Optoacoustic real-time dosimetry for selective retina treatment

Real-time OCT feedback-controlled RPE photodisruption in ex vivo porcine eyes using 8 microsecond laser pulses

Selective retinal pigment epithelium (RPE) photodisruption requires reliable real-time feedback dosimetry (RFD) to prevent unwanted overexposure. In this study, optical coherence tomography (OCT) based RFD was investigated in ex vivo porcine eyes exposed to laser pulses of 8 µs duration (wavelength: 532 nm, exposure area: 90 × 90 µm2, radiant exposure: 247 to 1975 mJ/µm2). For RFD, fringe washouts in time-resolved OCT M-scans (central wavelength: 870 nm, scan rate: 85 kHz) were compared to an RPE cell viability assay. Statistical analysis revealed a moderate correlation between RPE lesion size and applied treatment energy, suggesting RFD adaptation to inter- and intraindividual RPE pigmentation and ocular transmission.

Investigation of the Influence of Pulse Duration and Application Mode on Microsecond Laser Microsurgery of the Retinal Pigment Epithelium

Optical microsurgery confined to the retinal pigment epithelium (RPE) requires locally optimized laser parameters and reliable real-time feedback dosimetry (RFD) to prevent unwanted neuroretinal overexposure. This study aimed to compare pulses of different durations and application modes (single, ramp, burst). Moreover, optical coherence tomography (OCT)-based RFD was investigated in an ex vivo experiment, utilizing nine porcine eyes that were exposed to laser pulses of 8, 12, 16 and 20 µs duration (wavelength: 532 nm, exposure area: 90 × 90 µm², radiant exposure: 247 to 1975 mJ/µm²). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 85 kHz) for RFD. Post irradiation, retinal changes were assessed with color fundus photography (CFP) and cross-sectional OCT B-scans. RPE cell damage was quantified via fluorescence-based cell viability assay and compared to the OCT dosimetry feedback. Our experiments indicate cumulative RPE damage for pulse bursts of 16 µs and 20 µs, whereas no cumulative effects were found for pulse durations of 8 µs and 12 µs applied in ramp mode. According to statistical analysis, OCT-RFD correctly detected RPE cell damage with 96% sensitivity and 97% specificity using pulses of 8 µs duration in ramp mode.

The Effect of Selective Retina Therapy for Bevacizumab-Resistant Chronic Central Serous Chorioretinopathy

PURPOSE

The aim of this study was to evaluate the efficacy of selective retina therapy (SRT), used in conjunction with real-time feedback dosimetry (RFD), in the treatment of bevacizumab-resistant chronic central serous chorioretinopathy (CSC).

PATIENTS AND METHODS

In this retrospective cohort study, 22 eyes of 22 patients with bevacizumab-resistant chronic CSC, showing focal or diffuse foveal leakages on fundus fluorescein angiography (FFA), were included. After evaluation of the test spots at temporal arcades, SRT (wavelength, 527 nm; pulse repetition rate, 100 Hz; ramping over maximal 15 micropulses; and spot diameter, 200 μm) using RFD was applied to the leakage sites observed on FFA. Changes in the mean best-corrected visual acuity (BCVA), central macular thickness (CMT), and subretinal fluid (SRF) height were evaluated at baseline and at 1, 3, 6, 9, and 12 months following treatment.

RESULTS

SRF completely resolved in 81.8% (18/22 eyes) cases at 12 months post-treatment. The mean BCVA (logarithm of the minimum angle of resolution [logMAR]) improved from 0.49 ± 0.29 at baseline to 0.43 ± 0.36 at 12 months (p = 0.067). The mean BCVA gain was 0.06 logMAR, equivalent to 3 ETDRS letters. The CMT significantly decreased from 323 ± 85.6 μm at baseline to 221.5 ± 60.4 μm at 12 months (p < 0.001). The mean SRF height also significantly decreased from 174.6 ± 86.4 μm at baseline to 35.1 ± 75.4 μm at 12 months (p < 0.001).

CONCLUSION

SRT showed favorable visual and anatomical outcomes in patients with bevacizumab-resistant chronic CSC.

Investigations on Retinal Pigment Epithelial Damage at Laser Irradiation in the Lower Microsecond Time Regime

Purpose

New lasers with a continuous wave power exceeding 15 W are currently investigated for retinal therapies, promising highly localized effects at and close to the Retinal Pigment Epithelium (RPE). The goal of this work is to evaluate mechanisms and thresholds for RPE cell damage by means of pulse durations up to 50 µs.

