**7. Use of transurgical OCT for lamellar transplants (DALK, DSAEK, DMEK)**

The application of OCT to lamellar transplant surgery is a useful tool to visualize the tissue planes and depth in the different steps of the surgery. This system optimizes the surgical procedure by letting the surgeon observe high-resolution images both at the eyepiece level of the microscope and at an external screen. By objectively visualizing depth in the different steps of surgery, greater safety is achieved by decreasing the risk of complications and facilitating surgical maneuvers, thereby increasing the success rate.

#### **7.1. DALK**

With this new technology, the depth of trepanation can be assessed, avoiding corneal perforations, especially in patients with thickness irregularities, such as keratoconus [14] (**Figure 7**). It is also possible to verify the depth of the cut with the diamond scalpel in the pachy-bubble technique, which is of vital importance to achieve the air injection close to Descemet, avoiding perforation and superficial air injection. Sorcia observed a higher success rate in reaching the pre-Descemet planes when performing DALK pachy-bubble [15]. The measurement of

**Figure 7.** Trepanation depth check (red arrow) by intraoperative OCT.

trepanation seems to be useful to determine if the depth is adequate or there is a need for further dissection to reach the ideal depth for an air injection.

management of various corneal conditions. Now that it is one of the most important diagnostic tests in ophthalmology, it is natural to use this technology in the operating room, as it provides a unique feedback mechanism in real time and helps facilitate the achievement of

The authors use the OPMI Lumera® 700 and RESCAN™ microscope from Zeiss (**Figures 5** and **6**), and this microscope includes an integrated OCT system, which optimizes the proce-

The application of OCT to lamellar transplant surgery is a useful tool to visualize the tissue planes and depth in the different steps of the surgery. This system optimizes the surgical procedure by letting the surgeon observe high-resolution images both at the eyepiece level of the microscope and at an external screen. By objectively visualizing depth in the different steps of surgery, greater safety is achieved by decreasing the risk of complications and facilitating

With this new technology, the depth of trepanation can be assessed, avoiding corneal perforations, especially in patients with thickness irregularities, such as keratoconus [14] (**Figure 7**). It is also possible to verify the depth of the cut with the diamond scalpel in the pachy-bubble technique, which is of vital importance to achieve the air injection close to Descemet, avoiding perforation and superficial air injection. Sorcia observed a higher success rate in reaching the pre-Descemet planes when performing DALK pachy-bubble [15]. The measurement of

**7. Use of transurgical OCT for lamellar transplants (DALK, DSAEK,** 

dure of deep anterior lamellar keratoplasty and endothelial keratoplasty.

surgical maneuvers, thereby increasing the success rate.

**Figure 7.** Trepanation depth check (red arrow) by intraoperative OCT.

surgical objectives.

106 OCT - Applications in Ophthalmology

**DMEK)**

**7.1. DALK**

Once air is injected to create the bubble that will separate the Descemet membrane and stroma, OCT images are captured to verify the extent of the dissection, and to check whether it reached the trepanation mark limit. These images will help the surgeon assess if there is risk of perforation or if there exists an inadequate separation of the stroma and the Descemet membrane (**Figures 8**–**10**).

In cases of poor visibility secondary to injected intrastromal air, the OCT helps to see the extension of the big bubble in the anterior chamber to ensure it is complete and to prevent perforation when removing the stroma (**Figure 11**).

**Figure 8.** The red arrow points to the Descemet membrane separated from the stroma by air forming the big bubble.

**Figure 9.** Descemet membrane (red arrow) returning to its original location. This is after the perforation of the stroma.

**Figure 10.** Descemet membrane (red arrow) is completely adhered to the stroma.

in case a thinner donor button is required. Even in cases where the microkeratome is passed once, transoperative OCT evaluates the thickness of the donor cornea and helps to select the

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With the transurgical OCT, the state of the donor graft can be observed. In the case of precut grafts for DSAEK, the precut lines are visualized in the corneal images, as well as defects or detritus on the endothelial surface, although these changes have no clinical importance [17]. In the case of DMEK, in addition to showing the space between the endothelium-stroma interphase, another use of transurgical OCT is to prevent cases where the donor button is inverted

In donor grafts for DMEK surgery, partial detachments of the Descemet membrane can be observed. Other defects and detritus can also be observed. Therefore, transoperative OCT is

