**3. OCT in posterior lamellar keratoplasty**

Posterior lamellar keratoplasty has emerged as an alternative to PK to treat corneal endothelial pathology [63, 64]. Evolution of the posterior lamellar keratoplasty procedures began with Melles et al., who reported deep lamellar endothelial keratoplasty (DLEK) that includes sutureless transplantation of posterior lamellae of cornea from a scleral incision [65]. Following DLEK, Descemet's stripping endothelial keratoplasty (DSEK) and DSAEK were developed [3, 66]. Corneal graft is prepared with automated microkeratome in DSAEK and it has been used worldwide [67]. Recently, DMEK is introduced as the latest posterior lamellar keratoplasty technique by Melles et al. [4]. Today, DSAEK and DMEK are the most popular posterior lamellar keratoplasty procedures [68].

DSAEK and DMEK are completely different interventions and both have different maneuvers [69]. DSAEK needs a 4- or a 5-mm limbal or corneo-scleral incision to insert the donor lamella. Descemet stripping of the host cornea is performed over an 8-mm diameter circle with a reverse Sinskey hook. Preparation of donor cornea is performed with automated microkeratome. Donor button consists of a thin stroma and Descemet's endothelial complex. Femtosecond laser has also been used recently for the preparation of the DSAEK graft. After trephination of donor lamella, it is inserted into the anterior chamber. Graft is attached to the host cornea with an air bubble. By contrast, DMEK provides transplantation of the endothelium with DM layer with minimal or absent stroma [70]. DM is stripped from the posterior stroma [71]. There are two methods of stripping: the first described procedure consists of DM stripping after corneal button trephination and the other technique consists of scoring edge of DM and stripping away from the stroma nearly half way to the center for 360° before trephination. Recently, DM dissection can be performed by an automated microkeratome and called as Descemet's membrane automated endothelial keratoplasty (DMAEK) [72, 73].

Several studies and meta-analysis reported that DMEK has superiority over DSAEK, considering visual outcome and patient satisfaction but DSAEK is used more frequently because of the steeper learning curve of DMEK [1, 74–77]. DMEK and DSAEK have a similar complication profile [78–80]. The most common early complications following posterior lamellar keratoplasty are graft dislocation and primary graft failure [81]. Other complications are graft rejection, endothelial cell loss, iatrogenic pupillary block glaucoma, keratitis, and endophthalmitis.

better visual outcome in patients with chronic stromal edema [88]. AS-OCT was used to show corneal layers before and after endothelial keratoplasty which indicates that subepithelial

**Figure 3.** A patient with pseudophakic bullous keratopathy has underwent DMEK. (A) Preoperative anterior segment photography showing corneal edema. (B) Preoperative AS-OCT showing thickened corneal epithelium, subepithelial hyper-reflectance and corneal stromal edema. The central corneal thickness was 771 μm. (C) Early postoperative anterior segment photography shows reduced corneal edema. (D) Early postoperative AS-OCT shows reduced corneal edema and loss of subepithelial hyper-reflectance. The central corneal thickness was 615 μm. (E) Late postoperative anterior segment photography shows a clear cornea. (F) Late postoperative AS-OCT image shows normal corneal reflectance.

OCT in Lamellar Corneal Transplantation http://dx.doi.org/10.5772/intechopen.78294 121

DMEK needs special maneuvers to unfold the graft and attach to the host. Attachment of the graft in both DMEK and DSAEK was performed with an air bubble, and there should be no interface fluid. Intraoperative AS-OCT can evaluate the graft orientation and obtain images of interface. Ide et al. reported the successful use of intraoperative AS-OCT in six consecutive patients showing no interface fluid at the end of the DSAEK [89]. Knecht et al. reported that their intraoperative AS-OCT study with six cases underwent DSAEK and indicated that detectable interface space does not mean a failure because the fluid may regress 1 day after surgery [90]. They also reported that detectable interface fluid may disappear with vent incisions by the guidance of intraoperative AS-OCT. In addition to that, PIONEER study published two separate results from DSAEK surgery with intraoperative AS-OCT. The first study indicated that transient interface fluid at the end of the surgery and first postoperative day is more likely to develop textural interface opacity [91]. The second study reported that a larger residual interface fluid volume, area, and thickness at the end of surgery are associated with early-graft detachment [92]. These results emphasize

haze and opacification of cornea decreased with surgery (**Figure 4**).

