OK, here I go again...

[drk]

Had another episode of a recurrent problem with yet another patient. I doubt it's my pupillometer, but I'm open to anything...

Patient returns after dispensing of his first progressive,Complaint: OS near vision blurry unless turns head to right (has to look nasally). Distance vision has same effect, although less. OD is "perfect".

Rx: -0.25-0.75x163/ -0.25-1.75x 177, +0.75 add OU. PD is 29.5/29.5. Fit in Panamics. Refraction was double-checked, as was PD measurement and placement of fitting cross. The lenses were not rotated in the frame. The adjustment was as correct as adjustments get.

As I sometimes do, I viewed a vertical line (doorframe) while looking through the lens, and shook the lens to visualize the increased skew when the peripheral astigmatism was encountered in the near portion, but with the low add I couldn't outline the corridor and near portion as well as with a higher add.

Instead, I drew a "vertical" line down the lens along the image of the visualized doorframe in order to find the "optical center-line" of the corridor and near portion and distance portion (not unlike what used to be done to visualize the OC of an exec.) What I found is that the asymptomatic eye had a pretty much vertical, not inset, line from top to bottom of the lens. The symptomatic eye's lens had a line that tilted nasally, from top to bottom, as you would expect for an inset corridor and near portion.

Despite what looks more reasonable on the symptomatic left side, I concluded that somehow the lens has more inset than the patient needs, and reordered with 1.5 mm less inset.

Questions:
1.) What does my method really prove? Nothing?
2.) Can the inset be wrong on one eye? I know the OS Rx is different, and that the French like their segs inset more than we'd expect.
3.) Is the right lens the "wrong" lens, and he just prefers it?

Help, if you can!

[hcjilson]

My guess is that its #3. He prefers it. Had a very similar situation develop this afternoon and we'll have to wait to see if he adapts.I can hardly wait for Monday AM.

[Jason Carruthers]

OS cyl is the culprit. Patient instruction should be "get used to it."

[drk]

Jason,

I can believe that the near portion and corridor are narrower with more cylinder, but why not centered properly?

[Jason Carruthers]

It may or may not be centered. As a rule, when patient can perceive error that is unmeasurable by practitioner, it's because patient is hypersensitive, new presbyope. The human mind is not a perfect interpreter of ocular signals.

[Robert Martellaro]

DrK,

Here's my theory. The VA should be reduced in the left eye on the downgaze (or off-axis in general) due to induced oblique astigmatism. Turning the head induces another cylinder and axis that may be neutralizing the above. Possible remedies might be using a flatter BC or better still an atoric lens like the Definity.

Client is probably RT eye dominant so just tell him/her to use both eyes and stop testing the lens by covering one eye. Or Rx distance only and wait another year or two before trying multifocals.

Regards

[drk]

DrK,

Here's my theory. The VA should be reduced in the left eye on the downgaze (or off-axis in general) due to induced oblique astigmatism. Turning the head induces another cylinder and axis that may be neutralizing the above. Possible remedies might be using a flatter BC or better still an atoric lens like the Definity.

Client is probably RT eye dominant so just tell him/her to use both eyes and stop testing the lens by covering one eye. Or Rx distance only and wait another year or two before trying multifocals.

Regards

That's a sophisticated theory. Let's see if I understand: induced oblique astigmatism on downgaze from vertex distance. Serendipitous correcting cylinder in inferior periphery of lens. I'll buy it.

The guy feels binocular symptoms with the lenses, in this case, so I can't weasel out.

Distance only is probably going to be the option.

Thanks for your suggestions.

[ken@foothills]

I agree with the oblique explanation, the edge of the bifocal is more defined, however when ever I measure a half or as stated 29.5, I always go up to the whole number or 30. And I do that because if I am going to have someone complain about noticing the edge of the bifocal its always temporal not nasally.

[drk]

Well, the guy picked up tonight. My solution on the remake was a rather "stab in the dark" decentration outwards by 1.5 mm, to try to alleviate the symptom. He said initially it was better, but we'll see. Hardly scientific, but...

[spartus]

This is starting to sound remarkably familiar. I had a patient a few months back that complained of precisely the same things. The RXs are even very close, apart from the add power. Before I got to him, much like your case, they fiddled with PD, changed lenses, base curves, segs--everything you could think of. I came on it late in the process, and all he needed was a +0.25 bump in total lens power in the offending (offended?) eye.

What I did was have him put on the glasses and hold a +0.25 monocular lorgnette in front of his left eye. He blinked twice and said, "You're smart." Funny guy.

In your case, if it doesn't fix his problem, well, you're back at square one. :)