Methods

A diode laser with a wavelength of 514 nm, a power of 15 W, and adjustable pulse durations between 2 µs and 50 µs was used. Porcine RPE-choroidal explants (ex vivo) and chinchilla bastard rabbits (in vivo) were irradiated to determine threshold radiant exposures for RPE damage H¯Cell by calcein vitality staining and fluorescence angiography, respectively. Thresholds for microbubble formation (MBF) H¯MBF were evaluated by time-resolved optoacoustics. Exemplary histologies support the findings.

Results

H¯MBF is significantly higher than H¯Cell at pulse durations ≥ 5 µs (P < 0.05) ex vivo, while at 2 µs, no statistically significant difference was found. The ratios between H¯MBF and H¯Cell increase with pulse duration from 1.07 to 1.48 ex vivo and 1.1 to 1.6 in vivo, for 5.2 and 50 µs.

Conclusions

Cellular damage with and without MBF related disintegration are both present and very likely to play a role for pulse durations ≥ 5 µs. With the lower µs pulses, selective RPE disruption might be possible, while higher values allow achieving spatially limited thermal effects without MBF. However, both modi require a very accurate real-time dosing control in order to avoid extended retinal disintegration in this power range.

The Effect of Selective Retina Therapy with Automatic Real-Time Feedback-Controlled Dosimetry for Chronic Central Serous Chorioretinopathy: A Randomized, Open-Label, Controlled Clinical Trial

This prospective randomized controlled trial evaluated the safety and efficacy of real-time feedback-controlled dosimetry (RFD)-guided selective retina therapy (SRT) in chronic central serous chorioretinopathy (CSC). Forty-four participants with chronic CSC were included and randomly assigned to the control group or SRT group. The SRT laser system with RFD-guidance was applied to cover the entire leakage area. If SRF remained at the 6-week follow-up visit, re-treatment and rescue SRT was performed for the SRT group and crossover group, respectively. The rate of complete resolution of subretinal fluid (SRF), mean SRF height, and mean retinal sensitivity were compared between the two groups at 6-weeks post-treatment. The complete SRF resolution rate in all SRT-treated eyes was evaluated at 12-weeks post-treatment. The rate of complete SRF resolution was significantly higher in the SRT group (63.6%) than in the control group (23.8%) at 6-weeks post-treatment (p = 0.020). The mean SRF height at 6 weeks after SRT was significantly lower in the SRT group (p = 0.041). Overall, SRT-treated eyes showed complete SRF resolution in 70.3% of eyes at 12-weeks post-treatment. RFD-guided SRT was safe and effective to remove SRF in chronic CSC patients during the 3-month follow-up period.

Selective Large-Area Retinal Pigment Epithelial Removal by Microsecond Laser in Preparation for Cell Therapy

Purpose

Cell therapy is a promising treatment for retinal pigment epithelium (RPE)-associated eye diseases such as age-related macular degeneration. Herein, selective microsecond laser irradiation targeting RPE cells was used for minimally invasive, large-area RPE removal in preparation for delivery of retinal cell therapeutics.

Methods

Ten rabbit eyes were exposed to laser pulses 8, 12, 16, and 20 µs in duration (wavelength, 532 nm; top-hat beam profile, 223 × 223 µm²). Post-irradiation retinal changes were assessed with fluorescein angiography (FA), indocyanine green angiography (ICGA), and optical coherence tomography (OCT). RPE viability was evaluated with an angiographic probit model. Following vitrectomy, a subretinal injection of balanced salt solution was performed over a lasered (maximum 13.6 mm2) and untreated control area. Bleb retinal detachment (bRD) morphology was then evaluated by intraoperative OCT.

Results

Within 1 hour after irradiation, laser lesions showed FA and ICGA leakage. OCT revealed that large-area laser damage was limited to the RPE. The angiographic median effective dose irradiation thresholds (ED50) were 45 µJ (90 mJ/cm2) at 8 µs, 52 µJ (104 mJ/cm2) at 12 µs, 59 µJ (118 mJ/cm2) at 16 µs, and 71 µJ (142 mJ/cm2) at 20 µs. Subretinal injection over the lasered area resulted in a controlled, shallow bRD rise, whereas control blebs were convex in shape, with less predictable spread.

Conclusions

Large-area, laser-based removal of host RPE without visible photoreceptor damage is possible and facilitates surgical retinal detachment.

Translational Relevance

Selective microsecond laser-based, large-area RPE removal prior to retinal cell therapy may reduce iatrogenic trauma.

