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Yevgeniy Sychev, Raghu C Mudumbai; Proposing a new mechanism for chiasmal visual field loss in an unusual case of junctional scotoma: the degree of stretch of the anterior optic chiasm closely relates to the pattern of visual loss in a patient.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5560.
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© ARVO (1962-2015); The Authors (2016-present)
To report a case of an unusual junctional scotoma in a patient produced via a stretching of an anterior aspect of the optic chiasm.
A single case report describing a patient with an unusual mechanism of junctional scotoma is presented.
We present a case of an unusual junctional scotoma resulting from compression of the anterior optic chiasm by a pituitary macroadenoma. A patient presented complaining of unilateral vision loss in the left eye. Automated Humphrey visual field demonstrated dense temporal hemianopia in the left eye and only trace visual field change in the left eye. Magnetic Resonance Imaging demonstrated a macroadenoma under the anterior aspect of the optic chiasm resulting in marked stretch of the chiasm in the horizontal coronal axis. Following surgical decompression the visual field deficit has resolved. (see figure) Postoperative imaging demonstrated marked reduction in the degree of chiasm stretch.
The visual field deficit observed in the presented case cannot be explained by the classic theory that states that dysfunction of visual axons stems from their compression at the chiasm. The deficit observed is neither a bitemporal hemianopia, nor a typical junctional scotoma seen in syndromes of the middle and anterior chiasm compression respectively. Instead, the presented visual field defect implies involvement of predominantly the nasal fibers of the left optic nerve with sparing of the left temporal fibers and the right optic nerve. Pure compressive forces on the chiasm does not easily explain this pattern of visual loss. Close correlation between the degree of chiasm stretch and development of the temporal scotoma in this patient suggests that stretch of nerve fibers likely played an important role. The perpendicular relationship of the uncrossed fibers of the left optic nerve to the tumor with minimum lateral stretch forces at the chiasm may have lead to their relative protection. The crossing fibers may have been injured because of their partially parallel course to the horizontal stress forces in the anterior chiasm from the tumor. This mechanism of optic neurologic dysfunction may also be important contributor in other cases of bitemporal and junctional scotomas.
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