Selective retina therapy and thermal stimulation of the retina: different regenerative properties - implications for AMD therapy

Nanosecond laser induces proliferation and improved cellular health within the retinal pigment epithelium

Background

Age-related macular degeneration (AMD) is a leading cause of vision loss in those over 60 years of age. Although there are limited interventions that may prevent the development or progression of disease, more efficacious treatments are required. Short-pulsed laser treatment shows promise in delaying progression of early disease. This work details how nanosecond laser influences the retinal pigment epithelium (RPE), the principal cell type implicated in AMD.

Methods

C57BL/6J mice (3-month-old) underwent monocular nanosecond laser treatment to assess short-term RPE response, while 9-month-old C57BL/6J and ApoEnull mice were similarly treated and longer-term responses investigated after 3 months. Human tissue was also obtained after 2 nanosecond laser treatments (1 month apart). RPE proliferation was assessed using bromodeoxyuridine and RPE gene change explored using qPCR and RNAseq. Melanin and lipofuscin content were quantified using histological techniques.

Results

Nanosecond laser induced RPE proliferation in treated and fellow mouse eyes, with monolayer repair occurring within 3 days. This was replicated in human tissue, albeit over a longer duration (1-4 weeks). Wildtype animals showed no overt change in RPE gene expression after short or longer post-treatment durations, while laser treated ApoEnull animals showed increased Mertk and Pedf expression, and a reduced number of dysregulated aging genes in treated and fellow eyes after 3 months. Furthermore, melanin and lipofuscin content were restored to wildtype levels in laser-treated ApoEnull RPE, while melanolipofuscin granules were reduced within treated regions of human RPE.

Conclusion

This work shows nanosecond laser stimulates RPE proliferation and results in an improved cellular phenotype. These data provide a biological basis for the prophylactic use of nanosecond lasers in AMD.

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.

Detection sensitivity of fluorescence lifetime imaging ophthalmoscopy for laser-induced selective damage of retinal pigment epithelium

PURPOSE

To investigate the sensitivity of fluorescence lifetime imaging ophthalmoscopy (FLIO) to detect retinal laser spots by comparative analysis with other imaging modalities.

METHODS

A diode laser with a wavelength of 514 nm was applied with pulse durations of 5.2, 12, 20, and 50 µs. The laser pulse energy was increased so that the visibility of the laser spot by slit-lamp fundus examination (SL) under the irradiator's observation covers from the subvisible to visible range immediately after irradiation. The irradiated areas were then examined by fundus color photography (FC), optical coherence tomography (OCT), fundus autofluorescence (AF), FLIO, and fluorescein angiography (FA). The visibility of a total of over 2200 laser spots was evaluated by two independent researchers, and effective dose (ED) 50 laser pulse energy values were calculated for each imaging modality and compared.

RESULTS

Among examined modalities, FA showed the lowest mean of ED50 energy value and SL the highest, that is, they had the highest and lowest sensitivity to detect retinal pigment epithalium (RPE)-selective laser spots, respectively. FLIO also detected spots significantly more sensitively than SL at most laser pulse durations and was not significantly inferior to FA. AF was also often more sensitive than SL, but the difference was slightly less significant than FLIO.

CONCLUSION

Considering its high sensitivity in detecting laser spots and previously reported potential of indicating local wound healing and metabolic changes around laser spots, FLIO may be useful as a non-invasive monitoring tool during and after minimally invasive retinal laser treatment.

Long-Term Multimodal Imaging Analysis of Selective Retina Therapy Laser Lesions

This study evaluates the long-term effects of selective retina therapy (SRT) on the retinal pigment epithelium (RPE) and neuroretina in patients with central serous chorioretinopathy. SRT was performed on 36 patients using a Nd:YLF-Laser at 527 nm (R:GEN®, Lutronic, Goyang-Si, Republic of Korea). A total of 994 titration spots were examined using up to three years’ multimodal imaging. Leakage in fluorescein angiography (FA) was observed after SRT in 523 lesions and resolved after one month. SRT lesions were not visible clinically, but appeared as brightly reflective areas in infrared and multicolor images. Normal morphology was observed in optical coherence tomography (OCT) immediately after SRT. After one month, thickening of the RPE and interdigitation zone changes were seen and disappeared after 539 ± 308 days. No RPE atrophies occurred during the observation period. Decreased fundus autofluorescence (FAF) was mostly observed directly after SRT followed by increased FAF at one month, which faded over time. A significant decrease in the number of visible lesions in the FA and FAF was observed within the three-year follow-up. OCT findings are consistent with animal studies showing SRT-related defect closure by hypertrophy and migration of neighboring cells without RPE atrophy or photoreceptor damage. This suggests that SRT is a safe treatment option for macular diseases and does not lead to retinal atrophy.