What Are The Degrees Of Myopia?
Table Of Contents
What Are The Degrees Of Myopia?
A myopic or nearsighted person is known as ‘nearsighted,’ meaning they can see near objects without any problem but has difficulty seeing distant objects clearly.
However, different types of Myopia depend on their degree or etymology. In turn, we can also encounter false Myopia or over-accommodation.
In this article, we want to learn more about the visual refractive defect called ‘Myopia’ and learn to interpret its different degrees.
To do that, we will cover the following:
- What is Myopia,
- What is a visual refractive error (Myopia, hyperopia, astigmatism, and presbyopia)
- What is a diopter?
This will allow us to better understand how the degrees of ‘Myopia’ are measured.
We will then tell you all about the different degrees of Myopia (mild, moderate, severe, and high Myopia, Magna or pathological) and also discuss the differences between simple Myopia and Myopia Magna.
We will also cover the classification of Myopia according to its cause (axial Myopia, curvature myopia, index myopia, or mixed Myopia). Finally, we will see what false Myopia or Pseudomyopia is, how to differentiate false Myopia from real Myopia, and what types of false Myopia we can find.
What Is Myopia?
When we talk about Myopia, we refer to a refractive defect of the eye where distant images are focused in front of the retina, which causes the image to be out of focus.
When you have an emmetropic eye ( or normal/nominal), these are projected on the retina.
Myopia is corrected with negative or divergent lenses, which focus the images correctly on the retina to see clearly.
What is a Visual Refractive Defect?
It is a defect or anomaly of ocular refraction that refers to the lack of focus of the image projected on the retina, which is blurred.
In contrast, in the normal or emmetropic eye, the image projected on the retina is sharp after refraction through the cornea and lens.
There are several types of refractive errors in the eye or ametropia:
Myopia
Myopia is the most common refractive error and produces poor distance vision since the image created in the eye does so before reaching the retina, which generates a blur.
Hyperopia
Hyperopia, unlike Myopia, produces poor near vision since the image is created behind the retina of the eye, and this causes a blur.
Astigmatism
Astigmatism occurs when there are two different prescriptions in the same eye, which are on perpendicular axes or meridians.
The reason is that one part of the image is created at a different distance from the retina, generating a different defocus in each position.
Presbyopia
Presbyopia, also known as eyestrain, is the difficulty that develops after age 40-45 in focusing on close-up objects. This is due to the aging of the crystalline lens.
How Are Myopia Grades Measured?
To better understand what degrees of Myopia exist, we must know what a diopter is.
A diopter is the unit used to measure, either in positive or negative values, the power of the lenses (in glasses or contact lenses) and the prescription of the eyes.
Graduation is negative (-) when Myopia or some astigmatism is corrected with diverging lenses. The prescription is positive (+) when hyperopia or presbyopia is corrected with convergent lenses.
Myopia can be classified by its degree or by its cause:
According to its degree | According to its cause |
Mild Myopia (simple) | Axial Myopia |
Moderate Myopia | Curvature myopia |
Severe Myopia | Index myopia |
High Myopia (Magna) | Mixed Myopia |
Degrees Of Myopia
We can classify Myopia according to the diopters needed to compensate for the nearsighted eye to see clearly.
Mild Myopia, Simple or Low Myopia
Mild Myopia is Myopia that requires a prescription between -0.5 and -3 diopters. A person with simple Myopia will not see distant objects clearly.
Moderate Myopia
Moderate Myopia requires between -3 and -6 diopters to correct the refractive error.
A person with moderate Myopia will have difficulty seeing objects more than a few centimeters away. However, it is possible to remove glasses for close-up tasks.
Severe Myopia
Severe Myopia is between -6 and -8 diopters, and the person who suffers from it cannot see clearly if something is more than 30-40 centimeters away from them.
High Myopia, Pathological Myopia, Magna Myopia
Magna myopia, high Myopia, or pathological Myopia is an eye disease in which there is an excessive elongation of the eyeball, which causes all the structures of the eye (especially the retina) to be stretched abnormally.
It is considered to be high Myopia starting from -6 diopters. It can cause serious problems such as retinal detachment or irreversible blindness if not treated correctly.
Differences Between Simple Myopia And Magna Myopia
Simple Myopia is much more common than Myopia Magna. It is caused by a mismatch between the various components of the eye (lens power, corneal curvature, axial length, and anterior chamber depth).