Optical dosimeter for selective retinal therapy based on multi-port fiber-optic interferometry

Selective retinal therapy (SRT) employs a micro-second short-pulse lasers to induce localized destruction of the targeted retinal structures with a pulse duration and power aimed at minimal damage to other healthy retinal cells. SRT has demonstrated a great promise in the treatment of retinal diseases, but pulse energy thresholds for effective SRT procedures should be determined precisely and in real time, as the thresholds could vary with disease status and patients. In this study, we present the use of a multi-port fiber-based interferometer (MFI) for highly sensitive real-time SRT monitoring. We exploit distinct phase differences among the fiber ports in the MFI to quantitatively measure localized fluctuations of complex-valued information during the SRT procedure. We evaluate several metrics that can be computed from the full complex-valued information and demonstrate that the complex contour integration is highly sensitive and most correlative to pulse energies, acoustic outputs, and cell deaths. The validity of our method was demonstrated on excised porcine retinas, with a sensitivity and specificity of 0.92 and 0.88, respectively, as compared with the results from a cell viability assay.

Selective retina therapy (SRT) in patients with therapy refractory persistent acute central serous chorioretinopathy (CSC): 3 months functional and morphological results

PURPOSE

Central serous chorioretinopathy (CSC) is a disease presenting with detachment of the neurosensory retina and characteristic focal leakage on fluorescein angiography. The spontaneous remission rate is 84% within 6 months. In this study, the efficacy of selective retina therapy (SRT) was examined in patients with therapy refractory persistent acute CSC defined by symptoms for at least 6 months and persistent subretinal fluid (SRF) despite eplerenone therapy.

MATERIAL AND METHODS

This is a prospective, monocentric observational study in 17 eyes (16 patients, mean age 42 years, 2 female). SRT was performed with the approved R:GEN laser (Lutronic, South Korea), a micropulsed 527-nm Nd:YLF laser device, with a train of 30 pulses of 1.7 μs at 100-Hz repetition rate at the point of focal leakage determined by fluorescein angiography (FA) at baseline (BSL). Visits on BSL, week 4 (wk4), and week 12 (wk12) included best corrected visual acuity (BCVA, logMar), central retinal thickness (CRT) on spectral domain optical coherence tomography (SD-OCT), and FA. Statistical analysis was performed by pair-by-pair comparisons of multiple observations in each case with Bonferroni correction for multiple testing. (IBM SPSS Statistics 25®).

RESULTS

Mean CRT at BSL was 387.69 ± 110.4 μm. CRT significantly decreased by 106.31 μm in wk4 (95%-KI: 21.42-191.2; p = 0.01), by 133.63 μm in wk12 (95%-KI: 50.22-217.03; p = 0.001) and by 133.81 μm (95%-KI: 48.88-218.75; p = 0.001) compared to BSL. Treatment success defined as complete resolution of SRF occurred at wk4 in 7/17 eyes (35.3%) and at wk12 in 10/17 eyes (58.8%). Re-SRT was performed in 7/17 eyes (41.2%) after an average of 107.14 ± 96.59 days. Treatment success after Re-SRT was observed in 4/6 eyes (66.6%, 12 weeks after Re-SRT). Mean BCVA did not change significantly from BSL to any later timepoint after adjusting for multiple testing. Notably, eyes with treatment success showed better BCVA at all timepoints and gained more letters compared to failures.

CONCLUSION

Single or repetitive SRT may be an effective and safe treatment in 2 of 3 patients suffering from acute persistent CSC after 6 months of symptoms or more. We observed complete resolution of SRF in around 60% of eyes 12 weeks after first SRT treatment and also 12 weeks after Re-SRT treatment in eyes with persistent or recurrent SRF. Results on the long-term course after SRT are still pending.

Factors affecting resolution of subretinal fluid after selective retina therapy for central serous chorioretinopathy

The purpose of this study was to investigate the factors of clinical outcome of selective retina therapy (SRT) for central serous chorioretinopathy (CSC). This retrospective study included 77 eyes of 77 patients, who were treated with SRT for CSC and observed at least 6 months after the treatment. SRT laser (527 nm, 1.7 µs, 100 Hz) was used for treatment. The mean best-corrected visual acuity (logMAR), central macular thickness (CMT) and central choroidal thickness were changed from baseline to at 6-months follow-up with significant difference. The multivariate analyses found that the rate of change (reduction) in CMT was associated with focal leakage type on fluorescein angiography (FA) (p = 0.03, coefficient 15.26, 95% confidence interval 1.72–28.79) and larger baseline CMT (p < 0.01, coefficient − 0.13, 95% confidence interval − 0.13 to − 0.05). Complete resolution of subretinal fluid was associated with nonsmoking history (p = 0.03, odds ratio 0.276, 95% confidence interval 0.086–0.887) and focal leakage type on FA (p < 0.01, odds ratio 0.136, 95% confidence interval 0.042–0.437). These results may be useful for predicting the therapeutic effectiveness of SRT.

