Eyestrain (commonly called asthenopia) / by Ernest Clarke.

  • Ernest Clarke
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Eyestrain (commonly called asthenopia) / by Ernest Clarke. Source: Wellcome Collection.

    69/184 page 57
    The same happens, whatever the refractive condition of the eye, for instance, a hyperope of 4 D (fig. 4) at the age of 10, has his near point ten centimetres from the eye and p = -' p= 3-^- = 10 D, r is negative, and we have a = 10 - (-4) = 10 + 4 = 14 D i^O /£ 20 2S 30 3S 40 SO 6i 60 6S 70 7S 80 \ V r Fig. 4. Again, at 30 we see (fig. 4) that p = 3 D, P being now 33 centimetres from the eye, and we have a = 3 + 4 = 7 D A myope, say of 3 D (fig. 5) has his near point at the
    digitised image 1
    digitised image 2
    digitised image 3