Farsightedness

Hypermetropic eye, correction with convex lens

Farsightedness (hypermetropia). The far point is at a finite distance behind the eye. Parallel rays entering the eye are refracted to the focus, which is behind the eyeball (pic.). This is because:

• the eyeball is too short (a more common defect, created during embryonic development);
• the eye has less refraction of the optical system than a healthy eye.

In farsightedness, presbyopia manifests itself much earlier. With decreasing accodommodative ability, hypermetropia eventually needs distance glasses. A special case of hypermetropia is aphakia, which is a defect caused by removing the lens, for example for a cataract.

The defect is corrected with a convex lens.

Links

Related articles

• Nearsightedness (myopia)
• Refractive defects
• Biochemistry of the vision process
• Eye (Biophysics)
• Eye (biophysics)/Disorders of the eye
• Oculomotor muscles
• Eye (histology)

Source

• KYMPLOVÁ, Jaroslava. Katalog metod v biofyzice [online]. [cit. 2012-09-20]. <https://portal.lf1.cuni.cz/clanek-793-katalog-metod-v-biofyzice>.