Near Vision Prism Question

[bob_f_aboc]

Had a pt just pick up today. LASIK 7 years ago, monovision correction no longer working like it used to. Ordered FT28 Trivex, Rx: OD -.25 DS, OS -1.75 DS, Add +2.25 OU. Frame B=27 seg=12 OC=15.

When she put them on the distance was great, but she was complaining of double vision at near. I think I figured the prism at near correctly at ~1^ imbalance (OC 3mm above seg, allowing for 7mm drop to read). Is this normally an adaptable amount of imbalance at near?

[drk]

I don't get freaked until 2.0^ imbalance, but you're at 1.50 to 1.0^.

One negative factor is that her iatrogenic anisometropia was sudden onset vs. natural.

Believe me, offsetting surgical monvision is a biyatch. I universally undercorrect to leave no more than 1D imbalance, and patients generally see the glass half-full.

If she can't dig her specs in 1 week, to save a two lens remake consider remaking OS to about -1.00 /+2.25 add.

[bob_f_aboc]

She had the LASIK done in sunny California about 7 years ago and doesn't remember the name of the surgeon who did it. We were trying to get some records before LASIK but couldn't. I guess I don't have anywhere to send the thank you card. :angry:

Thanks Doc.

Bob

[DragonLensmanWV]

I am not a fan of monivision LASIK or post-cataract. You usually end up with glasses anyway and then you frequently need different base curves.
My sister-in-law got monovision LASIK eight years ago and one of the first things I had to do was make her a pair of reading glasses with largely different powers amd she complained of image size differential.

Boy, if she could see through my glasses now.:D
Is there a way to calculate image size say, relative to a -1.50 -1.00 and a -14.75-2.00?;)
My own estimate is image size is about 35% smaller through the higher minus.

[optical24/7]

.

Boy, if she could see through my glasses now.:D
Is there a way to calculate image size say, relative to a -1.50 -1.00 and a -14.75-2.00?;)
My own estimate is image size is about 35% smaller through the higher minus.

Assuming you have an OU axis of 180, with 2.2mm c.t.'s, 4 base OD 1 base OS 1.6 index and 13.5 vertex you've got a 15% difference in minification.

Now if you made yourself some iseikonics....
OD 1.5 ct (mm)
OS 30.0 (mm)

OD 2 base
OS 10 base

1.6 index OU

and 13.5 vertex , You could cut it down to 4.43% difference.


* note; that would be one funky lookin' pair of glasses!

:cheers:

[DragonLensmanWV]

Assuming you have an OU axis of 180, with 2.2mm c.t.'s, 4 base OD 1 base OS 1.6 index and 13.5 vertex you've got a 15% difference in minification.

Now if you made yourself some iseikonics....
OD 1.5 ct (mm)
OS 30.0 (mm)

OD 2 base
OS 10 base

1.6 index OU

and 13.5 vertex , You could cut it down to 4.43% difference.


* note; that would be one funky lookin' pair of glasses!

:cheers:

They're already funky.
OD -14.75 -2.00 X 20 1.70 index 1.5 CT
OS -1.50 -1.00 X 150 1.557 index CT 2.0

Tried using a plano in the OD today, as with my patching of the OS, I'm starting to see the OS get a bit lazy and getting hard to fuse. The OD is so blurry with the plano, I can hardly tell there's an eye there and switch easily to the non-dominant eye to see. Otherwise if I patch the dominant OD, I get headaches after a busy day using only the OS. Not mention (oh, wait I just did!) the damaged area left of center in the OS due to optic neuritis.