# Developments in Contact Lens Imaging: New Applications of Optical Coherence Tomography
## 2 Clinical Uses in CL Practice
### Qualitative and Quantitative Evaluation: Surface Topography and Biometric Data  
Differences in overall lens design characteristics may play a role in user comfort, although reports are contradictory, with evidence of thicker soft lenses being both less comfortable and more comfortable than thinner lenses [32]. [PERSON] et al. indicated that the interaction between the CL and ocular surface, especially near the edge, largely determines the comfort of the wearer and the health of the eye. They reported that a thinner edge configuration helps form a smoother transition between the edge of the lens and the conjunctiv and thus reduces mechanical irritation of the ocular surface, but may also depend on other lens factors, such as the material modulus, central thickness, base curve, and lens diameter [31]. The diameter of a soft CL is about 14 mm, and it covers the whole cornea aligned with the corneascleral transition zone and rests on the perilimbal sclera. In the conventional lens fitting procedure, the central corneal curvature is used to select the proper base curve of the soft CL [24]. However, the central corneal topography does not correlate with the best fitting curve for a soft CL [28]. Many researchers have assessed the corneascleral region, reporting that, contrary to usual depictions, it is often smooth and tangential and that its topography is relevant in a CL fitting approach [1; 22; 24; 27; 29; 33]. [PERSON] et al. evaluated the influence of corneascleral junction topography measured by OCT on soft CL fit and concluded that the architecture of the marginal cornea and perilimbal sclera significantly affects the optimal dynamic CL fitting [27]. Figure 2 presents a cross-sectional image of the cornea at the center (A) and the corneal center (B) and junction between the cornea and sclera (C) of an eye with a soft CL obtained with high-speed SSOCT. The peripheral lens fitting has been clearly visualized. The purposes of determining the corneal curvature profile (topography) in the initial assessments include looking for changes (particularly in terms of regularity), providing baseline data for monitoring purposes, and indicating appropriate initial fitting parameters for RGP [22]. A scleral lens requires a different fitting scheme than other lenses. Compared to corneal lenses, corneal topography is not useful as the lens rests entirely in the scleral region. Due to the knowledge of the ocular surface topography obtained from ASOCT, the corneascleral transition shape can be described [23; 28]. The first paper on using OCT data to design scleral lenses was published by Gemoules in 2008 [23]. Applying ASOCT, [PERSON] et al. measured the distance between the back surface of the scleral lens and the front surface of the cornea and reported that 90% of the eyes had a reduction in vault after four hours of lens wear compared with one hour (so one should select a trial lens with a higher than required vault) [34]. In a more recently published study on the OCT device, differences between scleral radii at the different locations (along eight meridians) were reported, and the mean scleral thickness was found to differ significantly between quadrants [35]. The measurement method discussed above may be preferred when fitting scleral lenses in the future considering the large individual differences and asymmetrical nature of the sclera. Scientific reports are lacking in the application of ASOCT in hybrid CL fitting. However, [PERSON] et al. concluded that to ensure adequate visual acuity, it is necessary to fit a hybrid lens accurately, and ASOCT optimizes the selection of the lens [36]. [PERSON] et al. showed that neither the central radius of the cornea, nor the corneal/scleral sagittal depth were highly predictive of the scleral shape. Measuring the sagittal depth directly, combining with the nasal and temporal angles when fitting very large diameter CLs may prove to be vital parameters that ASOCT can supply [37]. ASOCT is useful for the biometry of CL, cornea at the center and limbus, and sclera.