What’s the difference between plus and minus cylinder?
These are different ways to describe astigmatism correction in glasses. Ophthalmologists work in “plus” cylinder while optometrists like “minus” cylinder. Mathematically, they are the same.
Glasses are made to correct a certain amount of spherical error. However, people also have a certain amount of astigmatism that also needs to be corrected. Astigmatism is when the surface of the cornea is not perfectly round like a basketball, but more round like a football. The extra steepness along one axis needs to be corrected with a cylinder.
The cylinder correction can either be made with a positive convex lens or a negative convex lens, the end result is the same.
still i do not know the different
How do you calculate the power add on for the following:
OD Sph -1.50 Cyl -.75 Axis 178
OS -.50 -.50 Axis 168
The best I could find was Sph x 1/2 cyl., but, nothing works.
Thanks
OD Sph -0.75D Cyl plus 0.75 Axis 78
The add is neither in the sphere nor the cylinder space on a prescription. It’s a power added at the base of the lens that magnifies the near field of view.
Add power will have more to do with age than computing something from the distance prescription. For example, and child with the distance prescription you listed above does not require an add power (assuming they do not have accommodative esotropia) whereas an 80 year old with the same distance prescription will need a reading power because they no longer have the ability to accommodate or focus up close. Typically patients between 40-45 need +0.75 to +1.50, 45-50 need +1.50 to +2.00, 50-55 may need +2.00 to +2.50 and then close to 60-70 need +2.50 to +3.00. Usually, no more than +3.00 is given unless there is an underlying disease. Now, if you are talking about a computer add power typically the opticians making the glasses add the reading power and distance spherical power together to get the mid range add power strength. Hope this helps. Visit AAO (American academy of ophthalmology) for more info.
Are you trying to find the spherical equivalent of a lens?
You can do that by adding (algebraically)1/2 of the cylinder power to the spherical power.
For instance -1.50-0.75 x 178 has the spherical equivalent of a -2.12.
Plus cylinder has the astigmatic correction (cylinder)added to the sphere.
Minus cylinder subtracts cylindrical component from the spherical power.
Glasses, and contacts for that matter, are ground in minus cyl, so conversion is an important skill.
Woops! Bad math!!! I work in plus cyl most of the time.
The spherical equivalent of that formula is -1.87.
Sorry, checking my math worked! 1/2 of -.75 is -.37.
Ophthalmologist like to ”add power” – use the plus cylinder.
Ophthometrists preffer the minus cylinder (reduce power) because it is easier to grind into the lenses. The difference is really just the axis you’re looking at. If the correction is +0.75 at the 120 degree axis, then the correction on the 30 degree axis is -0.75. You just choose one axis and look at the power. The two axes are always perpendicular to eachother. So you just add/subtract 90 from one axis and change the sign in front of the cylinder (+ into – and viceversa).
Just do the lens transposition and you use lens transposition formula you will be ok
I have 2 prescriptions from 2 optometrists one marked -1 cilinder another one -1.5 cilinder the rest is the same what is a differrent an how is gone affect my vision. Thanks
The difference is either one will be over corrected or under correct .. As it’s the cylinder power, the effect may be severe head ache or clarity of vision..
Do you have blood pressure or diabetes? How frequent the prescriptions? Do you have both glasses?If yes, is the -1.5 sharper but strain your eye? If it strains, go for the -1.
It’s a 1/2 diopter difference. The RX is dependent on how you answer the ? which is better . Meaning you were liking more minus during one of the exams.
you might be a progressive myopic astigmat which can explain the two different prescriptions or it can also be affected if you have a sphere prescription too, if so those prescriptions might be the same. 0.50 might not have much difference in your vision but you can pick which one aids you better.
It all depends which doctor was correct, there’s a two-step difference in the cylinders the stronger the cylinder the harder to get used to, witch doctor could you see the best on the snellin chart with the two different cylinders it could either be an overcorrection or an under correction one might be perfect but you have to fill them to find out or go back to the doctor thank you Pete
if we give in plus power wht is the difference
Actually given plus power only farsightness people.and add plus power 40age r above better near vision.
Stating the cylinder in plus or appropriate minus form is mathematically the same . However when spectacle lenses are ground , a plus cylinder is placed on the anterior surface while a minus cylinder is ground on the back surface of the lens since generally it is convex in front and concave behind. Among the two, the minus cylinder is preferred as it keeps the front surface spherical which reduces image distortion ,if any.
Adaptation time with minus cylinder form is shorter than with plus cylinder form.
For the case of big cylinder values, plus cylinder forms may cause spectacle induced meridional aniseikonia.
None
What is the difference between following:
1. RE: SPH: -5.00, CYL:-.50, AXIS: 90
LE: SPH: -5.25, CYL:-.50, AXIS: 90
2. RE: SPH: -5.00, CYL:+.50, AXIS: 90
LH: SPH: -5.25, CYL:+.50, AXIS: 90
What I can see in this is that number one is minus cylinder form while the other one is plus cylinder form.thanks
1. RE: -5.50 SPH/+.50 CYL×180
LE: -5.75 SPH/+0.50 CYL×180
2. RE: -4.50 SPH/-0.50 CYL×180
LE: -4.75 SPH/-0.50 CYL×180
Sir there is no new difference. It is the effect of transpotion of the lens.
Agebrically adding SPH with CYL.
changing the sign of the CYL into opposite sign
and changing the AXIS by 90.
That is all. If you have any other difference please share it.
If you convert the Plus cyl to minus you get OD -4.50 -.50 X 180 and OS -4.75 -.50 X 180. The plus cyl is a flipped axis @ 90 degrees and just a little less myopic.
In case of the different btn plus cylinder lens we can differentiate by the reading of spherometer on the curveture inside and outside curvetures where we can obtain different reading on one side while the other ready the same. Do the same thing in minus cylinder lens.
Sir i have one query not regarding this issue.
most of time person accept minus cyl instead of plus cyl form.
why this is?
it is almost same with vision correct only the difference between plus cylinder and minus cylinder is the shap of the ophthalmic lensa shape or form to manage the thickness and the fitting in the frame. for example:
+5.00 sph. / +1.50 cyl x 90 axis
this lens is plus and the thickness it will be better than if we produce it as
+6.50 sph. / -1.50 cyl x180 axis.
so it is the same only the difference is the shape of the ophthalmic lens.
Can you explain which type of patient use plus cylinder lens
Great help Dr. Root.
Thank you, helps to rerun the basics and reminds a lot.
Can you have a prescription like +1.50 +1.50 x 085 for the right eye
+1.50 +1.50 x 090 for the left? It should convert to +3.00 -1.50 x175, +3.00 -1.50 x 180 Is this possible for an rx?
I recently had an eye exam and received my glasses. I believe my prescription is wrong. I have another appointment to check it. Is it possible to have a large difference between right eye and left for cylinder. OD +1.75 and OS -2.50. I know I have an astigmatism.
Can I get a corrective lens with two cylindrical axes ( at about 60 deg relative to each other)? I see one dot as 3 dots, very close to an equilateral triangle. This is only for one eye. For the other eye I see only two dots, which are perfectly corrected with one cylindrical lens.