Ophthalmology » Evaluation of common symptoms

Refractive errors

Refractive errors result from an imbalance between the refractive power of the optical system of the eye and its axial length (i.e. the position of the retina, the "film" of the eye). Patients in whom these factors are in balance are emmetropic. If they are unbalanced (ametropia), optical correction is needed to achieve emmetropia. Most children are hyperopic at birth, i.e. the eye is too short in relation to the lens system. By the age of 7 years, the eyeball reaches the length of 23 - 24 mm of an adult emmetropic eye. Strong hyperopia is rarer than myopia, but more unpleasant, as it prevents from seeing objects clearly at any distance. In myopia the eye is too long for its refractive power. Distance vision is blurred. Treatment is with concave (minus power) spectacles or contact lenses. Regular astigmatism is treated with cylinder lenses in which the refractive power is present only at an angle of 90 degrees towards its axis (regular astigmatism). Irregular astigmatism cannot be corrected with spectacles. It occurs in keratoconus and scarred corneas and can be corrected with rigid contact lenses, as long as the cornea itself is clear. If not effective, penetrating keratoplasty is indicated. By the age of 45 years, the loss of accommodative power begins to cause symptoms, causing presbyopia. . Virtually no accommodation is left by 60 years of age. Plus correction, which is added to the glasses needed to correct far vision. The amount of this "addition" is about +1.0 D for those aged 45, and a maximum of +2.5 D for those aged 60 years or more.

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