Short-pulse duration retinal lasers: a review

A versatile laser-induced porcine model of outer retinal and choroidal degeneration for preclinical testing

Over 30 million people worldwide suffer from untreatable vision loss and blindness associated with childhood-onset and age-related eye diseases caused by photoreceptor (PR), retinal pigment epithelium (RPE), and choriocapillaris (CC) degeneration. Recent work suggests that RPE-based cell therapy may slow down vision loss in late stages of age-related macular degeneration (AMD), a polygenic disease induced by RPE atrophy. However, accelerated development of effective cell therapies is hampered by the lack of large-animal models that allow testing safety and efficacy of clinical doses covering the human macula (20 mm2). We developed a versatile pig model to mimic different types and stages of retinal degeneration. Using an adjustable power micropulse laser, we generated varying degrees of RPE, PR, and CC damage and confirmed the damage by longitudinal analysis of clinically relevant outcomes, including analyses by adaptive optics and optical coherence tomography/angiography, along with automated image analysis. By imparting a tunable yet targeted damage to the porcine CC and visual streak - with a structure similar to the human macula - this model is optimal for testing cell and gene therapies for outer retinal diseases including AMD, retinitis pigmentosa, Stargardt, and choroideremia. The amenability of this model to clinically relevant imaging outcomes will facilitate faster translation to patients.

Effectiveness, Safety and Choroidal Changes of a Fovea-Sparing Technique for the Treatment of Chronic Central Serous Chorioretinopathy with Yellow Subthreshold Laser

The aim of this study was to evaluate the effectiveness and safety of a yellow subthreshold laser (STL) for the treatment of chronic central serous chorioretinopathy delivered in a fovea-sparing pattern and to analyze the post-laser changes in the choroidal structure by Swept-Source Optical Coherence Tomography. This study was a prospective case series of 43 eyes corresponding to 37 patients. Data were recorded at 6, 12 and 24 weeks after the STL treatment. The best-corrected visual acuity improved in 93% of the patients and remained stable in 7%. The subretinal fluid was completely reabsorbed in 27.9%, 32.6% and 69.8% of the patients at 6, 12 and 24 weeks, respectively. There were reductions in the choroidal thickness of 13.1% and 25.3% at 12 and 24 weeks, which corresponded to reductions of 17.5% and 45.9% in the choriocapillaris and Sattler layer and reductions of 12.2% and 21.2% in the Haller layer at 12 and 24 weeks, respectively (p < 0.05). This might account for the effect of the laser on the inner choroidal vasculature, the dysregulation of which is believed to be at the core of central serous chorioretinopathy. No laser-related complications were detected. Overall, the fovea-sparing STL was safe and effective in this series of patients.

Pascal short-pulse plus subthreshold endpoint management laser therapy for diabetic macular edema: the "sandwich technique"

Background

Diabetic macular edema (DME) is the main cause of visual loss in diabetic patients. Despite the use of anti-VEGF therapy as first-line treatment, there are many patients whose response to treatment is poor or transient at best. Sophisticated laser techniques have emerged aiming at low-intensity retinal damage, avoiding excessive heat that causes tissue necrosis and related collateral effects.

Objective

To evaluate the effect of combined sublethal laser modalities from short-pulse duration (SPD) with endpoint management (EpM) subthreshold laser [named the “sandwich technique” (SWiT)] on central subfield thickness (CST) and best-corrected visual acuity (BCVA) in patients with DME.

Material and methods

In this consecutive retrospective study, 37 patients (37 eyes) with center-involved (CI) DME were treated with SWiT laser therapy from April 2017 to June 2021. The technique consisted of a mean number of 200 (range number 50–400) SPD laser burns OCT-guided thickened area performed on the juxta- and perifoveal area 500 µm away from the foveal center, overlapping with a mean number of 1000 (range number 800–1200) EpM laser burns focused on 6 mm macular diameter area but saving 300 µm toward the foveal center. All patients underwent ophthalmological evaluations, including BCVA and CST measurement by spectral-domain optical coherence tomography (SD-OCT), before and after SWiT laser therapy. The mean follow-up time was 19.2 months (range 2–60 months).

