Evidence for Diffuse Central Retinal Edema In Vivo in Diabetic Male Sprague Dawley Rats
Figure 2
Representative structural and water content images.
Structural (top; unmodified spin-echo) and water content (bottom; turbo-FLASH) images from a diabetic rat (left column), and a second rat both before (control; middle column) and after (right column) dilutional hyponatremia. Top: Directly under each image, the central retina (±1 mm from the optic nerve head; yellow arrows in top center) is shown after linearization. Colored arrows to the left and right of those animals' linearized retinas indicate the location of the retina/choroid border for each; red – diabetic, blue – dilutional hyponatremia, green – control (before dilutional hyponatremia). Those arrows also indicate the outer border used for the central retinal thickness measurement, since the linearized retinas are shown after co-alignment of the vitreoretinal border. Consistent with the appearance of the structural images, the diabetic and dilutional hyponatremia retinas are visibly thicker than the control retina. The same pattern is visible in group average images, which are shown below each representative subject's linearized retina. The reduced clarity of the retina/choroid border in group average images is due to inter-individual differences in retinal thickness: Since linearized retinas are co-aligned to the vitreoretinal border in this figure, group average images (without spatial normalization) will average retina from one subject with non-retina of another at the retina/choroid border due to the range of retinal thicknesses in each group (diabetic: 199–244 µm; control: 149–203 µm; dilutional hyponatremia 198–227 µm). Such considerations motivated our resampling of retinal profiles onto a %thickness (rather than µm) scale prior to formal analysis (e.g. Figs. 3 and 5). Bottom: As above, the group average is presented directly beneath the linearized central retina for representative subjects. Here, though, the color-maps shows %water content (%v/v) values after setting vitreous to 99% (see 3rd paragraph of the ‘MRI Image Analysis’ section within Methods). Note that both retinal thickness and %water content will determine the total water content of a retina.