Journal of ophthalmology, otology and laryngology . t arc is reduced 7 mm., it is still as large as the nor-mal contact arc of an internus and is more than sufficient for anyfurther outward rotation that may be required. At D, shows the contact arc of the internus increased 7 mm., butas this increased contact arc has been obtained by stretching and at- tenuating the muscle, power has actually been lost, and consequentlythe increased contact arc is of no benefit; as the muscle lacks inherentrecuperative power a tenotomy of the externus could never give nor-mal converging power to the weakened i
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Journal of ophthalmology, otology and laryngology . t arc is reduced 7 mm., it is still as large as the nor-mal contact arc of an internus and is more than sufficient for anyfurther outward rotation that may be required. At D, shows the contact arc of the internus increased 7 mm., butas this increased contact arc has been obtained by stretching and at- tenuating the muscle, power has actually been lost, and consequentlythe increased contact arc is of no benefit; as the muscle lacks inherentrecuperative power a tenotomy of the externus could never give nor-mal converging power to the weakened internus, even if it succeededin correcting the divergence. In order to establish normal muscularmovements in all positions, it will be necessary to shorten andstrengthen the stretched internus, and displace the externus an equalamount, in order to overcome its inherent resistance and later re-cuperative effect. Fig. 4. D shows the right eye after having had a convergent straljis-mus of 7 mm. corrected by a tenotomy; the displacement of the tendin-. 290 OPERATIONS UPON THE LATERAL EYE MUSCLES. ous attachment of the internus of 7 mm. is seen to cause a complete lossof the contact arc, and a mechanical loss of at least 7 mm. of converg-ence, thus clearly demonstrating that there is a mechanical reason whya tenotomized internal rectus muscle loses power and can never there-after perform normal movements in all positions. This displacementand weakening of the internus also allows the externus to exert itsrecuperative power. Therefore under no circumstances is a tenotomyof the internal rectus justifiable. At E, shows the left eye after having had a divergent strabismusof 7 mm. corrected by a tenotomy. The displacement of the tendinousattachment of the externus of 7 mm. still leaves a 7 mm. contact arcas large as normally possessed by an internal rectus muscle. Thisfact, together with its inherent resistance, enables the muscle to imme-