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Astigmatism

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Soundmanpt 02 Jun 2018, 05:00

Just Asking

I assume that you're asking this for the purpose of buying contacts lenses so you don't have to buy the more expensive "toric lenses"? For glasses having the astigmatism correction properly included in your prescription costs nothing extra.

I agree with Lou and Maxim that at -1.25 CYL that is too much to simply increase the SOP by half the value.


Maxim 01 Jun 2018, 14:50

I should say, this rule of thumb applies to astigmatism up to 0.50 or 0.75, to leave them uncorrected. If the astigmatism goes beyond 1.00, or even up to 1.50 or 2.00, the correction is substantial, especially when it comes to letters or numbers reading (busses, car registration plates etc., street sign and indicators).

I feel, it's better for you to correct this astigmatim of 1.25.


Lou 01 Jun 2018, 14:19

Hi JustAsking

The general rule of thumb for example for someone who wants sphere only contact lenses, is to add 1/2 the cylinder to the sphere.

However this generally works better when someone only has a small amount of astigmatism, such as -0.50.

In your case, you'd divide your -1.25 cylinder by two, which equals -0.625. You could either round it down to -0.50 or up to -0.75, when added to your sphere would give -2.25 or -2.50. I honestly however think that neither would give you particularly good vision, as at least in my opinion, -1.25 is a fairly significant amount of astigmatism.


JustAsking 01 Jun 2018, 13:05

Hi,

I’ve read that astigmatism can be corrected to a point with a stronger prescription lens.

I only have an astigmatism in one eye, it’s -1.75, -1.25, 160. What prescription would be recommended to get the best sight without correcting the astigmatism?

Would it be just the -1.75 or should it be higher?

Thanks


JC 26 May 2018, 08:40

Leo:

To expand more on my last post... in my starting point suggestion for your right eye the cylinder changed from -1.00 to -0.75 because for soft contact lenses cylinders are commonly available in cylinder powers of -0.75 or -1.25 but not -1.00. It may be the case your eye was actually on the borderline of needing more then -1.00 and -1.25 would be better. Also for the sphere, by deceasing the cylinder from -1.00 to -0.75 the spherical equivalent of the lens was reduced. If you were on the borderline of -needing more then 3.00 then -3.25 might be better.

That might sound like some technical mumbo jumbo, but my point was to emphasize more that the RX I gave you was only a guess and a starting point.


JC 26 May 2018, 08:28

Leo:

We can't say for sure. In a contact lens fitting the eye care professional will test fit a lens and then evaluate the fit on your eye and then do an over refraction while wearing them to see if the prescription is okay. I'd say a reasonable starting point with parameters available in most brands would be:

R -3.00 cyl -0.75 ax 110

L -3.75 cyl -0.75 ax 90

Please consider not rushing out and buying some if you've never worn contacts -- you really want a professional to fit them and evaluate them on your eyes.


Leo 26 May 2018, 07:41

Question: if my glasses rx is:

R -3.00 cyl -1.00 ax 110

L -3.75 cyl -0.75 ax 87

What would my contacts prescription be?

Thanks!

Leo


Soundmanpt 14 May 2018, 13:36

Glasses Girl

I didn't mean to not answer you. I just missed seeing your comment for some reason.

I probably shouldn't be making guesses without actually knowing for sure how adding CYL to your contacts and glasses might effect your eyes long term. like Cactus Jack said getting a good combination of contacts and glasses for doing GOC by only using SPH is one thing and not too difficult to get a good match and combination.but much more tricky in figuring CYL. Being off i'm sure could result in unwanted headaches.


GlassGirl 14 Mar 2018, 15:39

Thank you for your message Soundmanpt. Do you think toric contacts or astigmatism glasses can cause permanent damage to my eyes? How can that be possible? I am full time GOC wearer for more than three years now, but only sphere (plus contacts and high minus glasses).

Cheers.


Soundmanpt 02 Mar 2018, 10:10

Glass Girl

I know that you are only wanting to experiment but like Cactus Jack said working with CYL is so much different than SPH and it could even cause permanent damage to your eyes. Not to mention even trying it would bed be expensive since you would need toric lenses which are quite expensive.


Weirdeyes 02 Mar 2018, 09:54

Something really surreal was getting my eye tested by the OD who first prescribed me glasses. My first glasses were R Plano and L +1.25. No cyl at all. I swear I remember having trouble seeing certain details far away back then. When I came back he prescribed the -0.75 and -1.25 cyl I usually get. Still don’t know if I developed more astigmatism or just got better at subjective refractions.


