. Refraction and muscular imbalance, as simplified through the use of the ski-optometer. actual instrument before him. Before proceeding, one should first under-stand the effect of a prism and what it ac-complishes. To determine this, close one eye,looking at some small, fixed object; at thesame time, hold a ten-degree prism base-inbefore the open eye, noting displacement ofthe object. This will clearly show that theeye behind the prism turns toward the prismapex. To carry the experiment further, the fol-lowing test may be employed on a one eye, direct his attention to afixed
. Refraction and muscular imbalance, as simplified through the use of the ski-optometer. actual instrument before him. Before proceeding, one should first under-stand the effect of a prism and what it ac-complishes. To determine this, close one eye,looking at some small, fixed object; at thesame time, hold a ten-degree prism base-inbefore the open eye, noting displacement ofthe object. This will clearly show that theeye behind the prism turns toward the prismapex. To carry the experiment further, the fol-lowing test may be employed on a one eye, direct his attention to afixed object, placing the ten degree prism be-fore the eye, but far enough away to see thepatients eye behind it. As the prism isbrought in to the line of vision, it will be seenthat the eye turns towards the apex of the [42] Refraction and Muscular Imbalance prism. When the prism is removed, the eyereturns to its normal position. Similar experiments enable the refraction-ist to make the most practical use of treatingphorias and ductions, as well as to compre-hend all other technical Fig. 13—An important part of the equipment for muscularwork. The Phorometer As previously stated, it is practically impos-sible to accurately diagnose a case of muscularimbalance with trial case prisms. For thisreason the phorometer forms an importantpart of the equipment for muscle testing in theSki-optometer, having proven both rapid and [43] Refraction and Muscular Imbalance accurate. It consists of two five-degree prismswith bases opposite, each reflecting an objecttoward the apex or thin edge. The patientwhose attention is directed to the usualmuscle-testing spot of light, will see two spots. Aside from the instrument itself, and infurther explanation of the phorometers prin-ciple and construction, when two five-degreeprisms are placed together so that their basesare directly opposite, they naturally neutral-ize; when their bases are together, theirstrength is doubled. Thus while the prisms
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