LCD, a clinically common hereditary disease, can lead to severe visual impairment and significant heritability. The condition is characterized by the deposition of amyloid in the cornea leading to the appearance of corneal stroma. These deposits create linear, lattice-like opacities arising primarily in the central cornea, while the peripheral cornea is often spared . When illuminated by post-illumination, the lattice lines and nodules are visible double-profiles with an optically transparent core that can be directed to the periphery (Generally, it does not reach the limbus of the cornea ) and deep expansion of the matrix; it can also stretch the epithelial layer to make the surface of the corneal epithelium irregular  .
We performed IVCM on the cornea of LCD patients at each follow-up. As suggested by Figure 2A-C, the amyloid deposit could have an increasing effect on the coarser nerve fibers running straight through the corneal stroma; the straight nerve fibers could not be affected by the lesions (Figure 2A); as the condition progressed, some of amyloid-like nerve fibers could have a tendency to be wrapped, with the nerves becoming beaded (Figure 2B); and at the late stage of the lesion, a large amount of amyloid could encapsulate the nerve fibers, with the nerves becoming significantly thickened (Figure 2C).
As suggested by the series of Figure 3A-C, the amyloid deposit, could affect the finer nerve fibers that were bent in the corneal stroma; the nerve fibers that were bent finely could not be affected by the lesions (Figure 3A); as the condition progressed, a small amount of amyloid-like nerve fibers, with time, could be wrapped, with the nerves irregularly ringed (Figure 3B); and at the late stage of the lesion, a large amount of amyloid could encapsulate the nerve fibers, with the nerves becoming significantly thicker and curved, and with multiple flower rings (Figure 3C) which could be connected into a mass, if they continued to develop.
As suggested by the series of Figure 4A-C, the amyloid deposit could have a tendency to affect the large corneal nerve branches; the lesion was unlikely to affect the branching of the corneal stroma, and the coarser nerve fibers (Figure 4A); as the condition progressed, some of amyloid-like nerve fibers could grow to be wrapped, the nerves becoming segmental (Figure 4B); and at the late stage of the lesion, a large amount of amyloid was likely to encapsulate the nerve fibers, the nerves becoming significantly thickened under the confocal microscope (Figure 4C).
We defined this phenomenon as neurotropic phenomenon that amyloid deposits could wrap along with the corneal nerve in LCD patients, eventually involving the entire corneal neural network. By using IVCM to observe the cornea of LCD patients at follow-ups for years, we could better understand the development of the lesion. While conventional light microscopes are limited by light scatter from structures outside of the focal plane, IVCM creates a point source of light by a pinhole aperture, focused by an objective lens on the tissue, which can well facilitate the observation of the structure of living lesions in LCD patients . Since the slit lamp examination shows no pathologic changes or mild lattice-like corneal turbidity at the early stage, corneal lesions and neurotropic phenomenon with mild degree could be observed by using IVCM, which will be better for early diagnosis . As previously reported, the progresses of corneal lesions in LCD patients could actually reflect the distribution of nerve fibers in the corneal stroma to some extent .
According to the trend charts (Figure 5A & Figure 5B), the normal corneal stromal nerve, defined as Grade 0, could have a tendency to deteriorate during the long-term observation. Moreover, the affected nerve wrapped in amyloid, defined as Grade I and II, could present a gradual increase. The statistical results also suggested that the corneal nerve invagination due to amyloid deposits in LCD patients tends to aggravate over time. In view of the findings, it can be hypothesized that the mechanism of corneal lesion in LCD refers to the nerve fibers in the corneal stroma which are wrapped and thickened, with their density increased over time.
As shown in Figure 5A, the observation time of 4.5 year is the break point whereas the time is 3.5 year in Figure 5B. The Grade 0 did a faster decrease and Grade I and II showed a faster increase after the break point time. This trend remind us to inform patients that the cornea lesions will aggravates after 3～4 years, which need a shorter regular visits to hospital, and corneal transplantation will be needed in severe cases.
Limitations of this study included the small sample size and inconsistency of observation time, which resulted in wide 95% CIs that could be reduced with a larger number of patients. Therefore, more LCD patients are needed to observe for a longer period of time. The extraction and identification of neurotropic substances can be of great benefit to the design of anti-neuronal drugs for clinical treatment of LCD patients, which may prevent the corneal lesions.