Which material appropriate for +15.00

[ilanh]

I have a patient who is approx +15.00-2.00x180. I called my VSP lab to see if this could be done in 1.74 or polythin but was told that it could only done in cr39 with aspheric and a lenticle. The patient is not aphakic but I imagine that this type of prescription must have been very common about 20 years ago with intracapsular cataract surgery and aphakic patients. Any ideas? She also wears RGP lenses which are working fine.

[DragonLensmanWV]

I have a patient who is approx +15.00-2.00x180. I called my VSP lab to see if this could be done in 1.74 or polythin but was told that it could only done in cr39 with aspheric and a lenticle. The patient is not aphakic but I imagine that this type of prescription must have been very common about 20 years ago with intracapsular cataract surgery and aphakic patients. Any ideas? She also wears RGP lenses which are working fine.

You need Essilor Super Modular Aspheric or Signet-Armorlite Hyper-aspheric lenses, only available in cr-39.

[gemstone]

The super modular would be the thinnest.

[obxeyeguy]

The super modular would be the thinnest.

My gosh, I can't tell how long its been since using that lens. It obviosly is still available. It will work fine doc.

[gemstone]

My gosh, I can't tell how long its been since using that lens. It obviosly is still available. It will work fine doc.

They discontinued it once for that reason. Not much market. I was so glad when they brought it back. Semi finished high index is difficult to make in high bases.

[obxeyeguy]

Hey Doc, a great candidate for corrective cataract surgery, but that a whole diff thread.

[Fezz]

I would suggest calling Allen at Ice-Tech or Mike Walach at Quest Optical labs. Both are Optiboarders, and they should be able to help you.


Mike= http://www.questopticallab.com/

Allen= http://www.ice-tech.com/

Good luck!!!!!

[HarryChiling]

The average transmission through a lens is given by:

Tavg = [(4*n)/(1+n)^2]^2/[1-(((1-n)/(1+n))^2)^2]
Tavg = [(4*1.74)/(1+1.74)^2]^2/[1-(((1-1.74)/(1+1.74))^2)^2]
Tavg = (6.96/7.51)^2/0.99
Tavg = 0.87

So the average transmission through a 1.74 lens is 87%, fine right, but a minus lens and a plus lens have one difference that makes it a problem and that is thickness for a +15.00 lens in lets say a 50mm lens the average thickness is going to be:

Sag = [D*(d/2)^2]/[2000(n-1)]
Sag = [15*(25)^2]/1480
Sag = 9375/1480
Sag = 6.33

Now transmission through a thick lens is:

It = Ie*(T)^q
It = 100*(0.87)^3.17
It = 100*0.64
It = 64

Now it's pretty easy to see why these really high plus lenses are often done in a plastic rather than a higher index material. In the case of a 1.74 the transmission of light through the lens is 64%, now imagine that same lens in a dim lit room.

[MarcE]

Now transmission through a thick lens is:

It = Ie*(T)^q
It = 100*(0.87)^3.17
It = 100*0.64
It = 64

Now it's pretty easy to see why these really high plus lenses are often done in a plastic rather than a higher index material. In the case of a 1.74 the transmission of light through the lens is 64%, now imagine that same lens in a dim lit room.

What is 'q'?
But on the other hand, doesn't this high plus lens focus light on the retina, making things look brighter, with a shawdow around it? Right?

Didn't they make these high plus hyper-aspheric lenses in 1.54-1.57? It seems that would help the thickness a bit w/o sacrificing optical quality. or light transmission.

[HarryChiling]

The equation is written that way at www.technicalopticians.org so I copied it over, but q is 1/2 the thickness in mm, since transmission is measured for every 2mm.

[Dougfir8]

We use 5-10 pairs of Aspheric lenticular and/or hyper aspherics and/or supermods per week. The sad thing is the doctor so often asks for hi-index or poly, and we always have to call and say, "Sorry". They often need to go from a FT-28 in a lighter material to a FT-22 or Round 22 in CR39.

[Laurie]

Hi,

Yes, the loss of light in higher index is greater, (as per calculations), however, adding AR is a simple step to regain the loss of light.

It is better to have high index, as long as you add AR as well.

: )

Laurie

[Robert Martellaro]

I have a patient who is approx +15.00-2.00x180. I called my VSP lab to see if this could be done in 1.74 or polythin but was told that it could only done in cr39 with aspheric and a lenticle. The patient is not aphakic but I imagine that this type of prescription must have been very common about 20 years ago with intracapsular cataract surgery and aphakic patients. Any ideas? She also wears RGP lenses which are working fine.

