An investigation of the retinal nerve fibre layer in progressive multiple sclerosis using optical coherence tomography

Axonal loss is thought to be the predominant cause of disabilityin progressive multiple sclerosis (MS).  The retinal nerve fibrelayer (RNFL) is composed largely of unmyelinated axons of retinalganglion cells, and is accessible to study with optical coherencetomography (OCT), giving a measure of axonal loss.  OCT measuresof the RNFL thickness (RNFLT) and macular volume were studiedin

23 patients with primary progressive multiple sclerosis (primaryprogressive MS) (13 male; 10 female; mean age 52 years;

Ø   medianEDSS 6.0;

Ø   mean disease duration 11 years), and

27 patients withsecondary progressive multiple sclerosis (secondary progressiveMS) (8 male; 19 female; mean age 50 years;

Ø   median EDSS 6;

Ø   meandisease duration 22 years).

Of the patients with secondary progressiveMS, 14 had clinical history of optic neuritis (ON) in a singleeye; the remaining patients had not had ON.

Twenty healthy controls(11 male; 9 female; mean age 46 years) had RNFLT and macularvolume studied.

Of the patients’ eyes not previously affectedby ON, both the mean RNFL thickness and macular volume werereduced when compared with control values. The mean RNFL thicknessand macular volume were significantly reduced in secondary progressiveMS, but not in primary progressive MS when compared with controlRNFL thickness and macular volume.  RNFL loss was most evidentin the temporal quadrant, where significant reduction was seenin primary progressive MS versus controls and in secondary versusprimary progressive MS.

There were significant correlationsof decreased RNFLT and macular volume with measures of visualacuity, low contrast visual acuity and visual field mean deviationin the MS patients.  There are significant global reductionsin RNFLT and macular volume in the eyes of secondary progressiveMS patients not previously affected by ON, but not in primaryprogressive MS patients, compared with controls. This may indicatea difference in the extent of the pathological processes thatcause axonal loss in the retina, and by inference the opticnerve, in secondary progressive MS and primary progressive MS.