In experimental ophthalmology, examination of retinal pathology is usually evaluated using histological techniques. However, histology requires animal euthanization and may cause alteration to the actual properties of the tissue. SD-OCT and SLO are routinely used in clinical ophthalmology for diagnostic purposes and for the monitoring of several retinal diseases such as diabetic macular edema9, anterior ischemic optic neuropathy10, or retinitis pigmentosa11. SD-OCT and SLO are non-invasive techniques that generate high-resolution images of the retina, which are visualized through the dilated pupil without further intervention. SD-OCT provides information of retinal structure and retinal thickness by collecting backscattering data to create cross-sectional images of the retina, while SLO collects fluorescence data to produce stereoscopic high-contrast images of the retina. Nowadays, both techniques are increasingly used in experimental ophthalmology using small rodents12,13,14,15 (or even zebrafish16,17) and can provide both qualitative and quantitative information12,17,18,19,20,21.
Accumulation of endogenous fluorophores like lipofuscins or the formation of drusen in the retina can be visualized by SLO as auto fluorescent signal. This feature makes SLO a valuable technique for diagnosis and monitoring of retinal diseases such as age-related macular degeneration or retinitis pigmentosa22,23. In experimental ophthalmology, auto fluorescence imaging (AF) can be used for the detection of specific cell types in reporter mouse lines. For example, mice heterozygous for the expression of gfp under the promoter of Cx3cr124 are advantageous for in vivo visualization of microglial cells in the normal retina and for the investigation of microglia/macrophage dynamics in retinal disease21. Microglia are the resident macrophages of the retina, which play a crucial role on tissue homeostasis and tissue repair upon injury1,25,26. Microglia activation in the retina has been reported in retinal injury, ischemia, and degeneration, suggesting a role of these cells in retinal disease2,3,4,5,6.
The aim of the present protocol is to describe a relatively simple method for retinal imaging and measurement of retinal thickness using SD-OCT, and for visualization of gfp positive microglia cells in the Cx3cr1gfp/gfp mouse retina using SLO (Heidelberg Spectralis HRA+OCT system). This protocol can be utilized for imaging and thickness measurements of healthy or diseased retinas in various mouse lines. Additionally, morphometric analyses can be performed for the identification and quantification of microglia numbers and microglia activation in the retina using SLO21. Microglia cells are associated with degenerative diseases in the central nervous system (CNS), including the retina27,28,29. Thus, by combining the two methods used in the present protocol, correlation of microglia distribution and retinal degeneration can be made, which can facilitate monitoring disease severity or the effectiveness of therapeutic approaches in vivo.