**5.3 Application of intraoperative OCT for monitoring corneal pachymetry during corneal collagen cross-linking**

Intraoperative OCT has been used to monitor the corneal pachymetry during CXL. The high resolution of OCT is especially advantageous in KCN patients, considering the marked epithelial and stromal irregularity in these patients.

In a study, Mazzotta and Karagiuli reported corneal pachymetric measurements in patients with keratoconus undergoing CXL. Pachymetric measurements were performed before, during, and after instillation of riboflavin using the timedomain Visante OCT (Zeiss, Jena, Germany). They showed significant corneal stromal shrinkage during the instillation of the riboflavin 0.1%-dextran T500 20% solution with 17.61, 25.44, and 32.07% reduction in the corneal thickness after 10, 20, and 30 minutes of riboflavin instillation, respectively [9].

#### **Figure 1.**

*Representative intraoperative OCT images of cases in the speculum-on (a–d) and speculum-off (f–i) groups. The images represent different stages of the procedure: at the baseline (a, f), after epithelial removal (b, g), after riboflavin saturation of the corneal stroma (c, h), and after UV-A irradiation (d, i).*

**43**

**Figure 2.**

*in the speculum-on group (c, h).*

*Intraoperative OCT for Monitoring Corneal Pachymetry during Corneal Collagen Cross-Linking…*

In another study, Rechichi et al. used intraoperative OCT to evaluate corneal pachymetry in keratoconic patients undergoing accelerated corneal collagen cross-linking with a dextran-free 0.1% riboflavin solution plus hydroxyl-propyl methylcellulose (HPMC). Intraoperative corneal thickness was evaluated by corneal optical coherence tomography (iVUE Optovue Inc., Fremont, CA, USA). Their results showed a central corneal thickness of 388.5 ± 36.8, 385.2 ± 37.8, and 379.4 ± 37.2 μm after epithelial removal, after 10 minutes of soaking with riboflavin, and after ultraviolet instillation, respectively. Their findings are compatible with those of a stable corneal pachymetry with the dextran-free riboflavin solution,

In our study, we used intraoperative OCT to compare the effect of eyelid specu-

utes) CXL protocol. In 14 patients, the speculum was removed during the riboflavin imbibition time (speculum-off group), while in 11 patients the speculum was retained during this period (speculum-on group). Intraoperative OCT (iVue 100-2; Optovue, Fremont, CA, USA) was used to measure the corneal thickness at baseline, after epithelial removal, after 30 minutes of 0.1% riboflavin in 20% dextran T-500 solution instillation, and after irradiation. The speculum-on group showed a significantly greater decrease in the corneal pachymetry (83.7 vs. 16.4 μm decrease in corneal thickness) during riboflavin instillation. As shown in the **Figures 1** and **2**, the speculum-off group had a more stable corneal pachymetry value during riboflavin instillation. On the other hand, the speculum-off group had a greater decrease in the corneal pachymetry value during the irradiation phase, further highlighting the limitations imposed by corneal stromal shrinkage using the isotonic dextran

*Representative OCT corneal thickness maps in the speculum-on (a–d) and speculum-off (f–i) groups. Note the marked thinning observed in the corneal thickness map during the riboflavin-dextran instillation of the cornea* 

for 10 min-

lum on corneal pachymetric changes using an accelerated (9 mW/cm2

*DOI: http://dx.doi.org/10.5772/intechopen.84243*

throughout the procedure [24].

containing riboflavin solution for CXL [25].

#### *Intraoperative OCT for Monitoring Corneal Pachymetry during Corneal Collagen Cross-Linking… DOI: http://dx.doi.org/10.5772/intechopen.84243*

In another study, Rechichi et al. used intraoperative OCT to evaluate corneal pachymetry in keratoconic patients undergoing accelerated corneal collagen cross-linking with a dextran-free 0.1% riboflavin solution plus hydroxyl-propyl methylcellulose (HPMC). Intraoperative corneal thickness was evaluated by corneal optical coherence tomography (iVUE Optovue Inc., Fremont, CA, USA). Their results showed a central corneal thickness of 388.5 ± 36.8, 385.2 ± 37.8, and 379.4 ± 37.2 μm after epithelial removal, after 10 minutes of soaking with riboflavin, and after ultraviolet instillation, respectively. Their findings are compatible with those of a stable corneal pachymetry with the dextran-free riboflavin solution, throughout the procedure [24].

In our study, we used intraoperative OCT to compare the effect of eyelid speculum on corneal pachymetric changes using an accelerated (9 mW/cm2 for 10 minutes) CXL protocol. In 14 patients, the speculum was removed during the riboflavin imbibition time (speculum-off group), while in 11 patients the speculum was retained during this period (speculum-on group). Intraoperative OCT (iVue 100-2; Optovue, Fremont, CA, USA) was used to measure the corneal thickness at baseline, after epithelial removal, after 30 minutes of 0.1% riboflavin in 20% dextran T-500 solution instillation, and after irradiation. The speculum-on group showed a significantly greater decrease in the corneal pachymetry (83.7 vs. 16.4 μm decrease in corneal thickness) during riboflavin instillation. As shown in the **Figures 1** and **2**, the speculum-off group had a more stable corneal pachymetry value during riboflavin instillation. On the other hand, the speculum-off group had a greater decrease in the corneal pachymetry value during the irradiation phase, further highlighting the limitations imposed by corneal stromal shrinkage using the isotonic dextran containing riboflavin solution for CXL [25].

#### **Figure 2.**

*A Practical Guide to Clinical Application of OCT in Ophthalmology*

**during corneal collagen cross-linking**

technology [19].

patients.

As another application of intraoperative OCT, this modality has been used for anterior segment examination of patients under general anesthesia, diagnosis of complex wound apposition problems, with the advantage of providing additional

With the adaptation of this technology, intraoperative online OCT provides additional information for anterior segment surgeons providing a real-time dynamic feedback of the various surgical steps during surgery. Nonetheless, shadowing produced by surgical instruments represents the main limitation of this

**5.3 Application of intraoperative OCT for monitoring corneal pachymetry** 

Intraoperative OCT has been used to monitor the corneal pachymetry during CXL. The high resolution of OCT is especially advantageous in KCN patients, considering the marked epithelial and stromal irregularity in these

In a study, Mazzotta and Karagiuli reported corneal pachymetric measurements in patients with keratoconus undergoing CXL. Pachymetric measurements were performed before, during, and after instillation of riboflavin using the timedomain Visante OCT (Zeiss, Jena, Germany). They showed significant corneal stromal shrinkage during the instillation of the riboflavin 0.1%-dextran T500 20% solution with 17.61, 25.44, and 32.07% reduction in the corneal thickness after

*Representative intraoperative OCT images of cases in the speculum-on (a–d) and speculum-off (f–i) groups. The images represent different stages of the procedure: at the baseline (a, f), after epithelial removal (b, g),* 

*after riboflavin saturation of the corneal stroma (c, h), and after UV-A irradiation (d, i).*

10, 20, and 30 minutes of riboflavin instillation, respectively [9].

information for understanding corneal wound-related problems [23].

**42**

**Figure 1.**

*Representative OCT corneal thickness maps in the speculum-on (a–d) and speculum-off (f–i) groups. Note the marked thinning observed in the corneal thickness map during the riboflavin-dextran instillation of the cornea in the speculum-on group (c, h).*
