Correcting esotropia by inducing prism

[ilanh]

I have an elderly patient with +3.50 OU. She has about 12 PD Esotropia at near and distance and is now slightly diplopic. I was thinking of prescribing glasses with induced base out prisms to correct the esotropia. I estimate that about 1.5mm decentration outward in each eye would help. This would imply increasing her PD by roughly 3mm. The strange thing is that her current glasses already have a PD which is 3 mm greater than what I am measuring her with a pupillometer. The optical centers of her current glasses are 64 (32/32) and the pupillometer readings are 61 (30.5/30.5). This implies that her current glasses are already doing what I was planning on doing for her (unless I'm misunderstanding). Any other suggestions?

[chip anderson]

Try whatever you want to do in a Fresnel Paster first. If this works, grind in. You will save yourself a lot of re-grinding this way.

Chip

[LENNY]

I bet you its a pretty large frame!

[ilanh]

Sorry, I think I mis-stated the case. If I decenter the lenses by 1mm I will only induce 0.33 diopter of prism in this patient. I wanted to induce about 4 diopters so I would need to decenter by a total of 12mm (6mm in each eye). I think this would be excessive and may tone it down to 4mm each eye.

[Ory]

You state she is esotropic. Is this longstanding esotropia or a phoria that is decompensating? Can you make her non-strabismic with prism, or are you simply trying to move her suppression scotoma to eliminate diplopia?

[ilanh]

It's the first time I'm seeing this patient but she complains that she has had this for over a year. When I put 4PD BO prism on her trial frames she felt that it was better. That's why I thought that with such a small amount of horizontal prism I would be able to achieve that with decentration.

IH

[ilanh]

Try whatever you want to do in a Fresnel Paster first. If this works, grind in. You will save yourself a lot of re-grinding this way.

Chip

Thanks Chip,
I've heard this before but for some reason Fresnel prisms have never worked for me. The patients always seem to complain that the blur induced by the plastic overwhelms their ability to judge the improvement (or lack thereof) of the diplopia.

[standarduck]

Sorry, I think I mis-stated the case. If I decenter the lenses by 1mm I will only induce 0.33 diopter of prism in this patient. I wanted to induce about 4 diopters so I would need to decenter by a total of 12mm (6mm in each eye). I think this would be excessive and may tone it down to 4mm each eye.

It wouldn't be excessive if you wanted to give 4BO though, would it? If you reduce to 4mm each eye, you'll giving less than 3. Obviously that might help, but you're best positioned to know if that's enough.

[braheem24]

If she can still read, it's not too much.