hyperopic lenses and at the dividing line of most bifocals. Caused prismatic effect. Light from around periphery of lens cannot reach the patients eye. |
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Real and Apparent Field of View |
Apparent: The angle subtending the eyes Centre of rotation by an empty frame aperture Real: angle subtending effective diameter of a lens conjugate with the eyes centre of rotation, taking into consideration that lenses refract light |
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Apparent Field of View Formulas |
y = semi diameter of lens z' = distance from aperture to eyes centre of rotation Z' = Dioptric value of z' tan° = yZ' / 1000 apparent FOV = 2theta |
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Jack in the Box Effect |
This effect is produced in hyperopic lenses where real FOV is smaller than apparent FOVCaused by prismatic effect of the positive lens Produces annual scotoma at periphery of lens Jumps in and out of pxs field of View at periphery of the lens |
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Spec Mag Formula |
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Notional Surface Power Formula |
F° = F sin2 ° |
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Formulas for position of optical centre in bifocal |
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