Hyperopia (hypermetropia) is one of the types of clinical refraction of the eye (see), characterized by the fact that the focus of parallel rays after refraction in the eye lies behind the retina (Figure 1). Hyperopia occurs in 50% of adults. Causes of hyperopia: weakness of the refractive apparatus of the eye (refractive hyperopia), short anterior-posterior axis of the eye (axial hyperopia); with the normal length of the axis and the refractive force - their disproportionate combination (combination farsightedness).
Fig. 1. The course of rays with farsightedness. Parallel rays entering the eye converge behind the mesh shell.
Fig. 2. The course of the rays when correcting the farsightedness with convex glass. Parallel rays falling into the eye, converge on the mesh shell.
Clear vision in the farsighted as at a distance vision, and even more so when seeing near is possible only with the voltage of accommodation of the eye (see).The
The diagnosis of hyperopia can be put in the process of determining visual acuity when examining glasses. Degree of farsightedness is determined by the strongest of the collective lenses giving the best vision. Visual acuity at farsightedness of weak and moderate degrees can be normal; At a hyperopia of high degrees (5,0-10,0 D and above) visual acuity is lowered, despite correction by points.
Correction of farsightedness is made by convex glasses, which enhance refraction (Fig. 2). In the absence of eyeglass correction, asthenopic asthenopia easily occurs (see), and often convergent strabismus develops (see).
See also Presbyopia .
For farsightedness is characterized by a weak refractive force of optical media or reduced in size eyeball, so that the light rays reflected from both distant and near objects located, after refraction in the cornea and lens, are focused not behind the retina, but behind it. In such cases, not a point is projected on the retina, but a circle of light scattering. And the images of objects blur.
Some believe that if the person is farsighted, then he should see well into the distance. Indeed, with farsightedness of a weak degree (up to 1.5 diopters), children and young men have good eyesight. With farsightedness in 2-4 dioltria, vision in the distance is usually quite satisfactory, and when working at close range, small objects under consideration, for example letters when reading, merge, there is pain in the eyes and in the forehead. And, at last, at a hyperopia of a high degree (more than 5 dioptres) the considerable weakening of vision both far away, and near is marked.
With farsightedness, constant tension often becomes familiar to the eye and even in rest does not completely relax the ciliary muscle. Therefore, in children and adolescents, only the apparent farsightedness is most often detected, and the latent farsightedness is revealed only with drug paralysis of accommodation, which is achieved by letting in the conjunctival cavity 1-2 drops of 0.5-1% atropine solution.
Thus, hyperopia is not a disease, but an optical defect in the eye. Only sometimes it can be the result of various painful processes. If you do not pick up glasses in time or do not wear them in time, especially in childhood, with farsightedness of medium and high degree, strabismus may develop and vision deteriorate significantly.
If there is a decrease in vision, which is no longer corrected by glasses, it is necessary to carry out treatment on special devices, to properly organize the workplace and the visual load regime.