**3. Pachymetric changes during CXL for KCN and importance of intraoperative pachymetric monitoring**

In addition to the initial pachymetric changes, significant changes in corneal pachymetry may occur during the different steps of the procedure [9–11]. Factors contributing to these changes include epithelial removal, dehydration due to corneal stroma due to exposure, osmotic effects of the riboflavin-dextran solution, and UV irradiation. The use of an eyelid speculum during instillation of riboflavin drops and the dextran containing riboflavin formulations (as compared to nondextran containing riboflavin iso-osmolar formulations) are especially among the potential factors associated with shrinkage of the corneal stroma during the procedure.

Kymionis et al. [10] reported a decrease of 75 μm and Muzzotta et al. [11] reported a 32.07% shrinkage of the corneal stromal thickness after riboflavin saturation of the stroma with the riboflavin-dextran solution. These findings indicate that despite an initial pachymetry value greater than 400 μm, a considerable proportion of patients will end up with a corneal pachymetry value below the critical thickness during the procedure, which may be a factor explaining complications like corneal edema despite an initial adequate pachymetry in some reports [12].

These pachymetric changes all could potentially jeopardize the safety of the procedure, further highlighting the importance of intraoperative pachymetric monitoring during the operation.

**41**

trabectome surgery [17–22].

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

**4. Current standard method used for intraoperative corneal pachymetry** 

Currently, ultrasound pachymetry is the most commonly used method for intraoperative pachymetry measurements during CXL. However, pachymetry measurements using this technique are subject to limitations: only single point measurements can be obtained and it is necessary to have contact to obtain the measurements, thus making the results more prone to inter- and intra-observer variability. In addition, vulnerability to infections due to contact with the surface of the eye and inadequate sterilization of the ultrasound tip during the procedure is another concern associated

**5. Application of intraoperative OCT for corneal pachymetry during** 

Anterior segment optical coherence tomography (AS-OCT) is a noninvasive imaging modality that can be used to obtain high-resolution, cross-sectional images of the anterior structures of the eye. In comparison with ultrasound pachymetry, AS-OCT has the advantage of providing a more detailed corneal anatomic profile during the procedure with a high degree of intra-observer repeatability and inter-

OCT has been proven to be a useful diagnostic imaging modality for the diagnosis of keratoconus. OCT-derived corneal thickness distribution and asymmetry parameters have been shown to have a good correlation with established Scheimpflug-derived anterior surface irregularity indices and proven useful to

The high resolution of the spectral domain OCT which allows for reconstruction of epithelial and stromal thickness profiles is another advantage of OCT to study the altered epithelial thickness pattern in keratoconus due to corneal surface irregularity. OCT-derived epithelial thickness map parameters have shown promis-

OCT has also been used for detection of demarcation lines after CXL which are considered as a measure of the treatment efficacy [16]. In addition, OCT has been proved to be useful to show changes after CXL including the epithelial remodeling

**5.2 Application of intraoperative OCT in corneal and anterior segment surgery**

OCT as a real-time and high-resolution imaging modality provides additional information regarding the angle, corneal thickness, and other structures that are otherwise invisible or difficult to visualize using the normal operating microscope, making it a potential beneficial tool for anterior segment surgery. In addition, it could provide valuable information in the cases like corneal opacity which preclude

Intraoperative OCT has also been used as a useful extension of the normal surgical microscope during anterior segment procedures for finding the plane of corneal dissection during anterior lamellar surgery, for assessment of graft-host relationship in penetrating keratoplasty, as a guide during the crucial aspects of posterior lamellar surgery, cataract surgery, and glaucoma procedures like canaloplasty or

**5.1 Advantages of OCT as a diagnostic tool for corneal imaging**

observer reproducibility of the pachymetric measurements.

ing results in early and advanced keratoconus detection [14, 15].

visualization of the anterior segment structures of the eye.

after CXL, resulting in a thinner and more regular thickness profile [7].

detect suspect, early, and clinical keratoconus [13].

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

**measurements**

with this method.

**collagen cross-linking**

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