Monocular PD's

[curtains1]

Hello,
How does a tablet and a frame stickactually take monocular pupil distances without the occlusion of oneeye at a time? Instead using a prism over one eye with the framestick. What about phorias or a tropias? Can I get a technical explanation?
Thank you

[Kwill212]

The prism over one eye is for measuring vertex. Occluding one eye at a time of the patient would be for strabismic patients. Patients without eye deviations shouldn't need occlusion when measuring PD. If they are going to have both eyes open when usuing the glasses, they need both eyes open during the measurements. Phorias I don't think are too much of a concern. Tropias are going to have to be treated on a case by case basis and may need occlusion and more manual measurement techniques depending on the situation. Is one eye always turned to a specific place? Does it move to a "normal" position when alternating vision? What were their previous glasses like, and did they like them? Things like that need to be considered.

I think what you meant to ask was how does the software measure distance PD while at a near distance, without having the subject shift focus from one of the providers closed eyes to the other? I don't know exactly. I would have to assume there is something built into the software to account for the convergence needed for the distance that the picture is taken.

[curtains1]

Well, yes, I guess I am curious about how it works. I know the light reflex is being used, obviously. I am guessing the frame stick reflects light at specific points to provide panto, and wrap. I am wondering more specifically as to how accurate is would be for patients with strabismus/deviation, when the eye will rotate back into place when the other is occluded. If the eye is always turned out of place, wouldn't that be just a balanced lens anyway? As far as distance and near pds, yes I don't know how it compensates, and don't you have to adjust for the power of the addition if it is a multifocal, or set of reading glasses anyway? The soft wear I use does not have the RX input.
Thanks for your reply!

[drk]

Just because a patient is strabismic, they don't get a balance lens. Peripheral optics matter.

Balance lenses are usually for patients that are "NLP" or "no light perception". Peripheral optics matter.

As to whether one should have an optical center aligned with a deviated eye: No. If the eye is deviating (unless there's a rare anomalous retinal correspondence, in which case the doctor should be keen enough to tell you, if he even knows what it is in the first place) the central vision is being suppressed, anyway, so don't worry about unintended prism or off-axis blur.