What is Astigmatism ?

It is arguably one of the most common refractive errors and is something most of us probably have to some degree. The most simple way to explain astigmatism is basically that the structures within the eye are not perfectly round in simple words there are a little bit warped and because of that it causes light to bend or refract a little bit uneven inside of the eye and that causes your vision to be blurred and distorted. However, the good news is that astigmatism isn't actually a disease, it is just a condition that we can correct with glasses, contact lenses, and even eye surgeries like LASIK. Now to better explain what astigmatism is let us learn about the Cornea

It is the window through which light enters the eye And it protects the inside of the eye from its outer environment it is also a refracting surface that bends light towards the inner eye in an ideal world it is smooth and evenly curved so that the light passes through in a uniform fashion however most of us have some unevenness on the surface of our cornea and that uneven curvature is what we call as corneal astigmatism

The curve on the cornea can be determined by finding the difference between the flattest and the steepest curve of the corneal surface. Most corneas have got curvature somewhere between 39 and 49 diopters and that number tells us the amount of curvature for power that the cornea has to bend the light

If there isn't astigmatism let's say the curvature is around 43 diopters in one place In the cornea and 41 diopters in another place in the cornea then the astigmatism is around 2 diopters ie., the variation in the curvature of the cornea at two separate locations is around to 2 diopters which are referred to as the corneal astigmatism

Now your eye doctor can usually measure this curvature using a couple of different instruments

Classically he will use an instrument called a Keratometer which will measure the curvature of the central 3 mm of the cornea

Keratometer

Corneal Topographer

A new instrument called Corneal topographer measures the entire front surface of the cornea with a significantly larger number of values with greater accuracy.

Now when light passes through a cornea with astigmatism that causes the light to be focussed irregularly inside the eye and that causes blurred and distorted image formation.

Most of us are born with some level of corneal astigmatism it may change in the first couple of months and then it tends to stabilize for the rest of our life

now there is another form of Astigmatism called lenticular astigmatism that has to do with the shape of the crystalline lens inside the eye and that astigmatism does tend to change throughout our lifetime now when the doctor usually corrects for astigmatism they usually correct for the combination of both the lenticular and corneal astigmatism. Usually, your doctor won't measure lenticular astigmatism by itself because it requires very expensive and high-tech equipment and it really just doesn't give us that much useful information.

You can easily figure out whether you have astigmatism or not by looking at your recent glass prescription(Cylinder values indicate you have astigmatism.)

The good news is that we can correct astigmatism with glasses contact lenses and forms of corrective surgery like LASIK. The most simple way to correct for astigmatism is with glasses, however, glasses aren't the best ways to correct it because glasses always tend to have some optical aberrations/ distortions which may cause problems to the astigmatic patient

there are options like contact lenses that provide greater effectiveness in astigmatic patients

Options like LASIK can correct up to 5 or 6 diopters of astigmatism so always ask your doctor if you are a good candidate for those procedures.

Now there are certain cases where people have a high level of astigmatism, some of them include:-

Keratoconus- A condition where the cornea resembles the structure of a cone thereby causing hi irregularities in the curvature leading to the highest astigmatism