The central corneal thickness was 555 μm.

that minimal or no interface fluid should be left at the end of the DSAEK surgery.

AS-OCT is a useful tool for posterior lamellar keratoplasty. It is valuable for preoperative assessment, intraoperative maneuvers, and postoperative follow-up. The preoperative duration of corneal stromal edema is found to be an important factor for visual outcome in patients who underwent endothelial keratoplasty [82]. It is known that the long duration of corneal stromal edema causes an increase in fibroblastic activity, irreversible fibrotic changes, and corneal scarring [83–85]. PK can be chosen in patients who have bullous keratopathy more than 12 months, instead of endothelial keratoplasty [82, 86]. AS-OCT may detect these stromal changes and obtain objective data for the decision of a planned surgery (**Figure 3**). AS-OCT images may help to decide which patients with stromal edema more than 12 months will benefit from endothelial surgery. AS-OCT can also obtain fine images of corneal epithelium. Long-standing bullous keratopathy may also cause subepithelial haze and fibrosis [87]. Agarwal et al. reported that endothelial keratoplasty with epithelial debridement provides a

**3. OCT in posterior lamellar keratoplasty**

120 OCT - Applications in Ophthalmology

posterior lamellar keratoplasty procedures [68].

Posterior lamellar keratoplasty has emerged as an alternative to PK to treat corneal endothelial pathology [63, 64]. Evolution of the posterior lamellar keratoplasty procedures began with Melles et al., who reported deep lamellar endothelial keratoplasty (DLEK) that includes sutureless transplantation of posterior lamellae of cornea from a scleral incision [65]. Following DLEK, Descemet's stripping endothelial keratoplasty (DSEK) and DSAEK were developed [3, 66]. Corneal graft is prepared with automated microkeratome in DSAEK and it has been used worldwide [67]. Recently, DMEK is introduced as the latest posterior lamellar keratoplasty technique by Melles et al. [4]. Today, DSAEK and DMEK are the most popular

DSAEK and DMEK are completely different interventions and both have different maneuvers [69]. DSAEK needs a 4- or a 5-mm limbal or corneo-scleral incision to insert the donor lamella. Descemet stripping of the host cornea is performed over an 8-mm diameter circle with a reverse Sinskey hook. Preparation of donor cornea is performed with automated microkeratome. Donor button consists of a thin stroma and Descemet's endothelial complex. Femtosecond laser has also been used recently for the preparation of the DSAEK graft. After trephination of donor lamella, it is inserted into the anterior chamber. Graft is attached to the host cornea with an air bubble. By contrast, DMEK provides transplantation of the endothelium with DM layer with minimal or absent stroma [70]. DM is stripped from the posterior stroma [71]. There are two methods of stripping: the first described procedure consists of DM stripping after corneal button trephination and the other technique consists of scoring edge of DM and stripping away from the stroma nearly half way to the center for 360° before trephination. Recently, DM dissection can be performed by an automated microkeratome and called as Descemet's membrane automated endothelial keratoplasty (DMAEK) [72, 73].

Several studies and meta-analysis reported that DMEK has superiority over DSAEK, considering visual outcome and patient satisfaction but DSAEK is used more frequently because of the steeper learning curve of DMEK [1, 74–77]. DMEK and DSAEK have a similar complication profile [78–80]. The most common early complications following posterior lamellar keratoplasty are graft dislocation and primary graft failure [81]. Other complications are graft rejection, endothelial cell loss, iatrogenic pupillary block glaucoma, keratitis, and endophthalmitis. AS-OCT is a useful tool for posterior lamellar keratoplasty. It is valuable for preoperative assessment, intraoperative maneuvers, and postoperative follow-up. The preoperative duration of corneal stromal edema is found to be an important factor for visual outcome in patients who underwent endothelial keratoplasty [82]. It is known that the long duration of corneal stromal edema causes an increase in fibroblastic activity, irreversible fibrotic changes, and corneal scarring [83–85]. PK can be chosen in patients who have bullous keratopathy more than 12 months, instead of endothelial keratoplasty [82, 86]. AS-OCT may detect these stromal changes and obtain objective data for the decision of a planned surgery (**Figure 3**). AS-OCT images may help to decide which patients with stromal edema more than 12 months will benefit from endothelial surgery. AS-OCT can also obtain fine images of corneal epithelium. Long-standing bullous keratopathy may also cause subepithelial haze and fibrosis [87]. Agarwal et al. reported that endothelial keratoplasty with epithelial debridement provides a

