Aerospace medicine is a branch of environmental medicine. In Aviation medicine field, hypoxia and decompression sickness associated with altitude changes are famous condition. In the space medicine field, problems include space sickness, fluid shifts, bone mineral loss associated with reduced gravity, and space radiation exposure.

　Aircrew and astronauts are subjected to health care under strict physical examination standards because they are required to continuously demonstrate advanced skills in those environments with reduced gravity and space radiation exposure.

　In the weightlessness of space, a variety of neuro-otological symptoms occur, and those manifesting as symptoms of space motion sickness—most of which are the same as those of terrestrial motion sickness—are very important. From this perspective, in collaboration with the National Space Development Agency of Japan, we studied changes in autonomic nervous system activity and stress hormones and the incidence of motion sickness in healthy male volunteers by applying various acceleration loads to the subjects while moving their heads. We also examined the incidence of motion sickness in subjects when the timing or spatial position of visual field information presented via a virtual reality headset was shifted with respect to the subjects’ head movement. When head and eye movements became unexpectedly asynchronous, the incidence of motion sickness increased and, at the same time, stress hormones such as ACTH and ADH rapidly increased. After stimulation on 3 consecutive days, adaptation occurred and the incidence of motion sickness sharply decreased. In subjects whose sympathetic nervous system was abnormally excited by gentle Coriolis stimulation, motion sickness was induced at significantly higher rates by subsequent more-intense stimulation, suggesting the involvement of the autonomic nervous system in susceptibility to motion sickness. We believe that motion sickness results from information that is unanticipated and is asynchronous in space or time, and that it is also a state that induces a dynamic process of adaptation in the brain.

　Astronauts have been reported to experience abnormalities, such as optic disc edema, globe flattening, and associated hyperopia and choroidal folds due to spaceflight. The National Aeronautics and Space Administration（NASA）had confirmed the incidence of intracranial hypertension in addition to eye abnormalities in astronauts; hence, these problems were once collectively referred to as visual impairment and intracranial pressure syndrome（VIIP）. Subsequently, astronauts experiencing ocular abnormalities without intracranial hypertension were confirmed; therefore, NASA has changed the collective term for these spaceflight-related abnormalities from VIIP to space flight-associated neuro-ocular syndrome（SANS）and focused on the search for the cause and treatment of SANS. Recently, astronauts staying in space for a long time have been reported to keep their brains shifted upward after their return from space and the Bruch’s membrane opening of the optic disc is pulled towards the brain.

　In addition, using magnetic resonance imaging, the total volume of the ventricular system has been found to increase after a prolonged stay compared to that at the pre-flight level. This paper introduces the ocular changes due to spaceflight based on various reports.

Purpose: The imbalance between the globe and orbit, that is, the volume ratio of the globe to the orbit（GOR）, and ratio of the equatorial diameter of the globe to the axial length（AL）（EAR）（an indicator of globe shape）were evaluated quantitatively using magnetic resonance imaging（MRI）in patients with highly myopic strabismus（HMS）.

Subjects and Methods: This was a retrospective case-series study, involving three patients（six eyes）with HMS. Globe volume, bony orbital volume, and the equatorial diameter of the globe were measured on MRI using image analysis software products. AL was measured using a biometer based on optical coherence tomography. The GOR and EAR were calculated.

Results: The right eye of one patient has a normal globe with a normal AL（24.06 mm）. The GOR and EAR were 0.34 and 1.01, respectively. The other five globes showed a posterior staphyloma and long AL（28.62-34.20 mm）. Their GOR and EAR ranged from 0.38 to 0.44 and 0.75 to 0.85, respectively（which were larger and smaller, respectively, than those of the normal globe）.

Conclusion: The globes of HMS patients exhibited an increased GOR and decreased EAR, producing elongated spheres, in which the AL functioned as the axis of rotation.