Aire-O-Lite and Bristol also have lenses that will work well. You'll need at least a true +15.00 to +15.50BC. Another possibility is a 1.67 high index lens with the back ground with a plus curve (saddleback). The lenses would look much thinner, although the vision off-axis would be very poor. Remember to adjust the powers for vertex distance as needed, fit close to the eyes, decentration less than 3mm, as round and symmetric of a frame as possible, and a vertical OC 1mm below the pupil center per every two degrees of Panto, eg; Panto of 10 degrees requires a vertical OC 5mm below central pupil, and would be best to get this primarily from frame position instead of decentration.

[HarryChiling]

Hi,

Yes, the loss of light in higher index is greater, (as per calculations), however, adding AR is a simple step to regain the loss of light.

It is better to have high index, as long as you add AR as well.

: )

Laurie

Laurie,

In this case the loss of light is due to absorbtion if I am correct, although AR would help I don't think it would be enough. Water for instance is clear, however you can't look at the bottom of the ocean even if you were to get AR on water.

[Michael Walach]

QUEST OPTICAL SPECIALTY LAB can make this lens in any index, lenticular, SV or FT28. Pertaing to your concern about transmitance--AR it. Longtitudinal abberation you will have to live with. Perhaps 1.55 index material with higher coeficient of chromatic abberation would be a better choice.

Michael Walach,
QUEST LAB
www.questopticallab.com

[HarryChiling]

QUEST OPTICAL SPECIALTY LAB can make this lens in any index, lenticular, SV or FT28. Pertaing to your concern about transmitance--AR it. Longtitudinal abberation you will have to live with. Perhaps 1.55 index material with higher coeficient of chromatic abberation would be a better choice.

Michael Walach,
QUEST LAB
www.questopticallab.com

I would agree with both AR and a 1.55, but wouldn't suggest an index any higher. Mike good to see a post from you guys Quest Lab has a great rep and I am sure you guys could do this type of lens no prob. I thought you guys were the labs lab, do you open up accounts direct with ECP's too?

[ayoco]

Bristolite-BCD
Availability


Material/Style
Design
Bases
Additions
Diameter
Power Range


Poly-B


Polycarbonate Aspheric SV HC
SV
4,6,8,
na
73
+1.00 to +8.00
10
na
70
+6.00 to +10.00
12
na
70
+8.00 to +12.00
Polycarbonate Aspheric FT HC
FT28
6
1.50-3.00
73
+1.00 to +6.00
10.50
2.00-3.50&4.00
70
+6.00 to +10.50
12.75
2.00-3.50&4.00
70
+10.50 to + 12.75








Bristolite



Hard Resin Aspheric SV
SV
2,4
na
75
+1.00 to +4.00
6,8
na
75
+1.00 to +8.00
10
na
75
+4.00 to +10.00
12
na
70
+6.00 to +12.00
14
na
70
+10.00 to +14.00
16
na
65
+12.00 to +16.00
Hard Resin Aspheric FT
FT28
4,6,8
1.00-3.50&4.00
75
+1.00 to +6.00
10
1.50-3.50&4.00
75
+6.00 to +10.00
12
1.75-3.50&4.00
70
+10.00 to +12.00
14
1.75-3.50&4.00
70
+10.00 to +14.00
Hard Resin Aspheric FT
FT35
6,8
1.00-3.50&4.00
75
+1.00 to +8.00
10
1.00-3.50&4.00
75
+6.00 to +10.00
12
1.00-3.50&4.00
70
+8.00 to +12.00
Hard Resin Aspheric Trifocal
7x28
6,8
1.75-3.50&4.00
75
+1.00 to +8.00
10
1.75-3.50&4.00
75
+6.00 to +10.00
12
1.75-3.50&4.00
70
+8.00 to +12.00
Hard Resin Aspheric Trifocal
9x35
8
1.75-3.50&4.00
75
+4.00 to +8.00
12
1.75-3.50&4.00
75
+8.00 to +12.00
Hard Resin Aspheric Invisable Trifocal
8x30
6
2.00-3.00&3.50&4.00
75
+1.00 to +6.00



BCD



Hard Resin Aspheric 5 Drop SV
SV
10,12
na
65
+6.00 to +12.00
14
na
65
+10.00 to +14.00
Hard Resin Aspheric 5 Drop Round Seg
R22
10,12
2.00-3.00&3.50&4.00
65
+6.00 to +12.00
14
2.00-3.00&3.50&4.00
65
+10.00 to +14.00
Hard Resin Aspheric 5 Drop FT
FT25
10,12
2.00-3.00&3.50&4.00
65
+6.00 to +12.00
14
2.00-3.00&3.50&4.00
65
+10.00 to +14.00

[allanon]

I've done about 8pr of these "Fried Eggs" this year. Always CR-39. There's a strong rumor that these will no longer be available in a couple years. I've heard that from my Zeiss and my Essilor labs.