**Figure 3.** A patient with pseudophakic bullous keratopathy has underwent DMEK. (A) Preoperative anterior segment photography showing corneal edema. (B) Preoperative AS-OCT showing thickened corneal epithelium, subepithelial hyper-reflectance and corneal stromal edema. The central corneal thickness was 771 μm. (C) Early postoperative anterior segment photography shows reduced corneal edema. (D) Early postoperative AS-OCT shows reduced corneal edema and loss of subepithelial hyper-reflectance. The central corneal thickness was 615 μm. (E) Late postoperative anterior segment photography shows a clear cornea. (F) Late postoperative AS-OCT image shows normal corneal reflectance. The central corneal thickness was 555 μm.

better visual outcome in patients with chronic stromal edema [88]. AS-OCT was used to show corneal layers before and after endothelial keratoplasty which indicates that subepithelial haze and opacification of cornea decreased with surgery (**Figure 4**).

DMEK needs special maneuvers to unfold the graft and attach to the host. Attachment of the graft in both DMEK and DSAEK was performed with an air bubble, and there should be no interface fluid. Intraoperative AS-OCT can evaluate the graft orientation and obtain images of interface. Ide et al. reported the successful use of intraoperative AS-OCT in six consecutive patients showing no interface fluid at the end of the DSAEK [89]. Knecht et al. reported that their intraoperative AS-OCT study with six cases underwent DSAEK and indicated that detectable interface space does not mean a failure because the fluid may regress 1 day after surgery [90]. They also reported that detectable interface fluid may disappear with vent incisions by the guidance of intraoperative AS-OCT. In addition to that, PIONEER study published two separate results from DSAEK surgery with intraoperative AS-OCT. The first study indicated that transient interface fluid at the end of the surgery and first postoperative day is more likely to develop textural interface opacity [91]. The second study reported that a larger residual interface fluid volume, area, and thickness at the end of surgery are associated with early-graft detachment [92]. These results emphasize that minimal or no interface fluid should be left at the end of the DSAEK surgery.

**Figure 4.** Triple-DMEK was performed successfully to a patient who had Fuchs endothelial dystrophy, severe corneal stromal edema with epithelial bullae, and angle closure glaucoma. (A) Preoperative anterior segment photography showing cataract and severe corneal edema. Visual acuity was hand movements. (B) Preoperative corneal thickness map in corneal topography. (C)preoperative AS-OCT image showing that corneal thickness was 917 μm. (D) Corneal edema was diminished 1 month after surgery and visual acuity was increased to 20/20. (E) Postoperative corneal thickness map showing resolved corneal edema. (F) AS-OCT image showing that corneal layers were returned to normal and the central corneal thickness was 530 μm.

Initial studies were performed with handheld AS-OCT devices, and imaging caused interruption of the surgery. Initial publications were followed by studies with real-time intraoperative AS-OCT which is integrated with the operating microscope [93–96]. Real-time imaging provided more comfortable surgery with simultaneous imaging. Besides evaluating interface fluid during surgery, intraoperative AS-OCT has additional benefits. Intraoperative AS-OCT assists in obtaining images of the nearly opaque corneas caused by stromal edema which could not be assessed well with an operation microscope [95]. This helps the surgeon to manipulate the graft easily in the operation.

