Monocular Occipital Temporal Crescent Syndrome
Temporal crescent syndrome is a rare visual field disorder that presents with monocular loss of vision in the temporal peripheral field caused by a retro-chiasmal lesion involving the anterior occipital cortex . Retro-chiasmal lesions typically present with contralateral homonymous visual field defects. One important exception, however, occurs with the monocular temporal crescent syndrome. The syndrome is named for the shape of the visual field loss in a crescent in the temporal visual field of the eye contralateral to the lesion.
The etiology for this special monocular visual field defect is due to the distribution and overlap of the nasal and temporal visual fields. The normal visual field in degrees from the central point is 60 degrees nasal, 50 degrees superiorly, and 90-100 degrees temporally (Figure 1). The nasal and temporal hemifields in each eye overlap but the monocular temporal crescent has no perimetric correlate in the fellow eye because the temporal visual field is larger than the nasal visual field. The most anterior portion of the striate cortex receives the input for the monocular temporal crescent in the visual field. . Thus, 30-40 degrees of the peripheral temporal visual field is unpaired and has unilateral representation in the contralateral visual cortex. Damage to this area of the visual cortex leads to the contralateral temporal crescent (Figure 2.)  .
The monocular temporal crescent syndrome can be congenital or acquired. In cases of congenital lesions, a complete homonymous hemianopsia may spare or involve the temporal crescent. Patients with congenital occipital lobe lesions may be asymptomatic . In acute acquired occipital lesions (e.g., occipital hemorrhage or stroke) the defect may be noticed acutely. However, slowly progressive lesions (e.g., occipital tumor or neurodegenerative disease) may produce symptoms over months to years . Other symptoms and signs (e.g., headache) may also be present in occipital lesions 
Yamaguchi et al. first described the temporal crescent in a lateral ventricular glioependymal cyst  but the most common cause in adults is a vascular event . Landau et al. later reported two cases of a missing temporal crescent with vascular lesions in the contralateral visual cortex. They hypothesized that the missing temporal crescent however may also be a result of damage to the optic radiations, cortical damage, or a combination of both as well as purely a cortical lesion . Chavis et al. reported a missing temporal crescent following moderate peripartum hypertension and a lesion in the deep white matter of the left frontal lobe on magnetic resonance imaging . Pellegrini et al. reported a case of temporal crescent syndrome due to Creutzfeldt-Jakob disease (CJD).  Another report described a patient with seizures and a hemorrhagic infarction of the anterior aspect of the parieto-occipital sulcus .
Patients may present with an isolated monocular crescent or other symptoms depending on localization. A history of stroke, birth injury, trauma, aneurysm, seizure, or migraine may be helpful. Severe headache accompanied by nausea, photophobia, along with the visual loss may occur . Any patient presenting with a monocular temporal crescentic visual field defect should have a full ocular exam to exclude intraocular causes of the visual field loss (e.g., retinal detachment). A relative afferent pupillary defect is generally present in such cases ipsilateral to the retinal or optic nerve lesion. Although Goldmann Kinetic Perimetry can detect the temporal crescentic peripheral field defect it is not universally available. The largest stimulus should be presented at the edge of the cupola, to include the temporal crescent for best results . It is important to understand that since lesions that cause a missing temporal crescent begin approximately 60 degrees from fixation, the central field is normal, and the nasal retinal periphery should be carefully examined ophthalmoscopically . Unfortunately, current central (30-2 or 24-2) automated perimetry (e.g., Humphrey Visual Field Analyzer) cannot detect a temporal crescent (which is beyond the central 30 degrees) . Confrontation visual field testing may be helpful in documenting the peripheral crescentic field loss. Some automated perimetry can test the peripheral visual field but the normative database is not as robust for such larger visual field tests.It has also been shown that a quick test can be used by the examiner by moving their hand slowly behind the patient's head, anteriorly, showcasing that the temporal visual field border extends beyond 90 degrees. A confrontation test can be used to detect constriction of the temporal aspect of the eye’s visual field but may not include all of the temporal peripheral field because the examiner’s hand is not long enough to enter the temporal crescent out of the blind area . Patients with a missing temporal crescent often showcase neurological deficits.Patients with an acute onset of the temporal crescent syndrome should undergo neuroimaging. Typically, computed tomography (CT) scan is the initial imaging to determine the underlying etiology in the acute setting (e.g., hemorrhage). If the CT scan is non-diagnostic or if further delineation of a CT lesion is necessary, then magnetic resonance imaging (MRI) may be helpful. Gradient echo sequences and T2 weighted spin-echo sequences can be used to detect subtle lesions (e.g., hemorrhage) in the monocular temporal crescent syndrome .
Management, treatment, and prognosis depend on the underlying etiology of the syndrome .
Clinicians should be aware that a monocular temporal crescentic visual field defect (temporal crescent syndrome) can occur from a contralateral, anterior occipital cortex lesion. The etiology for the temporal crescent syndrome is typically ischemic infarction or hemorrhage in the acute setting but neoplastic, infectious, and infiltrative etiologies may also occur. An RAPD should not be present in occipital lesions and careful examination of the retina and optic nerve should be performed to exclude non-occipital causes for the visual field loss. CT or MR scan of the brain may be necessary to confirm the diagnosis and etiology. Treatment should be directed at the underlying cause.
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