 14 Feb 2018, 20:01

wow, GlassesGirl, you seem to really know a lot about prescription numbers and what's important! many people only post partial prescriptions.


GlassGirl 14 Feb 2018, 17:45

Thank you for your replies. I have this combo in mind, which compensate my low astimatism and myopia of -0.25 CYL -0.75 AXIS 180 (LE).

EYEGLASSES:

RIGHT EYE: -7.00 -3.75 60

LEFT EYE: -7.25 -4.00 180

CONTACTS:

RIGHT EYE: +10.00 -3.50 150

LEFT EYE: +9.50 -3.00 90

I plan to buy Biofinity Toric XR contacts for arround 20 USD each 6 lens box, and 1.74 high-index eyeglasses for arround 200 USD.

Do you think this will make a big difference in appaerance and vision from my current combo of -6.50 eyeglasses with +6.00 contacts?


optional 11 Feb 2018, 19:12

GlassGirl

Have you been inspired by this?

anonymous oo 25 Nov 2017, 03:29

on the "glasses over contacts" thread


Weirdeyes 10 Feb 2018, 17:05

GlassGirl

I think you’d have better luck making your glasses have against the rule astigmatism(around 90 degrees instead of 180) because toric lenses for with the rule astigmatism are more stable. I have with the rule astigmatism, so toric lenses work pretty well for me. I use Acuvue Oasis two week torics. Unfortunately toric lenses do not tend to have good ranges for plus powers. Most only go to +4.00. Acuvue Oasis goes up to +6.00 and -2.75 in cyl. The other problem is that adding cyl will subtract plus power. So +6.00 -2.75 will only get you about -3.25 -2.75 in glasses. Bioinfinity torics go up to +8.00, but the cyl only goes up to -2.25. I’m pretty sure there’s an XR range, but that can get very expensive. Even the regular version is expensive.


Cactus Jack 10 Feb 2018, 12:24

GlassGirl,

You are asking someone to do about 15 to 30 minutes of work so you can do an experiment that probably won't be wearable and is extremely expensive.

I suggest that if you are serious about doing complex GOC, you need learn how to do the calculations yourself. There have been several explanations posted on the GOC thread.

Here is a hint about how to get started, which is not usually covered in the GOC posts:

You need to first do a trial calculation for Toric contacts. You will need to add an opposite +Cylinder element, with the same Axis as in the glasses, and then convert it to - Cylinder, because you can't buy Torics with + Cylinder. I think you will be surprised at the results. Don't forget to add or subtract 90 degrees to the axis when you do the conversion.

Please let us know how it all works out, both optically and financially.

C.


GlassGirl 09 Feb 2018, 11:06

Hi there,

I am currently wearing the following GOC combo:

EYEGLASSES:

LEFT EYE: -6.50 -0.75 180

RIGHT EYE: -6.25 0.0 0

CONTACTS:

LEFT EYE: +6.00

RIGHT EYE: +6.00

What prescription do I need in my contacts if I add the following astigmatism to my eyeglasses prescription?

EYEGLASSES:

LEFT EYE: -6.50 -3.75 180

RIGHT EYE: -6.25 -3.0 60

CONTACTS:

LEFT EYE: +6.00 ?? ??

RIGHT EYE: +6.00 ?? ??

I know astigmatism is not recomended with GOC, but I want to experiment... What will the lenses in my eyeglasses look like in comparison to my current pair?

Thanks


Weirdeyes 04 Dec 2017, 02:20

Here's an interesting thing I noticed. The new prescription in my right eye is +0.75 -0.75 165. When I was wearing my new contacts I was trying on my new glasses for fitting purposes. I noticed I could see pretty clearly out of my right eye. When I rotate the glasses 90 degrees I notice it gets noticeably less sharp. That same experiment works with glasses only. It's interesting I see better with -1.50 cyl than no cyl at all. I kind of had the feeling my right eye has been a bit low on cyl.


NNVisitor 16 Jul 2017, 18:02

Ellie

For whatever reasons few people wear glasses at the gym I go to. Maybe it's a safety issue.

You have some astigmatism in one eye only and not a lot. I've worn RGP contact lenses on most days for many years. They have to be fitted and are specialty made but my astigmatism is much higer than yours. Air Optix makes soft contact lenses for astigmatism and soft contacts for those without astigmatism. It might be an idea for you if you want to wear contact lenses only occasionally.