　A 50-year-old man was referred to our hospital with a diagnosis of right sixth nerve palsy. In addition to an insufficient abduction of the right eye, he complained of orthostatic headache and tinnitus. Magnetic resonance imaging（MRI）revealed an enlargement of the subdural space and a swollen pituitary gland, and these findings suggested a spontaneous intracranial hypotension（SIH）. Infusion was administered and rest was advised; however, alteration of consciousness was observed. MRI with gadolinium enhancement showed thickening of the dura mater, enhancement effect, and subdural hematoma, and the patient was diagnosed with SIH. After removal of the hematoma, an epidural blood patch was performed. Insufficient abduction due to sixth nerve palsy and orthostatic resolved. Thus, an epidural blood patch was an effective treatment for symptoms.

　We present the cases of two patients with unilateral compressive optic neuropathy and homonymous hemianopia following intracranial hemorrhage. Patient 1 was a 43-year-old man. He had aphasia, right hemiplegia, and left conjugate deviation and underwent craniotomy for left putaminal hemorrhage with midline shift on computed tomography. Four months after onset, visual acuity was 1.0 in the right eye and 0.6 in the left. Relative afferent pupillary defect（RAPD）was present in the left eye. Right quadrantanopia was detected by visual field test. Optic nerve atrophy in the left eye was observed. Ganglion cell complex（GCC）thickness on optical coherence tomography was 89.9 μm in the right eye and 73.1μm in the left with thinning around the fovea. Subsequently, GCC thickness in both eyes reduced gradually and progressively in the area, consistent with homonymous hemianopia. Patient 2 was a 72-year-old woman. She had headache, left hemiplegia, disturbance of consciousness and dysarthria and underwent endoscopic hematoma removal for right temporal lobe subcortical hemorrhage with midline shift on magnetic resonance imaging. Three months after onset, visual acuity was 0.2 in the right eye and 0.5 in the left. RAPD was present in the right eye. Optic nerve atrophy in the right eye was observed. GCC thickness was 71.3 μm in the right eye with thinning around the fovea and 94.3μm in the left. In patients with intracerebral hemorrhage with midline shift, direct compression or cerebral edema due to hematoma may cause compression of the intracranial optic nerve, leading to unilateral simple optic atrophy.

Case: The patient was a healthy 52-year-old woman. She visited a local doctor due to sudden ocular pain and exophthalmos in the right eye. Intracranial vascular lesions were not detected by contrast-enhanced computed tomography（CT）and computed tomography angiography（CTA）, and thyroid-associated ophthalmopathy was suspected due to the presence of external ocular muscle enlargement and elevated levels of anti-thyroglobulin antibodies. Exophthalmometry showed a proptosis of 22 mm on the right eye and 15 mm on the left eye; visual acuity was decreased and the intraocular pressure was high. Therefore, steroid pulse therapy and orbital decompression were performed, but the patient did not improve and was referred to our hospital. At the time of consultation, the patient’s visual acuity was 20 cm count fingers on the right eye and 0.04（1.2xS-5.50D=C-3.00D Ax 5°）on the left eye, and intraocular pressure was 27 and 17 mmHg on the right and left eye, respectively. Severe exophthalmos, upper conjunctiva, and upper scleral vascular distension were observed. We suspected a fistula of the internal carotid artery and cavernous sinus, and performed head magnetic resonance imaging（MRI）and magnetic resonance angiography（MRA）, which showed dilation of the superior ophthalmic vein and microvascular confluence near the anterior condylar confluence（ACC）. Afterwards, worsening of ocular pain and headache was observed. Angiography was thus performed at the department of neurosurgery to diagnose dural arteriovenous fistula（dAVF）near the ACC. The patient underwent transvenous embolization, and although the protrusion of the eye and the ocular movement disorder improved, severe visual dysfunction remained.

Conclusion: Among cases of dAVFs, the incidence of dAVFs occurring near the ACC is rare（3.6-4.2％）. However, when a sudden onset of unilateral ocular protrusion is observed, dAVFs near the ACC should be considered as a possible cause for further examination.