Results

Thirty-five out of 37 cases showed an improvement in CST and BCVA following treatment. At baseline, mean CST (µm) ± standard error (SE) and mean BCVA (logMAR) ± SE was 456.95 ± 37.00 and 0.71 ± 0.29, respectively. After a mean follow-up of 19.2 months, mean CST (µm) ± SE and BCVA (logMAR) ± SE were 272.09 ± 9.10 (p < 0.0001) and 0.54 ± 0.26 (p = 0.003), respectively. A statistically significant reduction in CST and improvement in BCVA was noted after laser therapy application. The anti-VEGF injection frequency was reduced during the mean 19.2 months of the study period.

Conclusions

The novel “sandwich” laser therapy aid reduced CST and improved BCVA in this retrospective case series. Further prospective studies are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40942-022-00381-5.

Comparison of short-pulse subthreshold (532 nm) and infrared micropulse (810 nm) macular laser for diabetic macular edema

The purpose of the study was to assess both anatomic and functional outcomes between short-pulse continuous wavelength and infrared micropulse lasers in the treatment of DME. This was a prospective interventional study from tertiary care eye hospital—King Khaled Eye Specialist Hospital (Riyadh, Saudi Arabia). Patients with center-involving diabetic macular edema were treated with subthreshold laser therapy. Patients in the micropulse group were treated with the 810-nm diode micropulse scanning laser TxCell (IRIDEX Corporation, Mountain View, CA, USA) (subthreshold micropulse—STMP group). Laser was applied according to recommendations for MicroPulse (125 microns spot size, 300 ms pulse duration and power adjustment following barely visible testing burn) in a confluent mode (low intensity/high density) to the entire area of the macular edema. Patients in the short-pulse group were treated with grid pattern laser with 20 ms pulse PASCAL laser 532 nm (TopCon Medical Laser Systems, Tokyo, Japan) with EndPoint algorithm, which was either 30% or 50% of testing burn (EndPoint 30% and EndPoint 50% groups, respectively). Main outcome measures included best-corrected visual acuity (BCVA in logMAR) and foveal thickness at baseline and the last follow-up visit at 6 months. There were 44 eyes in the micropulse group, 54 eyes in the EndPoint 50% group and 18 eyes in the EndPoint 30% group. BCVA for the whole cohort (logMAR) was 0.451 (Snellen equivalent 20/56) at baseline, 0.495 (Snellen equivalent 20/62) (p = 0.053) at 3 months, and 0.494 (Snellen equivalent 20/62) at the last follow-up (p = 0.052). Foveal thickness for the whole cohort was 378.2 ± 51.7 microns at baseline, 347.2 ± 61.3 microns (p = 0.002) at 3 months, and 346.0 ± 24.6 microns at the final follow-up (p = 0.027). As such the short-pulse system yields more temporary reduction in edema. Comparison of BCVA between baseline and 6 months for EndPoint 30%, EndPoint 50% and STMP groups was p = 0.88, p = 0.76 and p = 0.003, respectively. Comparison of foveal thickness between baseline and 6 months for EndPoint 30%, EndPoint 50% and STMP groups was p = 0.38, p = 0.22 and p = 0.14, respectively. We conclude that the infrared micropulse system seems to improve functional outcomes. When applied according to previously published reports, short-pulse system may yield more temporary reduction in edema while infrared micropulse system may yield slightly better functional outcomes.

Subthreshold yellow laser for fovea-involving diabetic macular edema in a series of patients with good vision: effectiveness and safety of a fovea-sparing technique

PURPOSE

Patients with center-involved diabetic macular edema (CI-DME) with good visual acuity (VA) represent a controversial clinical scenario in which a subthreshold laser might be a reasonable approach. We report a case series of patients with CI-DME with VA better than 20/32 who were treated with a subthreshold 577 nm (yellow) laser.

METHODS

The area of retinal thickening on OCT was treated with confluent laser spots at individually titrated power. The fovea was spared from treatment. Effectiveness and safety were evaluated through OCT and autofluorescence (AF) as well as BCVA.