Cactus Jack 15 Jul 2017, 14:07

Ellie,

When you get your glasses, I suggest wearing them full time for 10 days to 2 weeks before making a decision about when to wear them. Initially, you may feel like the glasses have made your vision without them, worse. That is not true. What happens is that Vision actually occurs in the brain, your eyes are merely biological cameras. Your brain can slightly blurry or distorted images, if it knows what something is supposed to look like, but it takes a lot of energy for that to occur. In fact, your brain can create images without any external input. Ever had a dream?

For the first few days after getting your glasses, some thing might appear slightly distorted. When I got my first glasses, it looks like ceiling corners did not meet at 90 degree angles. That soon went away and ceiling corners looked correct both with and without my glasses.

If you are concerned about comments about wearing glasses, please don't be. That will only last for a few days and then people will comment if you don't wear them. In many ways it is like getting some new shoes or a a new style hair do.

As far as contact go, the ideal thing would be a Sphere only contact for your Right Eye and a Topic Contact lens for your Left Eye. However, Toric Contact are more expensive and are often hard to fit properly so that they stay properly oriented. If they get out of position your vision is worse than without correction. One solution that is sometimes used is to add 1/2 of the Cylinder prescription to the Sphere and fit a Sphere only contact. In your case that would be -0.75 plus -0.375 or -1.125. Unfortunately, contacts only come in 0.25 increments, so you would wear either a -1.00 or -1.25 contact on your Left Eye and -0.75 on your Right. They might be a little hard to keep track of which is which, but your ECP can advise you better than I can.

Best wishes and please let us know how things work out for you.

C.


Ellie 15 Jul 2017, 13:40

Thank you that does make sense about the blurry and sharp images. Come to think of it I do struggle a bit when using computer for long period of time.

I will take the optometrist advice and wear them all day once I pick them up

Im.thinking of getting daily disposable contact lenses to wear every now and then and when I'm doing sport, I've been looking up and because of that left eye would I need a toric contact lens on ?


Cactus Jack 15 Jul 2017, 11:36

Ellie,

I believe you would benefit from full time wear. Let me explain why.

The first number, -0.75 in your prescription, indicates that your are mildly nearsighted in both eyes. That means that everything beyond about 1.33 meters or 53 inches is increasingly blurry. However, the -0.75 also means that you have very weak, built in reading glasses. Theoretically, that would help you focus close for a computer or reading, but that is a two edged sword. It means that when you don't wear your glasses, your Ciliary Muscles are not getting enough exercise when you focus close.

The real snag is the astigmatism in your Left Eye. You have no ability to compensate for astigmatism WITHOUT external correction. Astigmatism causes text, particularly small text, to be hard to read. When presented with the two images from your eyes, one sharp and the other a bit blurry, your brain will select the best image and pretty much ignore the other one. Vision is best with both eyes working together. Your glasses helps that to happen because the image from your Left Eye has been optically corrected by your glasses. The result is less fatigue and better depth perception (IOW 3D vision).

Of course the choice is up to you. You do not have to justify seeing well to anyone.

C.


Ellie 15 Jul 2017, 11:17

I had an eye test, thinking my eyesight was ok but at night seems to get bit more blurred so went in for a check. I was told I have an astigmatism in one eye and was recommended to wear glasses even for when on the computer and said I would benefit from wearing them all the time.this is my first prescription.

This is me prescription

Left eye -0.75 sph: -0.75 cyl:axis 10

Right eye -0.75 ds

With this sort of prescription would it be recommended to wear all the time?


Cactus Jack 18 May 2017, 21:39

Maria Et,

Here is a slightly edited version of the prescription you posted:

OD (right eye) Sphere +5.50, Cylinder -4.25, Axis 170 degrees

OS (left eye) Sphere +5.75, Cylinder -3.25, Axis 165 degrees

I listed the right eye first because that is the way prescriptions are usually written.

The Sphere number indicates that your BF has Hyperopia which is the medical name for Far or Long sightedness. Hyperopia is typically caused by a mismatch between the total PLUS power of his eye's lens system and the length of his eyeballs. Almost every baby is born with Hyperopia. That is because the eyeballs have to be small to fit in the small eye sockets in the baby's head. Fortunately, babies also have incredible accommodation, which they learn to use after about a month. This enables them to compensate for their Hyperopia. As the baby grows their eyeballs also grow and they typically become less Hyperopic. Eyeball growth is believed to be controlled by the genes. Some children's eyeballs grow too much and they become Myopic. Others don't grow quite enough and they remain Hyperopic. As they get older it becomes harder to focus close even focus for distance and they need external PLUS help to focus for distance and near. BTW the distances involved are small. About 0.3 mm per diopter which means that your BF's eyeballs are about 2 mm shorter than ideal.

