extreme myopia

**forward** · 12-06-2006, 02:53 PM

Hi Everyone,

for a prescription of OD -12.75 -1.75 x25 and OS -15.00 -2.00 x160 I went with a 1.67 index in a moderately small frame 44x29mm lens size and made out quite well [except for price!] with the actual lens thickness being OD 6.7 max 2.30 min OS 7.9 max 2.15 min.
Now however this prescription climbed to OD -13.50 -2.00 x25 OS -15.50 -200 x155 but the options on the market also increased, with 1.75 index approved.
SO my question to you - using these numbers can anyone calculate/project the actual thickness I can anticpate for every index from 1.67 thru 1.75 ??

LOOKing FORARD

**CME4SPECS** · 12-06-2006, 03:42 PM

try www.opticampus.com

**Robert Martellaro** · 12-06-2006, 03:56 PM

The new Rx should be about .3mm to .5mm thinner with 1.74. You might be able to get a slightly thinner center, resulting in further reductions in ET, if there are no unusual safety considerations.

Hope this helps,

**forward** · 12-06-2006, 04:05 PM

CU4SPECS,
Thank you for that wonderful link!

**CME4SPECS** · 12-06-2006, 04:22 PM

Originally Posted by forward

CU4SPECS,
Thank you for that wonderful link!

You can thank Darryl Meister, he developed the site.

**k12311997** · 12-06-2006, 04:53 PM

Originally Posted by forward

Hi Everyone,

for a prescription of OD -12.75 -1.75 x25 and OS -15.00 -2.00 x160 I went with a 1.67 index in a moderately small frame 44x29mm lens size and made out quite well [except for price!] with the actual lens thickness being OD 6.7 max 2.30 min OS 7.9 max 2.15 min.
Now however this prescription climbed to OD -13.50 -2.00 x25 OS -15.50 -200 x155 but the options on the market also increased, with 1.75 index approved.
SO my question to you - using these numbers can anyone calculate/project the actual thickness I can anticpate for every index from 1.67 thru 1.75 ??

LOOKing FORARD

why is the ct so thick? in 1.67 usually see between 1.5 and 1.8 in surfaced lenses.

**HarryChiling** · 12-06-2006, 06:30 PM

in 1.67 usually see between 1.5 and 1.8 in surfaced lenses

You should be able to specify a thickness, but if you don't, they could give you a 3.0mm ct thickness and claim it meets specifications.

**snowmonster** · 12-06-2006, 10:14 PM

Originally Posted by Robert Martellaro

The new Rx should be about .3mm to .5mm thinner with 1.74.

Shouldn't it be more like 1.3 mm thinner, assuming the same CT (which sounds rather thick in this case)? I used a PD of 64 with the calculator on OptiCampus.com.

-Steve

**LENNY** · 12-07-2006, 09:26 AM

Where do you people see the CT in the original post?

**DragonLensmanWV** · 12-07-2006, 11:57 AM

Originally Posted by forward

Hi Everyone,

for a prescription of OD -12.75 -1.75 x25 and OS -15.00 -2.00 x160 I went with a 1.67 index in a moderately small frame 44x29mm lens size and made out quite well [except for price!] with the actual lens thickness being OD 6.7 max 2.30 min OS 7.9 max 2.15 min.
Now however this prescription climbed to OD -13.50 -2.00 x25 OS -15.50 -200 x155 but the options on the market also increased, with 1.75 index approved.
SO my question to you - using these numbers can anyone calculate/project the actual thickness I can anticpate for every index from 1.67 thru 1.75 ??

LOOKing FORARD

As a person with an Rx in that range, I feel you should not focus entirely on thickness. You need a good balance between thinness and good vision. Surprisingly, most 1.67 lenses have poorer ABBE values than some 1.70 lenses. After all, what good is a thin lens when the patient cannot see out of them?
I would recommend Hoya's 1.70 lenses with a bearable ABBE of 36.. That's what I have now, and it's the first lenses that I can wear that are higher index than Spectralite (1.53). They are nice and thin and the vision is very good through them.

