# Developments in Contact Lens Imaging: New Applications of Optical Coherence Tomography
## 2 Clinical Uses in CL Practice
### Evaluation of Tear Fluid in CL Wearers  
Tear film function is an important factor in CL use. A large proportion of CL drop-outs cite discomfort and symptoms of dryness as reasons for ceasing lens wear [43; 44; 45; 46]. If the post-lens tear layer is diminished, as in tight lens fitting or dry eye syndrome, the accumulation of debris and dead cells may pose a significant risk to the ocular surface [25; 31]. A thorough assessment of the tear film allows a more suitable lens material to be selected, such as one with a low water content (to limit dehydration) and high lubricity (to minimize friction), which are associated with a positive impact on CL comfort.  
Using an older version of OCT, [PERSON] et al. showed that it is possible to measure pre-corneal and central pre- and post-lens tear film thickness with OCT, but given the limited axial resolution of OCT, these measurements have to be indirect [47]. Later, a full-field real-time OCT with high resolution that imaged the thickness of the tear film across the vertical meridian of the ocular aperture was described. The instrument was shown to be capable of imaging and measuring the tear film thickness and upper and lower tear menisci with good repeatability (Figure 4), both with and without CL wear, although an indirect method was used to measure the central tear film thickness [16; 46; 47; 48; 49; 50; 51]. Using ultra-high-resolution OCT, [PERSON] et al. proved that the thickness of the tear film under the lens edge differs with different types of soft lenses and base curves; in the case of RGP, the disparity of central tear thickness and under the edge was demonstrated [52].  
In 2003, for the first time, the thickness of the pre-lens tear film of RGP was examined. The results showed that the thickness of the pre-lens tear film on a polymethyl methacrylate lens was thicker than the thickness of the pre-corneal tear film and pre-lens tear film on soft lenses [47]. Comparatively, for the first time in 2012, OCT was used for measuring the post-lens tear film thickness in keratoconic eyes fitted with RGP lenses, without the aid of artificial tears to evaluate types of fitting patterns, either in the central fit or the variable edge lift in the examined patients [25].  
The first report of the measurement of the volume of the tear meniscus using OCT was that of [PERSON] et al. They demonstrated that SSOCT could measure the tear meniscus centrally in its natural state and in real time with satisfactory inter-grader and inter-image repeatability [15].  
The pilot study of [PERSON] et al. examined the mechanical effect of the CL on the bulbar conjunctiva and possible changes using the lid-parallel conjunctival fold (LIPCOF) grading system with the CL on and then off, and a significant increase in the OCT-LIPCOF grading was found when the CL were fitted on the patient [43]. [PERSON] et al. hypothesized that a higher level of conjunctival buildup around the lens edge reduced tear exchange beneath the lens and showed that OCT could  
Figure 4: Analysis of tear meniscus as a cross-sectional image (LTM, lower tear meniscus; UTM, upper tear meniscus; LL, lower lid; UL, upper lid). Adapted from [PERSON] et al. [16].  
provide an opportunity for a quick, noninvasive, and quantitative method for the assessment and follow-up of CL-related dry eye [31; 32; 43].