Your BF's real problem is Astigmatism as indicated by the need for significant Cylinder correction. Astigmatism is usually caused by uneven curvature of the front surface of the Cornea. The curve is steeper in one direction that it is in the other. If you can imagine it, his corneas are shaped like a section from an American Football.

The problem with Astigmatism is that you have no way to correct it without using external lenses (glasses or contacts) or sometimes it can be corrected by surgery. The biggest problem with Astigmatism is that it affects Visual Acuity at ALL distances. Uncorrected Astigmatism make Text very fatiguing to read. If your BF did not have any Astigmatism, he might be able to not wear his glasses for distance, but it would be fatiguing and he would probably have headaches.

The Axis number is ALWAYS required if a person has any Cylinder correction. That number is direction of the Long Axis of the Cylinder. By tradition. 0 degrees is Horizontal. 90 Degrees is Vertical. Looking at the wearer, the numbers increase in a counter-clockwise direction from 0 thru 90 and on around to 179. 180 is the same as 0.

He may be able to function without his glasses, but he can function much better and more comfortably, with them.

Hope this helps you understand. It might be possible for you to experience what he sees without his glasses if you know a friendly Optometrist or Optician. Do you wear any form of vision correction?

C.


Maxim 18 May 2017, 14:49

to Jenny

my sincere best wishes, and my gratulation!

You have been a tough woman, and now you are rewarded with superb vision!


Soundmanpt 18 May 2017, 14:05

Jenny

You were clearly stunned and shocked when you put your glasses on for the very first time. You're eyes really adjusted to them quite fast which of course was good for you. Now that you have your glasses you already seem reluctant to take them off. The added bonus besides being able to see so well is that you shouldn't be bothered by anymore headaches. And even though your eyesight is already greatly improved just wait until your eyes have fully adjusted to your glasses. things will even be sharper and clearer than they are now. If you find that you need to remove your glasses in order to read small print after your eyes have adjusted then you almost certainly will benefit from progressives down the road as the doctor suggested. But for now your glasses should make things about 95% better for you.The progressives will make it a full 100% better.

So it seems you're not having any problem with getting used to wearing glasses. That can sometimes be a bigger issue for some. What comments have you gotten so far about your wearing glasses? Since you're new to wearing glasses and that makes it hard to really know if they are as comfortable as they should be. You just need to know that if you find yourself pushing your glasses up quite bit because they are sliding down your nose or if the earpieces feel a little too tight behnd your ears you should stop at anyplace that sells glasses and have the, adjust them for you. They don't care taht your glasses came form another shop and there won't be any charge. You want your glasses to be completely comfortable to the point that you soon will hardly even think about the fact that you're wearing glasses. Do you have any questions about your glasses or eyesight?


Jenny 18 May 2017, 13:36

I picked up my glasses from Foreyes today and all I can say is OH MY GOD! While I did feel a little queasy at first, that feeling went away within a half hour or so. I can't believe the clarity the glasses give me. I truly can't believe what I've been missing. I kept them on at work all day and wore them to drive home. I'm also wearing them now watching television and typing this message. I can see what the doctor said about the possibility of having to remove my glasses to see small print clearly as I can see the difference. He told me that at about 43 I'd need progressives which is in about a year.


Maria Et  15 May 2017, 00:26

Can someone please explain my boyfriend's prescription to me?

left eye is +5.75-3.25x165

right eye is +5.50-4.25x170

His glasses magnify his eyes, I was always thought + was for reading but he wears his glasses or contacts for everything.

I want to understand his eyes more...


NNVisitor 14 May 2017, 21:06

How can anyone cheat on the eye exam? Don't they use different letter arrangements so people can't relay the information to others in order to prevent cheating?

I've never dealt with getting a drivers licence as I don't have an interest in driving even though I could if I wanted to and obtained a drivers license. It's not because of my vision as my corrected vision is usually 20/25 to 20/20 with my contact lenses. I just don't want to drive in crowded city traffic or even on the highway dealing with trucks etc.


Maxim 14 May 2017, 14:08

to Jenny:

It's a bit like in the swimming pool before you are in the water: you don't want to enter, because you think, the water is cold. When you're in the water, you are moving, and you don't feel the cold, you just feel fine.

I am convinced, that these glasses will solve your problems .....

"I've definitely had to deal with headaches especially when working on the computer for any length of time. I also haven't been able to read street signs or see faces of faraway people for quite some time especially at night".

.... and you're going to love them.

You will have such a rich vision with these glasses!

Make sure, that you buy nice frames, or buy a second or a third pair from Zenni's, just not only for a good vision, but for looking nice as well.


