The following article is presented to you by Miguel García & Pablo Sanz
For all the general public. Some concepts may require certain prior knowledge about the eye.
Since we already explained what Myopia means, some of you might be wondering why it is so important to struggle against it, even more when we can easily correct it with spectacles, contact lenses or even eye-surgeries.
Despite it is being referred mostly as an inconvenience rather than a disease, it can be nowadays found some controversy on how to describe a myopic person either as subject or a patient. In spite of terminology trend to be relying more upon the regional laws than into the subject´s actual conditions and limitations, it is, undoubtedly, more than a limitation and some different correlation effects have been found from this condition to major ocular disorders.
What is an Odds Ratio (OR)?
Before showing to you what are the risks of myopia for other diseases, let us introduce a concept: OR or odds ratio which is the possibility that a group of a population gets a disease vs the possibility that another group gets the same disease.
It is used normally to dictate how much in risk is a population in comparison with a normal healthy one. In our case, how much is the risk factor of developing some ocular diseases for myopes vs emmetropes or hypermetropes.
What happens when high levels of nearsightedness are reached?
There is no global consensus, but high levels of nearsightedness can be considered in case refractive errors are above -6 diopters. These levels should be taken very seriously, because we are talking about a process in which an excessive elongation of the axial length occurs, leading to eye complications that are associated with degenerative retinal changes and with a substantial visual loss.
Usually, nearsightedness (myopia) has been divided into the following two groups:
- > – 6 Diopters or physiological myopia.
- < -6 Diopters or pathological myopia.
The high levels of myopic refractive errors are associated with degenerative retinal changes in the posterior segment of the eye and are known as degenerative or pathological myopia. (1)
The rule of thumb is as follows: the higher the myopia is the higher the possibilities of developing a retinal complications.
“High levels (> 10 dpt) of myopia are associated with an impact on quality of life comparable with keratoconus” (2)
Some of these complications are: myopic maculopathy, posterior vitreous detachment, retinal detachment, glaucoma, cataracts, among others. (3)
But, what diseases can shortsightedness promote and in which measure?
- Myopic maculopathy
This untreatable condition is one of the most common causes of irreversible visual impairment and it is originated by an atrophy of the macula (main responsible of our vision and the place where the fovea is located). The following table gives an overview on the riks (in terms of the odd ratio) for the development of myopic maculopathy, depending on the present central myopia.
|-1Dpt to -3Dpt||x2|
|-3Dpt to -5Dpt||x10|
|-5Dpt to -7Dpt||x40|
|-7Dpt to -9Dpt||x120|
Table values based on (4) and adapted, for the original values go to the original articles.
The lens of our eye becomes opaque by clouding. It is a phenom related to the ageing but nearsighted people have an increased OR risk, for the devleopment of catracts, up to x12.34 (when more than 6 Diopters are present) or a minimum of 1.59 OR for low amounts (< 2 Diopters). On the other hand, it seems that the opposite error of myopia, hyperopia (farsightedness) can play a preventive role in the onset of some type of cataracts (Posterior Subcapsular). (5)
One of the main related problem in high myopes is the non-traumatic detachments, where retinal layers are detached due to the poor nexus that is caused by the great elongation of the eyes. The following table provides a summary of the risk for retinal detachment, depending on the present central myopia.
|-1Dpt to -3Dpt||x3|
|-3Dpt to -6Dpt||x9|
|-6Dpt to -9Dpt||x21|
|-9Dpt to -15Dpt||x44|
Table values based on (4) and adapted, for the original values go to the original articles. *
Glaucoma, is a “silent” progressive loss of vision, where the subject do not perceive this loss until late-stages due to the fact that it is usually painless. In this disease, the retina gets worse as high intraocular pressure is present on the eye. Nearsighted people have a greater chance to develop this condition in comparison with others groups, the OR is almost x2.5 for the highest levels of myopia (6).
* Dpt = Diopters or dioptres, the notation used in physicians to denotate it.
Due to the complications mentioned above, high levels of nearsightedness are one of the major causes of visual impairment in developed countries, with special emphasis on East Asia, (7, 8) where a huge economic impact due to the direct costs caused by problems related to pathological levels of this refractive error has been observed. (9)
Myopia is a refractive error which was reported to have cost US$4.6 billion globally in 1990. (10)
Zheng et al. (2013) reported large economic costs related to nearsightedness in the adult population of the Singapore area. The costs for the entire Singapore population were US$755.2 million (SGD$959.0 million), with an annual cost of US$709 (SGD$900) per person. These costs were related to glasses, contact lenses and solutions, refractive surgery, etc; where the highest cost was that related to the refractive correction (glasses, optometrist visits, contact lenses, etc.), with 65.2% of the total economic cost. On the other hand, the economic costs related to pathological myopia were considerably higher per person, reaching the SGD$1010 and were those related to all those eye changes caused by these levels of myopia.
As is well known, myopia and high myopia levels of the world population are expected to increase over the next 30 years, (11) so all these costs associated with refractive correction of nearsightedness and the treatment of its pathological levels will increase considerably.
Stay up-to-date, Keep on reading and…
1. Saw, S. (2006). How blinding is pathological myopia? Br J Ophthalmol. 2006 May;90(5):525-6. https://doi.org/10.1136/bjo.2005.087999. 2. Rose K, Harper R, Tromans C, Waterman C, Goldberg D, Haggerty C & Tullo A. (2000). Quality of life in myopia. Br. J. Ophthalmol. 84, 1031e1034. 3. Ohno-Matsui K, Lai TY, Lai CC, Cheung CM. (2016). Updates of pathologic myopia. Prog Retin Eye Res 2016;52:156-87. https://doi.org/10.1016/j.preteyeres.2015.12.001. 4. D.I. Flitcroft.(2012).The complex interactions of retinal, optical and environmental factors in myopia aetiology. Prog Retin Eye Res. 2012 Nov;31(6):622-60. https://doi.org/10.1016/j.preteyeres.2012.06.004. 5. Lim R, Mitchell P & Cumming RG. (1999). Refractive associations with cataract: the Blue Mountains Eye Study. Invest. Ophthalmol. Vis. Sci. 40, 3021e3026. 6. Marcus MW, de Vries MM, Junoy Montolio FG & Jansonius NM.(2011). Myopia as a risk factor for open-angle glaucoma: a systematic review and meta-analysis. Ophthalmology 118, 1989e1994. 7. Morgan IG, Ohno-Matsui K, Saw SM. (2012) Myopia. Lancet 2012;379(9827):1739-48. https://doi.org/10.1016/S0140-6736(12)60272-4. 8. Dolgin E. (2015). The myopia boom. Nature 2015;519(7543):276-8. https://doi.org/10.1038/519276a. 9. Zheng YF, Pan CW, Chay J, et al. The economic cost of myopia in adults aged over 40 years in Singapore. Invest Ophthalmol Vis Sci 2013;54(12):7532-7. https://doi.org/10.1167/iovs.13-12795. 10. Javitt JC, Chiang YP. (1994) The socioeconomic aspects of laser refractive surgery. Arch Ophthalmol 1994; 112: 1526–1530. 11. Holden BA, Fricke TR, Wilson DA, et al. (2016) Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology 2016;123(5):1036-42. https://doi.org/10.1016/j.ophtha.2016.01.006.