Author Topic: Quadrant specific e-values  (Read 5698 times)

poepol

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Quadrant specific e-values
« on: December 09, 2013, 08:52:17 pm »
Is there a way of accessing this info? If so can the quadrants be specified?

Thanks

Michael

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Re: Quadrant specific e-values
« Reply #1 on: December 10, 2013, 11:38:39 am »
Hi,

The answer is Yes you can get the E values for specific angles and distance from the center of the topography through the use of Custom Attributes. If you search for "Custom Attributes" in the E300 User Manual you will find a section that explains how to create them.

As a rough guide you will want to create a new 'Calculated Attribute'. Give it a name that helps you identify what you are measuring (i.e. Q1 E) and then you will need to use the Eccentricity data function. It takes in an angle in degrees and a half chord length. So to measure the E values at 2mm on a 45 degree angle you would use something like this:

Code: [Select]
Eccentricity(45, 2)
If you want the E value at multiple points then you will need to define multiple attributes.

As a side question, what are you intending to use this for? If it is as an aide to fitting contact lens we generally find that most people want to use specific height values rather than local eccentricity.
Senior Software Engineer
Medmont Pty. Ltd.

poepol

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Re: Quadrant specific e-values
« Reply #2 on: January 15, 2014, 06:08:43 pm »
Thanks Michael

I do use e-values for fitting (as well as height).

The method supplied above does not seem quadrant specific but gives the overall e-value along the specified chord angle (ie if 90 and 270 specified, these are always computed as being equal, even when the corneal eccentricities in these quadrants differ).

Michael

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Re: Quadrant specific e-values
« Reply #3 on: January 17, 2014, 09:17:39 am »
Hi,

I have confirmed that you are right, we are averaging the e-values across the chord. From what I can work out this is because these e-values are generally being used for fitting quadrant symmetric lens which use averaging in opposing quadrants to get the best possible fit.

Can I ask, are you calculating height from the E values or just using the height values provided by the software?

And are you fitting a QUAD type lens with different geometry in all 4 (or more) regions? If so you may want to talk to us about getting your contact lens design into our software with a dedicated designer to assist your simulated fittings.
Senior Software Engineer
Medmont Pty. Ltd.

poepol

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Re: Quadrant specific e-values
« Reply #4 on: January 22, 2014, 10:46:09 pm »
Hi Michael

I use heights as given by the software.

Quadrant-specific e-values are helpful in fitting quadrant-specific lenses, as in certain cases of ectasia where for example the e-value at 90 is higher than at 270 and both are different from 0 and 180.

Falco of Switzerland lenses are used (eg their FKQ lens).