Jenny 14 May 2017, 13:25

I've definitely had to deal with headaches especially when working on the computer for any length of time. I also haven't been able to read street signs or see faces of faraway people for quite some time especially at night. At least the last two times I've renewed my DL I've cheated on the eye exam part so I'm sure legally I need them to drive. I'm not so sure I'm ready to wear glasses all the time, but I won't know until I get them. I guess I'll just have to wait until they come in a week or so.


 14 May 2017, 11:52

to Jenny:

I can confirm, what Soundmanpt wrote to you - this will be the most different part of the adaptation to your glasses.

"Don't be surprised if the floor seems tilted or slanted and you may feel dizzy and sick to your stomach and have a headache as well".

This can last (my own experience many years ago) for up to four weeks - but these situations did not last for more than two or three minutes. I left the eyes bare eyed for this small moment and everything was o.k. Later, the brain had obviously learnt about the new situation of the 'modified optical input' (my own word creation).

But in the long run, it's worth everything wearing glasses instead seeing affected by the vision defect.

And, last not least, a lens for astigmatism is like holydays for the eye. With astigmatism uncorrected, the eye is always searching for a focus point, stressing the eye muscles and cannot find it (that is one of the causes of fatigue, strain, and headaches). With the correction lens, the eye is stable. This is very similar to an autofocus camera and the lens drive - this remark, if you are a photograpy fan.

Recently my daughter in law had this experience, she always suffered from headaches, and she had a -1.00 correction for astigmatism on one eye only, and she is so happy now!

Best wishes, and courage!


Tom1 14 May 2017, 06:56

The guy who answered before me is 100% right.

However, let me add a point. Did you have troubles so far due to your vision? Were there things you could not do since you didn't see well enough? Did astigmatism precluded something you wanted to do and cannot do since you do not have perfect vision?

If this is the case you life will certainly improve with glasses on since everything will be much more clear.

On the other hand, if this is not the case and you hardly realised you needed glasses, I'm wondering if it is really needed for you to get 20/20 vision and become accustomed to glasses. In fact, if and when you will start using glasses full time, it will be much more difficult for you to do without, as you are acually doing now...

You are the only one who can decide how much wearing your glasses (in fact glasses are not a cure for any vision defect, they are only an aid to improve your performance when you are wearing them).


Soundmanpt 13 May 2017, 20:00

Jenny

My first question to you is to ask if you often get headaches maybe around mid day? If you don't I am quite surprised considering you prescription. Quite often people start getting headaches when they only have a need for -.75 astigmatism correction and you're at -1.75. That is why the doctor and saleslady / optician was surprised that you aren't already wearing glasses. I think that you are likely to have a real problem with adjusting to your glasses once you get them. Unlike being near or farsighted where if your nearsighted you would simply wear glasses when you wanted to see something in the distance or if you were farsighted and only needed glasses for seeing close up such as for reading. But astigmatisms effects your eyesight at all distances. i'm almost positive that when you first put your glasses on you're going swear that they aren't the right prescription. Don't be surprised if the floor seems tilted or slanted and you may feel dizzy and sick to your stomach and have a headache as well. That is the reason the doctor is suggesting doing things where you won't be moving around too much such as sitting down watching TV with your glasses on. You're eyes are sure to go through an adjusting period. But once your eyes do adjust I think you will not be taking your glasses off except to clean them and to shower and at bedtime. Yes you're going to be wearing your glasses full time.


Jenny 13 May 2017, 15:19

Had my first eye exam yesterday in 20+ years at Foreyes. Doc and saleswoman were both shocked I hadn't been wearing glasses and said I would see a significant difference when my glasses arrived. My script was PL/-1.75 100 PL/-1.75 65. Don't know much about prescriptions but the doctor said I have a good amount of astigmatism and probably had it for years. I'm 42 currently btw. He also tested my near vision and even though I could see the smallest line only with help, he decided I could just take my glasses off if necessary for another year. He didn't really give me a recommendation of how often to wear the glasses, but he did say to get used to them while watching tv and doing things around the house because there will be an adjustment period.


Benn 13 May 2017, 07:30

Thanks a lot.


 13 May 2017, 06:20

to Benn:

Your confirming question to my answer ....

... the value stated in rx would be the placement in the circle . So does it mean that the max would be 12?

I think, you got it right.

The method is as followa:

The optician or eye practioner sits in front of person to wear these glasses:

Start with the right eye / right lens of the patient

Right eye: sph XY / cyl -3.00 at 0 degrees means axis horizontal fro the right to the left / looks like 3 o'clock.

