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Classification of myopia

The different forms of myopia: classifications

We can distinguish several types of myopia, according to the mechanism involved, the type of evolution, or the existence of associated pathologies. The degree of myopia is usually quantified based on the power of corrective lenses required to correct: the degree of short-sightedness, or myopia power is expressed as a number of vergence (negative convention). example:-3 D.  The calculation of the inverse of the vergence (ex: 1/3D = 0.33 m = 33 cm) provides the distance at which the nearsighted eye sees net without correction: this distance is by definition one of the punctum point (furthest point which is seen net). Beyond the point punctum, the vision is blurred (it's even more blurred as you move away from the point punctum)

Myopia is related to a power (posterior focal length) excessive retractives structures of the eye: rays from distant sources are focused by the cornea and the crystalline lens in front of the retina (see the blurred vision of the myopic). The power of glass needed for the correction of myopia correction indicates the severity of it (a myopia of 5 d is more severe than a myopia of 1 d), but not its cause, at least for low and medium myopia.

Severity of myopia and degree of correction

Can be arbitrarily classified depending on its importance, established myopia from the degree of correction needed (diopters) is it necessary to wear (in glasses):

-low myopia < 3D

-myopia average between 3 and 6 d

-high myopia > 6 d

This classification does not take into account associated pathologies that can participate in the severity of myopia (retinal pathologies, in particular). It is of some interest in refractive surgery; If the PKR is performing as well as the LASIK for the low and medium myopia, there (increased accuracy of the correction and less scarred regression) superiority of LASIK for the high myopia (greater than 6 D).

High myopia may also be defined biometric: it concerns in general eyes whose axial length is greater than 26 mm. The deformation of the posterior pole of the eyeball in high myopia case is responsible for the existence of retinal complications such as the posterior staphylome, or myopic choroidose;

 

Classification of myopia based on its mechanism

Recall that the focal power of the eye depends on the refractive elements of the eye: horny and crystalline. (Inversely proportional to focal length) focal power of these elements is so dependent on the power of the cornea, the distance between the cornea and the lens, and the power of the lens.

myopia focal power

Focal power of the couple horny and crystalline. The light rays emitted by a distant point source are under 4 successive refractions (anterior side of the cornea, corneal posterior, anterior side of the lens, posterior face of the Crystal). They then converge and the distance where should be the retina for an Emmetropic eye is precisely this focal length. If the eye is too long (towards), the retinal image will be more blurred.

 

Depending on the degree of eye elongation, and the existence of other anomalies, there are mainly the so-called myopia axiles so-called myopia refractive. Axiles myopia are associated with a "significant" increase in the axial length of the eyeball. The refractive myopia are related to a mismatch between the focal power (cornea/lens) and axial length (this axial length is relatively normal, but the cornea and the lens focus too incident light. This occurs when the cornea is particularly and snap, which increases sound Optical power - vergence).

 

Refractive myopia

Excessive axial length (the axial length is the distance between the top of the cornea, and the fovea which is a retinal fine vision) is an obvious cause of myopia. However, some short-sighted eyes present an identical to that of normalsighted eyes axial length, see sometimes lower!

length axial eye

Axial length is defined by the distance between the top of the cornea and the fovea, which is the seat of the fine vision at the level of the retina. It can be measured in an optical way (biometrics by Interferometry) or acoustic (ultrasonic ultrasound). It is statistically higher among short-sighted, and lower among the hypermetropia.

There are large variations between human eyes for a parameter as the corneal power (between 40 and 47 d for healthy corneas), as well as the depth of anterior Chamber, (and probably the lens power).

As a result, it is difficult to blame systematically isolated excessive axial length to explain the occurrence of myopia; We speak of refractive myopia when it is rather related to a sort of "disharmony" between axial length and focal power of the refractive elements of the eye. The length of the eye is not excessive in itself (close to 24 mm) with respect to a reference population composed of no myopic eye. but it is excessive with respect to the Optical power of the eye.  Generally, this type of short-sightedness does not exceed 3 or 4 diopters; beyond that, the probability of axile myopia is strong.

