The following article is presented to you by Pablo Sanz and Miguel García
Disclaimer: For all the general public, not technical knowledge is required.
Originally described by the ancient Greeks as “myopos”, this condition makes reference to how the myopic people squint their eyelids to create a sharp and clear image.
But what´s myopia? And why they do this characteristic grimace? Let us begin with how the image is formed into the eye.
In a normal eye, the ray-lights coming from far distance pass through the different mediums inside the eye creating a sharp point on the retina.
On the other hand, if we are dealing with any error condition, we have a mismatch between this focused image and the retina, where our light receptors reside. Both ray schemes are shown below:
Note that this is an easy approximation, while even in the best ideal case, a point refracted by crossing a circle(pupil) is not a point. Far from this, due to the eye aberrations, this merged point is always a stain/blur.
So, myopia also known as short-sightedness or nearsightedness , constitutes a failure of matching image formation and receptors location, being the image formed in front of them as shown in the right scheme.
Using a more accurate definition, myopia has been defined as a common optical aberration of the eye in which the conjugate focus of the retina is at some finite point in front of the eye, when the eye is not accommodating.
Some signs related to myopic subjects are primarily: blurred distance vision or out of focus image and deteriorated vision in low lighting conditions while better vision at short distance than hyperopes.
*Why they squint their eyes? With this characteristic gesture they are simulating a pinhole, reducing the amount of rays arriving to the eye and generating an artificial pupil of smaller size. This pupil reduces the size of the blur on the retina but also the amount of light and the area you can see.
As this post is supposed to be an easy explanation on myopia, further comprehension about aberrations of a myopic eye can be found in other entries:
Myopia and eye aberrations (Not available yet)
This refractive error is caused by many factors, but basically due to elongation of the eye.
Which is the prevalence of myopia?
Now, knowing what this refractive error is, you might be curious to know the predominance of this eye condition around the world.
Nearsightedness has been estimated that affects 1.6 billion people worldwide and during the year 2020, 2.5 billion people would be affected by myopia. (1)(2)
Furthermore, the prevalence of myopia varies with age and other factors: genetic, ethnicity, geographic location, environmental factors, lifestyle, etc. As you can found in the following post:
Current recommendations for Myopia (Not available yet)
Typically appears between 6 and 12 years of age, and the mean rate of progression is approximately 0.50 Diopters per year, based on studies of mostly Caucasian children. (3, 4)
The prevalence of myopia is approximately 25% in the western population and much higher (70% to 90%) in different regions of Asia (5, 6).
Among persons the prevalence is about 35% to 40% in their 20s to 40s and decreases to about 15% to 20% among those in their 60s, 70s, and 80s. (7, 8)
All these values led us to think that this optical condition is emerging as a major public health concern, generating an economic burden for each individual with myopia that does not have to go unnoticed. (9) For this reason, the research myopia field is focused on understand and reduce all the factors that may produce the increase and development of myopia.
Stay up-to-date, Keep on reading and…
(1) Kempen JH, et al. The prevalence of refractive errors among adults in the United States, Western Europe, and Australia. Arch Ophthalmol. Apr 2004;122(4):495-505. (2) Holden BA, et al. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology. 2016 May;123(5):1036-42. (3) Jensen H. Myopia progression in young school children and intraocular pressure. Doc Ophthalmol 1992;82:249-55. (4) Parssinen O, Hemminki E, Klemetti A. Effect of spectacle use and accommodation on myopic progression: final results of a three-year randomised clinical trial among schoolchildren. Br J Ophthalmol 1989; 73:547-51. (5) Shortt AJ, Allan BDS. Photorefractive keratectomy (PRK) versus laser-assisted in-situ keratomileusis (LASIK) formyopia. Cochrane Database Syst Rev 2006; (2):CD005135 3. Dirani M, Islam FMA, Baird PN. The role of birth weight in myopia – the Genes in Myopia twin study. Ophthalmic Res 2009; 41:154–159 (6) Saw SM, Tong L, Chua WH, Chia KS, Koh D, Tan DT et al. Incidence and progression of myopia in Singaporean school children. Invest Ophthalmol.Vis.Sci. 2005; 46:51-7. (7) Vitale S, Ellwein L, Cotch MF, et al. Prevalence of refractive error in the United States, 1999-2004. Arch Ophthalmol 2008; 126:1111-9. (8) Katz J, Tielsch JM, Sommer A. Prevalence and risk factors for refractive errors in an adult inner city population. Invest Ophthalmol Vis Sci 1997; 38:334-40. (9) Zheng YF et al. The economic cost of myopia in adults aged over 40 years in Singapore. Invest Ophthalmol Vis Sci. 2013 Nov 13;54(12):7532-7.