RESULTS

A total of 23 eyes from 19 patients were treated. VA ranged from 20/20 to 20/30. The follow-up period ranged from 6 to 18 months. Edema in OCT resolved completely at the end of follow-up in 56.5% (13/23) of the cases. Central retinal thickness was reduced at 12 weeks and at the end of follow-up, with a mean reduction of 16.9 μm and 22 μm, respectively (paired t-test p = 0.001 and 0.0003). VA remained stable. The laser was invisible (OCT, AF, Fundoscopy) in 91,3% (21/23) of eyes.

CONCLUSIONS

A fovea-sparing yellow subthreshold laser was safe and effective for treating CI-DME patients with good VA in this case series. This technique is of interest to prevent the progression of mild edema and might avoid or reduce the use of more invasive and expensive therapies. Excluding the fovea from the treated area does not seem to affect the results, which is of interest to novel laser practitioners.

Coherent beam combining of high power quasi continuous wave tapered amplifiers

We demonstrate coherent beam combining of four high brightness tapered amplifiers in pulsed, quasi continuous wave (QCW) operation, seeded by a 976 nm laser diode. The maximum power of 22.7 W was achieved with > 64% combining efficiency in a close to diffraction limited beam. We discuss turn-on dynamics of tapered amplifiers operated in pulsed mode in detail.

Single-Session Low Duration Panretinal Photocoagulation Using Conventional Laser on Central Subfield Macular Thickness in Diabetic Retinopathy

Objective:

To compare the change in central subfield macular thickness following single-session and multiple-session laser panretinal photocoagulation in subjects with diabetic retinopathy.

Methods:

A single-center, randomized controlled trial study was performed on 28 eyes of 16 patients with severe non-proliferative diabetic retinopathy or proliferative diabetic retinopathy. Eyes were randomly assigned for treatment with panretinal photocoagulation performed either in single-session or multiple-session divided into three sessions during two-week period. Central subfield macular thickness was quantified using spectral domain optical coherence tomography and changes at four weeks follow-up were compared to the baseline measurement.

Result:

Mean baseline central subfield macular thickness of 12 eyes underwent single-session and 16 eyes underwent multiple-session panretinal photocoagulation were 342.91+109.51 micrometers and 354+171.79 micrometers (p> .05), respectively. Mean post laser central subfield macular thickness in the single-session group was 305.83+81.95 micrometers and 389.75+229.51 micrometers in the multiple-session group (p> .05). Mean central subfield macular thickness changes four weeks post laser was 37.08+94.21 micrometers for eyes treated with single-session and -35.75+123.62 micrometers for the multiple-session treated eyes (p= .101).

Conclusion:

There was no significant difference in change of central subfield macular thickness at four weeks post laser from treatment with single-session and multiple-session panretinal photocoagulation. Single-session panretinal photocoagulation can be used as effective multiple-session panretinal photocoagulation for the treatment of diabetic retinopathy.

Bone Marrow-Derived Cell Recruitment to the Neurosensory Retina and Retinal Pigment Epithelial Cell Layer Following Subthreshold Retinal Phototherapy

Purpose

We investigated whether subthreshold retinal phototherapy (SRPT) was associated with recruitment of bone marrow (BM)–derived cells to the neurosensory retina (NSR) and RPE layer.

Methods

GFP chimeric mice and wild-type (WT) mice were subjected to SRPT using a slit-lamp infrared laser. Duty cycles of 5%, 10%, 15%, and 20% (0.1 seconds, 250 mW, spot size 50 μm) with 30 applications were placed 50 to 100 μm from the optic disc. In adoptive transfer studies, GFP⁺ cells were given intravenously immediately after WT mice received SRPT. Immunohistochemistry was done for ionized calcium-binding adapter molecule-1 (IBA-1⁺), CD45, Griffonia simplicifolia lectin isolectin B4, GFP or cytokeratin). Expression of Ccl2, Il1b, Il6, Hspa1a, Hsp90aa1, Cryab, Hif1a, Cxcl12, and Cxcr4 mRNA and flow cytometry of the NSR and RPE-choroid were performed.

