[Eye movement: experimental and clinical study using cine mode MRI]

As a special lecture at the 96th Annual Congress of the Japanese Ophthalmological Society in 1992, we presented experimental and clinical studies on eye movement using magnetic resonance imaging (MRI). MRI is more valuable than X-ray CT in defining external muscle anatomy in the orbit in a variety of pathological changes, and is free from the danger of radiation. Cine mode MRI, which was originally developed to observe cardiovascular function, was utilized experimentally for observation of eye movement. We invented two methods to produce a series of photographs. In the first method, "the moving eye method", the subjects were asked to perform 256 or 512 vertical and horizontal eye movements in synchronization with a sound trigger. In the second, "the fixed eye method", the subjects were asked to gaze at individual points in a 5 to 7 point sequence as indicated by the investigator. In both methods MRI data was generated and the resulting series of photographs were observed in cine mode on a television monitor. Displaying the MRI generated photographs in cine mode enables direct observation of the movement of the eye, optic nerve and extraocular muscles within the orbit. The moving eye method was more accurate in its portrayal of the actual movement of the eye, but the large number of eye movements, at least 256 movements, required about 5 minutes, and caused physical and mental fatigue for the subjects. The fixed eye method did not show actual movement of the eye, but was less fatiguing than the former method, and avoided several of its problems. A large number of ophthalmoplegia cases such as abducens palsy, oculomotor palsy, fracture of the orbital wall, foreign bodies in the orbit, Duane's syndrome, endocrine myopathy, esotropia, exotropia, etc., were examined using the fixed eye method of cine mode MRI. Using this technique, anatomical changes, such as atrophy or hypertrophy and the functional state demonstrated by the contraction and relaxation of the extraocular muscles could be investigated. Transposition of the extraocular muscles, an effective treatment for paralytic squint, was reexamined and a new surgical procedure was developed for abducens palsy. The measurement of the length, thickness and weight of the extraocular muscles from the MRI-generated photographs allowed for more accurate analysis. The three dimensional reconstructive method of MRI is very valuable for diagnosis in the orbit and is expected to contribute to future progress.