In cases where the surgeon's vision is obstructed, for example with corneal edema in a bullous keratopathy, the use of transurgical OCT can help with decision-making inside the operating room [13]. In cases with opaque or edematous corneas, the visualization of the Descemet is difficult, and transurgical OCT can help with its visualization and descemetorhexis. The remaining Descemet membrane can be identified in the case of fibrous or scarred corneas [16]. In this case, transurgical OCT also helps to monitor the insertion and unfolding of the graft, since it can inadvertently have an inverse configuration and result in a failed surgery. With this, the surgeon may ensure an adequate deployment and orientation of the graft, especially in the case of the DMEK surgery in which the graft is much thinner than that of DSAEK (**Figure 13**). Traditionally, the graft-recipient interphase is reviewed in the slit lamp or in the microscope, but with transoperative OCT, additional information is provided to the surgeon regarding the manipulation of the graft and the final interphase between the graft recipient (**Figure 14**),

an excellent alternative to observe the state of the donor tissue.

which can influence the postoperative results.

ideal size of the blade.

**Figure 12.** Descemet membrane without any stromal tissue.

in the anterior chamber [17].

**Figure 11.** Stromal dissection. The OCT images guide the surgeon to avoid perforation of the Descemet membrane (red arrow).

After the dissection is completed, the surgeon can evaluate if the stroma was completely removed (**Figure 12**). The donor button is allocated and sutured, and the position of both tissues is evaluated. The surgeon should look for irregularities, liquid or air that separates both tissues anywhere. With the OCT system, it is possible to optimize the approximation of graft and host.

#### **7.2. DSAEK/DMEK**

When preparing the donor button in the DSAEK transplant, after passing the microkeratome, the residual thickness of the donor can be evaluated with the help of transoperative OCT to guide the surgeon in selecting the ideal blade size for a second cut with the microkeratome [16],

**Figure 12.** Descemet membrane without any stromal tissue.

After the dissection is completed, the surgeon can evaluate if the stroma was completely removed (**Figure 12**). The donor button is allocated and sutured, and the position of both tissues is evaluated. The surgeon should look for irregularities, liquid or air that separates both tissues anywhere. With the OCT system, it is possible to optimize the approximation of graft and host.

**Figure 11.** Stromal dissection. The OCT images guide the surgeon to avoid perforation of the Descemet membrane (red

**Figure 10.** Descemet membrane (red arrow) is completely adhered to the stroma.

When preparing the donor button in the DSAEK transplant, after passing the microkeratome, the residual thickness of the donor can be evaluated with the help of transoperative OCT to guide the surgeon in selecting the ideal blade size for a second cut with the microkeratome [16],

**7.2. DSAEK/DMEK**

108 OCT - Applications in Ophthalmology

arrow).

in case a thinner donor button is required. Even in cases where the microkeratome is passed once, transoperative OCT evaluates the thickness of the donor cornea and helps to select the ideal size of the blade.

With the transurgical OCT, the state of the donor graft can be observed. In the case of precut grafts for DSAEK, the precut lines are visualized in the corneal images, as well as defects or detritus on the endothelial surface, although these changes have no clinical importance [17]. In the case of DMEK, in addition to showing the space between the endothelium-stroma interphase, another use of transurgical OCT is to prevent cases where the donor button is inverted in the anterior chamber [17].

In donor grafts for DMEK surgery, partial detachments of the Descemet membrane can be observed. Other defects and detritus can also be observed. Therefore, transoperative OCT is an excellent alternative to observe the state of the donor tissue.

In cases where the surgeon's vision is obstructed, for example with corneal edema in a bullous keratopathy, the use of transurgical OCT can help with decision-making inside the operating room [13]. In cases with opaque or edematous corneas, the visualization of the Descemet is difficult, and transurgical OCT can help with its visualization and descemetorhexis. The remaining Descemet membrane can be identified in the case of fibrous or scarred corneas [16]. In this case, transurgical OCT also helps to monitor the insertion and unfolding of the graft, since it can inadvertently have an inverse configuration and result in a failed surgery. With this, the surgeon may ensure an adequate deployment and orientation of the graft, especially in the case of the DMEK surgery in which the graft is much thinner than that of DSAEK (**Figure 13**).

Traditionally, the graft-recipient interphase is reviewed in the slit lamp or in the microscope, but with transoperative OCT, additional information is provided to the surgeon regarding the manipulation of the graft and the final interphase between the graft recipient (**Figure 14**), which can influence the postoperative results.

**Figure 13.** Unfolding of endothelial tissue (red arrow) in DMEK, verifying the tissue orientation. Courtesy of Zeiss.

If there is an incomplete apposition of the donor lenticule, various maneuvers can be performed such as corneal massage or air tamponade in the anterior chamber to ensure the complete elimination of the fluid between the stroma-Descemet interphase (**Figure 15**).

