Abstract
Purpose::
Fundus autofluorescence is now more widely being used for phenotyping of inherited retinal disease. Fluorescence imaging may provide a highly sensitive method for non-invasive quantitative assessment of laser-induced lesions in the retina by monitoring of changes in autofluorescence of fluorophores in the retinal pigment epithelium (RPE) following laser irradiation.as function of exposure parameters
Methods::
Retired female breeding stock Brown-Norway rats were purchased at an approximate age of 6 months. A modified Heidelberg Retina Angiograph (HRA I) was used to obtain images of the fundus by either infra red (IR) reflectance or autofluorescence using excitation wavelengths of 488 and 514 nm. A LaserTek Model 41 AK laser operating from 488-514nm in conjunction with a Zeiss Model 30 SL-M slit lamp was used to deliver laser radiation and induce lesions. Various powers ranging from 10-40mW were used to obtain both suprathreshold and subthreshold lesions. Subthreshold is defined a laser application that does not cause any minimal visible lesion (MVL). The lesions were imaged immediately post-irradiation and weekly for 5 weeks to follow any changes.
Results::
Individual lesions, both suprathreshold and subthreshold, were easily visualized immediately following laser treatment using HRA I in 488 and 514 autofluoresence mode. In fluorescence mode laser lesions appear as spots with reduced fluorescence relative to a broadly fluorescent background. In contrast, the same lesions visible by fluorescence were difficult to visualize in IR reflectance mode. Animals followed on a weekly basis reveal dynamic changes that begin with decreased autofluorescence immediately after laser treatment to increased autofluorescence at five weeks follow up.
Conclusions::
Autufluorescence imaging of retina shows that alterations to the RPE occur at laser powers below those that cause minimal visible lesions and offer potentially a highly sensitive technique for assessing the influence of exposure parameters on laser-induced lesion in the retina.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • laser • retinal pigment epithelium