Spectral Transmission of the Human Corneal Layers

Abstract

We have assessed the spectral transmittance of the different layers of the human cornea in the ultraviolet (UV), visible, and near-infrared (IR) spectral ranges. Seventy-four corneal sample donors were included in the study. Firstly, the corneal transmittance was measured using a spectrophotometer. Then, all samples were fixed for histopathological analysis, which allowed us to measure the thickness of each corneal layer. Finally, the absorption coefficients of the corneal layers were computed by a linear model reproducing total transmittance. The results show that corneal transmission was almost in unity at the visible and IR ranges but not at the UV range, in which the layer with higher transmission is Descemet’s membrane, whereas the stroma showed the lowest transmittance. Regarding the absorption coefficient, the most absorptive tissue was Bowman’s layer, followed by the endothelium. Variations on transmittance due to changes in the stroma, Bowman’s layer, or Descemet layer were simulated, and important transmission increases were found due to stroma and Bowman changes. To conclude, we have developed a method to measure the transmittance and thickness for each corneal layer. All corneal layers absorb UV light to a greater or lesser extent. The absorption coefficient is higher for Bowman’s layer, while the stroma is the layer with the lowest transmittance due to its thickness. Variations in stroma thickness or changes in the corneal tissue of Bowman’s layer or the endothelium layer due to some pathologies or surgeries could affect, to a greater or lesser degree, the total transmission of the cornea. Thus, obtaining accurate absorption coefficients for different layers would help us to predict and compensate these changes.

Mimicking the Physicochemical Properties of the Cornea: A Low-Cost Approximation Using Highly Available Biopolymers

“…At longer wavelengths, an almost full transmittance is observed for all the formulations. Thus, the results presented in Figure 3 are comparable to the previously described experimental results by Botettner and Wolter for a native cornea [ 46 ] and those estimated by Peris-Martinez et al [ 47 ], where it can be observed that there is a quick increment in the light transmitted between 300 and 500 nm (reaching around 70%) and, from there, a transmittance increase up to 98%.…”

Mesenchymal Stem Cell–Laden In Situ–Forming Hydrogel for Preventing Corneal Stromal Opacity

“…The light transmittance in the visible region of the short-chain gellan gum represents the transparency of the material and was as high as 89% to 92%, which is close to that of the human corneal stroma. 58,59 Moreover, we hope that the hydrogel can stay on the ocular surface for enough time and degrade slowly, so that Rb-BMSCs can be released slowly onto the ocular surface to acquire satisfactory therapeutic outcomes. The in vitro cell release rate of the short-chain gellan gum was (61.02 6 4.00) % on day 7 which was quite satisfactory.…”

Recent Progress of Solid Lipid Nanoparticles and Nanostructured Lipid Carriers as Ocular Drug Delivery Platforms

“…The cornea is the main route for drug absorption after topical instillation, often referred to as a static (anatomical) barrier ( Figure 1 B). It is a transparent, highly specialized, avascular structure comprising six layers: the corneal epithelium, Bowman’s layer, stroma, Dua’s layer, Descemet’s membrane, and endothelium [ 59 , 60 ]. Among these, the epithelium, the stroma, and the endothelium have a primary role in the drug/nanocarrier transport.…”