Results

Within 12 to 24 hours of SRPT, monocytes were detected in the NSR and RPE-choroid. Detection of reparative progenitors in the RPE occurred at 2 weeks using flow cytometry. Recruitment of GFP⁺ cells to the RPE layer occurred in a duty cycle–dependent manner in chimeric mice and in mice undergoing adoptive transfer. Hspa1a, Hsp90aa1, and Cryab mRNAs increased in the NSR at 2 hours post laser; Hif1a, Cxcl12, Hspa1a increased at 4 hours in the RPE-choroid; and Ccl2, Il1b, Ifng, and Il6 increased at 12 to 24 hours in the RPE-choroid.

Conclusions

SRPT induces monocyte recruitment to the RPE followed by hematopoietic progenitor cell homing at 2 weeks. Recruitment occurs in a duty cycle–dependent manner and potentially could contribute to the therapeutic efficacy of SRPT.

Deep modulation of second-harmonic light by wavelength detuning of a laser diode

Power modulated visible lasers are interesting for a number of applications within areas such as laser displays and medical laser treatments. In this paper, we present a system for modulating the second-harmonic light generated by single-pass frequency doubling of a distributed feedback (DFB) master oscillator power amplifier (MOPA) laser diode with separate electrical contacts for the MO and the PA. A modulation depth in excess of 97% from 0.1 Hz to 10 kHz is demonstrated. This is done by wavelength tuning of the laser diode using only a 40 mA adjustment of the current through the MO. The bandwidth of the modulation is limited by the electronics. This method has the potential to decrease the size as well as cost of modulated visible lasers. The achievable optical powers will increase as DFB MOPAs are further developed.

Subthreshold Nanosecond Laser Intervention in Intermediate Age-Related Macular Degeneration: Study Design and Baseline Characteristics of the Laser in Early Stages of Age-Related Macular Degeneration Study (Report Number 1)

PURPOSE

The Laser Intervention in Early Stages of Age-Related Macular Degeneration (LEAD) study is an investigation of the safety and efficacy of subthreshold nanosecond laser treatment to slow the progression of intermediate age-related macular degeneration (AMD). This report presents the novel study design and baseline characteristics.

DESIGN

Multicenter, double-masked, randomized controlled, medical device feasibility clinical trial.

PARTICIPANTS

Persons with bilateral drusen >125 μm within 1500 μm of the fovea, monocular best-corrected visual acuity (BCVA) ≥20/40, and microperimetric retinal sensitivity of <25 decibels (dB) in at least 1 location within central 6° in 1 eye. Signs of late AMD; choroidal neovascularization or geographic atrophy, or anatomic end points defined on multimodal imaging (MMI) as fundus autofluorescence-defined atrophy, spectral-domain OCT (SD-OCT)-defined atrophy, or nascent GA excluded participation.

METHODS

Participants were randomized to nanosecond or sham laser treatment. Twelve laser or sham spots are applied to the macular region of the study eye. Participants are reviewed in visits every 6 months with functional testing and MMI for 36 months and are re-treated at each visit (until 30 months) if an end point is not reached in the study eye.

MAIN OUTCOME MEASURES

Progression to late AMD or MMI-defined anatomic end points in the study eye.

RESULTS

A total of 292 participants across 6 centers were enrolled, with 145 participants randomized to arm 1 and 147 participants randomized to arm 2. Population characteristics at baseline were as follows: median age 70 years, 73% female, 90% Anglo-Saxon, and 3% current smokers. Baseline ocular characteristics of the study eyes were BCVA of 83 letters (20/25); low luminance visual acuity (LLVA) of 68 letters (20/50); hyperpigmentation, 33%; reticular pseudodrusen, 23%; square root drusen area (SD-OCT), 0.77 mm; square root drusen area (color photographs), 0.92 mm; cube root drusen volume (SD-OCT), 0.26 mm; average retinal sensitivity, 26 dB; and worst point retinal sensitivity, 20 dB. Only lutein supplement use was significantly different between treatment arms.

CONCLUSIONS

The LEAD study uses novel inclusion/exclusion criteria and end points in an attempt to optimize our study design. Risk characteristics for progression to study end points are equally distributed between treatment arms.