Astigmatism, and Red Dot Sights

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Astigmatism, and Red Dot Sights Empty Astigmatism, and Red Dot Sights

Post by mikemyers on 1/8/2020, 2:57 am

I volunteer at Aravind Eye Hospital in India.  They have a manufacturing facility to design, manufacture, and sell many of the things that are used at an eye hospital, Aurolab, where they are sold at much lower cost than what is available elsewhere.  They manufacture IOL's, (Intra Ocular Lenses) that are used to replace the opaque lens in cataract patients.  I had a discussion with Sundaraganesh this morning - he is the person that does the design of these IOL lenses.

Among other useful things he told me:

Astigmatism can be caused by a person's cornea, the lens in his eye, or both.

Astigmatism caused by the cornea means the curvature of the eye in one direction is different from the curvature of the eye in a different direction.  This is measuring the curvature of the cornea in both the horizontal and vertical planes (but if done by an ophthalmologist, the doctor will measure the exact angle of the planes.

Astigmatism can be corrected with a lens implanted into the eye (IOL), or corrective glasses.  To function properly, the corrective lens has to be held at a precise angle, as the astigmatism is due to different angles for light coming through the eye.


Of interest to shooters using red dot sights, there are options.  

If they have cataracts, and a new IOL will be placed inside their eye so they can see clearly.  This IOL can be designed to give not only the correct focus, but can also be designed to cancel out the astigmatism.  

if they wish, they can get corrective glasses, which again will cancel out the astigmatism, giving them good vision.  The glasses will be designed to hold the lens at the optimum angle in front of the eye.

What I didn't know until this morning, was that the corrective lens can also be placed directly onto a red dot sight, and it will correct the astigmatism for light coming through the sight, including the red dot.  What is important, is if someone does this, the lens has to be attached to the red dot sight at the proper angle to cancel the astigmatism.


I don't have astigmatism, so I can't test these ideas.  I told Sundaraganesh that on my next visit to India, I will bring a red dot sight with me, so he can try it himself.  In the meantime, I asked him if an ophthalmologist can help a person buy a small round lens, to be placed on the person's red dot sight.  The answer is yes.
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Post by dronning on 1/8/2020, 5:03 am

Interesting, I use a $25 EyePal and it works perfect for me.  Plus it helps me keep my head in position.
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Post by watercam on 1/8/2020, 5:51 pm

Better off with glasses if for no other reason they will work for any firearm one is shooting. Not just the one. I, too, have astigmatism and I shoot Highpower Long Range Rifle and Precision Pistol with the same Rx in my shooting glasses.
My $0.02.

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Post by L Valdez on 1/10/2020, 8:16 pm

I have astigmatism and use a contact lens on my shooting eye.  

If a person puts the lens on the red dot sight, he might not be able to see his 50 yard target number board with his naked eye.

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Post by mikemyers on 1/10/2020, 10:20 pm

(You would need to use a lens that corrects for astigmatism, oriented at the exact angle, and large enough to cover the optics from the dot sight.  

I didn't know that contact lenses could correct for astigmatism??  I wouldn't expect this to work with a contact lens, but I have no way to try.)
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Post by 301bruce on 1/11/2020, 12:22 am

Toric contact lenses correct astigmatism.  They are weighted on one edge so they maintain the desired orientation. I’ve worn them for many years.  I recently had cataract surgery which corrected my vision to 20/20 and corrected my astigmatism. The lenses have arms that keep them oriented in the eye. The cataract lenses don’t give me near vision so I use corrective safety glasses if required. For red dots, I need no correction and see almost no flaring or distortion.

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Post by mikemyers on 1/11/2020, 1:36 am

From what you've written, they gave you "tonic" IOL's, which replace the natural lens in each eye, and give you the best clear sharp vision at one distance, with no astigmatism.  The "arms" on the IOL keep them lined up perfectly.  Since most IOLs can't "focus", people need to wear glasses for closer vision.

They now make IOLs that have multi-prescriptions, potentially for distance, mid-range, and close-up, but one gets the best possible vision by doing what you did - and accepting glasses. The multi-focal IOL's also can create "halo's" and "reflections", especially at night.


We had a discussion at my hospital about "depth of field", but nobody other than Sundaraganesh understood it.  He calculated a prescription for my right IOL that keeps things sharp from 2 meters to infinity, without needing glasses.  Anyone who understands photography will know about "depth of field", but apparently not the people who work at the hospital - they understand lens "power", not lens "focal length", even though each is the reciprocal of the other.   1/power = focal-length.

Until you wrote what you just posted, I didn't realize that contact lenses could correct for astigmatism.  I've never worn contact lenses, but it seems that those people here who are not satisfied with their red dot, due to astigmatism, could get toxic contact lenses like what you used to wear.
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