Contact Lens Education

[chip anderson]

I had hoped to start a whole contact lens forum, but Steve feels this would not have enough interest. So I plan to start a string which will be to impart general knowledge of contact lenses. I seem to know quite a lot about rigid lenses an don't really think soft contact lenses require much intellect so I will to try to place a few posts each week starting with the more basic things of rigid contacts working to some of the more intricate ones. Will be happy to respond to anything anyone has to ask or say on the subject.

Chip Anderson, FCLSA

[stephanie]

Great idea Chip!! I for one am interested. I found a lot of the information on this board helped me with the ABO and am hoping it will help with the NCLE. Did you do this just for me?? I barely know anything about them except what I am currently learning.
Have a great day!!
Steph

[Darryl Meister]

Sounds like a great idea, Chip. Maybe we should do the same for spectacle lenses.

Best regards,
Darryl

[Sara]

Dear Uncle Chip,
Your ideas is fantastic!! PLease go ahead I for one would study your tread.
Thanks You.
Sara

[Maria]

Of course, in Nairobi, uncle means 'old dude'.... :D Just kidding Chip. You do give off that avuncluar vibe, though.
Tip to Sara - never ever mention ethics in dispensing, particulary not in relation to Drs filling their own prescriptions. You'll never shut him up :)
Seriously, it's nice to have input from a new country, and I'm a student too, so we can ask the masters questions together.

Maria

[chip anderson]

O.K. here it is, the first posting. I suppose I will start with what you should do when dispensing rigid contact lens to the patient. Teach the patient to wash his hands with a soap that does not contain oil, I always recommend: Ivory Bar for both rigid and soft contacts as it contains only soap, and since this isn't taught in school any more, tell the patient the purpose of soap is to mix oil and water. There by removing the oil and dirt with rinsing.

The patient rub the lens manually with the thumb and forefinger for one full minute with wetting solution or conditioning solution as the advertising men may refer to it. Rinse the lens by dipping it in a glass of water. When I had been in the business about six weeks I and we had only PMMA then, I found that polishing lenses would be a major part of my life. I spent five years interviewing five thousand patients on handleling and found that 99 out of 100 who handled their lenses over the sink (even with a towel over it) had scratched lenses. This was amazing because 80% of these will tell you "But I never drop one."

Stay with the patient an teach him to insert and remove his lenses (without the use of any anesthetics. Have him do it in your presence until you feel he can, do not allow him to take the lenses home with him if you don't think he can do this. Do not allow anyone else to do this for him except in the cases of the very young and the senile. If someone else will do this, the patient will never learn to do it by himself.

Teach the patient to clean, disinfect and store his lenses. No matter what the instructions say, tell the patient to scrub his case out weekly with a tooth brush and Johnson's Baby Shampoo. I know that the solution manufacturers want daily replacement of solution, I don't care too much about this but I want all dirt and cultures scrubbed out weekly.

enough for now, Chip

[EyeFitWell]

and since this isn't taught in school any more, tell the patient the purpose of soap is to mix oil and water.

They taught that at my school! (Graduated HS in 2002)
(This is really off-topic, but that is exactly why I think shampoo and conditioner in one doesn't make any sense. You're most likely just going to wash out the conditioner and leave the oil in your hair.)
LOL...I guess I just had to reply to that because I was surprised to see someone else who knew exactly what soap is.

[HarryChiling]

no longer playing in this sand box

[Dave Nelson]

Kinda reminds me of the paper I submitted to the CLSA a few years back titled: Sam and Lars- evil twins? It was about the dependance on acronyms to remember simple optical principles. Left add, right subtract for toric axis compensation. Are you kidding me? As a learning tool, maybe, but it's irritating to see it published in trade journals and optometric journals. Someone who has done 5000 refractions needs to know "LARS?"

