Severe Myopia and its complications

Severe Myopia and its complications

Myopia is most often caused by an eye that is too long. The image of a distant object is therefore focused in front of the retina and distance vision is blurred. On the other hand, near vision is clear. This makes it possible to read without glasses. The stronger it is, the closer the text must be. For a normal eye the punctum remotum (which is the furthest point of the eye that can be seen clearly) is located at infinity. For a myopic eye it is closer than 5 metres. This sharp reading distance is inversely proportional to myopia. For example, for -3 diopter it is 0.33 m, for – 5 diopter the punctum remotum is 0.20 m.

Evolution

Myopia usually appears in childhood at around 6 to 8 years of age and progresses until the age of 20-25 years and then stabilises. However, it can sometimes appear earlier (strong neonatal or congenital myopia) or later, after the age of 20, or stabilise earlier. The earlier it starts, the more progressive and significant it will be. There are two forms of severe myopia: one that progresses gradually up to the age of 30, the other that progresses permanently up to the age of 60. The myopia usually encountered is not a disease. Only the very short-sighted have a real ‘myopia disease’ which is accompanied by a progressive growth in the size of the eye throughout life and significant alterations to the visual retina.
Myopia does not prevent presbyopia. The myopic person with presbyopia sees blurred when he wears his glasses for reading at a distance. However, when they take them off, they can read at a different distance depending on the degree of myopia, which leads to the belief that they become presbyopic after others or, falsely, that myopia improves with age.

Complications of myopia

High myopia makes the eye more fragile than a normal eye. It is the 4th most common cause of visual impairment in Europe. It represents 5% of myopes in the United States and Western Europe, and 10% in some Asian countries. Severe myopia is a degenerative disease, a progressive myopia-disease defined by figures greater than -8 dioptres and an axial length (cornea-retina distance) greater than 26 mm (23 mm for a normal eye), which can reach 35 mm for extremely severe myopia. The elongation of the globe is at the expense of the posterior part of the eye.
Severe myopia is a severe condition because it means that the eye is much larger and, as a result, the retina is stretched, distended, thinned and susceptible to tearing. It is poorly irrigated, with the nourishing layer, the choriocapillaris, providing less blood flow.

Damage to the macula

Damage to the macula, the central area of the retina, is particularly worrying because it jeopardises the central visual function of the retina, i.e. the ability to read. In addition to a decrease in visual acuity, the warning sign that may suggest damage to the macula is the existence of metamorphopsia (line deformities). OCT (Optical Coherent Tomography) is a fundamental examination that makes it possible to highlight and monitor the state of the retina in cases of severe myopia.

High myopia can lead to macular pallor, myopic staphyloma (deformation of the globe backwards), ruptures of the visual retinal layers (rupture of the Bruch membrane), deep chorio-retinal atrophy, choroidal neovascularization.

Fovesoschisis is common. It is due to the existence of intraretinal cysts. It can be accompanied by an epiretinal membrane stretching the retina forward while the staphyloma stretches it backwards, macular detachment, a partial lamellar or complete macular hole and lead to retinal detachment.

Chorioretin atrophy is a common complication resulting in a progressive decrease in visual acuity.

The macular hole can also cause a loss of vision when reading with deformities (metamorphopsies). Surgery is possible.

Choroidal neovessels translate the passage of choroidal vessels through the retina resulting in edema and hemorrhages of the macula. They can be treated with focused argon laser, dynamic phototherapy (PDT) or intravitreal injections of anti-VGEF.

Great advances have been made recently in the diagnosis and treatment of these retinal complications concerning dynamic phototherapy, anti-angiogenic factors and endocular surgery.

The involvement of peripheral laretine

The periphery of the myopic retina should be monitored regularly by a 3-mirror glass examination or a panoramic lens. There may be palisades, holes, and tears on the periphery of the retina to be treated preventively by the argon laser to avoid more frequent retinal detachment in the myopic.

It is important to note that it is not uncommon to discover these dangerous retinal lesions, predisposing to retinal detachment, in a myopic subject, not being alarmed because complaining of no visual disorder, no pain, consulting

