Abstract
Purpose: :
The development of corneal cross-linking procedures for the rat eye requires knowledge of anterior segment biometry and UV transmittance characteristics for the cornea and lens. The purpose of this research was to make direct measurements of anterior segment biometry and spectral transmittance properties of the cornea and lens in the adult Brown Norway rat.
Methods: :
Biometric measurements were performed using OCT and in vivo confocal microscopy imaging of the anterior segment prior to ocular dissection. Circumlimbal corneal excision and lens removal was performed on 6 eyes of 4 aged adult Brown Norway rats (18 mo). Excised tissue was immediately mounted normal to a 0.6 mm diameter parallel light beam from a fiber optic light source (Ocean Optics DH2000) with the front end of a detecting fiber placed directly behind the test tissue coupling the light to fiber optic spectrometer (Ocean Optics USB4000). The spectral transmittance of test lenses and corneas (n=6), with and without epithelium, could therefore be determined from 250-700 nm.
Results: :
Mean total central corneal thickness was 175 ± 9 µm. Epithelial cell thickness was 46.2 ± 4.5 µm and mean endothelial cell density was 1904 ± 72 cells/mm2. The rat lens did not transmit wavelengths below 325 nm. Corneal tissue with the epithelium intact did not transmit below 290 nm. Without the epithelium, the cornea transmitted approximately 5% of light between 250-275 nm and spectral transmittance increased to 50% at 300 nm. Transmittance was similar to cornea with an intact epithelium above 300 nm.
Conclusions: :
Total central corneal thickness, epithelial thickness, and endothelial cell density measurements agree well with previous reports of corneal biometry in the aged rat. The cornea and lens of the adult brown Norway rat do transmit light >325 nm and passage of shorter wavelengths is limited by the lens. The cornea will transmit light >290 nm and with the epithelium removed, the cornea will pass wavelengths as short as 250 nm. This UV transmittance data combined with estimates of corneal thickness and endothelial cell density will help develop a model for corneal crosslinking in the rat eye.
Keywords: radiation damage: light/UV • anterior segment • anatomy