Abstract
Purpose: :
To assess the scattering measurements of the intraretinal layers in healthy normal and type 1 diabetic eyes using optical coherence tomography (OCT).
Methods: :
Unprocessed raw scan data were exported from the Stratus OCT machine after performing standard macular mapping in 74 healthy eyes (34±16 yrs, 51 female, 23 male) and 39 eyes with type 1 diabetes mellitus (DM) with no retinopathy (36±10 yrs, 19 female, 20 male) on biomicroscopy. Automatic layer segmentation was performed using a custom-built algorithm (OCTRIMA). Mean values of relative internal reflectivity (RIR) and reflectivity with normalization to the RPE reflectance (NRPE) were used in the comparisons. Mean light-backscattering, contrast measures and scattering coefficients of the RNFL, GCL+IPL, INL, OPL, ONL, IS/OS and OS/RPE junction were calculated. The scattering coefficients were calculated using a finite difference method. Mann-Whitney U test was used to test for differences between the groups. A modified p value of <0.001 was considered statistically significant. Missed significance (MS, 0.001<p<0.05) was also recorded.
Results: :
Scattering coefficients were significantly different between DM and healthy eyes for the IS/OS and OS/RPE junction for both types of normalization used (RIR: 9.84±2.05 mm-1 versus 8.49±1.12 mm-1 and 10.44±1.59 mm-1 versus 9.84±1.41 mm-1, p<0.001, respectively and; NRPE: 12.80±1.94 mm-1 versus 14.19±3.02 mm-1 and 14.69±2.34 mm-1 versus 15.18±2.71 mm-1, p<0.001, respectively). The mean light-backscattering and contrast measures between DM and healthy eyes were not significantly different.
Conclusions: :
Our results suggest that the optical properties of the intraretinal layers may provide useful information about the extent of intraretinal layer injury in diabetes. In previous studies, we have demonstrated that diabetes inflicts structural damage to the inner retinal segment supported by the thinning of the ganglion cell complex (RNFL+GCL+IPL). However, it appears that diabetes also inflicts additional damage to the outer retinal segment demonstrated by the optical changes of the IS/OS and OS/RPE junction. Further research is warranted to determine how this approach may be used to improve diagnosis and treatment of diabetes.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optical properties • diabetic retinopathy