[HarryChiling]

no longer playing in this sand box

[optiman37]

One general rule I have learned when you are cleanning contact lenses is not to use water even to soak the lenses because water contains amobes

jeff

[HarryChiling]

Z80.2 - 1989, is the RGP ANSI standard

[Maria]

We get taught that they should use CL solution, instead of baby shampoo, for cleaning the case. Is that worse, better of the same?
Maria
PS You are a bit like Master Yoda, with a little Mr Miaggi thrown in. :) Squish! Just like grape.

[Maria]

Also we get told that lenses should never touch ordinary water, because of all the crap that's in it. Is this what you think? Or do you think it's ok?

[chip anderson]

As to water (in regard to rigid lenses at least), I think it's just fine for rinsing lenses. I do know a lot of experts and biochemist opthalmologist who disagree with me. However that same old tapwater is exposed directly to the eye in the shower and if the bugs gonna get you. It's gonna get you. Now as to growing bugs in the case, I take this very seriously and think Johnson's Baby shampoo is much better than contact lens solution for cleaning the case. This upsets Johnson's but who cares?

Now as to a real source of eye infection: Wetting the lens with saliva. This can be cured in most cases by asking the patient to hold out his hand and close his eyes. Put an artificial eye (preferably in his color) in it and tell him this is what he is taking a chance on. You can even tell him he never had an "emergency" worth taking a chance on that.

[chip anderson]

My insight on Solutions:
Rigid PMMA lenses. Soaking solutions should be strictly a soaking or a combination soaking/cleaning solution. Wetting/soaking solutions should not be used. The gum~up the lenses and case. I used to have two compeditors, one recommended dry storage the other used the only combination soaking/wetting solution on the market at the time. Both had patients who ended up in my office and were "cured" when I buffed the encrusted solutions or dried on proteins off the lenses. The encrustations looked so similar that in RGP Lenses I often think a great many of our troubles are caused by the fact that combination wetting/soaking solutions are all that is available for them.

Also I shudder to think how many unsuspecting souls have been sold new lenses when all the old ones needed was the deposts removed (mostly from the posterior surface).

[chip anderson]

Rigid Lens Inspection

This is why you are entitled to a mark~up on rigid lenses. Regardless of what the FDA says or feels on this subject this is how you earn your salt as an optician/contact lens technician. Those who feel that they can say: "I trust my laboratory, will find that they are very wrong once they institute these practices.

1) Check the central posterior (base) curve of every lens. This may be done with a keratometer or a radiuscope or several automated devises. Tolerances should be no more than .02 mm (1/8 diopter) and no, this does not double for torics or bifocals.

2) Check the power (focal length) with a lensometer or automated devise. This should be withing 1/4 diopter+or- and should not be + on ½ of a pair and - on the other half.

3) The diameter should be checked with a measuring magnifier or a sliding diameter gauge. Tolerance should be .10 mm or less.

4) Check the thickness. This may be done with a thickness gauge or a lens clock. To use a lens clock place the lens on a flat surface and place the lens clock with the movable pin on the lens, it reads in 1 mm. increments.

5) Check the edge design with a measuring magnifier, this may also be profiled on some lensometers by holding the lens on the mirror(movable) at an angle 90 degrees from that for power and focusing near plano.

6) Check the surface quality, with a measuring magnifier and/or a radiuscope. Tolerance on lathe marks, casting marks, tool marks,

7) Check the optics: Should be done with both the lensometer and by holding lens at arm's length and viewing a flourescent tube through the lens. The lens should be moved and rotated, you will be amazed at the waves, rings, and other aberrations that appear with this technique.

8) Check the color.

9) There is not a whole lot you can do about checking the material, there are specific gravity tests for this but they are not a practical office procedure.

If you can't or won't or don't have the equipment to do all of the above, the patient would be served equally well by purchasing lenses from Linda Carter, who can't tell one lens from another. If you do all of the above even on replacements, you can truly say you have earned your salt. Your lab won't love you but they will learn to respect you.

Ole Chip

[stephanie]

Ok I have a couple of questions here that came right out of my book. Bear in mind that I do know the answer as I have the answer key. What I don't know is why?