On a related note though.... we just put up some Christmas lights that are the new LED variety that have a 25mm globe encrusted with bits of plastic that look like pretzel salt. Now, I can look at all the colors and move my head from side to side and the colors don't smear and spread very far, even the red one. BUT, the blue ones however, seem to move about a relative three inches on the tree if I move my head sideways.The smear on that particular color is large. Now you brainwave guys can tell me why. I'm guessing that whatever frequency the blue lights are is one of the freqs that are dispersed more than the other colors. I was expecting a similar dispersal with the red end of the spectrum, but it's not there. The green ones exhibit a lesser amount of smear, but more than any other color besides blue. So it seems obvious that this lens disperses more at the short end of the spectrum.

**Robert Martellaro** · 12-07-2006, 12:36 PM

Originally Posted by snowmonster

Shouldn't it be more like 1.3 mm thinner, assuming the same CT (which sounds rather thick in this case)? I used a PD of 64 with the calculator on OptiCampus.com.

-Steve

Hi Steve,

Due to index of refraction alone we would expect to see about a 9% reduction in thickness ((1.67 - 1.00) / (1.74 - 1.00) = .91). However, the increase in power offsets some of that reduction in edge thickness.

Regards,

**k12311997** · 12-07-2006, 01:20 PM

Originally Posted by LENNY

Where do you people see the CT in the original post?

Originally Posted by forward

Hi Everyone,

for a prescription of OD -12.75 -1.75 x25 and OS -15.00 -2.00 x160 I went with a 1.67 index in a moderately small frame 44x29mm lens size and made out quite well [except for price!] with the actual lens thickness being OD 6.7 max 2.30 min OS 7.9 max 2.15 min.
Now however this prescription climbed to OD -13.50 -2.00 x25 OS -15.50 -200 x155 but the options on the market also increased, with 1.75 index approved.
SO my question to you - using these numbers can anyone calculate/project the actual thickness I can anticpate for every index from 1.67 thru 1.75 ??

LOOKing FORARD

sorry making an assumption that min thicknesses 2.30 and 2.15 are ct's for it to be a min edge would have to be horribly decentered which it does not appear to be from the description

**LENNY** · 12-07-2006, 02:25 PM

FPD 73MM IF PD is lets say 56?
What would be the ET on nasal? on the 1.0 CT

**k12311997** · 12-07-2006, 02:32 PM

Originally Posted by LENNY

FPD 73MM IF PD is lets say 56?
What would be the ET on nasal? on the 1.0 CT

I don't know and really don't care. if that is the case the question is not what those measurements mean the question is what the he-double hockeysticks was that optician thinking decentering that Rx 8.5 in each eye.

**forward** · 12-07-2006, 03:40 PM

Hi all,
Thanks again for all this.
As to the FACTS, the pupillary distance in this case is 66.5 and the Minimum thicknesses are at center.

**LENNY** · 12-07-2006, 09:38 PM

Thank you can do better just reducing the CT!

**k12311997** · 12-07-2006, 09:41 PM

Originally Posted by k12311997

why is the ct so thick? in 1.67 usually see between 1.5 and 1.8 in surfaced lenses.

Originally Posted by LENNY

Thank you can do better just reducing the CT!

I thought I said that!?

**MarcE** · 12-08-2006, 12:57 AM

Yes, reduce the center thickness! Before you pay the extra for 1.74 index, make sure that the center thickness is tolerable. I have posted before that I would not pay a lab for a center thickness like that.
Hoya claims that they can surface their 1.70 material to 1.0mm CT and still meet FDA impact stds with the non-optional AR. If true, that will be your thinnest choice, assuming that the Essilor 1.74 will be surfaced to 1.5mm CT. I have no personal experience with Hoya's surfaced 1.70, but I have measured the stock 1.70 lenses with a center thickess of between 1.0 and 1.1mm. Hoya may also be able to do some double aspheric, atoric, black magic kind of stuff which could make it thinner.