Need Help Doing Monovision Contact Lens Trial
Posted , 4 users are following.
What am I doing wrong? I could not read at intermediate distance hardly at all with a soft contact lens in my right eye designed to achieve 0.75 under correction for myopia. I had expected it would work for computer work at intermediate distance, based on experiments with glasses.
My doctor recommended 2d under correction for my non-dominant eye and 0.75 under for my dominant eye, based on my preference for best near and intermediate vision, not wanting progressives and willingness to wear distance glasses for driving. So, I wanted to try out 2d/0.75d minimonovision before surgery.
Here's what I did.
Since I have severe astigmatism and mild diplopia (decompensating phoria), I had to do the test in combination with under-correcting glasses that have my astigmatism correction and prism. So:
step 1) I ordered reading glasses with my full astigmatism and prism correction that are 2d under on myopia correction. They work great for reading a book. Love them. But not great for computer, because I'm farther from the words.
Step 2) Using hand-held lenses provided by my optician I determined what power held against these new reading glasses was best for computer. Result was the -1.25 hand-held lens was best, indicating 0.75d under correction would be best for computer distance. So far so good. Exactly confirming my ophthalmologist's recommendation for reading and intermediate.
Step 3) ordered -1.25 contact lenses. I asked my ophthalmologist what contact lens power corresponded to -1.25 at the glasses plane and he said the difference was negligible - just order -1.25. He gave me a prescription for -1.25 that I sent off to Walmart. This was done by email, so there was no contact-lens fitting in his office. I had to guess at the curvature number, so I guessed the steepest of the 3 choices (8.4), since I have very long eyes (27.5mm).
Step 4) I put the -1.25 contact soft contact in my right eye and put on my 2d under- correcting reading glasses. It totally blurred my near and intermediate vision1 With the left eye shut, I could not read. Distance vision did improve in that eye when I put the lens in it. But intermediate vision was terrible.
step 5) Wondering if the contact lens did not fit my eye correctly, I put on +1.25 readers over the glasses, over the contact lens. Reading vision was totally fine with the 3 lenses in combination. So, it has to be the power, not some aberration introduced by a bad fit.
Why does adding -1.25 correction with a contact lens behind my reading glasses screw up my intermediate vision but doing the same thing with a handheld lens against the front of my reading glasses (i.e. step 2 above) makes it better?
Any theories or suggestions?
Anyone else have difficulties with a contact lens trial?
0 likes, 14 replies
RonAKA jimluck
Posted
No theories. It should work. I don't suspect the contact lens fit, but that may be possible. 8.4 is pretty standard, and I believe that was the curvature of the last contacts I wore. My eye for that contact was about a -2.0 and I used a -0.75 D contact to simulate -1.25 D myopia. It worked well for me. FWIW I tried simulated monovision with no correction which would give me -2.0 in the close eye and plano in the other eye. I didn't like that degree of monovision at all.
jimluck RonAKA
Edited
It seemed to induce residual astigmatism when I put the contact in and put the -2 glasses on.
My eye doc had no plausible theories either.
Myope_PSC jimluck
Posted
-0.75D focal point is 52 inches. Is your monocular vision clarity with the under-correcting glasses plus the contact lens at its best at around 52 inches? If so I think that would confirm that the combined resulting power is correct.
It doesn't help answer your question though.
jimluck Myope_PSC
Posted
My sharp-vision point is 12 inches for 2 diopters under, 24 inches for 1 diopter and about 28 inches for 0.75. Anything 3 feet or over is sharpest with full distance correction. All of this being for glasses. I understand that 1 meter divided by 0.75 = 52 inches, but that does not seem to applicable to determining my optimal under-correction. I'd love to understand why.
jimluck Myope_PSC
Edited
Myope,
Here is what I just learned about the near vision formula.
The formula for calculating diopters of near-vision glasses is
1/P - 1/Q = D, where P = the desired viewing distance in meters and Q = the nearest distance at which vision is sharp and D is the reading add in diopters. I think you are ignoring the 1/Q term.