**Figure 15.** Lack of apposition between donor and recipient tissues, which indicates that additional maneuvers must be

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A study to determine the feasibility and usefulness of transoperative OCT reported that it indeed helped in decision-making and demonstrated that additional maneuvers were required; this was based on images obtained by OCT in 41% of DSAEK cases. Transoperative OCT revealed persistent fluid in 19% of the cases where the surgeon believed the graft was completely adhered to the stroma. Another finding was that it was indeed adhered in 47% of the cases where the surgeon believed the graft was not completely adhered, therefore reducing the need for further unnecessary surgical manipulation. Transoperative OCT has the potential advantage of decreasing the duration of the surgical event, as well as minimizing

The use of this new transoperative OCT technology optimizes the identification of the corneal layer planes by providing a cross section with high-resolution images. These can be observed in real time both in the surgeon's microscope and in an external screen that can be observed by all the staff in the operating room, providing a valuable academic tool. By providing a direct visualization of the critical steps in lamellar transplants (DALK, DSAEK, DMEK), there is an increase in the procedure's safety, it decreases the learning curve of the surgeon in training

Transoperative OCT helps in determining the efficacy of these maneuvers [16].

graft dislocations [19].

performed to achieve correct placement.

**8. Conclusion**

**Figure 14.** Verification of complete apposition of the donor tissue to the recipient bed, without any space between.

The use of OCT has proved to be useful in detecting any residual space in the interphase at the end of DSAEK surgery. In 2010, Knecht published the first use of transurgical OCT in DSAEK and demonstrated serially the decrease of fluid in the interphase [16], doing manual measurements of the interphase's area of greatest amplitude (between the graft and the recipient). Hallahan correlated the transurgical interphase with the fluid measurements between the graft and the receiver and found that the greater the fluid measurements, the greater the risk for disinsertion and lack of graft adherence in the postoperative period [18].

**Figure 15.** Lack of apposition between donor and recipient tissues, which indicates that additional maneuvers must be performed to achieve correct placement.

If there is an incomplete apposition of the donor lenticule, various maneuvers can be performed such as corneal massage or air tamponade in the anterior chamber to ensure the complete elimination of the fluid between the stroma-Descemet interphase (**Figure 15**). Transoperative OCT helps in determining the efficacy of these maneuvers [16].

A study to determine the feasibility and usefulness of transoperative OCT reported that it indeed helped in decision-making and demonstrated that additional maneuvers were required; this was based on images obtained by OCT in 41% of DSAEK cases. Transoperative OCT revealed persistent fluid in 19% of the cases where the surgeon believed the graft was completely adhered to the stroma. Another finding was that it was indeed adhered in 47% of the cases where the surgeon believed the graft was not completely adhered, therefore reducing the need for further unnecessary surgical manipulation. Transoperative OCT has the potential advantage of decreasing the duration of the surgical event, as well as minimizing graft dislocations [19].

## **8. Conclusion**

The use of OCT has proved to be useful in detecting any residual space in the interphase at the end of DSAEK surgery. In 2010, Knecht published the first use of transurgical OCT in DSAEK and demonstrated serially the decrease of fluid in the interphase [16], doing manual measurements of the interphase's area of greatest amplitude (between the graft and the recipient). Hallahan correlated the transurgical interphase with the fluid measurements between the graft and the receiver and found that the greater the fluid measurements, the greater the risk

**Figure 14.** Verification of complete apposition of the donor tissue to the recipient bed, without any space between.

**Figure 13.** Unfolding of endothelial tissue (red arrow) in DMEK, verifying the tissue orientation. Courtesy of Zeiss.

110 OCT - Applications in Ophthalmology

for disinsertion and lack of graft adherence in the postoperative period [18].

The use of this new transoperative OCT technology optimizes the identification of the corneal layer planes by providing a cross section with high-resolution images. These can be observed in real time both in the surgeon's microscope and in an external screen that can be observed by all the staff in the operating room, providing a valuable academic tool. By providing a direct visualization of the critical steps in lamellar transplants (DALK, DSAEK, DMEK), there is an increase in the procedure's safety, it decreases the learning curve of the surgeon in training and facilitates the work of the experienced surgeon by providing detailed visual information in each surgical step, optimizing the decision-making and reducing the surgical event time.

[9] Melles GR, Lander F, Rietveld FJ. Transplantation of Descemet's membrane carry viable

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