Inferior visual fibers course from the LGB anteriorly in the Meyer loop of the temporal lobe (approximately 2.5 cm from the anterior tip of the temporal lobe). Superior fibers tend to course more directly posteriorly in the parietal lobe. Lesions affecting the Meyer loop thus produce superior, incongruous, homonymous defects contralateral to the lesion. These defects (so-called pie in the sky defects) spare fixation (Fig 4-31; see also Fig 4-25). Damage to the temporal lobe anterior to the Meyer loop does not cause visual field loss. Lesions affecting the radiations posterior to the loop produce homonymous hemianopic defects that extend inferiorly.
Tumors within the temporal lobe are a common cause of visual field loss (see Chapter 3). Neurologic findings of temporal lobe lesions include seizure activity, including olfactory seizures and formed visual hallucinations. Surgical excision of seizure foci in the temporal lobes may lead to visual field defects.
Figure 4-31 Visual field patterns after partial left temporal lobectomy for seizure disorder. A, Kinetic perimetry visual field results show a predominantly peripheral right superior homonymous quadrantanopia sparing fixation. B, Humphrey 30-2 perimetry testing detects a minimal portion of the field defects.
(Courtesy of Steven A. Newman, MD.)
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.