Slab Off Lenses

Scraps of Fresnel’s prisms in lower powers on underneath half a plano trial lens also works well in trial framing a patient. I know from old rules I learned that any 2-3 D difference slab off would be prescribed.
This is undoubtedly why so many patients with high anisometropia appear to function nicely without iseikonic lenses. When to improve varies between doctors almost all of the MD’s in this area say between 2 & 3D of imbalance is when to start out. Some OD’s and old schoolers start at 1.5D (because years back we couldn’t slab not glass and to do so was a fete.) Today reverse slab in plastic can take us to .75 in a few lens designs. How sensitive a patient is to image is an individual thing. This is mostly because of differences of widths in Panum’s area of the brain. That’s where our all of our senses and learned visual clues are encoded.

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Contact lenses tend to be more stationary on the eye, moving with it in order that prismatic effect is almost nonexistent. Our specialty lens offering includes double D segment bifocal lenses in +4, +6 and +8 base curves with add combinations of either 60% or 100%. You can expect hi-add bifocal lenses having an add of up to +8.00. Reverse slab-off lenses are available with prism up to 6.00 diopters. We continue to offer our Seamless 28 lens and also FT 28’s and FT 35’s and our FT 45 “Multiseg 45”. Round segment 22 & 40 lenses may also be available with adds up to +4.00.

How Will You Know In Case A Slab Is Prism?

If the prism is 2 or more vertical, then a slab off grind may apply. This is just a rule of thumb, you can find other circumstances which come into play that the ECP may decide not to use the slab off. Some have significantly more demanding visual needs than others, while some have requirements not met with today’s traditional lenses. Not only do we give the ECP more options to pick from, we also make an effort to ensure it is easier for the Prescription laboratory to fill that prescription.

Because reverse slab-off provides BD prism rather than BU it is usually used on the most plus, or least minus lens in the vertical meridian to offset excessive BU induced by its partner. A slab off is normally recommended once the difference in needed lens power causes problems because of the different prismatic effects. Those effects enter into play when the wearer of bifocal lenses or progressives perform eye movements up down, for example, to switch from distance vision into the reading distance. If the lens powers will be the same for the two 2 eyes, the displacement of each may be the same (Figs 4-27, 4-28).

What Does Slab Off Correct?

The average indivdual can adapt to a large prism imbalance. I would however choose the base curve and thickness in order that image sizes between both lenses were closer to agreement.

• In our state, it is considered a recommendation and I’d not tell the individual one way or the other.
• help you determine the volume of correction necessary for any prescription.
• In addition, the wider the bifocal used, the less noticeable the slab line will undoubtedly be.
• Working in a ophthalmological setting, I have the benefit of reading the patients chart and obtaining more info including visual acuity.

First off, I would never outright ignore any element of a prescription written down on that legal little bit of paper signed by the prescribing doctor. I would make a telephone call to the prescribing doctor to discuss the slab off and see what his/her thought processes were once the slab off was prescribed. Usually the lab will comp one redo, so that should not be a concern. It is important to be transparent when dealing with patients/consumers! Not disclosing information to patients can bite you in the butt.
a patient visually, I can’t justify the trouble and I don’t sell it in their mind. A slab-off lens is made utilizing a procedure called bi-centric grinding. After the front surface of the lens is finished in the most common manner, a dummy, or cover lens manufactured to match the bottom curve of the required lens is then cemented onto the front surface.

By increasing the distance between your 2 optical centers, this method achieves just as much as 4.00∆ of prism compensation at the reading position. To improve this diplopia, a form of lens fabrication called bicentric grinding, or slab off is used. Slab-off is a technique in which the base-up prism is ground on half the lens in either the most minus or least plus lens. The finished product looks as if a “slab” or portion of the lens has been removed, hence the name slab-off..