Physiological Optics 1.2 Flashcards
Lens power equation using diameter and sag
Power = 2(n2 - n1) sag / (0.5diameter)^2
Diameter may be given as cord
Diameter and sag in meters
Equation relating sag to r
sag = (0.5 diameter)^2 / 2r
r = (0.5 diameter)^2 / 2sag
diameter and sag in meters
Isothickness curves
Shows regions of constant curvature.
Lines close together indicate quick thickness changes
Minimum blank size
ED + 2(decentration) + 2mm
Major Reference Point
Point on lens through which the line of sight passes
How to find geometrical center of a lens
The point 1/2 way b/t two vertical lines tangent to the edges
Common OC distances for Seg types
FT-28: 5mm Executive: 0mm Round: radius of seg FT-35, curve top, panoptic, Ribbon-B: 4.5mm FT > 35: 0mm Ribbon-R: 7mm
Seg Depth vs Seg Height
Seg depth is the vertical dimension of the seg, Seg height is measured to the lowest point of the lens
Seg Drop
Top of the seg measured to the MAJOR REFERENCE POINT
Inset Calculation
1/2 (Frame PD - distance PD)
-AKA decentration
Seg Inset Calculation
1/2 (distance PD - near PD)
Total Inset Calulation
Inset/decentration + Seg Inset
1/2 (Frame PD - Near PD)
Adjustments when seg is too high
Decrease Vertex Distance
Widen or raise nosepads
Increase pantascopic tilt
Adjustments when seg is too low
Increase vertex distance
Narrow/lower pads
Decrease pantoscopic tilt
How much should you raise the seg for every degrees of pantoscopic tilt
0.5mm, raise 1mm per 2 degrees
