Editorial: Diagnostic and therapeutic applications of visible and near-infrared light for the retina

Malgorzata Barbara Rozanowska^1,2,3*Jennifer J. Hunter^4*

• ¹Cardiff University, Cardiff, United Kingdom
• ²Cardiff University School of Optometry and Vision Sciences, Cardiff, United Kingdom
• ³Cardiff Institute of Tissue Engineering and Repair, Cardiff University, Cardiff, United Kingdom
• ⁴University of Waterloo School of Optometry and Vision Sciences, Waterloo, Canada

Adaptive optics scanning light ophthalmoscopy (AOSLO), Light-induced retinal injury, optical coherence tomography (OCT), ophthalmic imaging techniques, optoretinography, photobiomodulation There are many applications that utilise visible and near infrared (NIR) light in helping to diagnose, monitor progression, and/or treat various diseases and retinal conditions. Among the diagnostic imaging techniques are optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO). They rely on visible or near-infrared (NIR) light reflected from the structures of the retina because of variations in refractive indices across different cellular layers. The SLO is a point scanning system, similar to a confocal microscope, that provides en face images of the structure at the back of the eye. Typically, it uses laser providing monochromatic exposure to visible and NIR wavelengths from the range of 488 nm to 830 nm and can be combined with many different imaging modalities, including fluorescence (1-3). In OCT, reflected light of the bandwidths of 40 to 150 nm, typically in 750-900 nm or 1000-1100 nm range, interacts with a reference beam, creating interference patterns that can be decoded into the amplitude and retinal depth of the reflected light, revealing retinal structure at an axial resolution of a few micrometres (4)(5)(6).In this Research Topic, Allegrini et al. report on using OCT and NIR reflectance funduscopy for monitoring the progression of tangential traction accompanying the epiretinal membrane (ERM). Fundus tracking was employed to co-localise the OCT and reflectance images from which 10 vessel crossings were manually selected. These vessel crossings were then followed at subsequent examinations taking place a week before and a month after the peeling surgery. OCT B-scans were used to segment the ERM and retinal pigment epithelium (RPE) and determine the vertical projections of each vessel crossing onto the ERM/inner limiting membrane (ILM) and RPE. The vertical projection of the vessel crossing on the RPE recorded a month after surgery served as a reference point for measuring the horizontal shift of the crossings measured in B scan in the previous examinations and is defined as the relaxation index (RI). The measurements performed on 9 eyes of 9 patients demonstrated that there was a statistically significant increase in RI between the initial examination and the examination a week before the surgery, and that there was a statistically significant decrease in RI between the examinations before the surgery and a month post-surgery, suggesting that RI can be as an objective parameter to measure the ERM traction and relaxation 37 after its surgical removal. 38 Intensity-based optoretinography (iORG) measures changes in the amplitude of the back-39 scattered/reflected from photoreceptors after a light stimulus (7-9). safety for tissues other than the retina. For most reports from clinical trials, the parameters of 59 exposure provided in publications are not sufficient to evaluate the retinal irradiance and compare the 60 radiant exposure with the safety thresholds established for ophthalmic devices with respect to retinal 61 susceptibility to light-induced injury (10). It has been evaluated that a device used for the treatment 62 of myopia, which emits 654 nm wavelength with a power of 0.2 mW over the aperture of 7 mm in 63 diameter, exceeds the photochemical and photothermal safety limits within 34 and 33 s of exposure, 64 respectively (11,12). Yet, children using such devices are instructed to look directly into the beam for 65 180 s twice a day, 5 days a week, over a period of years. While the safety aspects of PBM for myopia 66 control have been questioned (11-15), leading to requirements for manufacturers of PBM devices to 67 provide a thorough safety evaluation, including trials on primates, before any further clinical trials 68 can be approved in China (16), the irradiance levels used for treatment of age-related macular 69 degeneration (AMD) and other retinal conditions are several orders of magnitude greater than those 70 used for myopia.