Myopia corneal

Corneal myopia is a special type of refractive myopia. The increase in power corneal trained an increase in focal power of the eye: from light rays from a distant source are too refracted by the cornea (they converge in front of the retina), while the axial length is not statistically higher than the average.  This mechanism is at least partially offending in myopia associated to the Keratoconus, because this condition causes a central corneal curve, and therefore a marked increase in the corneal vergence. The risk factors for Keratoconus are genetic and environmental. According to the author of this site, the repeated rubbing of the eyes which are the direct and necessary of Keratoconus cause.

Here is an example of corneal myopia, for which the measure of the axial length in optical biometry is normal, while the keratometry is high.

myopia by accented corneal camber

Corneal myopia: objective refraction is-3.50 D. The axial length of the eye is normal or even slightly below the average (22.59 mm optical biometry). The keratometry is high (46.5 D); the cornea has an excessive vergence to the axial length of the eye and explains myopia.

 

 

 

Axile myopia

It's a myopia that the main mechanism is the elongation of the eyeball. The average axial length of the human eye "Emmetropic" is close to 23 mm (2.3 cm).

axile myopia

Axile myopia

A study found that the axial length of farsighted eyes averaged 22.62 ± 0.76 mm), and was therefore logically shorter than short-sighted eyes, who was measured at 25.16 ± 1.23 mm (axile and refractive myopia combined). These figures show that axial length values differ on average, but in terms of the standard deviation of the respective distributions, they overlap significantly between the two groups (farsighted vs myopic). In this study, the myopic eyes had a slightly more powerful than the farsighted eyes cornea, but the measured difference was not significant)Llorente et al. Myopic versus hyperopic eyes: axial length, corneal shape and optical aberrations. Journal of Vision, 2004; 4, 288-298).

It is difficult to distinguish some axiles 'refractive' myopia myopia, because the variability of the axial length in the general population is important. However, most of the myopia greater than 4 D are axiles, and most of the eyes with axial length greater than 25.5 mm are achieved axial myopia (Hendicott and Lam. Myopic crescent, refractive error and axial length in Chinese eyes. Blink Exp Optom, 1991; 74:168 - 174).

Axiles myopia, include the scalable high myopia, characterised by a progressive distension of the posterior pole and the appearance of associated pathologies related to it.  These misuse are often referred to as pathological.

See also:  calculation of the relationship between elongation of the eye (increase in axial length) and induced myopia

Pathological myopia

The most easily recognizable myopia is definitely pathological, also called myopia "evolutionary" myopia, progressive myopia, degenerative myopia. It is characterized by an appearance more early (early childhood, before adolescence) and progresses quickly. It is characterized by an excessive distension of the posterior pole of the eye, with important extension of the length of the eye, and is accompanied by degenerative retinal chorio. This degeneration is related to the fact that the chorio-retinal, little stretch fabric, is undergoing a significant increase of the inner surface of the eye (linked to sclerale expansion). This tissue thins, rips and atrophy according to the degree of myopia. Fortunately, the prevalence of this type of myopia seems in regression. Myopia may exceed 10 D (up to 30 D into serious, sometimes called shapes "") malignant myopia »). Axial length is reached, see exceeds 30 mm.

The optical correction of these myopias appealed to rigid contact lenses. Glasses, the thickness of the concave lenses (even at high factor) is such that sometimes, special equipment must be designed.

high pathological myopia

Pathological myopia: the axial length (AL, red box) is greater than 30 mm on both sides. the concave glasses induce an apparent narrowing of the eyes of the patients generally considered unsightly. These special glasses induce share their concave geometry marked some peripheral distortion. Like all glass correction of myopia, they induce a narrowing and the image of the objects seen through the distance.

These misuse are also associated with a risk of loss of best corrected Visual acuity. In other words, retinal lesions observed in patients with severe myopia can result in a functional loss not correctable by glasses or lenses. Refractive surgery of this type of short-sightedness, when it is possible, is generally based on the placement of an implant (implant phakic) eye intra or excision of the lens and its replacement with an implant whose power is calculated to reduce myopia.

