Association Between Corneal Changes and Retinal Oximetry in Diabetes Mellitus

Diabetes mellitus (DM) causes different corneal changes that are associated with the severity of diabetic retinopathy. To identify the pathophysiological reasons for this, corneal tomography and optical densitometry (COD) were combined with retinal oximetry.

Patients with DM and healthy subjects were included in this pilot study. Spatially resolved corneal thickness and COD were assessed using the Pentacam HR (Oculus). The pachymetry difference (PAC_Diff) was calculated as an indicator of an increase in the peripheral corneal thickness. Oxygen saturation (SO₂) of the retinal vessels was measured using the Retinal Vessel Analyzer (Imedos Systems UG). Subsequently, the associations between corneal and retinal parameters were analyzed.

Data from 30 patients with DM were compared with those from 30 age-matched healthy subjects. In DM, arterial (P = 0.048) and venous (P < 0.001) SO₂ levels were increased, and arteriovenous SO₂ difference was decreased (P < 0.001). In patients, PAC_Diff was higher than that in healthy subjects (P < 0.05), indicating a stronger increase in peripheral corneal thickness. The COD was reduced in DM (P = 0.004). The PAC_Diff of concentric rings with a diameter of 4 mm (r = -0.404; P = 0.033) to 8 mm (r = -0.522; P = 0.004) was inversely correlated with the arteriovenous SO₂ difference. Furthermore, PAC_Diff 4 mm was negatively associated with arterial SO₂ (r = -0.389; P = 0.041), and the COD of the peripheral corneal areas correlated positive with arterial SO₂ (COD total 10-12 mm: r = 0.408; P = 0.025).

These associations might indicate a common pathogenesis of corneal and retinal changes in DM, which could be caused by reduced oxygen supply, mitochondrial dysfunction, oxidative stress, and cytokine effects.