How to have "thin" lens in plus power?

**Reylynn** · 05-04-2010, 01:20 AM

Here are the parameters of the prescription:

OD +7.50/-2.50 X 80
OS +3.00/-2.00 X 90
PD 64/62

Full metal frame
Eye size : 48mm
Bridge : 18mm
Longest axes : 50mm

What dia. of lens shld. be order?
Does "precal" works in this one?

**Yeap** · 05-04-2010, 04:17 AM

i'm not an expert in lenses but i think you may consider using high index and full rim frame so the side thickness can be made to then minimum.

hope it helps..

**Reylynn** · 05-04-2010, 05:29 AM

Thanks for the reply Yeap! I already ordered 1.67 index but the patient is not satisfied with the thickness,that's why I need to reorder. Does anyone knows how to calculate the effective diameter of the lens that I shld. order? Or any brand you can suggest?

**For-Life** · 05-04-2010, 06:16 AM

In addition
- Use a round frame, as it will limit the ED length.
- Try to match the frame PD as close as possible to the person's PD.
- Order the lenses with a knife edge. Sometimes a lab will just give you a 2mm edge. Unacceptable. They should be able to order the lens to be surfaced for that frame.
- Get an aspheric lens

**cocoisland58** · 05-04-2010, 06:19 AM

Can you just have your lab surface the lens as thin as possible using whatever they feel would give the best finished product?

**Diane** · 05-04-2010, 06:41 AM

Order thinnest material designed in aspheric.

Diane

**AngeHamm** · 05-04-2010, 08:56 AM

Yes. Good stuff here.

Thin material, 1.67 or 1.74 hyper high index, aspheric lens. A/R, of course. Small eye size, with a frame PD as close to the patient's PD as possible. Plastic frame to conceal edge and mount the lenses firmly. Ask the lab for a knife-edge.

But your patient needs to accept the fact that she has a high power in that right eye, and physics is physics. It takes a lot of lens to refract with that amount of power. I'm a -8.75 total power in my left eye and I don't complain about it; I just wear a small frame, a dense lens and a big smile. Most of my 23 frames are small plastics (an embarrassing number of Prodesign), and I have no visible edge thickness in them.

Your patient should be encouraged to select a frame so awesome that it makes her friends jealous of her prescription.

**shanbaum** · 05-04-2010, 10:02 AM

I don't know what the custom is in Dubai, but in much of the world, lenses are ordered uncut from surfacing labs, with only the required blank size specified on the order. While it's easy to do a rough approximation of minimum blank size, it's non-trivial to do a precise one, and if the only information the lab has is the required uncut diameter, the finished thickness (after edging) is going to be approximate in any case.

This Rx is a near-worst-case example. Even if you order a 52mm round lens (the approximate minimum), because the meridia of highest plus powers in the two lenses are both vertical, chances are good, unless the shape is quite round (so that the A and B are similar), that you'll get a thicker edge than necessary - largely because the B dimension may not be provided, and might be substantially less than the A.

"Precal" provides more information - usually, the A and B dimensions, and either selection from a group of standard shapes, or a drawing of the subject shape. The latter is the next best thing to a tracing, and either should provide a substantially better result than merely indicating needed diameter.

**Reylynn** · 05-04-2010, 01:11 PM

That was very helpful Sir! (Mr.Shanbaum)Thank you. I fully understand what you said. But just for your info. also,here in Dubai...the manufacturer of lenses have the blanks and semi-finished lenses as well. I will try to let the patient change the frame into more roundish one,so it will come out nice thickness. Thanks!

**DragonLensmanWV** · 05-04-2010, 01:22 PM

Yes, that will help to get a rounder frame. Your decentration on the old pair is good, fortunately they have a fairly wide PD, and your sizes indicate only one mm decentration. But if the frame is a narrow "B" rectangle, even only one mm decentration will not make the lenses look optimum.

**shanbaum** · 05-06-2010, 07:38 AM

Originally Posted by Reylynn

That was very helpful Sir! (Mr.Shanbaum)Thank you. I fully understand what you said. But just for your info. also,here in Dubai...the manufacturer of lenses have the blanks and semi-finished lenses as well. I will try to let the patient change the frame into more roundish one,so it will come out nice thickness. Thanks!

A more round frame in this case is not necessarily the best choice (in terms of minimizing thickness); the best choice will be the frame with the smallest practical "B" measurement.

**Speed** · 05-06-2010, 07:46 AM

Originally Posted by shanbaum

A more round frame in this case is not necessarily the best choice (in terms of minimizing thickness); the best choice will be the frame with the smallest practical "B" measurement.

Nope. Round is better because when you cut down the B you are exposing the thicker part of the lens. Small, round, with as little dec as possible.

**shanbaum** · 05-06-2010, 07:50 AM

Originally Posted by Speed

Nope. Round is better because when you cut down the B you are exposing the thicker part of the lens. Small, round, with as little dec as possible.

Nope, with a smaller B, you will be able to make that section of the lens thinner. There's a two-diopter difference here. I suppose "smallest" may be an overstatement; ideally, you would want a difference between the lateral and vertical dimensions that would result in the same thickness laterally and vertically, and that will not be round.

You're correct about decentration (again, both laterally and vertically).

**Speed** · 05-06-2010, 09:03 AM

I supose you are accounting for the cylinder power at the 90. I guess round is not best. Due to the 90 axis you could cut a bit into the B, but not too much. Just enough to take advantage of the cylinder power.

**shanbaum** · 05-06-2010, 09:27 AM

Something in the vicinity of 48 X 39 would be about right.

**Fezz** · 05-06-2010, 09:57 AM

I'll step in for my missing friend, Chip, and suggest a well fit contact lens for this patient!

**LENNY** · 05-06-2010, 07:20 PM

Originally Posted by shanbaum

Nope, with a smaller B, you will be able to make that section of the lens thinner. There's a two-diopter difference here. I suppose "smallest" may be an overstatement; ideally, you would want a difference between the lateral and vertical dimensions that would result in the same thickness laterally and vertically, and that will not be round.

You're correct about decentration (again, both laterally and vertically).

I would not question this guy!

**LENNY** · 05-06-2010, 07:22 PM

For some of my nuttiest patients that only care how thin the lens feels we drop the oc 3-4 mm down. That makes the top much thinner when they look at the job and touch it with their fingers! Comon most of the time they cant even see good without glasses on +7.00 RX!

**Wes** · 05-06-2010, 08:30 PM

Originally Posted by shanbaum

A more round frame in this case is not necessarily the best choice (in terms of minimizing thickness); the best choice will be the frame with the smallest practical "B" measurement.

Originally Posted by shanbaum

Nope, with a smaller B, you will be able to make that section of the lens thinner. There's a two-diopter difference here. I suppose "smallest" may be an overstatement; ideally, you would want a difference between the lateral and vertical dimensions that would result in the same thickness laterally and vertically, and that will not be round.

You're correct about decentration (again, both laterally and vertically).

Originally Posted by shanbaum

Something in the vicinity of 48 X 39 would be about right.

Originally Posted by Fezz

I'll step in for my missing friend, Chip, and suggest a well fit contact lens for this patient!

As someone who often edges over a thousand pair of lenses per day, I can confirm that Shanbaum is spot on in his assessment. Also, Fezz is correct of course.