Junctional Scotoma and Patterns of Visual Field Defects Produced by Lesions Involving the Optic Chiasm.

BACKGROUND: Lesions of the optic chiasm (OC) typically produce bitemporal hemianopia (BTH) on visual field (VF) testing, whereas lesions located at the nasal optic nerve-chiasmal (ON-OC) junction have been proposed to produce junctional scotoma (JXS), a central defect in the ipsilateral eye with temporal field loss in the contralateral eye. In this study, we investigated whether the pattern of VF loss in patients with chiasmal compression predicted the appearance of the causative lesion on neuroimaging and described the clinical presentation of these patients with different types of VF defect. METHODS: Retrospective chart review of patients seen in tertiary neuro-ophthalmology practice over 6 consecutive years with lesions abutting or displacing the OC was performed. Lesion size and location relative to the OC on neuroimaging was determined and correlated with VF defects as well as optical coherence tomography (OCT) of the peripapillary retinal nerve fiber layer and macular ganglion cell complex (GCC). RESULTS: Fifty-three patients were enrolled. VFs demonstrated JXS (n = 18), BTH (n = 14), monocular VF defect (n = 4), and no VF defect (n = 17); 64.7% of cases with normal VFs had radiologic OC compression. Lesion volume was highest in the JXS group, and these patients also had the poorest presenting visual acuity. All patients with JXS showed involvement of the ON-OC junction; however, not all cases showed compression of the OC from the nasal direction (15 of 18), and 17 of 18 also showed compression of one or both prechiasmatic ONs. Compression of the ON-OC junction was also seen in 79% of BTH, 100% of monocular VF defect, and 59% of no VF defect cases. Fifty percent of patients with normal VFs already had thinning of the GCC on OCT. GCC thinning was most pronounced nasally in the BTH group, but diffuse bilateral thinning was found in 38% of cases compared with 60% of JXS. VFs improved in 6 of 6 patients with BTH but only in 5 of 8 JXS cases after treatment. CONCLUSIONS: JXS is more often seen with larger lesions and when there is compression of both the prechiasmatic ON and ON-OC junction. These patients have worse presenting visual acuity and poorer outcomes. Not all patients with radiologic compression had VF defects, although 50% of patients with normal VFs had evidence of compression on the macular GCC analysis, emphasizing the importance of macular OCT in the evaluation of patients with lesions involving the OC.

Body regional distribution and stratification of fatty acids in the blubber of New Zealand sea lions: implications for diet predictions.

Fatty acids (FAs) from blubber are often analysed to assess the diet of marine mammals. However, distribution of blubber FAs is not necessarily uniform along the body. It is therefore important to understand the deposition of dietary fat to be able to estimate the diet. We analysed the FA compositions of the thoracic ventral (T region) blubber of 28 New Zealand (NZ) sea lions Phocarctos hookeri by-caught by the southern arrow squid Nototodarus sloani fishery. Each blubber sample was divided into an inner and an outer layer. For 16 of these 28 animals, the pelvic dorsal (P) region was also sampled. The influence of body region and layer was statistically tested on the distribution of blubber FAs. We found minimal differences between the P and T regions (3 out of 29 FAs). The outer blubber layer was more concentrated in short-chain monounsaturated FAs, and less concentrated in saturated FAs, but the degree of stratification was small. Diet predictions from quantitative FA signature analysis (QFASA) applied on different body regions were similar. When applied to different blubber layers, QFASA gave some variation in the contribution of rattails (~25 % in outer blubber vs. ~12 % in inner blubber). Nonetheless, diet predicted from both layers was dominated by similar prey species: octopus, hoki and rattails. Hoki and rattails shared a similar ecological niche. Therefore, feeding ecology of NZ sea lions inferred from the inner or the outer blubber would lead to the same conclusions. In the case of NZ sea lions, the outer layer of blubber, if the only sample accessible, could be a useful tissue for diet inference from FAs.