An interesting phenomenon is often noted during surgery of the lens on eyes with high myopia. by the focus on the cornea, then moving away slightly the microscope of a few centimetres from the eye, it is possible to observe the details of the eye (retina) the myopic background hard. This is the to the fact that the retina of the strong myopic is combined with the map of the punctum point, which is located at a distance (in meters) equal to the inverse of the myopic correction (expressed in diopters). For example, the plan of the punctum point is located about 7 cm for a myopic to-15 D (1/15 = 0.07 about).

myopia strong punctum point

(Without optics suppelentaire) 'direct' visualization of the retina of the myopic strong occurs when the punctum point is located in a close enough eye plan so that the operating microscope can there be also focused. This is the prerogative of the eyes which present high nearsightedness.

 

Myopias: rarer forms

There are far less frequent than the refractive myopia myopia forms and or axiles.

Transient myopia:

It is associated with diabetes, some pathological States and pregnancy, and based on likely changes the refractive media (mood acqueuse) chemicals, responsible for an increase in their refractive index, more or less associated with accommodatifs spames.

The myopia of index:

Index myopia is a form of refractive myopia: she is related to nuclear cataract: the nucleus of the lens is bomb and its index increases. The myopia of index may appear at an Emmetropic, at a former farsighted, or aggravate a pre-existing myopia (see the page dedicated to) the study aberrometrique of the myopia of index)

Accommodative myopia (or by "accommodative spasm" ""): 

It's a myopia caused by a prolonged contraction of the ciliary muscle secondary to sustained efforts in vision (fine craftwork, school work or computer very extended, etc.). The instillation of eyedrops "cycloplegics" (paralyzing the ciliary muscle), allows to correct the myopia.

Myopia associated with a subluxation of the lens

This exceptional shape surprises with the 'normal' dimensions of the eyeball with respect to the degree of myopia, which is linked to a loosening of the suspensory ligament of the lens (zonule). The lens spontaneously adopts a more rounded form, increasing its refractive power and causes excessive convergence of the refracted rays (see the) description of a case of myopia by subluxation of the lens)

 

Type of myopia and refractive surgery

(PKR, LASIK) excimer laser refractive surgery concerns mainly the refractive myopia, and part of the axiles myopias (keeping in mind that the border between these types of myopia is fuzzy). Axiles myopia are the myopias characterized by a generally more important (more than 6 D) correction and are rather corrected by LASIK, as long as the thickness and corneal regularity are compatible with this technique. Axiles myopia have a longer evolution: they start earlier in childhood, and change later than «refractive» say myopia Low myopia of refractive type (ex:-2.50 D) is generally stable around the age of 20 to 22 years, a high myopia of refractive type (ex:-8 d) tends to stabilize later (25-30 years), and keeps an 'evolutionary potential. "

The myopia corneal can receive a LASIK or a PKR, to the exclusion of the related to Keratoconus, corneal myopia who are against formal indication to LASIK.

The pathologic myopia (scalable high myopia, etc.) are by definition of 'fragile' eyes: refractive surgery is conceived as a functional surgery. The appearance of cataract (more frequent and earlier on this type of eyes) is an occaseion to reduce myopia through the removal of the lens, and its replacement by an intra ocular lens whose power is calculated to compensate for the excessive lengthening of the posterior segment of the eye. The lens usually has an optical power of 22D (in the plane of the lens). Emmetropic patient therefore, wishing to stay that boasts an implant of power close to 22D. On the other hand, a myopic-16 d surgery of cataract and wishing a total reduction of near-sightedness in theory benefit from the implementation of an implant whose optical power (vergence) will be close to 6 D.

Finally, the myopia of index is an indication of the cataract surgery.