R.E.: sph XY / cyl -3.00 at 15 degrees would be at 2.30 on the clock

axis at 30 degrees would correspond to 2.00 o'clock.

axis at 45 degrees (halfway, just diagonal) would be at 1.30 on the clock, etc.,

until we reach at 12.00 (noon/midnight) with the 90 degree axle.

But 12 / 90 is just a position, not a maximum!

The axle can turn outwards, reaching for example 105 degrees, this corresponds to 11.00 on the clock, and it closes with 179 degrees at 9.01 approximately.

The denominations of the lower part of the circle (from 181 to 360 - corresponding 8.59 to 6.01 on the clock are not used).

I personally have a prescription for astigmatism.

The minus cylinder is nearly vertical (up-down)

Right eye: sph xxxx / cyl - 2.00 A 100 degrees

Left eye: sph xxxx / cyl - 1.00 A 95 degrees


Maxim 12 May 2017, 16:48

Unfortunately not in English -

https://www.youtube.com/watch?v=WB7hzW1Zg4g#t=72.703695

Two screens are used: corner right down the lens, center effect of turning the lens.

Demo of astigmatism starts at 2 minutes 50 seconds.


Benn 12 May 2017, 07:41

Wow...thanks. It is very complicated. I appreciate your help.

So if I am getting it at all, the value stated in rx would be the placement in the circle . So does it mean that the max would be 12?


Maxim 12 May 2017, 00:15

This object

00000

00000

00000

00000

1. seen through a prescription lens

+/- 0 (plano, no myopia, no hyperopia) but cyl - 3.00 at 0 / 180 degrees:

00000

00000

2. the same object, seen through sph 0 / cyl - 3.00 at

90 degrees:

00

00

00

00

00

3. same object, now combined correction for myopia and astigmatism, e.g.

sph - 3.00 / cyl - 3.00 at 0 / 180 degrees:

oo

4 same object, now combined for myopia and astigmatism,

e.g. sph - 3.00 / cyl - 3.00 at 90 degrees:

0

0

5./6. You can also look through lenses with combined correction for hypermetropia and astigmatism (plus lenses), but this cannot be presented as simple her, plus lenses are causing a kind of blurr.

An example for a combined plus prescription:

Right eye: sph + 4.00 / cyl - 2.00 90 degrees

Left eye: sph + 3.75 / cyl - 1.50 100 degrees


Maxim 11 May 2017, 16:14

I could also describe the system by a clock.

Your lens with an astigmatism correction of - 3.00 cyl with no myopia or hyperopia correction could be mounted

at 0 degrees = 3 o'clock or 9 o'clock

at 90 degrees = 6 o'clock or 12 o'clock -

other examples could be:

Right eye at 45 degrees 1:30 and

left eye at 135 degrees = 10:30

and so forth.

The surface of the lens with a cylinder (=astigmatic) correction hasn't got the shape of a perfect ball, but the shape of an egg, of a mango, of an american football instead.

When you put those lenses in light beams (bicycle lamp, pocket lamp, sun shining etc.) the plus lenses concentrate the light in two lines, and not in a punctual structure. The minus lenses for myopia don't spread the light evenly, but more in one direction than into the other direction.


Maxim 11 May 2017, 16:02

PS: Have you been a good scholar in mathematics and/or in geography?

These degrees refer to the 360 degrees of a full circle (in two dimensions a cylinder, or a ball), similar to the East-/West and North-/South degrees describing a position on the earth.


Maxim 11 May 2017, 15:52

No answer so far to Benn's question? I'll try it.

1) astigmatism comes together with myopia, with hyperopia or with +/+ 0.00 (plano).

2) astigmatism correction is defined from the left to the right, then as = degrees or 180 degrees

OR from top to bottom (vertical) as 90 degrees,

OR as values between those (diagonals etc.).

3) if you look through a lens with no correction for myopia or hyperopia, but with a -3.00 cyl correction for astigmatism at 0 degrees / 180 degrees, a person like Arnold Schwarzenegger with shrink, and would look like a little fat man like Laurel from Stan and Laurel.

If you look throught the sam lens, but turned by 90 degrees (now -3.00 cyl at 90 degrees) Arnold wil look same size, however much slimmer and thinner, like Stan now.

You can make a simple check, if a given pair of glasses has a correction for astigmatism:

When you turn the glasses, looking through the lens, and a person (or a door, a cupboard, a window etc. - everything) changes change theier shape from fat to thin, then the lens provides correction for astigmatism. When they don't change their shape / their form, then we have a simple myopia or hyperopia correction (or no correction at all) without corretion for astigmatism.


