1. What is myopia?
Myopia is a refractive error. Theoretically, in far vision, the light from the objects enters the eye in parallel rays that are deviated by the optical system of the eye (cornea and crystalline lens) in order to converge on the retina: a nervous membrane that receives light and converts it into a nerve impulse transmitted to the visual cortex, where it is decoded into a perceivable image. This image will be clear if the focusing occurs precisely on the retina.
In case of myopia, in far vision, the light is focused in front of the retina (as if the eye was too long or the optical system of the eye was too convergent) and therefore the images are blurred.
In near vision, the rays enter the eye diverging and are focused farther, resulting in clear images.
Briefly, myopes have blurry far vision and, as a rule, clear near vision.
But there are various types of myopia and the inherent risks are also different. The most serious forms, known as pathological myopias, may involve complications with severe visual consequences. Fortunately, the great majority of the cases are not serious forms of myopia and need only to be corrected by glasses or contact lenses.
2. Can intense reading cause myopia?
Reading is not a cause of myopia. This idea is due to the fact that in a great percentage of cases myopia appears or increases during school-age, when children use more near vision. Some studies, more superficial, suggest the existence of a relation between reading and the appearing or increase of myopia. But rigorous studies, in which the analysis of a relation between reading and myopia is deepened through the study of all variables involved, concluded that reading cannot be considered a cause of myopia.
3. Is one of the eyes always more efficient than the other?
No. In principle, the two eyes have a very similar visual acuity. Nevertheless, many people have the subjective sensation of seeing better with one of the eyes, in spite of equal acuity in both eyes.
4. At what age can a person wear contact lenses?
Age does not determine when to start wearing contact lenses. The younger the organism, the greater is its reactivity and consequently the greater the probability of developing complications due to contact lenses.
If there is no specific reason that justifies a more precocious option, the advisable minimum age for wearing contact lenses should be 15 – 16 years old.
5. How does laser surgery correct myopia?
The optical system of the eye is fundamentally composed by the cornea (transparent part of the membrane of the eyeball that covers the pupil and the iris) and by the crystalline lens (situated inside the eye). The optical power of the cornea is related to its curvature: the greater the curvature, the greater the power. Laser surgery of myopia consists in flattening the cornea to lessen its power; thus, light converges less and is focused on a more posterior plan of the eye, where the retina is situated.
6. Can children be submitted to this surgery?
In principle, myopia surgery is not advised for children. Surgery corrects the refractive error then existing but does not prevent its progression; therefore, it should only be performed when the refractive error is stable, which is in adulthood.
7. Is the number of myopic persons increasing or is this a myth? Is the evolutional tendency towards worse eyesight?
The number of persons with a diagnosis of myopia has increased in the last decades. But it is difficult to know if this increase is real or if it is due to an increment of the number of cases diagnosed.
The incidence of diagnosed myopia varies significantly with geographic location and race (for example, Asians have a much higher incidence than Europeans). Socioeconomic and sociocultural factors also determine to a great extent the values of this incidence.
On one hand, the access to a diagnosis increases the number of cases diagnosed (in most African regions the diagnosis is not made). On the other hand, individual needs related to a person’s activities and cultural interests are also determinative of the increase of the number of cases diagnosed.
The great majority of the cases of myopia mentioned are very easy to correct with optical aid, such as glasses or contact lenses, and they do not represent serious situations nor imply risks of blindness.
8. What is a dioptre?
The dioptre is a unit of optical measurement, as the metre is a unit of length. It translates the capacity of a transparent medium to deviate the path of a beam of light.
In the case of a lens, the number of dioptres indicates the power of the lens.
9. Are computers noxious for the eyes?
It is not proved that computers cause ocular diseases. In normal conditions, the harmful radiation emitted by the screens is minimum or practically null. The general idea of computers being noxious for the eyes results from the existence of frequent complaints of eyestrain related to their use.
But eyestrain has usually other causes, such as, for example, inadequately corrected refractive errors (myopias, hypermetropias and astigmatisms), inappropriate light conditions, incorrect position of the screen, dirt and reflections of the screen, or simply eyes overuse. To prevent eyestrain it is necessary to rest at regular intervals.
10. Why do ophthalmologists always use the red/green test? Why do myopes see better the red colour?
The red/green test consists in showing the patient a line of printed characters over a partly red and partly green background, in order to ascertain in which case the patient sees better.
But ophthalmologists do not always apply the red/green test. In fact, they do not use it most of the times. Yet, this test can be useful to evaluate subjectively the visual comfort provided by a lens compared to another and thus to improve the prescription.
Myopes see better the red colour because the wavelength of the several components of light is different. The greater the wavelength, the farther is situated the focusing point. Therefore, red is focused farther in the eye than blue or green because it has a greater wavelength. This fact benefits myopic persons whose visual defect places the focusing of light in front of the retina.
11. When is a person blind? Is it when the person cannot see the first line of printed characters of a vision test?
The concept of blindness is legally defined. A person is considered blind when visual acuity is less than 1/10 in a decimal scale, if this sight deficiency cannot be corrected. A myope can have a vision of less than 1/10 (the first line of printed characters) without corrective glasses and with appropriate lenses she/he can have a vision of 10/10, which is a normal vision.
The other condition considered as blindness is the loss of visual field to less than 10 degrees, as occurs for instance in terminal stages of glaucoma.
12. Can blind people see again?
It depends on the cause of blindness: some causes can be treated with medicines or through surgery and other are irreversible.
Cataract, for instance, is the major cause of blindness in the world, but it is completely reversible with surgery. On the contrary, glaucoma or age-related macular degeneration, in late stages, lead to forms of blindness that are not reversible with treatment.