. Refraction and muscular imbalance, as simplified through the use of the ski-optometer. s ofexercises, or calisthenics. 3. The use of Prisms: When the secondmethod fails, prisms are supplied, with baseof prism before the weak muscle, for restonly. 4. Operation : If the above three methods,as outlined in the following chapters, havebeen carefully investigated, nothing remainsbut a tetonomy or advancement, or other op-erative means for relief and satisfaction tothe patient. The Rotary Prism The rotary prism of the Ski-optometer,(Fig. 21) consists of a prism unit, having atotal equivalent of thi
. Refraction and muscular imbalance, as simplified through the use of the ski-optometer. s ofexercises, or calisthenics. 3. The use of Prisms: When the secondmethod fails, prisms are supplied, with baseof prism before the weak muscle, for restonly. 4. Operation : If the above three methods,as outlined in the following chapters, havebeen carefully investigated, nothing remainsbut a tetonomy or advancement, or other op-erative means for relief and satisfaction tothe patient. The Rotary Prism The rotary prism of the Ski-optometer,(Fig. 21) consists of a prism unit, having atotal equivalent of thirty degrees. It is com-posed of two fifteen-degree prisms, back to [54] Refraction and Muscular Imbalance back, so that the turn of its pinion or handlecauses each of its lenses to revolve, one on theother. When its bases are opposite, they neu-tralize; when directly together, they give atotal value of thirty degrees. While revolv-ing from zero to maximum strength, they giveprism values w^hich are indicated on the scaleof measurements, the red line denoting thetotal prism Fig. 21—Turning rotary prisms pinioned handle gives prism value from zero to 30° as indicated by prisms red line indicator. It is obviously essential to know^ where thebase of the rotary prism is located. Thereforeif prism in or out is desired, the zero gradua-tions should be placed vertically and the redline or indicator set at the upper zero (). A rotation inward to 10 would give a prism [55] Refraction and Muscular Imbalance equivalent of ten degrees, base in. A rotationfrom zero to 10 outward would give a prismequivalent of ten degrees, base out, etc. Withzero graduations horizontal and the red. lineor indicator set therewith, a rotation upwardto ten on the scale would give a prism equi-valent of ten degrees, base up. A rotationfrom zero downward to 10 would give aprism equivalent of ten degrees, base understanding of the foregoing willshow that a rotation of the red line, or
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