Retinal thickness measured with optical coherence tomography in patients with multiple sclerosis

The retina offers a unique window to the brain with its unmyelinated axons that converge to the optic nerve. Optical coherence tomography (OCT) is a well-established and non-invasive imaging technique in the ophthalmology field. The retinal layers can be imaged directly, and OCT is often described as an optical biopsy of retinal tissue. OCT has many practical advantages, as ease of use, short acquisition time and being relatively inexpensive. During the past decade the interest in OCT has grown in the neurology field and its potentials as an imaging modality that might complement magnetic resonance imaging (MRI). Multiple sclerosis is a complex chronic neurological disease that leads to both gray and white matter damage. OCT has shown promising results in several studies focusing on MS and neurodegeneration in the brain.

Paper 1 evaluated the repeatability of images taken by Canon OCT-HS100 with the new automatic eye track function. The results showed good correlation with the well-established Zeiss Cirrus HD-OCT 5000, however it was clear that OCTs are not interchangeable due to differences in thickness estimations. Paper 2 confirmed in a large MS cohort, findings from previous studies that the peripapillary retinal nerve fiber layer (pRNFL) is reduced in eyes of MS patients compared with healthy controls (HCs), regardless of optic neuritis (ON) history. The temporal quadrant of pRNFL (T-pRNFL) demonstrated the strongest correlation to both physical disability, assessed with the Expanded Disability Status Scale (EDSS) and cognitive impairment, measured with Symbol Digit Modalities Test (SDMT). Paper 3 aimed to evaluate different OCT parameters in MS patients and investigate which might best describe physical disability and cognitive impairment. All of four included OCT measures showed a statistically significant thickness reduction in MS eyes compared with HCs. The T-pRNFL of primary progressive MS patients had the largest atrophy of the inner retinal layers compared with HCs. The EDSS showed a strong and significant inverse correlation with all four OCT measures. SDMT had the strongest correlation with average pRNFL and T-pRNFL thicknesses.

In conclusion, OCT is a sensitive method to assess structural damage of neurons and their axons in the visual pathway in MS. It is a reliable imaging technique with high repeatability. Retinal thickness loss was found in all MS subtypes and is associated with both physical and cognitive dysfunction. Our findings suggest the usefulness of measuring pRNFL thickness with OCT in MS eyes. In particular, the T-pRNFL thickness might be an important measurement to differentiate MS subtypes.

List of scientific papers

I. Brautaset, R., Birkeldh, U., Frehr Alstig, P., Wikén, P., Nilsson, M. Repeatability using automatic tracing with Canon OCT- HS100 and Zeiss Cirrus HD-OCT 5000. PLoS One. 2016;11(2):e0149138.
https://doi.org/10.1371/journal.pone.0149138

II. Birkeldh, U., Manouchehrinia, A., Hietala, M.A., Hillert, J., Olsson, T., Piehl, F., Skelton Kockum, I., Brundin, L., Zahavi, O., Wahlberg Ramsay, M., Brautaset, R., Nilsson, M. Retinal nerve fiber layer thickness associates with cognitive impairment and physical disability in multiple sclerosis. [Submitted]

III. Birkeldh, U., Manouchehrinia, A., Hietala, M.A., Hillert, J., Olsson, T., Piehl, F., Skelton Kockum, I., Brundin, L., Zahavi, O., Wahlberg Ramsay, M., Brautaset, R., Nilsson, M. The temporal retinal nerve fiber layer thickness is the most important optical coherence tomography estimate in multiple sclerosis. Frontiers in neurology. 2017;8:675.
https://doi.org/10.3389/fneur.2017.00675