So, let's say I want to see something at 1.33 meters and things are only sharp at infinity (false, for me, but let's say). In that case, the term 1/Q is treated as zero and the answer is 0.75 diopters (= 1/P) and you would be correct.
But if the image is sharp to begin with at 1.33 meters (as is true in my case), then 1/P = 1/Q = 0.75. Their difference is zero so the answer is 0.0 D. No reading add needed or wanted. In fact, for me, it would make something at 52 inches fuzzy if you took away some of my myopia correction.
An object is perfectly sharp to me at 52 inches using my full myopia prescription. In fact, that's about the nearest it can be and still be sharp. Therefore, when wearing glasses that correct me to emmetropia, 1.33 meters is my Q.
I want to use the computer at about .67 meter. So 1/P = 1.5 and 1/Q = 0.75 so the diopters I need = 1.5 - 0.75 = +0.75.
Different people get different amounts of "add" in their eyeglass prescription. I assume P is about the same for everyone. So it must be that they have different Qs. Why? I guess their visual systems -- eyes + distance correction -- are different. Maybe a long eye like mine (27.5mm) needs less add for near vision than a typical eye (24mm) or a short eye (22 mm). And/or maybe it has to do with accommodation, so it will no longer hold true after cataract surgery. I would like to know. Why does Q differ even with distance glasses on that get the wearer to their best distance vision?
jimluck
Posted
The 1/p-1/q formula is from a Youtube video: "Calculating the diopters of reading glasses" by Stefan Bracher
Myope_PSC jimluck
Posted
Interesting video and formula. It works for me. I don't understand it well enough to apply it to your situation (myope becoming less myopic vs the video hyperope becoming myopic).
(-2)+(-1.25)=(-3.25)
So at -3.25 you see computer clearly and at -2.00 you see clearly to read a book.
I can simulate what you did with glasses & trial lens and get the same result as you. From -2.00, book at -2.00 & computer at -3.25. Your contact lens trial should work.
From plano and at 26" (monocular), I can see my computer screen sharpest with a +1.25 lens. I can read the screen without that lens but adding it makes the text much sharper. Note that I have an Eyhance lens and it presumably affects the power needed.
jimluck Myope_PSC
Posted
Yeah, soft contacts do something screwy in my eyes. It's not the normal out of focus from having a wrong power. It's just messed up.
billy111 jimluck
Posted
Jim, I have forgotten your original post. You have a lot of astigmatism. Why don't you get a toric IOL to fix your astigmatism ? I have 2D astigmatism and I was a candidate for a toric, but I just wanted to keep my surgery simple. I also have droopy eyelids, which can affect IOL calculations and even the toric IOL itself.
You are doing the right thing trying out mini-monovision with contacts. I am 70 and have never worn them.
jimluck billy111
Edited
Billy,
I plan to get a toric for the right eye. I'll have to travel to another country to get one strong enough, since US torics only go up to 6d. I'll also get one here for the left, unless I get the IC-8, which doesn't need to be toric for astigmatism up to 1.5d (mine is less than that on the left once the lenticular component of it is removed). But, in the meantime, I'm trying to simulate minimonovision and I'm temporarily stumped. They say not to do it with glasses, because differing powers means differing amounts of minification, which isn't the case for contacts and IOLs, and which can annoy the brain. So, I have to do it with contacts. But how to do that when I have more astigmatism than a soft contact can correct? I tried small hard contacts 35 years ago -- great vision, unacceptable discomfort. I had less astigmatism in the right eye back then, so I don't know if they would still work so well. As I recall, no toricity was needed. The cornea just conformed.
Scleral hard contacts are another possibility. I tried them in the doctor's office recently. Great comfort but they didn't have my prescription in them, so I don't know how the vision would be. Over refraction got me to decent vision, but not equal to glasses. And they are several thousand dollars and very tricky to put in and take out. Medicare would pay, because I have keratoconus, but I feel bad about the expense nevertheless since it's just an experiment.