understanding of the reason to the solution of these difficulties [85]. Suh et al. reported that the evaluation of epithelial ingrowth in DSAEK patient can be possible with AS-OCT [101]. Kymionis et al. reported a case with residual DM after DSAEK that was shown with AS-OCT [102]. Lopez and Melles et al. published a study that described rebubbling techniques in DMEK, and they showed detached and folded DM with AS-OCT [103]. The assistance of AS-OCT for the assessment and management of complications in DMEK was studied in

**Figure 5.** A patient who underwent DSAEK surgery for pseudophakic bullous keratopathy, presented with primary graft failure. DMEK was performed as a second surgery and corneal edema reduced. (A) Anterior segment photography before surgery showing severe edema. (B) Corneal thickness map in corneal topography showing corneal edema. (C) Corneal thickness was 753 μm and DSAEK graft's thickness was 113 μm. Hyperreflective line shown with white arrow shows interphase between posterior corneal stroma and DSAEK graft. (D) Anterior segment photography 1 day after DMEK; there was corneal haze without edema. (E) Corneal thickness map in corneal topography showing thinning in central cornea. (F) AS-OCT image showing that the central corneal thickness was 515 μm. DMEK graft cannot be visualized by AS-OCT. White arrow shows a horizontal hyperreflective posterior corneal stromal scar surface.

OCT in Lamellar Corneal Transplantation http://dx.doi.org/10.5772/intechopen.78294 123

AS-OCT is a valuable tool for assessing lamellar keratoplasty in all steps of the surgery. The use of AS-OCT starts from patient selection to postoperative late complications. Both anterior and posterior lamellar procedures need proper patient selection to obtain desired outcomes. Imaging the graft-host relationship with AS-OCT allows proper assessment of interface and helps surgeon to perform fast and successful surgeries. Some complications such as graft detachment can be visualized with AS-OCT postoperatively, more accurate than a conventional slit-lamp examination. AS-OCT is currently being used widely in corneal surgeries, and

The authors thank the technicians of anterior segment imaging, Gazi University Medical School Department of Ophthalmology (Aynur Kartal, Cengiz Aksel, Nilgun Taşçı, Suat Avcı, Şenay Çay, Zafer Yıldırım), for the excellent photographs that have been used in this chapter.

many publications [104–107].

its role in lamellar keratoplasty seems to be increasing.

**4. Conclusion**

**Acknowledgements**

DMEK is a relatively new technique than DSAEK, and studies on DMEK with intraoperative AS-OCT are fewer. Steven et al. published a study with 26 patients who underwent DMEK and reported that the usage of intraoperative AS-OCT enhances the graft visibility and surgeon's orientation [97]. Saad et al. reported that intraoperative AS-OCT enables a faster graft positioning with less manipulation in DMEK [96]. DISCOVER study indicated that intraoperative AS-OCT is very useful to confirm graft orientation and to reduce the iatrogenic graft failure [98].

Postoperative follow-up for graft dehiscence and graft failure is crucial in posterior lamellar keratoplasty. The fluid between the cornea and the graft can be seen with a slit-lamp biomicroscopy but Tarnawska and Wylegala reported that half of the interface fluid cannot be seen with examination which was detected by AS-OCT [99]. Early detection of interface fluid and graft detachment provides early intervention. In addition to that, postoperative measurement of graft thickness is an important factor for graft failure in DSAEK patients [100]. Eyes with thick grafts are more prone to graft failure (**Figure 5**). It is important to provide improvement in visual acuity after endothelial keratoplasty but fewer patients achieve excellent quality of vision. Many reasons were suggested including anterior stromal changes, graft-related problems, induced high-order aberrations, and interface-related problems. Turnbull et al. commented that the evolving anterior segment imaging could increase our

**Figure 5.** A patient who underwent DSAEK surgery for pseudophakic bullous keratopathy, presented with primary graft failure. DMEK was performed as a second surgery and corneal edema reduced. (A) Anterior segment photography before surgery showing severe edema. (B) Corneal thickness map in corneal topography showing corneal edema. (C) Corneal thickness was 753 μm and DSAEK graft's thickness was 113 μm. Hyperreflective line shown with white arrow shows interphase between posterior corneal stroma and DSAEK graft. (D) Anterior segment photography 1 day after DMEK; there was corneal haze without edema. (E) Corneal thickness map in corneal topography showing thinning in central cornea. (F) AS-OCT image showing that the central corneal thickness was 515 μm. DMEK graft cannot be visualized by AS-OCT. White arrow shows a horizontal hyperreflective posterior corneal stromal scar surface.

