First of all my respectful greetings to all the academic and scientific community of Hive.blog, we continue with our efforts to expand the learning related to the essential phenomenon of light, which as we have seen so far is responsible for transporting each of the images that our optical systems can observe around us.

Introduction

Every person on this planet, without any doubt, by having their normal vision conditions, can make use of the different light rays that come from their environment, this of course, makes us see the wonderful world around us, which is why our commitment to continue expanding the learning related to this type of electromagnetic energy which has the natural ability to propagate even through the vacuum.

Understanding the nature of light has cost us many years of our history, however, these remarkable learnings have allowed us to develop exponentially in all senses, this makes us express that thanks to the understanding of light have come the countless knowledge we have achieved from our natural environment, because without this type of energy our eyes would not be able to perceive our environment.

In previous presentations or articles we have been related to a wonderful physical magnitude which we know as Diopter and it represents the refractive power of any material or elastic medium, in our case of artificial or natural lenses, and also, we have seen how the combination of both (lenses) has allowed us to correct some unfocused projections of images on our retina.

It is always important to point out that when talking about our natural optical system, we must emphasize that in this system we can find natural lenses such as the cornea and the crystalline lens, and these are directly responsible for the proper focus of the images on our retina, and thus with refraction capacity, which can also be measured in Diopters.

It is important to remember that the Diopter magnitude represents the inverse value of the focal length of any optical element or system, and also the higher this value is, the more intense the refractive power of the lenses in relation to the light rays will be and vice versa, that is, the amount of Diopter is proportional to the refractive power of the different lenses.

In the same way that in the previous articles we will be able to perform a representative practical experience in order to continue expanding the knowledge related to the refraction of light rays as they pass through different natural media as they do with our natural lenses, and also we will continue linking with other ametropias developed by some anomaly in the refraction of light rays within our optical system, this time we will relate in a general way with astigmatism.

Refraction of light rays in a material medium

As in previous deliveries I wanted to show you a small practice of the refractive power of a material medium in order to be able to relate in the best way with the ametropia previously mentioned, for this I could get a wonderful material medium as you will see below in the following figure 1.

_{Figure 1. Refractive power of a material medium}

Clearly my dear readers could realize the phenomenon of refraction, and thus the refractive power of a certain material medium that in this case is represented by a small transparent sphere as you could see in the previous figure, such refractive power makes the initial image is reversed when passing through this small sphere, and this is achieved by bending or refraction of light rays as we can detail in the following figure 2.

_{Figure 2. Behavior of light rays in the aforementioned material media}

This allows us to point out that in the same way our natural lenses such as the cornea and the crystalline lens refract the luminous rays when they pass through them and reach our natural receptor screen such as the retina, the action of these lenses is to try to converge as much as possible the luminous rays on the retina, and this will depend on whether or not the so-called ametropias originate, as already analyzed, myopia, hyperopia and now astigmatism.

Light rays in an eye with astigmatism

As astigmatism is an ametropia this makes us relate to a bad focus of light rays on the retina, and generally this is due to the variation in relation to the curvature of both the cornea or lens, and thus two focal lines are generated instead of a point, then we can see the behavior of light rays in this type of ametropia in the detailed figure 3.

_{Figure 3. Behavior of light rays in an eye with astigmatism}

In the previous figure 3, we could first observe an emmetropic or normal human eye whose refraction of light rays converge on the retina without any refractive problem.

Then we observed in detail the behavior of light rays and the various forms of presentation of this refractive defect such as astigmatism, in the second (2) case we noticed how both focal lines are projected in front of the retina, in the third (3) case one is projected in front and the other on the retina, in our fourth (4) case one line in front of the retina and the other behind, in the fifth (5) case one line on the retina and the other behind the retina and in our sixth (6) case both lines are projected behind the retina.

As we have already pointed out, these types of ametropia can generally be corrected by implementing artificial lenses with spherical and cylindrical surfaces, with the clear purpose of helping the inadequate curvature of either the cornea or the crystalline lens and achieving convergent focusing of light rays on the retina, as shown in figure 4 below.

_{Figure 4. Correction of the refraction of light rays in an eye with astigmatism}

Conclusion

Undoubtedly, my dear readers, it is exciting to be able to understand more and more the essential phenomenon of light, which together with that of movement, in my humble opinion, represent the whole of the existence of the universe as well as our own, without them, nothing would be possible, a remarkable aspect that has motivated us throughout our history to know as much as possible about these vital phenomena.

Light, like other phenomena, represents a very remarkable and abstract knowledge which thanks to the field of science has managed to translate into a language understandable to the rest of humanity, our brain or logical understanding works more effectively when it manages to perceive images of any activity inherent in our existence, which is why through small practical experience was able to notice the purpose of achieving to show the refractive power of certain material medium.

Of course, all the above described led us to a better introduction at the time of analyzing in a general way the ametropia as astigmatism and the different ways to present themselves at the time of a bad focus of the luminous rays in our retina, concluding with the correction of such ametropia through the implementation of artificial lenses.

Until another opportunity my dear Hive readers, especially to the members of the great #stemsocial community, for which I highly recommend being part of this beautiful project, as it highlights the excellent work of academia and the great work of the entire exciting scientific field.

Note: All images were created using the Power Point application and the animated gif was created using the PhotoScape application, the photographic images were captured using the camera of the Samsung Galaxy J2 Pro cell phone.