Relationship between intensity of reflected light and temperature increase: assessment of fundus pigmentation for transpupillary thermotherapy

Detecting irreversible cone photoreceptors injury caused by whole-body hyperthermia

Whole-body hyperthermia (WBH) has been used as an adjunctive strategy for treating malignant and viral diseases. However, WBH can cause toxic reactions in the brain and affect cerebral function. The retina is an extension of the brain. This study concerned about the effects of WBH on murine retinas. Under general anesthesia, the C57BL/6J mice in the WBH group were maintained abdomen-down position on a thermostatic platform, the temperature of which ranged from 40 to 43 °C. Ultimately, murine rectal temperatures reached a recommended high point, approximately 42 °C. However, rectal temperatures of the control mice were maintained within the normal range from 37 to 38 °C. The WBH and sham heating process lasted 2 h. Due to loss of eye blinks during general anesthesia, artificial tears were used to prevent cornea dehydration. 3 days after the WBH, full-field electroretinograms (ERGs) elicited by white-light stimuli showed reduced amplitudes of scotopic and photopic responses. 7 days after the hyperthermia, rod-driven ERG amplitudes were almost normal, but photopic ERG amplitudes were still statistically smaller than the normal values. Under dark adaptation, 35 Hz flicker ERGs confirmed that the change of cone-driven responses is irreversible. Retinal cones of the C57BL/6J mice include middlewave-sensitive (M) and ultraviolet-sensitive (UV) subtypes. Here, both M- and UV-cone ERGs showed abnormally reduced amplitudes at the two time points after the WBH. Further study focused on retinal cone opsins, which are definitive markers of cone subtypes and participate in perception of color light with different wavelengths. Analyzing whole-mounted retinas, the hyperthermia led to lower density (less counts per microscopic field) of M- and UV-cone opsins. The change might imply cone death caused by the WBH. Our study immunohistochemically displayed the hyperthermia-induced retinal injury at the microscope level. There were no abnormal findings in fundus photography and retinal optical coherence tomography imaging. Clinically, measuring cone-driven ERGs is suggested to detect potential retinal neuron injury caused by WBH administration.

Regenerative Retinal Laser and Light Therapies (RELITE): Proposal of a New Nomenclature, Categorization, and Trial Reporting Standard

OBJECTIVES

Numerous laser and light therapies have been developed to induce regenerative processes in the choroid/retinal pigment epithelium (RPE)/photoreceptor complex, leaving the neuroretina undamaged. These therapies are applied to the macula for the treatment of various diseases, most prominently diabetic maculopathy, retinal vein occlusion, central serous chorioretinopathy, and age-related macular degeneration. However, the abundance of technologies, treatment patterns, and dosimetry protocols has made understanding these therapies and comparing different approaches increasingly complex and challenging. To address this, we propose a new nomenclature system with a clear categorization that will allow for better understanding and comparability between different laser and light modalities. We propose this nomenclature system as an open standard that may be adapted in future toward new technical developments or medical advancements.

METHODS

A systematic literature review of reported macular laser and light therapies was conducted. A categorization into a standardized system was proposed and discussed among experts and professionals in the field. This paper does not aim to assess, compare, or evaluate the efficacy of different laser or dosimetry techniques or treatment patterns.

RESULTS

The literature search yielded 194 papers describing laser techniques, 50 studies describing dosimetry, 272 studies with relevant clinical trials, and 82 reviews. Following the common therapeutic aim, we propose "regenerative retinal laser and light therapies (RELITE)" as the general header. We subdivided RELITE into four main categories that refer to the intended physical and biochemical effects of temperature increase (photothermal therapy, PTT), RPE regeneration (photomicrodisruption therapy, PMT), photochemical processes (photochemical therapy, PCT), and photobiomodulation (photobiomodulation therapy, PBT). Further, we categorized the different dosimetry approaches and treatment regimens. We propose the following nomenclature system that integrates the most important parameters to enable understanding and comparability: Pattern-Dosimetry-Exposure Time/Frequency, Duty Cycle/Irradiation Diameter/Wavelength-Subcategory-Category.

CONCLUSION

Regenerative retinal laser and light therapies are widely used for different diseases and may become valuable in the future. A precise nomenclature system and strict reporting standards are needed to allow for a better understanding, reproduceable and comparable clinical trials, and overall acceptance. We defined categories for a systematic therapeutic goal-based nomenclature to facilitate future research in this field.