26 responses to "myopia classification"

  1. CLEMENT huge, Marie says:

    Hello
    At 35 years old, my daughter has a very strong myopia always evolving. In the family, there is a history: his father and my sister (who have not lost sight). She is very worried and afraid to become blind. What should I tell him? In advance thank you.

  2. Dr. Damien Gatinel says:

    The scalable high myopia is actually a condition that the complications can be serious, but if careful and regular ophthalmologic follow-up is done, so most of these complications can be prevented or treated in time. It's not the myopia itself which may go blind, but certain retinal conditions associated with high myopia (for example the retinal detachment, or the occurrence of an in retinal neovascularization).

  3. Cynthia roukoz says:

    Hello, I have a high myopia - 7, -10, my eye doctor told me that I have a good retina without signs of pathological degenerative myopia. I am 28 years old, is what I might see more late ube myopia pathological even if today no sign?

  4. Dr. Damien Gatinel says:

    It is difficult to predict to high myopia, but the presence of a retina "of good quality" is rather reassuring. Regular monitoring (ex: annual) is indicated in your case.

  5. Altruy says:

    Hello my daughter 12 years ago is in a very severe myopia - 7 D and - 6.5 D us worried a lot t risk of becoming blind. Thanks in advance for your answer.

  6. Dr. Damien Gatinel says:

    High myopia is likely to expose certain complications in the Court of the existence but they can now be the subject of a prevention and support adapted. Regular follow-up (annually) is indicated. There is no risk of loss of vision, or so very small.

  7. Ms Juliana says:

    Hello
    I am 19 years old with a high myopia of-7.25 and-7.75, evolving since my childhood, with also a risk of detachment of the retina.
    I'm considering laser surgery, which do you recommend?
    Thank you in advance for your answer.

  8. LEOPOLD HEYMONET says:

    Hello;
    I'm an intern in general medicine

    My friend is short-sighted strong; She has 23 years; his eye follows her since birth; She's wearing lenses of contact semi-rigid. his sight is deteriorating in recent years.
    For his glasses: OD-21.5 (-2.25 a 15 °) OG-21.25 (-1.25 a 160 °)
    For its lenses: OD/OG-17

    We saw 2 ophthalmologists to see some different options in terms of treatment; the answers given were not very clear, I felt that they were not very at ease with myopia at this very late stage.

    My questions are the following:
    – With its lenses it managed to have 5/10 to both eyes; Can't have more by putting a stronger correction?
    – What is the best surgical option in terms of implants for this stage, knowing its 23ans age?
    -What can be hoped for as a benefit of such surgery in terms of vision (5/10 without glasses or more?)

    Thanking you

  9. Dr. Damien Gatinel says:

    The extreme myopia are unfortunately often associated with retinal pathologies that can reduce the best corrected Visual acuity. The lens correction is by far the best solution for extreme myopia at a young woman. Later, towards the end of the thirty or a quarantine, a so-called implantation of phakic may can be be considered. But for now, it is wise to encourage the patient to continue wearing lenses, because complications caused by implants phakes long-term (glaucoma, cataract) Guide to abstinence in a a strong myopic of less than 30 years.

  10. Dr. Damien Gatinel says:

    For-7.50 diopter of myopia, LASIK is certainly the technique of choice. It is necessary to make a detailed report including the topographic maps of the cornea (including thickness measurement). Finally, unfortunately it is not certain that your myopia is stabilized (at age 19).

  11. Asma says:

    Good evening
    I am 24 years old with a high myopia of-7.50 for both eyes and that has evolved in recent years
    Is this a normal evolution??? What is the most suitable surgery for this case and what is its percentage of success or you have to simply wear corrective glasses and contact lenses.
    Thank you in advance for your answer.

  12. Dr. Damien Gatinel says:

    Characteristic of the strong myopia (beyond of - 6 d about) is to progress, somewhat inexorable way unfortunately. This is because myopia progresses steadily achieved this degree of correction. There is no very proven to slow the progression of myopia in adults. The prolonged close work seems to be an aggravating factor. Regular monitoring may be necessary.

