**2. OCT in deep anterior lamellar keratoplasty**

DALK has been introduced as an alternative to penetrating keratoplasty (PK) for the diseases that affect anterior layers of cornea [14, 15]. Preserving the endothelium in DALK obtains reduced graft rejections [16, 17]. Many techniques have been described to separate corneal stroma and Descemet's membrane (DM). Peeling stroma up to near DM is called manual dissection [18, 19]. This procedure can be used as the first choice in some situations such as deep scarring, or the second choice intraoperatively when it cannot be progressed with other techniques [20–22]. Other option is the separation of stroma and DM with injection of air, fluid, or viscoelastic into deep stroma [14, 23–25].

Anterior lamellar keratoplasty was described first by Gasset in keratoconus patients which was named as conectomy and included transplantation of DM stripped full thickness graft [26]. Archila et al. introduced deep lamellar keratoplasty, using intrastromal air to separate stroma from DM [27]. After that, different techniques have been described, and today, the most frequently used procedure is "Big Bubble" that Anwar and Teichmann reported [14]. The technique includes 27-gauge needle with air-filled syringe inserted into deep stroma for 3–4 mm centrally and air injection to separate DM from stroma. It has been shown that outcomes of DALK were similar to PK with lower rejection or failure rates. However, Big Bubble can be obtained in only 56–82% of eyes [28–30].

For the improvement of these surgical techniques, new and unique complications beside advantages have emerged. The main purpose during separation of stroma from DM is to obtain a non-damaged DM [31]. But perforation or tears in DM occur in 4–20% of cases which is the most important complication during surgery [28–30, 32]. The risk of perforation is higher if proper big bubble formation is not achieved [33]. Unsuccessful big bubble formation is more frequently seen in patients with keratoconus and deep corneal scar involving DM [34–36]. Microperforations can be managed with air injection to the anterior chamber and careful manual dissection, but most of the macroperforations need to be converted to PK [14, 37]. The other complication is pseudoanterior chamber [38]. It can occur as double or triple anterior chamber [39, 40]. It usually develops after perforation in DM [41]. Remnant viscoelastic material may also cause double anterior chamber [42]. Pseudoanterior chamber may resolve spontaneously when it is shallow but larger chambers should need surgical intervention [43].

managed by posterior lamellar procedures such as Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK) [6–8]. Each technique requires specific experience and tricks and has their own difficulties and complications. Beside these challenges, all these procedures provide safer surgery, faster rehabilita-

Anterior segment optical coherence tomography (AS-OCT) is a non-contact imaging system that obtains high-resolution images of cornea and anterior chamber [9, 10]. It allows visualizing the shape and depth of corneal lesions such as scarring, measuring central corneal thickness, and lesion size [11, 12]. It can be used before, during, and after lamellar keratoplasty to evaluate the cornea [13]. In this chapter, we discuss the role of AS-OCT on the basis of

DALK has been introduced as an alternative to penetrating keratoplasty (PK) for the diseases that affect anterior layers of cornea [14, 15]. Preserving the endothelium in DALK obtains reduced graft rejections [16, 17]. Many techniques have been described to separate corneal stroma and Descemet's membrane (DM). Peeling stroma up to near DM is called manual dissection [18, 19]. This procedure can be used as the first choice in some situations such as deep scarring, or the second choice intraoperatively when it cannot be progressed with other techniques [20–22]. Other option is the separation of stroma and DM with injection of air,

Anterior lamellar keratoplasty was described first by Gasset in keratoconus patients which was named as conectomy and included transplantation of DM stripped full thickness graft [26]. Archila et al. introduced deep lamellar keratoplasty, using intrastromal air to separate stroma from DM [27]. After that, different techniques have been described, and today, the most frequently used procedure is "Big Bubble" that Anwar and Teichmann reported [14]. The technique includes 27-gauge needle with air-filled syringe inserted into deep stroma for 3–4 mm centrally and air injection to separate DM from stroma. It has been shown that outcomes of DALK were similar to PK with lower rejection or failure rates. However, Big Bubble

For the improvement of these surgical techniques, new and unique complications beside advantages have emerged. The main purpose during separation of stroma from DM is to obtain a non-damaged DM [31]. But perforation or tears in DM occur in 4–20% of cases which is the most important complication during surgery [28–30, 32]. The risk of perforation is higher if proper big bubble formation is not achieved [33]. Unsuccessful big bubble formation is more frequently seen in patients with keratoconus and deep corneal scar involving DM [34–36]. Microperforations can be managed with air injection to the anterior chamber and careful manual dissection, but most of the macroperforations need to be converted to PK [14, 37]. The other complication is pseudoanterior chamber [38]. It can occur as double or triple anterior chamber [39, 40]. It usually develops after perforation in DM [41]. Remnant viscoelastic

different corneal lamellar procedures such as DALK, DSAEK, and DMEK.

tion, better functional, and anatomical outcomes [1].

