The prescribing of spectacles / by Archibald Stanley Percival.

  • Percival, A. S. (Archibald Stanley), 1862-
Date:
1910
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Licence: In copyright

Credit: The prescribing of spectacles / by Archibald Stanley Percival. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    directed towards the single vision area. In paralysis of the right superior rectus, the diplopia is greatest in the right superior area ; hence, if the patient directs his face upwards and to the right, he will be least inconvenienced by his diplopia, as for an object immediately in front of him he will have to direct his eyes downwards and to the left. This gives us the key by which we may solve all these problems. We must first consider the line of action of the muscles. The external and internal recti of course act in the horizontal direction ; the superior or inferior rectus elevates or depresses the eye simply (i.e., without any torsion) when it is turned 27° outwards ; the inferior or superior oblique would simply elevate or depress the eye if it could be turned 51° inwards. Hence, both eyes will be turned to the right by the action of the right external rectus and the left internal rectus ; when they are in this eyes right position, both eyes will be elevated by the action of the right superior rectus and the left inferior oblique almost entirely. Consequently, the twelve muscles of the eyes may be divided into three groups of four each, four moving the eyes laterally, four upwards, and four downwards. Each group is divided into two pairs, one muscle of each pair being in the right eye and one in the left eye. 1 Lateral \a' Right turners R. ext. rect. and L. int. rect. \b. Left turners L. ext. rect. and R. int. rect. 2 Elevators {a' Eyes right Rl sup- rect and L inf- obli(lue 1 b. Eyes left L. sup. rect. and R. inf. oblique o Depressors {a' Eyes right R* inf' rect and L- sup obhque 1 \b. Eyes left L. inf. rect. and R. sup. oblique Each of these six pairs of muscles consists of Graefe's True Associates, and are easily remembered by Dr. Maddox's mnemonic that their names are the most contrary possible, e.g., right external rectus and left