Purpose. To determine the optimal channel parameters in the deep layers of the corneal stroma when performing deep anterior lamellar keratoplasty (DALK), providing the maximum frequency of air bubble formation, under the control of intraoperative optical coherence tomography. Material and methods. The study was performed at 30 patients (30 eyes) with a diagnosis of stage III keratoconus. The average age of patients is 31±7 years. All patients were divided into groups consisting of 10 patients, depending on the choice of the topographic orientation of the channel for pneumodissection in the deep layers of the corneal stroma when performing DALK: 1st group – the channel is located towards the center of the cornea; 2nd group – the channel is located paracentral to the temporal side; 3rd group – the channel is located paracentral to the nasal side. In all cases, DALK was performed with a femtosecond laser Femto LDV Z8 (Ziemer, Switzerland). The length of the formed femto channels were variable and amounted to 1.0, 1.5, 2.0, 2.5 and 3.0 mm in each group. Results. The use of intraoperative OCT demonstrated that in all 30 cases the depth of the channel for pneumodissection corresponded to preoperative calculations and amounted to 97±5µm to DM. It was found that the bedding of the channel at a distance of 100µm to the descemet membrane (DM) and its paracentral orientation is characterized by a greater frequency of formation of the «Big Bubble» in comparison with its central orientation: 3rd group – 90% and 2nd group – 80% against 1st group – 60% of cases. The study of the effect of the length of the channel for pneumodissection on the ease of formation of the "Big Bubble" demonstrated that more attempts are required to inject sterile air when channels of 2.0, 2.5, 3.0 mm being used than with short channels of 1.0, and 1, 5 mm (average 3 attempts versus 1.5 attempts, respectively). Conclusion. The paracentral orientation of the location of the channel for pneumodissection is accompanied by a higher percentage of formation of the "Big Bubble" than the central location of the channel. Manual extension of femtochannels having length of 1.0, 1.5 mm, directly with a microsurgical spatula 30G followed by inserting a metal cannula into the channel minimizes the number of attempts to inject sterile air, that facilitates the formation of the "Big Bubble". Performing DALK applying the function of intraoperative OCT allows to control the accuracy of all stages of the operation, including the stage of formation of a large air bubble. Performing DALK with the applying of the function of intraoperative OCT allows to control the accuracy of all stages of the operation, including the stage of formation of a large air bubble. Key words: deep anterior lamellar keratoplasty, Big Bubble, channel for pneumodissection
Effect of Air Injection Depth on Big-bubble Formation in Lamellar Keratoplasty: an Ex Vivo Study