116 OCT - Applications in Ophthalmology

**2. OCT in deep anterior lamellar keratoplasty**

fluid, or viscoelastic into deep stroma [14, 23–25].

can be obtained in only 56–82% of eyes [28–30].

The role of AS-OCT in DALK begins at a preoperative assessment. Patient selection and the right indication for surgery can be decided with many variables including AS-OCT findings. AS-OCT images provide central corneal thickness, anterior chamber biometry, angle and iris measurements, and lens thickness [13]. These findings help planning trephination depth during surgery, intraocular lens power assessment if needed combined with phacoemulsification and intraocular lens implantation, detecting narrow angle before surgery [11]. AS-OCT can also visualize corneal pathologies such as scarring in central or periphery, corneal degenerations or dystrophies and cysts. The importance of the imaging is to inform the surgeon about the location, size, and depth of the corneal lesion.

Big bubble procedure in DALK requires well-adjusted trephination depth and centrally inserted air cannula without damaging DM. This technique needs experience and has a steep learning curve. One of the difficulties is reaching the intended depth of the cornea with cannula and advancement to the central stroma. To overcome this challenge, preoperative central and peripheral corneal thickness measurement with AS-OCT is sensible. Busin et al. reported a modified big bubble technique, which needs AS-OCT [44]. They evaluated the thickness of trephination size with AS-OCT and aimed to reach a depth within 50 μm from the internal corneal surface. Air cannula was advanced only 1 mm into the cornea and air injected. They reported a successful pneumatic dissection in 85% of patients with this procedure. AS-OCT was very useful to show the depth of trephination site, and perforation during trephination occurred in only 2.3% (two patients) of patients. Moreover, AS-OCT has superiority over topography with Scheimpflug camera while planning the depth of trephination for DALK. Riss et al. measured corneal thickness with Scheimpflug camera, planned the depth of trephination to 90% of the thinnest pachymetric value, and faced perforation during trephination in 30.1% of patients [45]. Intraoperative AS-OCT seems to increase the choice of DALK rather than PK with easing lack of experience and surgical difficulties.

It is known that corneal stromal scar has effect on the success rate of DALK. Big bubble can be achieved in 56–82% of keratoconus patients without a corneal stromal scar. The success rate varies from keratoconus grade, central corneal thickness, and trephination size in these patients [28, 29, 46]. Corneal stromal scar is a very important risk factor in keratoconus patients and other corneal diseases influencing DALK success rate. Ozmen et al. reported that big bubble formation was achieved in 63.2% of patients and DALK was completed in 91% of patients [47]. The most important factor affecting DALK and big bubble success was the ratio of corneal scar depth and central corneal thickness (scar depth/central corneal thickness) which was calculated with AS-OCT, a cut-off point was given as >53% for scar depth/central corneal thickness, which has an acceptable sensitivity (100%) and specificity (67%). AS-OCT has been evaluated as crucial for measuring this risk factor and planning the right operation for patients. Corneal scar in keratoconus patients may be caused by hydrops. DALK has a relative contraindication for patients with stromal scar [38]. But considering rejection rates after PK, DALK can be an option when carried with great attention in patients with stromal scar. To avoid macroperforation during DALK, preoperative assessment and planning should be proper (**Figure 1**). Nanavaty et al. reported that all of their patients had successful DALK and none required PK even though microperforation occurred in 60% of patients, with the help of AS-OCT at preoperative evaluation [48].

hexafluoride injection and visualized re-attachment of DM with real-time images. Chaniyara et al. reported a complicated DALK case with repair of graft dehiscence with descemetopexy under the guidance of continuous intraoperative AS-OCT [56]. The use of real-time intraop-

OCT in Lamellar Corneal Transplantation http://dx.doi.org/10.5772/intechopen.78294 119

