OC heights on SV?

[Paul Smith LDO]

Well said, drk. I like to stay consistent with all of my measuring techniques for all of my patients, for optimum results. With that being said, how would you fit a BFF, who happens to be a BBW, drives a BMW, but doesn't like the PAL nor a FT.

[Hayde]

You gotta keep things simple and consistent!
1. Split distance pds with pupillometer for everyone
2. Dot the pupil with a marker for everyone.

This gives you the position of the eye in the lens, then you can do with it whatever you want...fit a BF. Fit a PAL. Fit SV. Whatever.

drk, monocular OCs no matter what? Ok to not to worry about eyes that are already accustomed to minute grades of yoked vertical prism?

(Also, I'm not sure I'm construing you correctly on 1. By 'split' you mean use monocular values---not halve the total distance PD, right?)

Thank you : )

[Uncle Fester]

Well said, drk. I like to stay consistent with all of my measuring techniques for all of my patients, for optimum results. With that being said, how would you fit a BFF, who happens to be a BBW, drives a BMW, but doesn't like the PAL nor a FT.

In layers of dark flowing fabric, colorful scarf and a large shoulder bag (Jimmy Choo) as an accessory with MF contacts.

[Paul Smith LDO]

In layers of dark flowing fabric, colorful scarf and a large shoulder bag (Jimmy Choo) as an accessory with MF contacts.

Oh yeah, you had me at, "flowing fabric"

[drk]

drk, monocular OCs no matter what? Ok to not to worry about eyes that are already accustomed to minute grades of yoked vertical prism?

(Also, I'm not sure I'm construing you correctly on 1. By 'split' you mean use monocular values---not halve the total distance PD, right?)

Thank you : )

We do specify, whether it matters or not on a specific case. Just for uniformity in procedure. But occasionally it will save our butts.

(Yes, monocular p.d.'s. Sorry.)

[drk]

Well said, drk. I like to stay consistent with all of my measuring techniques for all of my patients, for optimum results. With that being said, how would you fit a BFF, who happens to be a BBW, drives a BMW, but doesn't like the PAL nor a FT.

Yeah, you'd then have to use TLC.

[Paul Smith LDO]

Yeah, you'd then have to use TLC.

TLC, got it. I live in Seattle, can I substitute with THC.

[drk]

TLC, got it. I live in Seattle, can I substitute with THC.

Tee-hee.

[Hayde]

Here is what happens if we don't get the eye's center of rotation/panto relationship right.

Martin's formula for tilt

S'= S{1+(sin a)^2/(2n)}
C'= S'(tan a)^2

S sph power
S' new power
a tilt
n index of refraction
C' induced cyl
Axis is 180 and the sign is equal to the sphere power

Rx is -10.00DS, panto 15 degrees, Trivex, 180 line bisects the pupil. I see this happen on a fairly frequent basis, usually with a narrow frame that sits too high.

Using the above formula, the power that the eye sees is -10.22 -.73 x 180.

To eliminate this error, the OC needs to be lowered 7.5mm (1mm per two degrees of tilt). The best way to do this is to pick a frame that puts the 180 line about 5mm below the pupil, and reduce the panto 5 degrees or lower the OC to 2.5mm below the 180. If a high dispersion lens is used, one might want to reduce the panto so that the OC can be closer the pupil, reducing chromatic aberration on the distance gaze.

So this thread has motivated me to do an experiment to track potential tilt distortion! Working on my spreadsheet and have oblique cylinder cacluations verified. But this equation is giving me fits, Robert. Can someone spot what I'm doing wrong?

I've parsed out components of the calculation so I can try to spot the goofiness at a glance.

box E7 is my tilt input, so...

(Good ol' VB wants Radians, so) h7: =radians(e7)
(Then the sin function works) h8: =sin(h7)
(square it!) h9: =(h8)^2

all accurate so far.

box q2 has my 90-degree oblique power calculation from (F'=F+FCyl(sin(Theta)^2) which checks out fine.
index of refraction input is e8, so

(wrapping up the spherical calculation in a bow): e9=q2*(1+h9)/(2*e8)

q2 Power on the 90 (for 10.00 DS): 10.00
e7 Tilt: 15
e8 Index of Refraction: 1.53

e9 New Spherical Power is giving me: -3.49. Walked through it with a calculator and get the same thing. There's something I'm misunderstanding about the equation, or we have a typo.

Thanks for your help!

[Robert Martellaro]

Here's the formula with the numbers punched in. I thought I had the notation pretty much cleaned up, but maybe not.

sin a = .259 squared = .067 / 3.06 = .022 +1 = 1.022

New sphere power = 10.00 x 1.022 = 10.22 DS

tan a = .0268 squared = .072 +1 = 1.072

New cyl power = 10.00 x 1.072 = .72 DC

[Hayde]

Thank you Robert, the error was mine.

I tried to include the "1+" in the numerator along with the trig term.

Much obliged!

edit:
e9 should really = q2*(1+h9/(2*e8))

[Robert Martellaro]

Your welcome.

Check out this tool...

http://www.opticampus.com/tools/tilt.php

Note the discrepancy in the compensation. The basic formula above ignores lens form, resulting in error with ophthalmic lenses.

[Oculista Carioca]

Usually all jobs around the (+/-4) range and/or if the pupil is not centered directly in the middle of the frame. I also measure it if vertical prism is involved as the lab ought to know where the actual eye is corresponding to where the prism is going to start.