thickness subsided after 3 and 6 months while the change in the choroidal thickness sustained for a long time. The different change in the retina and the choroid cannot be explained by refractive change after surgery. With the aid of image registration and tracking and with another recently published report2 with the same conclusion, we consider our results reliable. YASUO NODA ASAKO OGAWA TAKU TOYAMA TAKASHI UETA

Tokyo, Japan CONFLICT OF INTEREST DISCLOSURES: SEE THE ORIGINAL article for any disclosures of the authors.

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 C ¸ oskun 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 pO2 levels beneath the central cornea. UMIT YOLCU

Kars, Turkey ABDULLAH ILHAN

Erzurum, Turkey

REFERENCES

FATIH C. GUNDOGAN

1. Ohsugi H, Ikuno Y, Ohara Z, et al. Changes in choroidal thickness after cataract surgery. J Cataract Refract Surg 2014;40(2):184–191. 2. Pierru A, Carles M, Gastaud P, Baillif S. Measurement of subfoveal choroidal thickness after cataract surgery in enhanced depth imaging optical coherence tomography. Invest Ophthalmol Vis Sci 2014;55(8):4967–4974.

Central Corneal Thickness Correlates With Oxygen Levels in the Human Anterior Chamber Angle EDITOR: WE READ WITH INTEREST THE ARTICLE BY SIEGFRIED

and associates1 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 (pO2) 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 pO2 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.2,3 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, C ¸ oskun and associates investigated the effects of the sub-Tenon anesthesia with adrenaline on ocular hemodynamics.4 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 610

UZEYIR ERDEM

Ankara, Turkey THE AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. The authors indicate no financial support.

REFERENCES

1. Siegfried CJ, Shui YB, Bai F, Beebe DC. Central corneal thickness correlates with oxygen levels in the human anterior chamber angle. Am J Ophthalmol 2015;159(3):457–462. 2. Findl O, Dallinger S, Menapace R, et al. Effects of peribulbar anesthesia on ocular blood flow in patients undergoing cataract surgery. Am J Ophthalmol 1999;127(6):645–649. 3. Huber KK, Remky A. Colour Doppler imaging before and after retrobulbar anaesthesia in patients undergoing cataract surgery. Graefes Arch Clin Exp Ophthalmol 2005;243(11): 1141–1146. 4. C ¸ oskun M, Daglioglu MC, Davran R, et al. Effects of subTenon’s anaesthesia on ocular hemodynamics. Can J Ophthalmol 2014;49(2):141–144.

REPLY WE APPRECIATE THE CORRESPONDENCE FROM YOLCU AND

associates and are pleased to respond to their concerns about the effects of sub-Tenon local anesthetic on the results of our recently published study.1 As noted in our Methods section, we performed an injection of 3 mL of 2% lidocaine and 0.375% bupivacaine in a 50:50 solution, using a blunt cannula through a small incision in the inferior fornix. In fact, not all patients received the full amount of anesthetic at the time of the measurement prior to initiation of the surgical procedure, as many received

AMERICAN JOURNAL OF OPHTHALMOLOGY

MARCH 2015

Central corneal thickness correlates with oxygen levels in the human anterior chamber angle.

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