in the current study, we evaluated polarization
analysis as a noninvasive technique for the evaluation of the extent of subretinal fluid and the localization of the pinpoint areas of light scattering in CSR. Polarization analysis could selectively emphasize the different features of the retina, visualizing more as opposed to less superficial layers depending upon polarization content. In the depolarized light image, the leakage areas presented as high intensity areas, indicating a high degree of multiple scattering of the returning light at those locations, in turn implying local tissue disorder. In recent OCT studies, various morphologic changes at the leakage areas were reported, for example, pigment epithelial detachment, 10
abridging lesion, 11
and bulges from retinal pigment epithelium.13
Our findings in the depolarized light image represent the morphologic changes at the leakage areas and agree with these OCT findings. In the chronic cases, CSR may be accompanied by retinal pigment epithelium atrophy, 14
extensive pigmentary change, 14
or fibrinous exudates.1,15
Multiple dots and high intensity area around the leakage area in the depolarized light images could provide important information about the retinal pigment epithelium impairment around leakage areas.
The polarimetry technique has the advantage of being a noninvasive technique, which does not require pupil dilation, and provides en face results for a 15 degree region in one measurement. Testing time is short (0.7 seconds), and there is live viewing of the fundus during image acquisition to help ensure positive findings. The leakage point could readily be detected in the depolarized images without the need of repeated scans, so that existing treatment modalities could be applied with familiar landmarks. In some cases, the exact area for focal photocoagulation could not be determined, but an approximate area for photocoagulation might be obtained. Treatment outcomes based on the existing diagnostic and treatment modalities would then provide the necessary data as to the success of localization by polarimetry. Polarimetric analysis could also be a useful tool as a preparatory test before fluorescein angiography.
The average reflectance and the parallel polarized images did not show the leakage areas as well as the depolarized light image, but did localize in high contrast the neurosensory retinal detachment. This was expected since the former two image types are generated by polarization preserving light, emphasizing more superficial structures. The average reflectance image is similar to an image of a confocal scanning laser ophthalmoscope, which has been shown to emphasize more superficial retinal structures. 16–18
The contrast of the fluid surrounding the leakage areas in CSR is high in these image types because there is a reduction of transmission of light both into the and out of the fluid, accompanied by a loss of polarization of the light that does pass through. Additionally, the average reflectance and parallel images have strong light return off the healthier regions of the retina, so that the resulting contrast with the darker region of fluid is high.
The birefringence image, which is generated from the modulation of the polarization preserving light, was not expected to enhance the visualization of key features of CSR. In 29 eyes of our case series, there was a macular bow-tie, which is attributable to the interaction of corneal and retinal birefringence. The presence of a macular bow-tie implies incomplete correction for corneal birefringence by the fixed compensator, 19
yet the presence of a macular bow-tie could help to localize the fovea. In CSR cases, the foveal reflex can be missing because of abnormal light-tissue interactions. Localization of the fovea can be useful when focal photocoagulation is being considered. Even in eyes with sufficient compensation for the corneal birefringence and absence of a macular bow-tie, this structure might easily be regenerated by tilting of the patient’s head.
Polarimetry analysis has potentialities for further progress. Summary statistics from features or entire images may provide additional information, analogous to that used in nerve fiber layer analysis in glaucoma. The possible improvement of using full Mueller matrix polarimetry remains to be investigated. 20,21
These newer methods might more accurately separate polarization preserving from depolarized light, allowing more accurate quantification of retinal birefringence22
as well as avoiding the possible artifacts of over-estimating depolarized light. 7
Further study is necessary for the rapid, noninvasive assessment of the intrinsic changes in CSR.