Abstract
Infrared (IR) spectroscopy has been used to quantify chemical and structural characteristics of a wide range of materials including biological tissues. In this study, we examined spatial changes in the chemical characteristics of rat retina in response to intraocular pressure (IOP) elevation using synchrotron infrared microscopy (SIRM), a non-destructive imaging approach. IOP elevation was induced by placing a suture around the eye of anaesthetised rats. Retinal sections were collected onto transparent CaF2 slides 10 days following IOP elevation. Using combined SIRM spectra and chemical mapping approaches it was possible to quantify IOP induced changes in protein conformation and chemical distribution in various layers of the rat retina. We showed that 10 days following IOP elevation there was an increase in lipid and protein levels in the inner nuclear layer (INL) and ganglion cell layer (GCL). IOP elevation also resulted in an increase in nucleic acids in the INL. Analysis of SIRM spectra revealed a shift in amide peaks to lower vibrational frequencies with a more prominent second shoulder, which is consistent with the presence of cell death in specific layers of the retina. These changes were more substantial in the INL and GCL layers compared with those occurring in the outer nuclear layer. These outcomes demonstrate the utility of SIRM to quantify the effect of IOP elevation on specific layers of the retina. Thus SIRM may be a useful tool for the study of localised tissue changes in glaucoma and other eye diseases.
Highlights
Glaucoma is a relatively common age-related retinal neurodegenerative disease, estimated to affect over 80-million people worldwide [1]
Our data show that synchrotron infrared microscopy (SIRM) imaging enables chemical mapping across freshly thawed retinal cross sections with enough spatial resolution to allow the key layers of the retina to be identified
We showed that SIRM imaging is sensitive enough to quantify changes arising from a mild injury to the eye induced by intraocular pressure (IOP) elevation, without need of exogenous probes
Summary
Glaucoma is a relatively common age-related retinal neurodegenerative disease, estimated to affect over 80-million people worldwide [1]. It is characterised by the death of retinal ganglion cells, which convey visual information to the brain. There is a need for sensitive tools with the capacity to study localised changes such as those occurring in the ganglion cell layer. Such approaches have the potential to provide a deeper understanding of molecular and biochemical changes occurring in the retina with IOP elevation
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