The following article is presented to you by Pablo Sanz & Miguel García Revisited 09.2017 by Nikolai Suchkov, Alessandra Carmichael & Neeraj K. Singh
Disclaimer: For all the general public, not technical knowledge is required.
Look around you – how many people wear glasses? Most of them suffer from near-sightedness, which is also known as “myopia”. This condition restricts the quality of their vision at a distance. It currently affects 20% of the population, and will rise to 50% worldwide.
Over 2000 years ago, near-sightedness was already known by the ancient Greeks as “myopos”, which referred to how myopic people squint their eyes to create a sharp and clear image. With this characteristic gesture, they are simulating a pinhole, that is, an artificial pupil of a smaller size. This pupil reduces the amount of blur on the retina but also the amount of light and the area you can see.
But what is myopia? Let’s begin with how our eyes work.
In a healthy eye, light rays from a distance enter the eye through the pupil, and are redirected to meet at the sensor located at the back of the eye, known as the “retina” and produce a sharp image. On the other hand, a mismatch between the focus point of the rays and the retina causes a blur. This can occur in front (Myopia) or behind (Hyperopia) the retina, as is 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 symptoms of myopic subjects are: blurred distance vision or out of focus image, and deteriorated vision in low lighting conditions.
*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)
What is the prevalence of myopia?
Knowing what this refractive error is, how does it affect the global population? Currently 1.6 billion people worldwide suffer from myopia and it is estimated to increase to 2.5 billion people by 2020 . (1)(2)
Furthermore, the prevalence of myopia varies with age and other factors: genetic, ethnicity, geographic location, environmental factors, lifestyle, etc. Learn more about at the following post:
Current recommendations for Myopia (Not available yet)
Near-sightedness typically appears at an early age, between 6 and 12 year olds, 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 20 to 40 year olds, this prevalence is about 35% to 40% 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 affected individual (9). In order to prevent the rapid growth of myopia, researchers around the globe are developing new strategies and treatment modalities, backed by the economic support from major companies and government funding bodies worldwide.
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.