The word myopia (lat. Myopia) means short vision and mouse hole, and the verb myein means to close the eyes. Myopia is a refractive anomaly (error of the eye) due to which light rays focus in front of the retina, therefore creating a blurred image of the observed object on the retina.
This means that myopic people see nearby objects better, and distant objects are seen more dimly and dimly. It occurs more often in people with a family history of myopia, but this does not mean that the child of myopic parents will automatically be myopic.
The far point (Punctum remotum) is located in front of the eye at an exact distance that depends on the degree of myopia.
The near point (punctumproximum) is closer than usual.
Signs of myopia:
- blurred distance vision
- headache
- the patient’s tendency to squint and squeeze his eyelids when he wants to see better at a distance
- good near vision
Myopia is corrected with concave, distracting, minus glasses or contact lenses. Nowadays, myopia can be corrected surgically (refractive surgery).
Unlike farsightedness, nearsightedness does not have the possibility of self-correction.
In myopia, the dioptric power of the eye and the size of the eye are not in the correct relationship, either the dioptric power of the refractive system of the eye is too large or the eye axis is too long (too large an eye).
In the refractive view, myopia is divided into:
- Axial myopia – it is caused by the stretching of the back half of the eye, and the optical axis is longer than 24 mm. The cornea and the eye lens are normally curved, and the eye lens is normally positioned.
- Refractive myopia – the eye is of normal size, but there is a greater curvature of the cornea (˃48.83 dsph) or the eye lens (curvature of the anterior surface ˃19.11 dsph).
- Accommodative myopia – is a consequence of accommodation spasm, whereby the lens moves forward.
- Index myopia – is caused by a change in the refractive index of the internal optical media of the eye (lens, aqueous humor or vitreous). Changes in index myopia are common in diabetics and can occur in avitaminosis A and D.
According to the size of the dioptric power, myopia is divided into:
- Low myopia – up to -3 dptr
- Medium myopia – up to -8 dptr
- High myopia – above -8 dptr
In the case of high myopia, unlike low and medium, there are certain changes in the background of the eye that occur due to the stretching of the eye, so regular ophthalmological eye control is required. These changes are permanent and cannot be cured, but the visual acuity itself can be improved in any case with different techniques.
Night myopia
Night myopia occurs only in some patients. During the day, the patient can be emmetropic (normal vision), short-sighted or far-sighted, and becomes more short-sighted in the dark. Sometimes additional glasses are needed to correct night myopia because the prescribed daytime glasses do not fit.
Causes of night myopia:
- wide pupil =˃ spherical aberration
- night color spectrum =˃ different sensitivity of the eye to colors
Autor:
bc. Livio Svržnjak, optometrist
