Visual field analysis and diffusion tensor imaging after temporal lobectomy to map the functional anatomy of the anterior optic radiations

The optic radiation is a very important brain structure, situated in the
temporal lobe and connecting the lateral geniculate body with the visual
cortex. Current knowledge of the functional anatomy of the optic radiation is
based on the classical theory of Van Buren and Baldwin, dating from 1956.
According to this theory, the most anterior fibers of the optic radiation, also
called *Meyer*s loop*, represent the visual field sector adjacent to the
vertical meridian. As one proceeds further backwards within Meyer*s loop, the
corresponding visual field extends radially into the inferior quadrant.
Visual field defects produced by a temporal lobe resection in patients with
intractable epilepsy provide valuable information on the anatomy of the optic
radiations. However, in the literature there is a lot of discussion regarding
frequency, size and shape of these visual field defects. Strong evidence to
either support or reject the classical theory on the functional anatomy of the
optic radiation is still lacking.

The main goal of this study is to map the functional anatomy of the anterior
optic radiations by correlating the visual field defects to the surgical
defects in Meyer*s loop in epilepsy patients after temporal lobectomy.

Observational, prospective cohort study.
Methods: before and after temporal lobe resection, patients will undergo visual
field examination (Peritest and Goldmann) and diffusion tensor imaging. Using
the diffusion tensor images, tractography will be performed to visualize the
optic radiations.

No risks are associated with participation in the study. Ophthalmologic
examination, visual field analysis and diffusion tensor imaging are part of the
clinical routine. For our patients, the only burden is a second visual field
examination (Goldmann perimetry), which takes approximately 20 minutes pre- and
post-operatively.