Altered birefringence of peripapillary retinal nerve fiber layer in multiple sclerosis measured by polarization sensitive optical coherence tomography

Background:The retina has been used to study the pathophysiology of multiple sclerosis(MS).Peripapillary retinal nerve fiber layer(pRNFL)thinning has been suggested as an ocular biomarker of neurodegeneration in MS.The goal of this project was to determine the birefringence of the pRNFL by measuring the fiber birefringence using polarization sensitive optical coherence tomography(PS-OCT).Methods:Sixty-six MS patients without history of optic neuritis(age:39.9±11.0 yrs.old,53 females and 13 males)and 66 age-and gender-matched normal controls(age:40.7±11.4 yrs.old)were recruited.Custom built PS-OCT was used to measure phase retardation per unit depth(PR/UD,proportional to the birefringence)and pRNFL thickness in each quadrant of the pRNFL.In addition,clinical manifestation was used to correlate with the pRNFL birefringence.Results:The pRNFL was thinner in the temporal and inferior quadrants in MS patients compared with normal controls(P<0.05).The PR/UD of the pRNFL was significantly decreased in MS patients(P<0.05)in all quadrants except for the nasal quadrant.In both groups,the PR/UD from all four quadrants was not related to the averaged pRNFL thickness(P>0.05).In MS patients,the PR/UD was not related to the expanded disability status scale(EDSS)nor disease duration(r ranged from−0.17 to 0.02,P>0.05).Conclusion:This is the first study using PS-OCT to study the pRNFL birefringence in MS patients.Decreased birefringence of the pRNFL may indicate microtubule abnormality,and could be a potential biomarker for detecting early neurodegeneration in MS.

Technology developments and biomedical applications of polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomo- graphy （PS-OCT） enables depth-resolved mapping of sample polarization information, such as phase-retardation and optical axis orientation, which is particularly useful when the nano-scale organization of tissue that are difficult to be observed in the intensity images of a regular optical coherence tomography （OCT）. In this review, we survey two types of methods and systems of PS-OCT. The first type is PS-OCT with single input polarization state, which contain bulk optics or polarization maintaining fiber （PMF） based systems and single-mode fiber （SMF） based systems. The second type is PS-OCT with two different input polarization states, which contain SMF based systems and PMF based systems, through either time, frequency, or depth multiplexing. In addition, representa- tive biomedical applications using PS-OCT, such as retinal imaging, skin cancer detection, and brain mapping, are demonstrated.