Blocking Prism lenses for Edging

[farrukhk]

I need help in blocking prism lenses for edging. I have a prescription with OD 1.50 Base up and OS 1.50 Base down. Theses lenses were done by the surfacing lab and I have to block it for edging. What is the right way to block prism lenses.

[Don Gilman]

I need help in blocking prism lenses for edging. I have a prescription with OD 1.50 Base up and OS 1.50 Base down. Theses lenses were done by the surfacing lab and I have to block it for edging. What is the right way to block prism lenses.

Since you have had no replies I would guess no one really understands the question. Me either. It seems obvious OD thick edge up OS thick edge down.

[MakeOptics]

I need help in blocking prism lenses for edging. I have a prescription with OD 1.50 Base up and OS 1.50 Base down. Theses lenses were done by the surfacing lab and I have to block it for edging. What is the right way to block prism lenses.

OD - 0.25 to 0.5mm lower
OS - 0.25 to 0.5mm higher
(Block offset towards the base, explanation below)

TL;DR

The blockers demarcation lines are going to be displaced when viewing in the case of lined multifocal's it's more apparent, what happens is you block the lens up and they look good, then you edge them the seg heights are off. The amount of displacement will vary depending on your blocker and the lens from the blocking plate. The santinelli manual blockers have a bulbous lens on the blocker that helps the blocker reach up and remove some of that distance from the back vertex of the lens from the plate. For three diopters total I would displace about 0.5mm total if I didn't know your machine and was blocking for the first time. If you are looking for directions keep in mind that the image you see is displaced towards the apex or thin lens substance, so if you try to block it spot on your height will come out too high so block it lower.

[Dbanks]

I find it much easier to spot the prism in the lenses, thus creating a new MRP then block as usual.