Scott Kolbe and his colleagues have been developing magnetic resonance imaging (MRI) techniques which can reveal abnormalities in the microscopic structure of the optic nerve after optic neuritis in human patients. These microscopic changes are related to axonal degeneration after optic neuritis, but preliminary evidence from animal models suggests that these MRI measures could even detect axonal degeneration at the earliest stages of inflammation.
This study will determine whether MRI can detect axonal degeneration at the first stages of optic neuritis in human patients and even predict later permanent loss of vision. The success of this project could see MRI used to measure neurodegeneration in therapy trials of drugs which act to protect neurons.
The optic nerve is affected in 40% of MS patients, a presentation known as optic neuritis. After temporary loss of vision due inflammation resolves, patients can exhibit permanent visual dysfunctions such as loss of visual acuity, loss of contrast sensitivity or loss of colour vision or even blindness. In addition, electrical signals transmitted from the eye to the brain are diminished and retinal thinning is commonly observed, both indicating that axonal degeneration is the cause of permanent vision loss.
However, studies of animals have shown that axonal degeneration can occur at the very earliest stages of inflammation. Unfortunately, degeneration is difficult to detect at this time because the complex changes occurs during the brain’s inflammatory response can mask subtle changes.
Developing optic nerve MRI techniques is challenging because of the nerve’s is small and highly mobile. Despite this Scott has developed an optic nerve imaging sequence called diffusion tensor imaging (DTI) which is sensitive to damage to the microstructure of the optic nerve in patients with a history of optic neuritis. Scott has also found that DTI-indicated optic nerve damage in those patients was associated with loss of optic nerve function. Scott did not, however, observe any association between optic nerve injury and loss of visual acuity, the principal clinical measure of visual function.
To further investigate the lack of association between optic nerve injury and clinical visual impairment, Scott has studied patients with a history of optic neuritis and extant loss of visual acuity. Scott found that optic nerve injury did not differentiate patients with severe visual impairment from those with mild impairment. In fact, many patients with severe optic nerve injury had near-normal visual acuity. These results suggest that visual recovery following optic neuritis could be strongly influenced by neuroplasticity, the brains inherent ability to change in response to injury to maintain function. Scott will be further investigating the role of neuroplasticity in mediating visual recovery in future research studies.
Updated: 30 June 2012
Updated: 05 January, 2010