Many patients with multiple sclerosis (MS) experience cognitive impairment, which studies have shown can begin 1.2 years before clinical signs of the disease and is attributed to axonal and neuronal degeneration. The thinning of the retinal nerve fiber layer (RNFL) and ganglion cell inner plexiform layer (GCIPL) are both associated with white and grey matter atrophy in MS, suggesting that these parameters could help assess neurodegeneration and measure cognitive performance. In this study, researchers successfully used OCT to evaluate cognitive decline in MS patients by examining the nonmyelinated axons in the anterior visual pathway (anterior to the lamina cribrosa).
Researchers retrospectively analyzed the data of 204 study participants who were diagnosed with MS and followed between 2010 and 2020. Included participants had no prior event of optic neuritis (ON). SD-OCT exams were conducted to measure RNFL thickness in all patients and GCIPL thickness in a subgroup of patients (n=104). Computerized cognitive assessments were also completed by each patient.
The OCT results demonstrated that MS patients have reduced RNFL and GCIPL thicknesses when compared with healthy individuals, as observed in previous studies.
“OCT results demonstrated a reduced thickness for both the RNFL and GCIPL in our MS cohort compared with the normal ranges,” the study authors wrote. “Seventy-seven patients (37.7%) showed mild-to-moderate RNFL thinning (RNFL ≤89µm and >77.4µm) and 74 cases (36%) displayed severe RNFL thinning (RNFL ≤77.4µm). Twenty-five patients (24%) had mild-to-moderate GCIPL thinning (GCIPL ≤75.9µm and >69.7µm) and 29 of our MS subjects (27.9%) had severe GCIPL thinning (GCIPL ≤69.7µm).”
As for cognitive performance, a mild decrease in cognitive functioning was observed in the MS cohort compared with an age- and education-matched healthy population. The authors wrote that “26 MS patients (12.7%) presented with mild-to-moderate cognitive impairment and 13 patients (6.4%) with severe cognitive impairment.”
“As expected, the MS patients in our present series with a longer disease duration were significantly older, had a higher degree of disability and more prominent RNFL and GCIPL thinning. In cognition, patients with a longer disease duration had a lower score than cases with more recent MS diagnosis across all domains, although only executive function, attention and motor skills showed significant differences.”
GCIPL rather than RNFL thickness may be a better biomarker for cognitive performance, as it “includes the ganglion cell layer and its thinning signifies axonal loss, whereas the RNFL is formed by the expansion of the fibers of the optic nerve,” the authors wrote. In conclusion, both OCT parameters will aid in your assessment of neurodegeneration in MS patients with no history of ON or other eye conditions that could influence measurements.
Dreyer-Alster S, Gal A, Achiron A. Optical coherence tomography is associated with cognitive impairment in multiple sclerosis. J Neuro-Ophthalmol. 2021;00:1-8.