Ophthalmic Prisms Research Articles

Distortion of the image by ophthalmic prisms.

THAT THE image seen through an ophthalmic prism is distorted is well known to every refractionist, and this distortion is especially apparent through large prisms, and even through the usual Risley rotary prisms. Although known qualitatively, a general quantitative discussion of this distortion has never appeared in the literature. This situation can be accounted for not only because of the mathematical complications involved but also, and probably more so, because of the general lack of interest in such distortion, except as a phenomenon to be tolerated. In 1927 Hartinger1calculated the magnitude of this distortion for particular prisms with plane surfaces, especially those of high deviating power. He did not give a quantitative description that was applicable to ophthalmic prisms in general. There has been more interest of late in this distortion because of its influence on stereoscopic spatial localization when ophthalmic prisms are worn before the two eyes.

Distortion of the Image by Prisms

The distortion of the image formed by a prism, principally an ophthalmic prism, is shown to be adequately described quantitatively by five parameters. Expressions are derived which relate the physical constants of the prism and the position of the prism before the eye to these five parameters. Comparisons of measurements and theory are given. This theory is useful for the study of this distortion and for designing prisms with a minimum of certain aspects of this distortion.

CLINICAL USE OF OPHTHALMIC PRISMS (METRIC)

In a previous report 1 the origins and developments of the present systems of numbering ophthalmic prisms were discussed, and attention was called to three important facts: The power of prisms frequently departs unjustifiably from reasonable manufacturing standards. Different units of power are used, but the unit used is rarely indicated on the label. Enormous errors are introduced in using strong prisms unless careful precautions are taken respecting the position in which the prism is held and the unit used. Both the Dennett 2 system of utilizing the prism centrad (▽) as a unit and the Prentice system 3 of utilizing the prism diopter (△) as a unit require that all refractive effect must take place at one surface. This condition is violated more frequently than it is observed in clinical practice. I have watched many ophthalmologists, teachers as well as students, in making their measurements of squint, and the

Ophthalmic Prisms, Some Uses In Ophthalmology

Ophthalmic Prisms, Some Uses In Ophthalmology

Ophthalmic Prisms, Some Uses in Ophthalmology

Ophthalmic Prisms, Some Uses in Ophthalmology