Magna myopia is due to excessive elongation of the eyeball, with the anteroposterior axis being more than 26 mm. It begins in childhood and may progress into adulthood.
Simple Myopia starts between 5 years old and puberty, progresses for several years, and stabilizes after adolescence.
The refractive error in the case of simple Myopia is less than -6 diopters and more than -6 diopters in the case of Myopia Magna.
Simple Myopia is not accompanied by associated ocular alterations. It is an optical refractive defect, unlike Myopia Magna, which is considered an ocular pathology and must be controlled periodically. It may be accompanied by alterations that can seriously affect the person’s vision.
Magna Myopia does not only refer to having a higher number of diopters; the person who suffers from this type of Myopia is also more susceptible to other ocular complications, such as glaucoma, cataracts, or alterations of the posterior pole of the eye.
However, having Myopia Magna does not necessarily imply having ocular complications, but there is a risk. The more stretched the eyeball is, the greater the risk.
Myopia Classification According To their Cause
Myopia can also be classified according to its cause or the anatomy of the eye.
Axial Myopia
In axial Myopia, the eyeball is longer than normal (more than 24 mm) in the anteroposterior axis.
Curvature Myopia
Curvature myopia refers to an increase in the curvature of the cornea or lens.
Index Myopia
An index myopia develops when there is a variation in the refractive index, either by a decrease in the corneal refractive index or by an increase in the refractive index in the lens, when the clouding of the lens begins, which will lead to cataracts.
Mixed Myopia
Mixed Myopia is a combination of the myopias mentioned earlier.
Clinically, Myopia is classified into two types Myopia: benign or simple Myopia and pathologic or degenerative Myopia.
In benign Myopia, the refractive error does not exceed -6D and does not cause problems in the fundus.
On the contrary, in pathologic Myopia, it exceeds -6D, and there is an alteration in the fundus.
On the other hand, we have false Myopia or pseudomyopia:
What Is False Myopia?
False Myopia appears when there is a blockage in the accommodation mechanism when focusing on distant objects.
The ciliary muscle is responsible for increasing the power of the crystalline lens to focus correctly, thus establishing the accommodation mechanism.
In false Myopia, the ciliary muscle remains contracted, causing images to be blurred. This is not an anatomical problem but a functional problem: the ciliary muscle has not relaxed.
How to Differentiate False Myopia From Real Myopia?
To differentiate it from ‘real Myopia,’ ‘false Myopia’ can be detected if we see that the graduation varies a lot in a short period of time or by applying cycloplegic drops (diopters disappear).
When these drops are applied, the ciliary muscle, which is responsible for accommodation, is paralyzed. If it is false Myopia, it disappears.
Although the main symptom of both myopias is the same: the difficulty in focusing on distant objects, false Myopia is due to a problem in the functioning of the eye (there is a blockage in the focusing system), unlike real Myopia, which is due to the shape of the eye.
What Types of False Myopia Are There?
False Myopias: accommodative spasm, nocturnal Myopia, and instrumental Myopia. To understand the different types of False Miopia, let’s briefly discuss the mechanism of accommodation.
Accommodation is a mechanism of the eye in which the power of the optical system increases so that we can focus on objects in near vision. This mechanism activates and relaxes automatically, modifying the curvature of the crystalline lens.
It is activated when focusing on a near object and relaxes to be able to focus on distant objects sharply.
With Myopia, there is an excess of power, which means that the eye has more power than necessary to focus on distant objects. The image is focused in front of the retina and is not sharp.
In the case of false Myopia, it is due to the fact that the accommodation system is still active in the eye when it should relax to focus on the eyes at a far distance, so they will be blurred, as in real Myopia.
False Myopias: accommodative spasm, nocturnal Myopia, and instrumental Myopia.
Accommodative Spasm
Accommodative spasm is the excess of accommodation and occurs when the accommodative process remains active.
It is an occasional transient block where the eye has too much power. It cannot see well at a distance but has good nearby vision because the accommodative mechanism is not relaxed.
Nocturnal Myopia
Nocturnal Myopia occurs in low light because we do not relax accommodation. The pupil becomes larger when we are in the dark, and this causes a lower visual acuity.
Miopía instrumental
Instrumental Myopia is the inability to relax accommodation due to the sensation of the proximity of objects, such as after using a microscope.
In any case, seeing a vision specialist for a periodic check-up is advisable to detect any anomaly we may have.
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