Benn 10 May 2017, 11:00

Okay I need help. I understand plus and memos numbers. I can see a -3.00 lens looks like or a plus 3.00. But what does a minos three in astigmatism look like.

Sorry to be so dumb.


Cactus Jack 12 Mar 2017, 19:46

Wondering,

I think you may find this helpful, particularly the part about Astigmatism.HOW TO STUDY FOR AN EYE EXAM

An eye exam is not like an exam that you might take in school and there is really no way to study for it. However, you can prepare for it and learn about your role in the exam. The best eye exams are a team effort between you and the Examiner. Part of the preparation is to learn what to expect, particularly if this is your first eye exam.

One important thing you need to keep in mind is that the Examiner has no way to experience what you are seeing. He/she has to depend on your answers to questions.

There are two parts to an eye exam. The first part is the Objective part. This part consists of:

1. Taking a Visual History where you describe your vision and the kinds of problems you are having.

2. Checking the internal pressure in your eyes for symptoms of Glaucoma. This is one of the very few parts of an eye exam that is even mildly uncomfortable and the discomfort only lasts for a few seconds. There are two basic ways to do the pressure test.

A. Using a special instrument to lightly touch your Cornea. Not to worry here. Before doing this type of test a drop of mild anesthetic will make sure you don’t even feel it.

B. There is a new type instrument that uses a puff of air directed against your cornea. No anesthetic is required, but the puff will startle you. The puff of air is harmless and there are huge benefits. Detecting Glaucoma early, before it can do damage can save your eyesight.

3. The examiner will also get a preliminary estimate of your refractive error by using an Auto-Refractor or manually by using a small hand held instrument called an Ophthalmoscope or Retinoscope.

The Auto-Refractor is a relatively new instrument that was developed in conjunction with NASA to check Astronauts vision in space. You look into the machine with each eye individually where you will see a scene or a pattern. The machine will adjust its internal lenses to focus the image you see on your retina. The Auto-Refractor only takes a few seconds for each eye and it then prints out your estimated prescription.

Some Examiners prefer to use manual methods that have been used for many years. Using an Ophthalmoscope or Retinoscope and a Trial Lens set or a Phoropter (a fancy machine with a built in lens set), the Examiner will look into your eyes and select the lenses that allow him to see your retina, most clearly.

The object of this part of the exam is to get a starting place for the Subjective part of the exam where you have to describe what you see.

Typically the Subjective part of the exam starts with the Right Eye shutter open and the Left Eye shutter closed.

Step 1 is typically determining the cylinder and axis of any Astigmatism correction you need. This is actually the hardest part of the exam because you will be asked to judge relative blurriness of two images rather than the sharpness of an image.

You will be shown a line of text and a supplemental lens will be rotated into place. This lens is a cylinder lens that is mounted on a 45 degree pivot and can be flopped back an forth to bracket a trial axis or orientation of the long axis of the cylinder lens. The thing that is confusing about this test is that the straight lines (strokes) of the letters will alternate in clarity as the lens is flipped back and forth depending on their direction. I suggest concentrating on an “O” if possible. Depending on your answers, the examiner will adjust the axis knob unit the image you see is equally blurry with the supplemental lens 45 degrees each side of the selected axis.

At this point the Examiner will probably swing the supplemental lens out of the way and may change the cylinder power while asking you which lens in clearer.

For your first exam, you may be uncomfortable asking the Examiner to let you fine tune the Cylinder Axis, but I have found that most will appreciate your wanting to actively participate. The way that works is that he will place your hand on the Axis control knob. This time, you move it back and forth a few degrees looking for the sharpest image. It is a bit like “Fine Tuning” an old Analog TV set or moving the tuning knob on an analog AM radio for the best signal.

The next step is determining the Sphere correction. This is an easy part of the exam because all you have to do is pick the sharpest image, but there is a tricky part. Your auto-focus mechanism will try to help, if it gets a chance. The Examiner has a couple of ways to minimize the action of your ciliary muscles and crystalline lenses.

The Examiner can, in effect, sneak up on your Sphere prescription or he can use drops to Dilate your eyes. Lets talk about sneaking up on your prescription first. There are actually 4 lenses in your eye’s lens system. All of them are PLUS lenses and the total power is about +56 to +60 diopters. The only variable focus lens is the crystalline lens whose PLUS power is controlled by your ciliary muscles. For distance, your Crystalline lens is fully relaxed and has somewhere around +15 diopters. When you focus to read, your Ciliary Muscles squeeze the Crystalline lens to increase its PLUS power by the amount necessary to focus which depends on the distance to the object.

