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D.T. Yee, P.A. Tenzel, D.P. Tenzel; Calculation of Gold Weight Replacement After Partial Resolution of 7th Nerve Palsy With Correlation of the Anatomy and Pathophysiology of the Eyelid Dysfunction . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3775.
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To formulate a calculation to predict the mass of a gold weight replacement needed after partial resolution of a 7th nerve palsy.
The mass of a gold weight needed to treat lagophthalmos in a patient with 7th nerve palsy can diminish with partial resolution of the nerve palsy over several years. Unlike worsening lagophthalmos, which can be treated with gold weights of increasing mass that can be tested pre–operatively by addition of more mass, subtraction of weight is not possible without surgical removal of the existing gold weight implant. The anatomy and physiology of eyelid function is examined to confirm the pathophysiology of the problem. Subjects with gold weights can be examined in a reclined position and the amount of recline measured and compared with improvement in lagophthalmos.
Vector force calculations of the mass required to reduce the effective mass which depresses the upper eyelid is performed. The is verified with a patient with improving lagophthalmos which requires exchange of a gold weight with one of lesser mass. The new (effective) mass of gold weight is equal to the originally place mass of the gold weight multiplied by the cosine of the angle of recline of the patient when improved lagophthalmos and eyelid function is achieved.
Calculation of gold weight replacement pre–opreatively is a useful method that can be done prior to actual surgical replacement of a gold weight with one of lesser mass. This calculation can be done in lieu of trial and error replacement. Placement of the correct mass would likely reduce the incidence of additional re–operations because measurement of a gold weight without removal of the existing gold weight cannot be otherwise done pre–operatively. The anatomy and pathophysiology of the eyelid structures is consistent with the vector force calculation proposed.
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