Intraoperative AS-OCT may obtain the depth and central advancement of the cannula while performing surgery. Image distortion caused by metallic objects is the major disadvantage of intraoperative AS-OCT [53]. The depth of the cannula could be assessed with only the image of the tunnel that is created by the cannula. With the manufacturing of plastic needles instead of metallic ones, one may overcome this drawback. Another disadvantage of intraoperative AS-OCT is caused by the devices which are mounted on the operation microscope separately. These devices have a handicap that they need to interrupt the surgery to take AS-OCT images. This disadvantage causes a delay in surgery. New devices that could obtain real-time images

Pseudoanterior chamber due to DM detachment is frequently associated with microperforations during surgery, and management includes observation, intracameral gas injection, or reoperation (**Figure 2**). Slit-lamp biomicroscopy is enough to detect clinically significant detachment, but minimal double anterior chamber may not be seen by examination. The decision of treatment type and follow-up requires documentation of the patient. AS-OCT is very helpful to detect DM detachment and follow-up of the patient [57]. It allows to measure the size of pseudoanterior chamber initially and after the treatment [58]. AS-OCT can also visual-

AS-OCT can evaluate other postoperative complications of DALK.Bahadir et al. reported a candida interface keratitis after DALK, showing the keratitis site at AS-OCT [59]. Mukhopadhyay et al. reported a rhinosporidiosis keratitis case and they performed a repeat DALK procedure successfully after determining the site of the infiltrate in corneal stroma with AS-OCT [60]. Muller et al. published a case report with granular corneal dystrophy type-1 and reported that although they achieved pneumatic dissection to predescemetic layer during DALK, AS-OCT showed granular opacities between DM and graft [61]. It is thought that granular deposition occurs at predescemetic layer in granular corneal dystrophy type-1 and PK could be a better alternative than DALK. Costa et al. reported an iris cyst seen after DALK which was docu-

that are integrated into the operating microscope are being developed.

ize Dua's layer in case of triple anterior chamber occurrence [40].

mented with AS-OCT and anterior segment photography [62].

**Figure 2.** AS-OCT of a patient who had DALK surgery showing pseudoanterior chamber.

erative AS-OCT seems to increase.

Recent improvements in surgical devices allow us to use AS-OCT at intraoperative evaluation. Several studies point out that visual acuity after DALK is better when stromal dissection is carried to the DM or when there is minimal residual stroma [20, 49–51]. AS-OCT provides intraoperative assessment of the cornea with high resolution. AS-OCT can be used to measure the depth of air cannula while using big bubble technique and may increase the rate of a successful big bubble formation. Scorcia et al. reported the first study in 2013 using intraoperative AS-OCT to visualize air cannula depth and big bubble formation [52]. It was emphasized that if the cannula reached the optimal depth, big bubble could be obtained more probably, but bubble achievement reduced when air was injected superficially. Successful big bubble in 90% of patients was obtained when the cannula reached within 100 μm from the DM. De Benito-Llopis et al. reported similar results and indicated that AS-OCT is also useful when big bubble could not be achieved and manual dissection was performed [53]. AS-OCT images can be used to evaluate a residual stromal bed during the manual dissection of corneal stroma.

Real-time intraoperative AS-OCT device provides imaging of all surgical steps continuously. Steven et al. reported a case series with using intraoperative AS-OCT. They succeeded monitoring big bubble formation in two of six patients [54]. They performed a micro-bubble incision technique in a patient that they could not obtain big bubble and documented with AS-OCT. Half of the patients was complicated with DM rupture. They indicated that the accurate measurement of trephination depth and cannula advancement into the deep central stroma is possible with real-time intraoperative AS-OCT. Sharma et al. published a case report of a patient who has undergone DALK. The procedure was complicated with DM detachment [55]. They used continuous intraoperative AS-OCT while intracameral sulfur

**Figure 1.** A patient with keratoconus who has an apical scar. (A) Anterior segment photography showing corneal scar. (B) AS-OCT showing corneal scar, which does not involve deep stromal layers and Descemet's membrane. With these findings, DALK was performed. (C) Anterior segment photography after surgery. (D) AS-OCT image of the patient after surgery.

hexafluoride injection and visualized re-attachment of DM with real-time images. Chaniyara et al. reported a complicated DALK case with repair of graft dehiscence with descemetopexy under the guidance of continuous intraoperative AS-OCT [56]. The use of real-time intraoperative AS-OCT seems to increase.

