NONCONFOCAL ULTRA-WIDEFIELD SCANNING LASER OPHTHALMOSCOPY: Polarization Artifacts and Diabetic Macular Edema

Nonconfocal ultra-widefield scanning laser ophthalmoscopes produce foveal polarization artifacts that require normal Henle layer structure and are suppressed by center-involving diabetic macular edema. Polarization sensitivity is insufficient for the artifacts to be reliable clinical screening biomarkers.
Purpose: Bowtie-shaped polarization artifacts are often present in nonconfocal ultra-widefield scanning laser ophthalmoscope (SLO) images. We studied these artifacts and evaluated their potential value as clinical biomarkers in screening for center-involving diabetic macular edema (DME). Methods: We performed a retrospective, observational, cohort study on 78 diabetic adult patients (143 eyes) who had spectral domain optical coherence tomography and nonmydriatic nonconfocal ultra-widefield SLO testing on the same day. Scanning laser ophthalmoscope green-only (532 nm), red-only (635 nm), and composite pseudocolor (532 plus 635 nm) images were examined for the presence of a foveal bowtie polarization artifact. Results: Polarization artifacts were absent in all but one eye with center-involving DME (32 of 33 eyes). Polarization artifacts were also absent in many eyes without center-involving DME (49 of 110 eyes in pseudocolor images). As clinical biomarkers of center-involving DME, artifact absence has high specificity (99, 100, and 98% for green, red, and pseudocolor images, respectively) but poor sensitivity (49, 31, and 40% for green, red, and pseudocolor images, respectively). Conclusion: Foveal bowtie-shaped polarization artifacts occur routinely in nonconfocal ultra-widefield SLO images. Their presence indicates preserved foveal Henle fiber layer structure. Contemporary nonconfocal ultra-widefield SLO images lack the sensitivity for their bowtie artifacts to serve as reliable biomarkers in screening for center-involving DME.