  13. Eddii says:

    Hello
    I never wore glasses I had a vision of 10/10 and now I am a student in medicine in 4th year, I wore glasses from the 1st year (-0.25 D) for the 2 yeux...et now I wear glasses (-2 D) for both eyes.

  14. Dr. Damien Gatinel says:

    Prolonged and sustained studies are implicated in the onset and progression of myopia. This is especially true for medicine, many students see their myopia progress in the first and second cycle studies in particular.

  15. Tabor says:

    Good evening
    I'm 24 years old and I'm a twin we both have a myopia of-12D that date of birth there has been no progress it remains stable so far and we have been wearing glasses for 7 years
    Is there anything we can do to make it regress?

  16. Dr. Damien Gatinel says:

    Myopia never regresses (when it is caused by excessive length of the eyeball), unfortunately.

  17. CARSUZAA says:

    Hello

    I'm a doctor, I just finished my studies. I have never been myopic in childhood only since my studies. I am myopic og-4.5 and OD-3.25. I'm under corrected a-4 by Loeil G. My ophthalmologist told me that I had frost on the retina left without explanations. Jai currently under floating bodies. Can m explain for the frost? Do we have to do lasers? Do I have to increase my, correction?
    Thank you, Claire.

  18. Dr. Damien Gatinel says:

    A simple annual monitoring of the bottom of the eye is enough. Frost corresponds to a particular insertion of the glazed base on the peripheral retina, it is not a priori dangerous in the absence of symptoms suggestive of marked traction of the glazed on the retina. It is certainly best to be well corrected to both eyes to enjoy a good vision from afar.

  19. Paul T says:

    My 12 year old daughter has been myopic for 4 years, if her left eye remains stable-0.5 for 4 years, the right eye keeps dropping, it is currently de-4, it can no longer be corrected by glasses and must switch to lenses. What can I do to slow this down, can surgery be considered and from what age?

  20. Dr. Damien Gatinel says:

    It is difficult to provide advice or means other than those intended to correct the right eye (and the left eye of course). The correction in glasses is now difficult because of the correction gap between the two eyes (source of a different image size between the two eyes, what is referred to as the term "Anéisoconie"). It is therefore important to adapt one Contact lens to overcome this disadvantage.

  21. Adel says:

    Hello, my 6 year old child
    Measuring test
    OD-11 (20 °,-1.00)
    OG-10 (140 °,-1.00)
    He wears glasses of sight, to read or write of Meadows he removed his glasses
    I want to know if possible the type of myopia and the correct solution? Because despite the glasses his vision is still low 3/10

  22. Dr. Damien Gatinel says:

    Your child has a severe acute myopia, which needs to be corrected in glasses, and can then be in lentils in a few years. Regular ophthalmological surveillance is essential.

  23. B says:

    Hello, Myope since childhood, I have-17.25 OG and-14.00 OD
    I'm wearing contact lenses. My view goes down. At 61 years is an operation possible?

  24. Dr. Damien Gatinel says:

    If your vision decrease corresponds to the installation of a beginner cataract, it might be interesting to propose an intervention. By choosing a suitable power implant, it is possible to aim for a total or partial correction of your strong myopia.

  25. Bob Mohammed says:

    Hello, I have a strong myopia that continues to evolve since childhood, today at the age of 49 years, it is stable a 19,75 (-1.75) 30 ° right eye and – 22.75 (-0.25) 115 °, the doctor has detected me a moderate cataract, and offers me a cataract surgery with the establishment of semi multifocal implants of the type lentid confort MF15, and correction of corneal astigmatism by relaxing incisions, knowing that the rear dilated segment is showing a CHOROIDOSE MYOPIC MAGEURe, for which another ophthalmo says that this type of implant would not be suitable to see would be contraindicated, and offers me monofocal, without incision of the cornea, the Act that it deems very stressful and heavy for the cornea, what to do, I remain puzzled

  26. Dr. Damien Gatinel says:

    It is indeed preferable to opt for monofocal implants in the context of strong myopia with corneal astigmatism.

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