Multimodal imaging quality control of epithelia regenerated with cultured human donor corneal limbal epithelial stem cells

Distribution of 50-layer corneal densitometry values and related factors

PURPOSE

To investigate the distribution of 50 layers of corneal densitometry and related factors.

METHODS

Clinical data, including age, sex, central corneal thickness, corneal keratometry, and diopters, were collected from 102 healthy participants (102 eyes) in this retrospective study. The cornea was divided into 50 layers, and densitometry of each layer at 19 points was measured by the Pentacam. The value versus the depth curve was plotted. Paired-sample t test and one-way analysis of variance were used to compare densitometry in different regions or depth. Statistical significance was defined as P < .05.

RESULTS

The densitometry values of the Bowman membrane (10-14% depth), anterior stroma (14-30% depth), epithelium (0-10% depth), and Descemet membrane (94-98% depth) decreased sequentially, and the densitometry values of the middle and posterior stroma (30-94% depth) and endothelium (98-100% depth) were the lowest. The higher the degree of astigmatism, the higher the second densitometry peak (R = 0.277, P < .001). The densitometry values of the vertex and superior parts of the cornea were higher than those in the periphery and inferior parts, respectively (all P < .001). In the Bowman membrane, the densitometry is lowest in the inferior nasal part, while in the Descemet membrane, it is lowest in the inferior temporal part.

CONCLUSION

Two densitometry peaks appeared near the Bowman membrane and Descemet membrane. For different depths, the distribution of densitometry within a layer is different. We provide a methodological reference and data basis for corneal research based on local changes in densitometry, and help understand the details of corneal structure from an optical perspective through detailed layering and zoning analysis of densitometry.

Femtosecond Lasers in Cornea & Refractive Surgery

Since the introduction of femtosecond laser (FS) systems for corneal flap creation in laser-assisted in-situ keratomileusis there have been numerous applications for FS laser in corneal surgery. This manuscript details the utility of FS lasers in corneal surgical procedures including refractive laser surgeries, intracorneal ring segment tunnels, presbyopic treatments, and FS-assisted keratoplasty. We also review the role of FS lasers in diagnostic procedures such as two photon excitation fluorescence and second harmonic generation.

In vivo two-photon microscopy of the human eye

Two-photon (2P) microscopy is a powerful tool for imaging and exploring label-free biological tissues at high resolution. Although this type of microscopy has been demonstrated in ex vivo ocular tissues of both humans and animal models, imaging the human eye in vivo has always been challenging. This work presents a novel compact 2P microscope for non-contact imaging of the anterior part of the living human eye. The performance of the instrument was tested and the maximum permissible exposure to protect ocular tissues established. To the best of our knowledge, 2P images of the in vivo human cornea, the sclera and the trabecular meshwork are shown for the very first time. Acquired images are of enough quality to visualize collagen arrangement and morphological features of clinical interest. Future implementations of this technique may constitute a potential tool for early diagnosis of ocular diseases at submicron scale.

Quantitative Discrimination of Healthy and Diseased Corneas With Second Harmonic Generation Microscopy

Purpose

To analyze the spatial organization of pathological corneas with second harmonic generation (SHG) imaging and to provide a proof of concept to objectively distinguish these from the healthy corneas.

Methods

A custom-built SHG microscope was used to image the anterior stroma of ex vivo corneas, both control and affected by some representative pathologies. The structure tensor (ST) was employed as a metric to explore and quantify the alterations in the spatial distribution of the collagen lamellae.

Results

The collagen arrangement differed between healthy and pathological samples. The former showed a regular distribution and a low structural dispersion (SD < 40°) within the stroma with a well-defined dominant orientation. This regular arrangement drastically turns into a disorganized pattern in pathological corneas (SD > 40°).

Conclusions

The combination of SHG imaging and the ST allows obtaining quantitative information to differentiate the stromal collagen organization in healthy and diseased corneas. This approach represents a feasible and powerful technique with potential applications in clinical corneal diagnoses.

Translational Relevance

The ST applied to SHG microscopy images of the corneal stroma provides an experimental objective score to differentiate control from pathological or damaged corneas. Future implementations of this technique in clinical environments might might be a promising tool in Ophthalmology, not only to diagnose and monitor corneal diseases, but also to follow-up surgical outcome.

Quantitative Analysis of the Corneal Collagen Distribution after In Vivo Cross-Linking with Second Harmonic Microscopy

Corneal cross-linking (CXL) is a surgical procedure able to modify corneal biomechanics and stabilize keratoconus progression. Although it is known that CXL produces changes in corneal collagen distribution, these are still a topic of discussion. Here we quantitatively compare the corneal stroma architecture between two animal models four weeks after in vivo conventional CXL treatment, with second harmonic generation (SHG) imaging microscopy and the structure tensor (ST). The healing stage and the stroma recovery were also analyzed by means of histological sections. Results show that the CXL effects depend on the initial arrangement of the corneal collagen. While the treatment increases the order in corneas with a low level of initial organization, corneas presenting a fairly regular pattern are hardly affected. Histological samples showed active keratocytes in anterior and middle stroma, what means that the recovery is still in progress. The combination of SHG imaging and the ST is able to objectively discriminate the changes suffered by the collagen arrangement after the CXL treatment, whose effectiveness depends on the initial organization of the collagen fibers within the corneal stroma.