Long-term SD-OCT/SLO imaging of neuroretina and retinal pigment epithelium after subthreshold infrared laser treatment of drusen

Subthreshold Nanosecond Laser, from Trials to Real-Life Clinical Practice: A Cohort Study

Background

Age-related macular degeneration (AMD), a degenerative disorder, is a major cause of irreversible severe visual deterioration in the older Western population. Thus, treatments that resolve drusen may prove helpful in limiting the progression of AMD. The study aimed to evaluate the clinical outcome of sub-threshold nanosecond laser therapy (SNL) using a double-frequency nanosecond-pulsed laser with discontinuous energy beam distribution in the early stages of age-related macular degeneration (AMD).

Methods

In a single-center cohort study, 64 eyes with early or intermediate AMD were treated using SNL and then compared to 77 untreated, control eyes. The primary outcome measures included the area and amount of drusen, and the secondary outcome measures included change in visual acuity and rate of drusen progression within 6 months of follow-up.

Results

A total of 64 patients’ eyes following SNL treatment showed a significant reduction in the area and amount of drusen after 6 months in comparison to the corresponding values in the control group (p<0.001, respectively). There was no significant difference in visual acuity change after 6 months in both groups (p\documentclass[12pt]{minimal} \usepackage{wasysym} \usepackage[substack]{amsmath} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage[mathscr]{eucal} \usepackage{mathrsfs} \DeclareFontFamily{T1}{linotext}{} \DeclareFontShape{T1}{linotext}{m}{n} {linotext }{} \DeclareSymbolFont{linotext}{T1}{linotext}{m}{n} \DeclareSymbolFontAlphabet{\mathLINOTEXT}{linotext} \begin{document} $$ \ge $$ \end{document}0.59, respectively). Within the 6-month follow-up, the rate of progression in drusen size and number was significantly lower in the SNL group (26%) than in the control group (69%; p<0.001).

Discussion

SNL therapy is a novel, promising approach for improving the macular morphology in patients with early and intermediate AMD. Further studies are necessary to reveal the potential to reduce the risk of transformation into advanced or wet AMD and to retain vision.

Preventing Progression in Nonexudative Age-Related Macular Degeneration With Subthreshold Laser Therapy: A Systematic Review

BACKGROUND AND OBJECTIVE

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness among the elderly in developed countries. Subthreshold retinal laser therapy is a new technique that targets drusen - a marker of nonexudative AMD - without causing incidental retinal damage associated with conventional laser photocoagulation. This review summarizes published literature on subthreshold retinal laser therapy as prophylactic treatment of nonexudative AMD.

PATIENTS AND METHODS

A literature search of the PubMed, Medline, and Embase databases was conducted from January 1997 to April 2018. Studies were analyzed based upon study design, laser parameters, drusen reduction, changes in visual acuity (VA), and the development of choroidal neovascularization (CNV) and/or geographic atrophy (GA).

RESULTS

Twelve studies involving 2,481 eyes treated with subthreshold retinal laser therapy were included in this review. Treatment led to increased drusen reduction, and studies with significant VA improvement were associated with significant drusen reduction. There was no significant change in the risk of developing CNV or GA.

CONCLUSIONS

Subthreshold retinal laser therapy is effective for reducing drusen and potentially improving vision in patients with nonexudative AMD. This therapy does not show benefits in reducing development of CNV or GA. Thus, its long-term efficacy to prevent progression to advanced AMD cannot yet be recommended. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:e61-e70.].

Application of subthreshold laser therapy in retinal diseases: a review

Introduction

Laser photocoagulation has been a valuable tool in the ophthalmologist's armamentarium for decades. Conventional laser photocoagulation relies on visible retinal burns as a treatment endpoint, which is thought to result in photocoagulative necrosis of retinal tissue. Recent studies have suggested that using subthreshold (ST) laser, which does not cause detectable damage to the retina may also have therapeutic effects in a variety of retinal diseases. Areas covered: We review the proposed biological mechanisms mediating the therapeutic effects of subthreshold laser on the retina, followed by the evidence for ST laser efficacy in retinal diseases such as diabetic macular edema, central serous chorioretinopathy, age-related macular degeneration, and retinal vein occlusion.

Expert Commentary

Multiple clinical studies demonstrate that subthreshold laser does not cause structural damage to the retina based on multimodal imaging. Evidence suggests that there is a therapeutic effect on decreasing diabetic macular edema and subretinal fluid in chronic central serous retinopathy; however, the effect may be relatively modest and is not as efficacious as first line treatments for these diseases. Given the repeatability and lack of damage to the retina by this treatment, subthreshold laser deserves further study to determine its place in the retina specialist's armamentarium.

Prophylactic laser in age-related macular degeneration: the past, the present and the future

The presence of drusen in the posterior eye is a hallmark feature of the early stages of age-related macular degeneration and their size is an indicator of risk of progression to vision-threatening forms of the disease. Since the initial observations that laser treatment can resolve drusen, there has been great interest in whether laser treatment can be used to reduce the progression of age-related macular degeneration. In this article, we review the development of lasers for the treatment of those with age-related macular degeneration. We provide an overview of the clinical trial results that demonstrated drusen resolution but that had mixed effects on progression of disease. In addition, we provide a summary of the recent developments in pulsed lasers that are designed to reduce the energy applied to the posterior eye to provide the therapeutic effects of conventional continuous wave lasers while reducing the secondary tissue effects.