Myopia correction To obtain clear vision, the image of distant objects must be focused on the retina. The purpose of the correction of myopia is therefore to modify the path of the light rays so that they converge on the retina. • The correction can be done by glasses whose diverging concave glass pushes the image on the retina. The stronger the correction, the more the myope perceives what surrounds him smaller than in reality. The stronger the correction, the heavier the glass, thicker at the edge and thinner in the center. This unsightly appearance is reduced by the use of glasses with an increased refractive index allowing them to be thinned. The subject has the choice between mineral glasses of higher index, thinner but heavier or lighter organic glasses. The choice of a small frame limits the thickness at the edge of the lenses. The higher the index, the more light reflections form on their surface. Hence the interest of an anti-reflective treatment for thinned glasses. • The correction can be done by disposable soft contact lenses (daily or monthly) or traditional or by rigid lenses. The lenses make it possible to restore a normal image size because bringing the correction closer to the cornea enlarges the retinal image. The image being larger than with a spectacle lens, visual acuity is often better in cases of high myopia, which can reach 2/10 for myopia of -8 diopters. The visual field is more important, that is to say that peripheral vision is wider, especially for high myopia. With lenses there is better night vision by increasing retinal illumination compared to glasses (25% for myopia of -10 D). Note that from a certain degree of myopia (-4 diopter) the power of the lens is lower than the power of the spectacle lens (for example -7 diopter in glasses corresponds to -6.50 diopter in lenses ). Wearing rigid oxygen permeable lenses in children promotes visual maturation, improves quality of life and can slow down the evolution according to certain studies. They can be worn from the age of 6-7 if the child is cooperative. Sometimes earlier in case of high myopia which can lead to amblyopia or strabismus. It is necessary to choose a material with high transmissibility to oxygen whether with a rigid lens or a soft lens. The slowing effect of rigid lenses on evolution has been mentioned, although not proven. It would be due to the correction of optical aberrations stimulating the retinal visual cells and inhibiting the growth of the eyeball. In the future, optical corrections based on the theory of defocus and para-sympathicolytic treatments could become useful. It is common to observe an intolerance to contact lenses worn for many years, requiring intermittent wear or their abandonment. • The surgical correction of myopia can be done by a myopia operation which consists in modifying the curvature of the cornea by excimer laser or, for high myopia, in placing an implant inside the eye. The various current operations can be carried out by subtraction or by addition. The subtractive way consists in ‘erasing’ by the excimer laser the surface of the cornea to make it less convergent. This ablation of the corneal tissue can be done superficially (PKR, lasek, epi-lasik) or deep after lifting a corneal flap (classic lasik or femtosecond lasik).

Wearing rigid oxygen permeable lenses in children promotes visual maturation, improves quality of life and can slow down the evolution according to certain studies. They can be worn from the age of 6-7 if the child is cooperative. Sometimes earlier in case of high myopia which can lead to amblyopia or strabismus. It is necessary to choose a material with high transmissibility to oxygen whether with a rigid lens or a soft lens. The slowing effect of rigid lenses on evolution has been mentioned, although not proven. It would be due to the correction of optical aberrations stimulating the retinal visual cells and inhibiting the growth of the eyeball. In the future, optical corrections based on the theory of defocus and para-sympathicolytic treatments could become useful. It is common to observe an intolerance to contact lenses worn for many years, requiring intermittent wear or their abandonment. • The surgical correction of myopia can be done by a myopia operation which consists in modifying the curvature of the cornea by excimer laser or, for high myopia, in placing an implant inside the eye. The various current operations can be carried out by subtraction or by addition. The subtractive way consists in ‘erasing’ by the excimer laser the surface of the cornea to make it less convergent. This ablation of the corneal tissue can be done superficially (PKR, lasek, epi-lasik) or deep after lifting a corneal flap (classic lasik or femtosecond lasik). The patient’s quality of vision is an important concept, different from visual acuity. Visual acuity may be 10/10 and poor quality vision. Quality of vision means seeing better at night, in fog, in rain, in bright light. Better perception of distances, relief, speeds, absence of secondary effects: nocturnal halos, split, blurred, fluctuating vision, veil, glare. Myopia surgery has gone from standard surgery where each patient was treated identically based on their myopia number to personalized surgery, optimized for each case. It is possible to adapt the profile of each treatment to improve the quality of vision and avoid side effects. One of the means used is the treatment of optical aberrations due to the cornea or the crystalline variable from one individual to another. The quantification of these aberrations is done by examining the wave front, which makes it possible to study the irregular behavior of each light ray entering the eye and the way in which it arrives on the retina. The additive way, on the other hand, consists of introducing an implant – in the anterior chamber of the eye in front of the iris (phakic implant), either with angular support (abandoned) due to corneal complications or fixed to the iris (Artisan or Artiflex). – in the posterior chamber behind the iris: – implant in place of the lens (extraction of the clear lens to be reserved for high myopia in subjects over 50 years old because it removes accommodation), – implant in front of the lens (ICL) – implant in the cornea (inlay). Let us recall for documentary purposes two operations which aimed to flatten the cornea to make it less convergent and which are no longer performed: radial keratotomy was the first myopia operation to be commonly performed in the 1980s, the placement of intra -corneals was also practiced.