This will take a little thought to get your mind around, but if you are nearsighted, your lens system has too much PLUS for the distance from the lens system to your retina and you need MINUS lenses to neutralize some of that excess PLUS power. You ONLY have the ability to increase the PLUS power of your lens system. You have NO ability to reduce the PLUS power of your Crystalline lenses more that fully relaxed.

To try to keep your Ciliary Muscles and Crystalline lenses from getting in the act, the examiner will start with NOT ENOUGH MINUS or TOO MUCH PLUS (same thing) and gradually increase the MINUS one or two steps at a time, while reducing the size of the line you are asked to read. He will not tell you what power lens or what line you are looking at. Eventually, he will reach the 20/20 line and a lens power that lets you read it with no mistakes.

He will then follow the same procedure with your Left Eye.

When he has completed both eyes, he will open the shutters and you may see two images. This part of the test is to check your muscle balance using some prisms. He will probably ask you to tell him when the two images are aligned horizontally and then vertically. While the images are separated, you have an important check to make. Compare the sharpness of the two images. If they are not equally sharp, be sure and tell the Examiner which image is clearer. If there is a difference, he will likely reduce the sharpness of the clearest image until they match. The important thing at this point is that they match. That lack of sharpness will be corrected in the next phase with both eyes working together.

Next he will fuse the images so both eyes are working together and repeat the Sphere procedure by gradually increasing the MINUS or decreasing the PLUS until you see the smallest line of letters very clearly.

That pretty much completes the exam except for checking your near vision with a small chart about 14 to 16 inches from you.

Many people, who wear glasses, actually look forward to eye exams. Once you have become accustomed to having very good vision, you will probably find anything less, unacceptable. Many times, after the exam, it will be suggested that you get another exam some time in the future. Note that I used the word “suggested”. it is NOT a Command. If your detect a problem or if your vision seems uncomfortable, please don’t wait until the “suggested” date to seek an appointment to get your vision checked.

C.


Wondering 12 Mar 2017, 11:16

Thanks Soundmanpt, I think I get it! So for example is an axis of 10 an equivalent of 170? Just looked at an astigmatism axis chart. So the numbers I have have only moved approx 20 degrees . My short sightedness started at -0.50 in both eyes with no astigmatism, several years later it's-1.25 and -1.00


Soundmanpt 12 Mar 2017, 10:22

Wondering

Prescribing for someone with astigmatism is the most difficult part of an eye exam for any optometrist. First of all let me assure you that even though the numbers may seem quite different to you they actually aren't. You mentioned that you're mildly shortsighted so you have probably noticed that since you first started wearing glasses you SPH has either not changed or changed very little but any change was always an increase. That is very normal for everyone. But CYL is seems to increase or decrease from one exam to the next but generally it usually doesn't change too much aver time which as you can see yours hasn't. The axis first of all is not a power value so being a 2 or 180 doesn't mean your eyesight has changed. That number determines the positioning of the lens for each eye and goes from "0" to 180. Now try and think of these numbers going around a circle much like looking at a clock with 180 numbers going around it. So then you have had an axis of 180 if you go backwards isn't that far from 20. It's not 160 numbers away but rather only 20 number away. I hope this helps.


Wondering 12 Mar 2017, 09:55

Hi all, ok so got a bit bored and sorting through paperwork, I have kept copies of my eye test prescriptions.

I've noticed that every time I go to the opticians I get different results for cylinder and axis, sometimes none at all, why is this? Are my changes drastic or just minor and stable? I'm mildly short sighted

My most recent test early this March shows

R-0.25 x165 L-0.50 x180

Previous tests over the years:just Cly and axis shown:

R 0 L-0.25x20

R-0.50x170 L-0.50x10

R-0.25x180 L-0.50x5

R-0 L-0.50x10

R-0.25x160 L-0.50x15

R-0 L-0.50x180

R-0 L-0.25x15

R 0 L 0


Maxim 27 Feb 2017, 17:06

Clearly "yes".

Your prescription is a minor prescription, and it would optimize your vision.

But the vision is clearly sufficient for driving, as far as the resolution is sufficient.

You could compare this to the 'pixels' in a digital camera. You obviously have eyes with sufficient 'pixels, and also with sharpness below the optimum, the acuity is still sufficent.

However, you should buy cheap glasses with this prescription, you might like the optimization of your vision.

Astigmatism means, that the surface of your lens is not a perfect ball surface, and every moment the muscles are trying to force the surface in the perfet shape. With this prescription, these muscles could relax. That's the effect.

I have not enough time in the moment to give a more thorough explanation, but that is the idea.

Best wishes!


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