# Thread: Lens thickness calculator that takes OC height into account?

1. ## Lens thickness calculator that takes OC height into account?

Opticampus one does not - http://64.50.176.246/tools/thickness.php

2. Literally any lens supplier's online ordering system???

3. Apparently not mine's. Does any supplier offer it publicly?

4. Q: What would define the OC height? The actual OC or the value at the PRP?

5. I just want to be able to tell patients how thick their lenses will be. If OC height differs significantly from the geo-center, the thickness difference might be significant and therefore patient's expectations not met = patient unhappy.

6. Originally Posted by donjuan
I just want to be able to tell patients how thick their lenses will be. If OC height differs significantly from the geo-center, the thickness difference might be significant and therefore patient's expectations not met = patient unhappy.
You are right but shape matter too if you want be accurate.

7. First of all, the effect would be seen along the vertical, whereas the thickness on the horizontal is more commonly the big issue. But you can dot the position of the proposed OC, measure the resultant ED at any point on the lens, and plug that in as the eyesize in Opticampus.

8. Originally Posted by finefocus
First of all, the effect would be seen along the vertical, whereas the thickness on the horizontal is more commonly the big issue. But you can dot the position of the proposed OC, measure the resultant ED at any point on the lens, and plug that in as the eyesize in Opticampus.
Not necessarily. There are a whole lot of frames with very deep B measurements, especially round ones. I personally have a couple frames with more decentration from the OC to the bottom than from the OC to the temporal edge. Hell, I'm wearing one right now; the thickest part of the lens is the bottom.

9. To expand on what finefocus was saying, you have to “trick” the calculator. Example;

Power -4.00 -2.00 x 180 OD

You are going to place the OC 4 above datum. What is the approximate thickness at the lower, temporal edge (axis 225)?

1st, you need the power @225. (-5.00)
Dot the lens at the point you want the OC. Measure from that point to the furthest point @ axis 225, then double it.
Plug that doubled measurement into the “eye size” box. It doesn’t matter what bridge and PD you use as long as the frame PD and patients PD equals out ( 55 eye + 15 dbl = 70, use 70 in the PD box.)

Basically, you need the power at the meridian you wish to know the approximate thickness. You need to measure from the OC out to that point, double it, then use that number as the “eye size”. And it doesn’t matter what PD or dbl you use as long as there is no decentration in the calculation. Do not enter a cyl or axis.

10. Optical21/7 is correct just one item to add. If the longest radius is on the nasal side you have to reduce the decentration by the number mm that the radius is longer on the nasal side than the temporal side. This occurs in many shapes in particular a pilot.

11. (I somehow lost 3 hours...) The method I described above eliminates decentration in the equation. You are simply having the calculator figure the thickness of a certain power with a certain radius. If you wanted to figure the thickness of the upper nasal (like a pilot shape) you would measure from the OC to the upper nasal (45 degrees) then double that measurement and use it for the “eye size”. (Once again, using the same frame *PD* as the patient PD).

12. Let’s not forget donjuan wants to know the thickest point which surely does not have to be located at the longest radius. Lab calculation software will tell you the thickest and thinnest point and give the location.

13. Originally Posted by Barry Santini
Q: What would define the OC height? The actual OC or the value at the PRP?
The actual OC.

To expand on what finefocus was saying, you have to “trick” the calculator. Example;

Power -4.00 -2.00 x 180 OD

You are going to place the OC 4 above datum. What is the approximate thickness at the lower, temporal edge (axis 225)?

1st, you need the power @225. (-5.00)
Dot the lens at the point you want the OC. Measure from that point to the furthest point @ axis 225, then double it.
Plug that doubled measurement into the “eye size” box. It doesn’t matter what bridge and PD you use as long as the frame PD and patients PD equals out ( 55 eye + 15 dbl = 70, use 70 in the PD box.)

Basically, you need the power at the meridian you wish to know the approximate thickness. You need to measure from the OC out to that point, double it, then use that number as the “eye size”. And it doesn’t matter what PD or dbl you use as long as there is no decentration in the calculation. Do not enter a cyl or axis.
If I want to calculate thickness at the farthest point right below the OC for sphere -7.25 no cyl, real frame eyesize 42mm, real OC 27mm, real bridge 21mm, are these the correct values to enter?
Sphere Power (D)? -7.25
Cylinder Power (D)? 0.00
Cylinder Axis (°)? 0
Interpupillary Distance (mm)? 75 (54+21)
Frame Eyesize (mm)? 54 (2xOC = 2x27)
Frame Bridge (mm)? 21 (real bridge)

Is there a calculator for calculating power at a given axis when Rx has a cylinder?

Originally Posted by Lensman11
Let’s not forget donjuan wants to know the thickest point which surely does not have to be located at the longest radius. Lab calculation software will tell you the thickest and thinnest point and give the location.
TBF, what I want is to know the thickness at the lower rim, knowing it just at the farthest point below the OC is fine, but of course additional lower nasal and temporal measurements would be useful for non-round frames. This is just to approximate the thickness impact of lens decentration, so that I can tell patients what to expect, I think that would be useful.

14. Originally Posted by donjuan

If I want to calculate thickness at the farthest point right below the OC for sphere -7.25 no cyl, real frame eyesize 42mm, real OC 27mm, real bridge 21mm, are these the correct values to enter?
Sphere Power (D)? -7.25
Cylinder Power (D)? 0.00
Cylinder Axis (°)? 0
Interpupillary Distance (mm)? 75 (54+21)
Frame Eyesize (mm)? 54 (2xOC = 2x27)
Frame Bridge (mm)? 21 (real bridge)

.
Even though you are decentering the OC, you need to eliminate decentration to trick the calculator. It makes no difference what bridge size you enter (or PD for that matter), as long as the frame PD and the Patient’s PD are equal. What you wrote above is correct. Entering that info, along with selecting the lens index will give you an approximation of how thick a -7.25 would be 27mm from the OC.

15. As optical 24/7 says, that is the thickness 27 mm from OC - which is to say straight down to the bottom edge, but not to, say, the lower temple corner - that would be more than 27 mm from the OC unless the OC is horizontally centered and the shape is round or nearly so.

16. Originally Posted by finefocus
As optical 24/7 says, that is the thickness 27 mm from OC - which is to say straight down to the bottom edge, but not to, say, the lower temple corner - that would be more than 27 mm from the OC unless the OC is horizontally centered and the shape is round or nearly so.
Optical24/7 has already quite clearly, and concisely, explained how to calculate thickness at any axis using this method.

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