The structures of the visual pathways (the optic nerve, chiasm, and tract) exhibit a much higher sensitivity to single-fraction radiation than other cranial nerves, and their particular dose-response characteristics can be defined. In contrast, the oculomotor and trigeminal nerves have a much higher dose tolerance.
Adverse effects of stereotactic radiosurgery on cranial nerves, especially the optic nerve and its pathways, are not yet sufficiently understood. 29 patients who underwent Gamma Knife radiosurgery for benign skull base tumors were reviewed. In all of them, parts of the visual pathways and/or other cranial nerves in the middle cranial fossa received significant doses of radiation. The dose given was correlated with neuro-ophthalmological findings during a follow-up period of 6–24 months. Cranial nerves III, IV and VI within the cavernous sinus, exposed to a dose from 4.5 to 30 Gy, did not develop signs of a neuropathy. Neither did the trigeminal nerve which received between 5 and 20 Gy. In patients with normal neuro-ophthalmological findings prior to radiosurgery, the visual pathways tolerated a dose between 7.5 to 15 Gy. However, in a group of patients with visual deficits before treatment and where the visual fibers-jeceived between 6 and 16.6 Gy, 31% deteriorated afterwards. These results indicate that the visual pathways are more at risk for radiation damage than the other cranial nerves in the region and that they may be even more vulnerable to radiation if prior to radiosurgery their function has been compromised by tumor or previous surgery.
Lyme borreliosis is an emerging tick-borne spirochetal infection characterized by a broad variety of symptoms, ranging from neurologic disorders and different skin manifestations to cardiac symptoms. Many ocular and neuro-ophthalmic symptoms have recently been attributed to Lyme disease. Especially in endemic areas ophthalmologists need to be aware of Borrelia burgdorferi as a possible causal agent. The aim of this paper is to present a short review of the literature of ophthalmic disorders resulting from Borrelia burgdorferi infections.
The HELP system seems to be safe and more effective than hemodilution in improving the hemorheological and the functional situation in NAION and could be a promising regimen in the treatment of NAION.
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