be proper (**Figure 1**). Nanavaty et al. reported that all of their patients had successful DALK and none required PK even though microperforation occurred in 60% of patients, with the

Recent improvements in surgical devices allow us to use AS-OCT at intraoperative evaluation. Several studies point out that visual acuity after DALK is better when stromal dissection is carried to the DM or when there is minimal residual stroma [20, 49–51]. AS-OCT provides intraoperative assessment of the cornea with high resolution. AS-OCT can be used to measure the depth of air cannula while using big bubble technique and may increase the rate of a successful big bubble formation. Scorcia et al. reported the first study in 2013 using intraoperative AS-OCT to visualize air cannula depth and big bubble formation [52]. It was emphasized that if the cannula reached the optimal depth, big bubble could be obtained more probably, but bubble achievement reduced when air was injected superficially. Successful big bubble in 90% of patients was obtained when the cannula reached within 100 μm from the DM. De Benito-Llopis et al. reported similar results and indicated that AS-OCT is also useful when big bubble could not be achieved and manual dissection was performed [53]. AS-OCT images can be used to evaluate a residual stromal bed during the manual dissection of corneal stroma.

Real-time intraoperative AS-OCT device provides imaging of all surgical steps continuously. Steven et al. reported a case series with using intraoperative AS-OCT. They succeeded monitoring big bubble formation in two of six patients [54]. They performed a micro-bubble incision technique in a patient that they could not obtain big bubble and documented with AS-OCT. Half of the patients was complicated with DM rupture. They indicated that the accurate measurement of trephination depth and cannula advancement into the deep central stroma is possible with real-time intraoperative AS-OCT. Sharma et al. published a case report of a patient who has undergone DALK. The procedure was complicated with DM detachment [55]. They used continuous intraoperative AS-OCT while intracameral sulfur

**Figure 1.** A patient with keratoconus who has an apical scar. (A) Anterior segment photography showing corneal scar. (B) AS-OCT showing corneal scar, which does not involve deep stromal layers and Descemet's membrane. With these findings, DALK was performed. (C) Anterior segment photography after surgery. (D) AS-OCT image of the patient after

surgery.

help of AS-OCT at preoperative evaluation [48].

118 OCT - Applications in Ophthalmology

Intraoperative AS-OCT may obtain the depth and central advancement of the cannula while performing surgery. Image distortion caused by metallic objects is the major disadvantage of intraoperative AS-OCT [53]. The depth of the cannula could be assessed with only the image of the tunnel that is created by the cannula. With the manufacturing of plastic needles instead of metallic ones, one may overcome this drawback. Another disadvantage of intraoperative AS-OCT is caused by the devices which are mounted on the operation microscope separately. These devices have a handicap that they need to interrupt the surgery to take AS-OCT images. This disadvantage causes a delay in surgery. New devices that could obtain real-time images that are integrated into the operating microscope are being developed.

Pseudoanterior chamber due to DM detachment is frequently associated with microperforations during surgery, and management includes observation, intracameral gas injection, or reoperation (**Figure 2**). Slit-lamp biomicroscopy is enough to detect clinically significant detachment, but minimal double anterior chamber may not be seen by examination. The decision of treatment type and follow-up requires documentation of the patient. AS-OCT is very helpful to detect DM detachment and follow-up of the patient [57]. It allows to measure the size of pseudoanterior chamber initially and after the treatment [58]. AS-OCT can also visualize Dua's layer in case of triple anterior chamber occurrence [40].

AS-OCT can evaluate other postoperative complications of DALK.Bahadir et al. reported a candida interface keratitis after DALK, showing the keratitis site at AS-OCT [59]. Mukhopadhyay et al. reported a rhinosporidiosis keratitis case and they performed a repeat DALK procedure successfully after determining the site of the infiltrate in corneal stroma with AS-OCT [60]. Muller et al. published a case report with granular corneal dystrophy type-1 and reported that although they achieved pneumatic dissection to predescemetic layer during DALK, AS-OCT showed granular opacities between DM and graft [61]. It is thought that granular deposition occurs at predescemetic layer in granular corneal dystrophy type-1 and PK could be a better alternative than DALK. Costa et al. reported an iris cyst seen after DALK which was documented with AS-OCT and anterior segment photography [62].

**Figure 2.** AS-OCT of a patient who had DALK surgery showing pseudoanterior chamber.
