Background: We studied the association between (1) the retinal thickness, volume and structure assessed by optical coherence tomography (OCT), and (2) vascular changes around the fovea in FA to define the role of these methods in the detection of ischemic diabetic maculopathy.
Methods: This retrospective observational study included 51 eyes of 51 patients with severe non-proliferative and proliferative diabetic retinopathy, considering that they present advanced ischemic retinal changes. Based on the clinical examination and presence of leakage on FA, patients with clinically significant macular edema were excluded. On FA, foveal avascular zone (FAZ) corresponds to capillary loss and reflects ischemic processes. Its outline and size were assessed according to the ETDRS standards. Patients were divided in two groups according to the severity of damage of the FAZ outline: ≤ grade 2 (n = 28) and ≥ grade 3 (n = 23). As we expected ischemia-related damage, SD-OCT images were evaluated for retinal structure, volume, total thickness with division into the outer and inner retina (to assess the influence of two, non-overlapping blood sources) and ganglion cell layer thickness.
Results: The comparisons revealed that at least currently with described methods: 1. There is no significant association between FAZ outline and retinal volume, total thickness, and thickness of the outer and inner retina and ganglion cell layer. 2. There is no significant association between FAZ outline and following retinal structure characteristics: continuity of the external limiting membrane and inner segment/outer segment junction, and identification of the inner/outer retina boundary. 3. The identification of ganglion cell layer boundaries was significantly more difficult in more advanced FAZ outline grades. 4. FAZ size is not correlated with the retinal thickness and volume.
Conclusions: In patients with severe non-proliferative and proliferative diabetic retinopathy, it is not possible to predict FAZ outline/size based solely on the measurements assessing volume and thickness or retinal structure evaluation on OCT. Consequently, at present OCT cannot replace FA in the detection of ischemic diabetic maculopathy.