1. A contact lens has a base curve of 7.50mm. Its posterior peripheral curve would most likely be:
A) 7.45mm
B) 42.50 D
C) 7.35 mm
D) 30.00 D

2. Of the curves listed which indicates the flattest base curve?

A) 7.50mm
B) 37.50 D
C) 8.60 mm
D) 49.00 D
Like I said I do know what the answer is but I do not understand why.
Thanks!!
Steph

[rdcoach5]

Ok I have a couple of questions here that came right out of my book. Bear in mind that I do know the answer as I have the answer key. What I don't know is why?

1. A contact lens has a base curve of 7.50mm. Its posterior peripheral curve would most likely be:
A) 7.45mm
B) 42.50 D
C) 7.35 mm
D) 30.00 D

2. Of the curves listed which indicates the flattest base curve?

A) 7.50mm
B) 37.50 D
C) 8.60 mm
D) 49.00 D
Like I said I do know what the answer is but I do not understand why.
Thanks!!
Steph

My standard P.C. is 4.5 diop flatter than the Base Curve. A 7.50 B.C would have a 1st intermediate curve of 9.00 2nd int of 10.50 and peripheral curve of 12.00. the width of each is specified, such as .25/9.00 .25/10.50 and .2/12.00. If your diameter was 9.5 , the optic zone is 8.1

[chip anderson]

RDcoach:
What you have listed is 1.5 mm not 1.5 diopter radius changes. mm is correct but done as written you will have a lot very small optical zones and not much edge lift.

[rdcoach5]

You are correct.

[chip anderson]

Stephanie:
The answers to your questions are:
1=D 2=B
The reasons why are:
Question 1
7.45(45.37+or-) and 7.35(46.00-) are shorter in radius than the base (central posterior) curve. Any grinding of these curves to the base would touch in the center. 42.50(7.94 mm) is rather close to 45.00(7.50) and would not provide much relief at the periphery of the lens. In fact if ground into a 7.50 radius it would soon grind very wide and approach the center (trust me on this my first job in the contact lens industry was cutting an polishing base curves). Now 30:00 Diopters has a radius of about 10.0 mm (I think) and would grind into the periphery quite well and provide some relief for tear circulation and limbral clearance during movement. I would not chose this a peripheral curve on a lens of this radius myself, but it obviously would grind into the periphery.

Question 2
37.50 D= 9.00 mm.
Try to think of any lens surface as having: less power as it grows longer in radius. This is true no matter what the lens is for or what it is made of.

Now as to Base curve charts. Do you have a copy of Contact Lens Quarterly? If you do at the end of the "RGP/PMMA National Distributors" and before the solutions you will find a very good chart in every issue. Tear one out and put it with your reference materials. There is also a vertex (unfortunately a front vertex) chart on the same page. If you don't have a quarterly, let me know and I will E.Mail you a chart.

Chip

Chip

[stephanie]

Ah Chip!! I believe me book has some wrong answers. I have for the answers both as being B. Hmmmm... interesting. Well at least now I know when I question things it is usually with good reason. I don't have a chart as I have never had a reason to get the contact lens books. Thanks for all your help this has cleared some things up. At least til I get stuck again. Lord knows it is likely to happen any minute.
Thanks Again!
Steph"I am gonna end up in a rubber room before I am finished with cls."D

[rdcoach5]

As a general rule, I add 1.5 mm for each of three radius tools to get the desired ski curves. In this example , 7.50 base curve, use 9.00, 10.50 and 12.00. The width of each is also specified, such as .25/9.00 .25/10.50 and .2/12.00. If your diameter was 9.5, yout optical zone is 8.1.
Bob Taylor

[Berno]

Hi Steph!
Just another way to answer your first question- I think B is the right answer and the reason is because 42.5D (7.9mm) is flatter by 0.4mm than the base curve [this corresponds with the cornea's shape which is steeper in the centre and getting flatter toward the periphery (assuming it's not a postK cornea and it's not RGL lens)
(a) and (c) are steeper which is not likely in normal geometry lenses and (d) 30 is way too flat.
Hope I helped.