understanding of the reason to the solution of these difficulties [85]. Suh et al. reported that the evaluation of epithelial ingrowth in DSAEK patient can be possible with AS-OCT [101]. Kymionis et al. reported a case with residual DM after DSAEK that was shown with AS-OCT [102]. Lopez and Melles et al. published a study that described rebubbling techniques in DMEK, and they showed detached and folded DM with AS-OCT [103]. The assistance of AS-OCT for the assessment and management of complications in DMEK was studied in many publications [104–107].

## **4. Conclusion**

Initial studies were performed with handheld AS-OCT devices, and imaging caused interruption of the surgery. Initial publications were followed by studies with real-time intraoperative AS-OCT which is integrated with the operating microscope [93–96]. Real-time imaging provided more comfortable surgery with simultaneous imaging. Besides evaluating interface fluid during surgery, intraoperative AS-OCT has additional benefits. Intraoperative AS-OCT assists in obtaining images of the nearly opaque corneas caused by stromal edema which could not be assessed well with an operation microscope [95]. This helps the surgeon to

**Figure 4.** Triple-DMEK was performed successfully to a patient who had Fuchs endothelial dystrophy, severe corneal stromal edema with epithelial bullae, and angle closure glaucoma. (A) Preoperative anterior segment photography showing cataract and severe corneal edema. Visual acuity was hand movements. (B) Preoperative corneal thickness map in corneal topography. (C)preoperative AS-OCT image showing that corneal thickness was 917 μm. (D) Corneal edema was diminished 1 month after surgery and visual acuity was increased to 20/20. (E) Postoperative corneal thickness map showing resolved corneal edema. (F) AS-OCT image showing that corneal layers were returned to normal and the

DMEK is a relatively new technique than DSAEK, and studies on DMEK with intraoperative AS-OCT are fewer. Steven et al. published a study with 26 patients who underwent DMEK and reported that the usage of intraoperative AS-OCT enhances the graft visibility and surgeon's orientation [97]. Saad et al. reported that intraoperative AS-OCT enables a faster graft positioning with less manipulation in DMEK [96]. DISCOVER study indicated that intraoperative AS-OCT is very useful to confirm graft orientation and to reduce the iatrogenic graft

Postoperative follow-up for graft dehiscence and graft failure is crucial in posterior lamellar keratoplasty. The fluid between the cornea and the graft can be seen with a slit-lamp biomicroscopy but Tarnawska and Wylegala reported that half of the interface fluid cannot be seen with examination which was detected by AS-OCT [99]. Early detection of interface fluid and graft detachment provides early intervention. In addition to that, postoperative measurement of graft thickness is an important factor for graft failure in DSAEK patients [100]. Eyes with thick grafts are more prone to graft failure (**Figure 5**). It is important to provide improvement in visual acuity after endothelial keratoplasty but fewer patients achieve excellent quality of vision. Many reasons were suggested including anterior stromal changes, graft-related problems, induced high-order aberrations, and interface-related problems. Turnbull et al. commented that the evolving anterior segment imaging could increase our

manipulate the graft easily in the operation.

central corneal thickness was 530 μm.

122 OCT - Applications in Ophthalmology

failure [98].

AS-OCT is a valuable tool for assessing lamellar keratoplasty in all steps of the surgery. The use of AS-OCT starts from patient selection to postoperative late complications. Both anterior and posterior lamellar procedures need proper patient selection to obtain desired outcomes. Imaging the graft-host relationship with AS-OCT allows proper assessment of interface and helps surgeon to perform fast and successful surgeries. Some complications such as graft detachment can be visualized with AS-OCT postoperatively, more accurate than a conventional slit-lamp examination. AS-OCT is currently being used widely in corneal surgeries, and its role in lamellar keratoplasty seems to be increasing.
