How to find out my astigmatism?

Question

Hi,

I have problem in understanding my eye test report

Anyone could help?

Right: Sph: -4.25 Cyl -2.00 axis 3

Left: Sph: -3.25 Cyl -3.00 axis 177

Would anyone explain what is Sph, Cyl and Axis mean?

I want to avoid go back to the optician.

Thanks

Answer 1

Take the left eye:

the -3.25 is the spherical power.

Actually -3.25 is the power of lens necessary to focus lines which are at 3 degrees.

The degrees are measured from the horizontal; that is, form the 3 Oclock position.  Call that O degrees (zero).  Then from that position count the degrees counter clockwise.  If you count through 2, and 1, and 12, and 11, and 10, you will come to 9:00 which is 180 degrees.  Your axis is 177 degrees.  That's almost horizontal.  So the 180 axis and the 0 axis are the same.

So for black lines on a chart or piece of paper, the 177 degree power of your glasses is -3.25.  With 3.00 Dioptors of astigmatism, the power of your left eye 90 degrees from 177 (87 degrees) is the sum of the sphere and the cylinder, (-3.25 plus -3.00 or -6.25.

-3.00 corresponds to 1 / 3 of a meter.  -6.25 corresponds to 1 / 6.25 meters.

1 / 3 meter is 33.3 cm.   1 / 6.25 meters is 16 cm.

Take a piece of paper and draw some horizontal lines on it and some vertical lines on it. 3or 4

Now with your right eye closed and glasses off, hold the paper about 18 inches away and bring it slowly towards you looking at the lines.

As the paper comes closer , all at once the horizontal lines will come into focus but the vertical lines will still be blurry.  As you keep bringing the paper closer, the vertical lines will come into focus.  The lines cannot all be sharp and clear at the same time. This is because of astigmatism.  A means without. Stigma means point.  So with astigmatism your eyes are without a point focus.  To see clearly you need a point focus.

With your glasses on, however, you will find that both sets of lines are now in good focus.  The lenses have corrected your astigmatism.  They have corrected your spherical error and your cylindrical both at the same time!

The situation with the right eye is similar.

Many Opticians, Some Optometrists, and some Ophthalmologists do not fully understand this and remain confused by it.  Now you know more about this than your optician or the doctors "tech" that did your refraction.

A lens that corrects for astigmatism has a spherical correction on the front surface and a toric correction on the back surface.  A toric surface has one radius of curvature in one direction and another radius of curvature 90 degrees from that direction.  If you slice a donut near the edge you will get a toric piece of donut.  If you cut a tennis ball you will get a spherical piece of it.

With your glassses you can notice that the tops and botttoms of the lenses are thicker than the sides.  (This would be strictly true if your  lenses were round.

When you hold your glasses in front of you and rotate them, you can immediately see that astigmatism correction is present.

The term cylinder comes in because a cylinder correction combined with a spherical correction gives a toric surface.

Answer 2

the - 4.25 is your myopia correction...( nearsightedness )

the - 2.00 is your astigmatism correction

the   3...is 3 degrees...the direction your astigmatism correction is ground at in your lenses.

Then the same for your left eye...different numbers, but works the same way.

The numbers are dioptres...a unit of power used to determine the amount of correction needed.

1.00 dioptre, 2.00 dioptres...ect.

Did that clear it up ?