. Refraction and muscular imbalance, as simplified through the use of the ski-optometer. nces,this may vary in different cases. SUPERDUCTION Superduction, sometimes termed sursum-duction, is the relative power of the superiorrecti to turn the eyes upward. Prism powerbase down and apex up is employed. Totest superduction, the rotary prism should beplaced in position with the two cypherslying horizontally, with the handle pointedvertically (Fig. 23). The patients atten-tion should again be directed to the largeletter E\ and the indicator or red lineshould be rotated downward from zero. Thehighes
. Refraction and muscular imbalance, as simplified through the use of the ski-optometer. nces,this may vary in different cases. SUPERDUCTION Superduction, sometimes termed sursum-duction, is the relative power of the superiorrecti to turn the eyes upward. Prism powerbase down and apex up is employed. Totest superduction, the rotary prism should beplaced in position with the two cypherslying horizontally, with the handle pointedvertically (Fig. 23). The patients atten-tion should again be directed to the largeletter E\ and the indicator or red lineshould be rotated downward from zero. Thehighest prism power that the patient will ac-cept before the object appears to double inthe vertical plane will indicate the degree ofright superduction. This should be recordedaccordingly. Conditions of this kind do not [62] Refraction and Muscular Imbalance usually exceed two or three degrees. Thetest, however, should be repeated severaltimes before the final result is recorded, asindicated in Fig. 24. The amount of super-duction ranges from 1 to 4 prism normal average is Fig. 23—To test superduction, base down is prisms line or indicator should be rotated down-ward from zero. To test subduction, base up is should be rotated upward from zero. Subduction Subduction, sometimes termed infraduc-tion or deorsumduction, is the relative powerof the inferior recti to turn the eyes power base up and apex down is em-ployed. To test subduction, the rotary prismshould be operated with zero graduations [63] Refraction and Muscular Imbaland placed horizontally, as in the superductiontest (Fig. 23), but the indicator should beslowly rotated in the reverse direction, or up-ward from zero. With the patients attentionagain directed to the large letter E, or theGreek cross, the strongest degree prism thus se-cured without diplopia will indicate the rightsubduction. The amount of subduction rangesfrom 1 to 4 prism dioptres. The norma
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