Myopia

Blick durch Brille bei Kurzsichtigkeit

With short-sighted vision your eyes are too long; images of objects in the distance are not placed on to the retina (fundus) but are displayed before it (Fig. 1). Without glasses everything in the distance appears blurred.

Short-sighted eye up to c. 40 years, view into the distance without accommodation

Fig. 1: Short-sighted eye up to c. 40 years.
View into the distance without accommodation Sicht in die Ferne ohne Akkommodation

The closer the observed object, the further back it is mapped on the retina. In an emmetropic eye, the image is “moved” by curvature of the lens (accommodation) to the front of the retina to be clearly seen. In myopia the eye is too long. Thus the image of a nearby object automatically comes directly on to the retina and is clearly seen (Fig. 2). Only in close up can you see clearly. The condition is called myopia, or short-sightedness.

Short-sighted eye up to c. 40 years, view in the close vicinity without accommodation

Fig. 2: Short-sighted eye up to c. 40 years.
View in the close vicinity without accommodation

 

The stronger the myopia, the sooner you can no longer see clearly looking into the distance. With myopia of 1 dpt (diopter) you can see clearly up to a distance of about 1 m, everything beyond out of focus; with 2 dpt from about 50 cm; with 3 diopters from about 33.3 cm. With 5 diopters you can no longer see clearly at about 20 cm and beyond.

A myopia can be compensated with minus glasses (concave shape) (e.g. sph = – 3.25 diopters.). A minus lens causes an image shift backward. The image is moved by the minus-glass back on to the retina, resulting in a clear vision (Fig. 3). That is, a minus lens causes a displacement of the image to the rear, a plus lens, a shift forward.

 

 Short-sighted eye up to c. 40 years, view into the distance without accommodation with glasses

Fig. 3: Short-sighted eye up to c. 40 years.
View into the distance without accommodation with glasses

When looking into the near vicinity with glasses a distinct image would actually end up behind the retina, because the image is moved further backward by the minus glasses. This is compensated by the lens in the eye. Through the curvature of the eye-lens (accommodation), which is a plus lens, the image is significantly returned to the front on the retina, as shown in Fig. 4 and vision becomes clear.

Fig. 4: Short-sighted eye up to c. 40 years, view in the vicinity with accommodation and with glasses

Fig. 4: Short-sighted eye up to c. 40 years
View in the vicinity with accommodation and with glasses

If you are already shortsighted at a young age, it will usually continue to get worse with age, as the eye can further lengthen in its growth phase. In myopia from about 3 diopters, you should regularly (every 2-3 years) have your retina examined by an ophthalmologist to avoid damage caused by stretching of the retina.

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