Effects of photocoagulation on ocular blood flow in patients with severe non-proliferative diabetic retinopathy

Abstract

Purpose: To investigate ocular blood flow and correlations between ocular blood flow and variables in patients with severe non-proliferative diabetic retinopathy (S-NPDR) following panretinal photocoagulation (PRP).

Methods: In this retrospective, cross-sectional study, the blood flow on the optic nerve head (ONH) and choroid was assessed with laser speckle flowgraphy (LSFG) using the mean blur rate (MBR) in 76 eyes of 76 patients with S-NPDR who underwent PRP, 39 eyes of 39 patients with S-NPDR who did not undergo PRP, and 71 eyes of 71 normal subjects. The correlation between MBR and variables, including visual acuity (VA) and choroidal area determined by binarization method, was analyzed.

Results: The mean age was 62.9 ± 11.9 years in the S-NPDR with PRP eyes, 55.6 ± 11.4 years in the S-NPDR without PRP eyes, and 60.3 ± 11.1 years in the normal subject eyes. The ONH MBR in vessel and tissue areas and the choroidal MBR were significantly lower in the S-NDR with PRP group than in the other groups (p < 0.001, p < 0.001, and p < 0.001, respectively). The luminal and the stromal areas were significantly smaller in the S-NDR with PRP group than in the other groups (p < 0.001 and p < 0.001, respectively). LogMAR best corrected visual acuity (BCVA) exhibited significant negative correlation with the ONH MBR in vessel (r = -0.386, p < 0.001), tissue (r = -0.348, p < 0.001), and the choroid MBR (r = -0.339, p = 0.002) in the S-NDR with PRP group. Stepwise multiple regression analysis demonstrated that BCVA was a common independent factor associated with the ONH MBR in vessel, tissue, and the choroidal MBR in the S-NDR with PRP group.

Conclusions: ONH and choroid MBR in addition to choroidal component, including the luminal area, were significantly lower in eyes of patients with S-NPDR after PRP compared with no PRP and normal subjects group. This could suggest that the significantly reduced ocular blood flow in PRP-treated S-NPDR eyes correlated with long-term decreased post-PRP luminal area and visual acuity.

Fig 1. Representative composite color maps reflecting the mean blur rate (MBR) as measured by laser speckle flowgraphy (LSFG).

Red color indicates a high MBR, and blue color indicates a low MBR. To measure the MBR of the optic nerve head (ONH) blood flow and choroidal blood, a circle was set around the ONH (left) and the center of a rectangle was set at the fovea (250 × 250 pixels, degree: 6.31° × 6.31°) (right). Eyes of i) normal subjects (A, B), ii) severe non-proliferative diabetic retinopathy (S-NPDR) patients without panretinal photocoagulation (PRP) (C, D), and iii) S-NPDR patients with PRP (E, F) are demonstrated. The blue color is dominant in the ONH and choroid in S-NPDR patient eyes with PRP (E, F).

Fig 2. Representative binarization image of a choroidal area in an enhanced depth imaging (EDI) optical coherence tomography (OCT) image.

The eyes with normal subject (A), severe non-proliferative diabetic retinopathy (S-NPDR) patients with panretinal photocoagulation (PRP) (B), and S-NPDR patients without PRP (C) are demonstrated. The area of interest of the choroid is demarcated (top). The EDI-OCT image was converted to a binary image using ImageJ software. The rectangle surrounded by the red line was excised, and the dark areas were traced by the modified Niblack method (middle). The binarized image and the margin of the traced area were merged, demonstrating that the traced area represented the luminal area, being consistent with the dark areas of the choroidal areas observed in the OCT image (bottom). The choroidal and luminal areas in the eyes of S-NPDR patients with PRP were smaller than those in the eyes of normal subjects or S-NPDR patients without PRP.

Fig 3. Differences between the eyes of normal subjects and those of patients with severe non-proliferative diabetic retinopathy (S-NPDR) in terms of mean blur rate (MBR) as determined by laser speckle flowgraphy (LSFG).

The MBR of the optic nerve head (ONH) in the vessel and the tissue in the S-NPDR with panretinal photocoagulation (PRP) group was significantly lower than that in the S-NPDR without PRP and normal subjects groups (A) (B) (p < 0.001, p < 0.001, respectively). The choroidal MBR in the S-NPDR with PRP group was significantly lower than that in the S-NPDR without PRP and the normal subjects groups (p = 0.028, p < 0.001).

Fig 4. Differences between the eyes of normal subjects and those of patients with severe non-proliferative diabetic retinopathy (S-NPDR) with regard to subfoveal choroidal area as determined by binarization.

The choroidal (A), luminal (B), and stromal area (C) in the S-NPDR with panretinal photocoagulation (PRP) group were significantly smaller than that in the S-NPDR without PRP and the normal subjects groups (p < 0.001, p < 0.001, p < 0.001, respectively). The luminal/stromal ratio in the S-NPDR with PRP group was significantly smaller than that in the S-NPDR without PRP and the normal subjects groups (p < 0.001, p < 0.001, respectively).

Fig 5. Relationship between best-corrected visual acuity (BCVA), optic nerve head (ONH), and choroid mean blur rate (MBR).

The BCVA correlated with ONH MBR in the vessel (r = −0.386, p < 0.001), in the tissue (r = −0.348, p < 0.001), and choroidal MBR (r = −0.339, p = 0.002). AU = arbitrary units.

Fig 6. Optical coherence tomography angiography showing an eye with S-NPDR following PRP.

Fundus photograph (A) and fluorescence angiography (B) taken with the Optomap® camera showing an eye with S-NPDR following PRP. Optical coherence tomography (OCT) angiography of the photocoagulated area showing choroidal major vessel because of the defect of RPE and choriocapillaris (C). An SD-OCT Spectralis® image was taken at the red line of the angiography (D). Photocoagulated regions (red arrow head) indicates absence of the outer nuclear layer and photoreceptor cells with the inner retinal layers lying in close apposition to Bruch's membrane and disruption of RPE layer and choriocapillaris.