Understanding Refractive Errors: Astigmatism

Greetings to all and sundry,

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It has been quite a while since we had our last lesson on refractive errors looking at myopia and hyperopia. Today we would like to jump back on our train and continue with the trinity of refractive errors known as astigmatism.

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Before we move on however, let's do a quick recap of the things we have already learnt. First, refractive error is not a disease rather a condition of the eye where light do not simply focus on the expected point for sharp vision.

When light falls behind the retina (the area within the eye which transduce light energy into electrical impulses) we have what we call hyperopia as the eye may pull in extra effort in an attempt to correct this. For the opposite which is myopia, the eye is not able to do much about that hence the myopic patient may visit the optometrist earlier than the hyperope.

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Myopia is also known as short sightedness whereas hyperopia is known as farsightedness, you may also find that other journals refer to them as hypermetropia for farsightedness and nearsightedness for myopia

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Astigmatism

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Astigmatism is just a little bit complicated that the ones that we have already discussed and so i would need you to stay with me on this one if you are going to get it well.

Now the cornea and the lens are the main refractive media that gets lights into the eye, imagine them as curve interface with different meridians like a ball with stripes on it. Now each of these stripes represent a curvature with different powers and its when they are have the same power that we get simple cases of myopia and hyperopia.

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In the case of astigmastism these stripes are not of uniform power and thus ought to be tackled individually. Most often it happens that the 90 degree meridian and the 180 degree meridian after the issues to deal with, sometimes you get this happening in the other meridians aside these two.

So when we have any of these particular meridians acting in the ways of hyperopia or myopia as already discussed previously we end up with the various types of astigmatism, including simple hyperopic astigmatism, simple myopic astigmatism, compound astigmatism. Let's leave the in-depth complications to the specialists.

Management

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As already discussed refractive error is not a disease and as such cannot be treated with medications however there are cases where surgery may be applied for those who would like a more permanent solution to glasses.

There are many options available for the management of refractive errors the most common of them been the use of spectacles or glasses which can be made to suit the wear to enhance aesthetics. There is also the option of contact lenses which provide same feature as spectacles and may also be altered in some cases to enhance aesthetics.

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One may also consider Laser or Lasik which corrects the error by altering the shape or nature of the cornea to get things sorted out.

Conclusion

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In all refractive errors have most often simple solutions and should not be a headache for the majority, unfortunately it is the leading cause of preventable blindness across the globe.

It is thus pertinent that we make effort to educate others and get ourselves and out wards to the optometrist when we fall within some of these categories. Thanks for reading and for your time. Thanks for reading and thanks to everyone for having me and greetings to prof @lemouth and @gentleshaid. Love from Ghana.

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For extra reading

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Kee C. S. (2013). Astigmatism and its role in emmetropization. Experimental eye research, 114, 89–95. https://doi.org/10.1016/j.exer.2013.04.020

Remón, L., Monsoriu, J. A., & Furlan, W. D. (2017). Influence of different types of astigmatism on visual acuity. Journal of optometry, 10(3), 141–148. https://doi.org/10.1016/j.optom.2016.07.003

Shao, X., Zhou, K. J., Pan, A. P., Cheng, X. Y., Cai, H. X., Huang, J. H., & Yu, A. Y. (2017). Age-Related Changes in Corneal Astigmatism. Journal of refractive surgery (Thorofare, N.J. : 1995), 33(10), 696–703. https://doi.org/10.3928/1081597X-20170718-04

Read, S. A., Vincent, S. J., & Collins, M. J. (2014). The visual and functional impacts of astigmatism and its clinical management. Ophthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists), 34(3), 267–294. https://doi.org/10.1111/opo.12128