We read with interest the article by Siegfried and associates describing the measurement of oxygen distribution in different regions of the anterior segment of the eye.
The authors reported that thinner corneas are associated with increased partial pressure of oxygen (pO 2 ) in the anterior chamber angle. Their findings are providing important insights in understanding the anterior chamber oxygen distribution in various conditions.
In that study, the authors held the pO 2 measurements under local anesthesia with sub-Tenon injection of 3 mL of 2% lidocaine and 0.375% bupivacaine (50:50). It is known that peribulbar and retrobulbar anesthesia without adrenaline affects the ocular hemodynamics significantly. In the literature, it has been suggested that hemodynamic alteration may be attributable to the drug-induced vasoconstrictive effect of the local anesthetics in both techniques. In a recent paper, Çoskun and associates investigated the effects of the sub-Tenon anesthesia with adrenaline on ocular hemodynamics. They found that blood flow of the ophthalmic artery, central retinal artery, and central retinal vein were significantly affected after sub-Tenon anesthesia. They reported that sub-Tenon injection possibly affects the ocular hemodynamics owing to the vasoconstrictor effect of adrenaline. But, they also suggested that mechanical compression effect of the injected volume makes a contribution to the alteration of ocular hemodynamics. Moreover, the anatomic region of the sub-Tenon injection is closer to the vascular tissues than that of retrobulbar and peribulbar injections.
In the study, Siegfried and associates used a 3 mL volume in sub-Tenon anesthesia, which is 50% more than Çoskun and associates’ study. Therefore, we think that using sub-Tenon injection may have altered their results. This condition may also explain their unexpected findings of correlation between central corneal thickness and pO 2 levels beneath the central cornea.