In vivo confocal microscopy study of climatic droplet keratopathy

Sir,

Climatic droplet keratopathy (CDK) is a corneal degenerative disease characterized by its progressive opacity because of accumulation of globular deposits in Bowman’s layer (BL) and anterior stroma (AS), as well as abnormal corneal sensitivity.^{1, 2}

We report herein for the first time the study of three patients each with different grades of CDK using in vivo confocal microscopy (iVCM), a technique that has allowed the measurement of normal and pathological corneal components.^{3, 4, 5}

Table 1, Figures 1 and 2 summarize the corneal abnormalities found in these patients. Cochet-Bonnet aesthesiometry (CBA) demonstrated a decrease of the mechanical sensitivity of the cornea in eyes with grade II and III CDK. Grade I CDK was characterized by incipient changes in the BL and AS but normal sub-basal and stromal nerve plexus. Grade II CDK showed hyper-reflectivity and globular non-reflective deposits in the BL and AS. In grade III, the AS showed fibrosis with increment of diffused hyper-reflective deposits and large non-reflective deposits. Concomitant to these changes, there was an increased number of dendritic cells (DC) at the peripheral cornea and limbus, but their role in the progression of CDK needs further studies. No abnormalities were found in the rest of the stroma and endothelium.

Figure 1

In vivo confocal laser scanning microscopy images. BL: (a) Grade 1: dot-like hyper-reflective deposits in the central cornea. (b) Grade 2: increased density of the deposits. (c) Grade 3: confluent hyper-reflective deposits. Sub-basal nerves: (d) Grade 1: normal appearance and density of sub basal nerve plexus. (e) Grade 2: decrease density of nerve fibres with abrupt nerve termination. (f) Grade 3: extremely diminished nerve density and fragmented nerve fibres (arrows). Stromal nerves: (g) Grade 1: normal nerve and branching (arrow). (h) Grade 2: nerve with uneven thickness (i) Grade 3: irregular configuration of nerve (bar=50 μm).

Figure 2

In vivo confocal laser scanning microscopy images. Deposits at the peripheral cornea: (a) Grade 1: reflective punctiform or dot-like deposits. (b) Grade 2: hyper-reflective punctate and homogeneous round globular non-reflective deposits. (c) Grade 3: condensation of punctiform deposits; large globular non-reflective deposits. DC at the peripheral cornea and limbus: (d) Grade 1: low density of DC. (e) Grade 2: moderate density of DC and (f) Grade 3: high density of DC (bar=50 μm).

Table 1 Abnormalities found in corneas of CDK eyes according to biomicroscopic grade of the disease

Although we were unable to study sub-epithelial nerves because they occupied the same area of the deposits in CDK, we found that the early changes in CDK did not affect the sub-basal and stromal nerves, but the progression of the disease lead to a significant density decrease of sub-basal nerves, and some structural changes in stromal nerves, such as uneven thickness and irregular configuration, that might be responsible for corneal hyposensitivity found in advanced stages of CDK.

In a recent study, Patel et al⁵ showed that sub-basal nerve tortuosity but not mean total sub-basal nerve density varied with age in normal individuals. The loss of corneal sensation could not be attributed to the age of our patients as we have previously found in a case–control study that corneal sensation was related to CDK grades and not to the age of individuals.²