Now that I write the above, it jogs my thinking along. I'm struggling with computer vision and I plan to wait a year for surgery, at least. Maybe I would find the scleral contacts a real benefit during that year, and that would justify the expense. I have 0.75 under-corrected glasses on order, so if those don't solve the computer vision problem I'll consider the scleral contacts further for that reason. Getting rid of the minification of glasses would help computer use, if nothing else. (The glasses came a few days ago, but were made wrong -- grrr! --. I saw double at distance binocularly. The optician said the pupillary distance was off.)
Myope_PSC jimluck
Edited
I wonder if your normal Rx is under corrected (over-plussed) a bit? 20' is -0.16D to start with. From reading stuff on optical forums it seem some optometrists factor that in and some don't. It's possible to be at -0.50D and still have a 20/20 result. That would mess up what you're trying to do with glasses and the contact lens. It would greatly affect your 0.75 under-corrected glasses for example. If one of your optometrists or ophthalmologists can loan you a Trial Frame and Trial Lens kit you might be able to figure it out.
jimluck Myope_PSC
Posted
Interesting suggestion about getting the loan of a trial frame and trial lens kit. I don't know too much about that. Thanks. I'll look into it.
I doubt that I'm undercorrected. At my last appointment, she said "Last year you could read that line. Now you can't. And there is nothing I can do with changing the correction that seems to enable you to. Here's your new prescription, but don't bother filling it. You won't notice a difference. Next year, go to an ophthalmologist instead of me. I think he'll recommend cataract surgery."
I went away for a few weeks and then made another appointment and asked her to try again. The earlier refraction had been done dilated and I felt I could give her better answers undilated.
She did the whole routine over, undilated, and then gave me a further update to the prescription, which was half a diopter stronger on the sphere on both eyes, half a diopter less on the add for both eyes and a few degrees different on the cylinder axis. I filled it and the new glasses made a noticeable improvement to my distance vision, but I was already satisfied with distance vision, so I wasn't thrilled. My complaint is computer vision, and it did not help with that. So, I'm hoping dedicated computer glasses (on order) will help.
I went through my large collection of old eyeglasses, some going back 35 years, and found a pair that gave good reading vision on the left eye. I took those to an optician and asked her to tell me how much weaker they were than my current distance prescription. She said exactly 2 diopters. So, I ordered a pair of monofocal glasses that were undercorrected by 2 diopters. They are great for reading (11 to 17 inches_, but I would have to be too close to the computer screen to use them for computer. So I went back to the optician with the reading glasses and asked for a collection of minus lenses and a seat at a desk with a computer screen. She obliged and I found the -1.25 lenses, held against the -2 undercorrected reading glasses, were perfect for the computer (about 2 feet -- I didn't have a ruler-- to I forget how much). So, I ordered -0.75 undercorrected glasses and I'm waiting for those. I think that whole cumbersome process was kind of a makeshift trial frame.
jimluck
Posted
Update: Just ordered a trial frame ($60) and trial set of lenses ($218) from Amazon.
Myope_PSC jimluck
Edited
That should be useful. As your cataracts progress you'll be able to know whether a new prescription is beneficial or not.
It would have been nice for me to have before surgery because I did end up wasting money on one prescription change along with the cost of the interim exam for a lens that did not improve my vision much if at all.
You'll also be able to confirm that your current prescription gives you the best possible distance vision or if it needs a small adjustment for your test purpose. Then you can change the lenses as needed to figure out what you want to end up with after cataract surgery.
If you can test to 100' or more that should give you the best distance correction. I look at the detail on a neighbors house about 500' away. I know that your vision is somewhat compromised now so you'll figure out what distance works.
Infinity = absolute zero
300 feet = -0.01 D
200 feet = -0.02 D
100 feet = -0.03 D
50 feet = -0.07 D
40 feet = -0.08 D
30 feet = -0.11 D
20 feet = -0.16 D
Post-op, you'll be able to figure out the basic correction needed. Cylinder is probably difficult to figure out from scratch . Once you get a new prescription with sph & cyl from your optometrist post-op you'll be able to confirm that it's good for you before having to purchase it.