Investigation of Thermal Effects of Photocoagulation on Retinal Tissue Using Fine-Motion-Sensitive Dynamic Optical Coherence Tomography

To enable an objective evaluation of photocoagulation, we characterize thermal tissue changes induced by laser irradiation with different laser parameters using optical coherence tomography (OCT). Spectral-domain OCT with a newly developed image processing method was used to monitor the thermal changes of ex vivo porcine retina. A sequence of OCT B-scans was obtained at the same retinal position simultaneously with the photocoagulation. Cross-sectional tissue displacement maps with respect to an OCT image taken before laser irradiation were computed for images taken before, during, and after laser irradiation, by using a correlation-based custom algorithm. Cross-sectional correlation maps (OCT correlation maps) were also computed from an OCT image taken before laser irradiation as a base-line to visualize alterations of tissue microstructure induced by laser irradiation. By systematically controlling laser power and exposure times, tissue displacements and structural changes of 200 retinal regions of 10 porcine eyes were characterized. Thermal tissue changes were characterized by B-scan images, OCT correlation maps, and tissue displacement maps. Larger tissue deformation was induced with higher laser power and shorter exposure time, while the same total laser energy (10 mJ) was applied. The measured tissue displacements revealed the complicated dynamics of tissue displacements. Three types of dynamics were observed; lateral expansion, lateral constriction, and a type showing more complicated dynamics. The results demonstrated the ability of this OCT-based method to evaluate retinal changes induced by laser irradiation. This evaluation could lead to further understanding of thermal effects, and increasing reproducibility of photocoagulation therapy.

Comprehensive detection, grading, and growth behavior evaluation of subthreshold and low intensity photocoagulation lesions by optical coherence tomographic and infrared image analysis

Purpose. To correlate the long-term clinical effect of photocoagulation lesions after 6 months, as measured by their retinal damage size, to exposure parameters. We used optical coherence tomographic (OCT)-based lesion classes in order to detect and assess clinically invisible and mild lesions. Methods. In this prospective study, 488 photocoagulation lesions were imaged in 20 patients. We varied irradiation diameters (100/300 µm), exposure-times (20–200 ms), and power. Intensities were classified in OCT images after one hour, and we evaluated OCT and infrared (IR) images over six months after exposure. Results. For six consecutive OCT-based lesion classes, the following parameters increased with the class: ophthalmoscopic, OCT and IR visibility rate, fundus and OCT diameter, and IR area, but not irradiation power. OCT diameters correlated with exposure-time, irradiation diameter, and OCT class. OCT classes discriminated the largest bandwidth of OCT diameters. Conclusion. OCT classes represent objective and valid endpoints of photocoagulation intensity even for “subthreshold” intensities. They are suitable to calculate the treated retinal area. As the area is critical for treatment efficacy, OCT classes are useful to define treatment intensity, calculate necessary lesion numbers, and universally categorize lesions in clinical studies.

Effect of change in drusen evolution on photoreceptor inner segment/outer segment junction

PURPOSE

To evaluate the integrity of photoreceptor inner segment/outer segment (IS/OS) junction after change of drusen size in age-related macular degeneration using spectral-domain optical coherence tomography.

METHODS

Drusen volume raster scans were performed with the Spectralis spectral-domain optical coherence tomography (Heidelberg Engineering) through 2,624 drusen in 14 eyes with clinically dry age-related macular degeneration, which had been longitudinally followed-up between 23 and 28 months without intervention (mean, 26.3 months). All eyes had Early Treatment Diabetic Retinopathy Study visual acuity. A total of 416 of 2,624 drusen were analyzed.

RESULTS

Of 416 drusen, 83 (20%) were found to have regressed spontaneously (Group A), 212 (51%) showed no change in size (Group B), and 121 (29%) progressed (Group C). Mean drusen size of all drusen was 63.7 ± 25.7 μm. Cross-sectional analysis of drusen morphology showed a correlation between drusen size and disrupted IS/OS junction/photoreceptor integrity (r = -0.48, P < 0.001). Of the drusen that regressed over time, there was intact IS/OS junction integrity. Even drusen that caused a major disruption showed IS/OS restoration in 74% of the drusen (P < 0.001).

CONCLUSION

Progression of drusen shows structural disruption of the IS/OS junction. After drusen regression, the IS/OS junction is either able to restore as drusen regress or was artifactitiously compressed and not initially visible because of the initial drusen compression of the IS/OS junctional line. Therefore, drusen evolution may play an important role in affecting the photoreceptor IS/OS junction integrity.

Correlation of temperature rise and optical coherence tomography characteristics in patient retinal photocoagulation

We conducted a study to correlate the retinal temperature rise during photocoagulation to the afterward detected tissue effect in optical coherence tomography (OCT). 504 photocoagulation lesions were examined in 20 patients. The retinal temperature increase was determined in real-time during treatment based on thermoelastic tissue expansion which was probed by repetitively applied ns laser pulses. The tissue effect was examined on fundus images and OCT images of individualized lesions. We discerned seven characteristic morphological OCT lesion classes. Their validity was confirmed by increasing visibility and diameters. Mean peak temperatures at the end of irradiation ranged from approx. 60 °C to beyond 100 °C, depending on burn intensity.