Effect of laser pulse shaping on photoacoustic dosimetry in retinal models

Photoacoustic sensing can be a powerful technique to obtain real-time feedback of laser energy dose in treatments of biological tissue. However, when laser therapy uses pulses with microsecond duration, they are not optimal for photoacoustic pressure wave generation. This study examines a programmable fiber laser technique using pulse modulation in order to optimize the photoacoustic feedback signal to noise ratio (SNR) in a context where longer laser pulses are employed, such as in selective retinal therapy. We have demonstrated with a homogeneous tissue phantom that this method can yield a greater than seven-fold improvement in SNR over non-modulated square pulses of the same duration and pulse energy. This technique was further investigated for assessment of treatment outcomes in leporine retinal explants by photoacoustic mapping around the cavitation-induced frequency band.

Selective retina therapy (SRT) for macular serous retinal detachment associated with tilted disc syndrome

PURPOSE

Tilted disc syndrome (TDS) may be associated with a macular serous retinal detachment (MSRD). However, ideal therapy for this complication is still unestablished yet to date. The purpose of this study is to investigate the effect of selective retina therapy (SRT) for MSRD associated with TDS.

METHODS

This retrospective study included 11 eyes of 10 patients (1 male and 9 females), who were treated with SRT for MSRD associated with TDS, and observed at least 12 months after treatment. The mean age was 56 years old (range 44-66). An SRT laser (527 nm, 1.7 μs, 100 Hz; Medical Laser Center Lübeck, Germany) was used for treatment. The changes of best-corrected visual acuity (BCVA), central macular thickness (CMT), and central choroidal thickness (CCT) were examined. Subfoveal curve height (SFCH) was calculated at baseline.

RESULTS

The mean follow-up period was 24.4 months (range 12-48 months). The mean BCVA (logMAR), CMT, and CCT changed from 0.03 ± 0.10, 324 ± 82 μm, and 194 ± 68 μm preoperatively to 0.07 ± 0.17, 274 ± 94 μm, and 188 ± 65 μm at final follow-up, respectively, with significant difference on CMT (BCVA: p = 0.44, CMT: p < 0.05, CCT: p = 0.21). The MSRD disappeared in 6 eyes (55%) and the average number of SRT irradiations until resolution of MSRD was 2.6 times (range 1-5 times). There was no significant association between SFCH and resolution of MSRD (p = 0.19).

CONCLUSIONS

SRT may promote absorption of MSRD and maintenance of BCVA for TDS. Randomized and prospective clinical studies are needed to evaluate the effectiveness of SRT for MSRD associated with TDS.

Retinal pigment epithelial responses based on the irradiation density of selective retina therapy

PURPOSE

We evaluated the response of the retinal pigment epithelium (RPE) to high-density (HD) or low-density (LD)-selective retina therapy (SRT) with real-time feedback-controlled dosimetry (RFD) in rabbits.

METHODS

Sixteen eyes of 8 Chinchilla Bastard rabbits underwent SRT with RFD (527-nm wavelength, 1.7-μs pulse duration), using automatically titrated pulse energy, by using optoacoustic dosimetry or real-time reflectometry. Fifty-six 25-μJ SRT, including LD-SRT (1-spot or 2-spot-spacing) and HD-SRT (4-spot, 7-spot, or 9-spot-no-spacing), were applied per eye. Color fundus photography and fundus fluorescein angiography (FFA) were used to confirm SRT spots 1-h post-SRT. Light microscopy and scanning electron microscopy (SEM) were performed at 2-h, 3-day, 7-day, and 1-month post-treatment.

RESULTS

We tested 896 spots irradiated by SRT with RFD and confirmed that SRT lesions were adequate, based on invisibility on fundoscopy and visibility on FFA. On SEM, at 2-h post-SRT, flattened RPE cells were observed in the center of the SRT lesion. While normal RPE cells were clearly observed between LD-SRT lesions, healthy RPE cells were rare in HD-SRT lesions at 2-h post-treatment. At 7-day post-SRT, SEM revealed completely restored LD-SRT lesions with small or large RPE cells with microvilli, whereas HD-SRT lesions were covered with RPE cells without microvilli. At 1-month post-SRT, SEM revealed restored RPE cells with microvilli in HD-SRT lesions. On light microscopy, both HD- and LD-SRT lesions were completely restored with adjacent RPE cells and spared photoreceptors at 1-month post-treatment.

CONCLUSIONS

Although both HD- and LD-SRT lesions had recovered at 1-month post-SRT, LD-SRT lesions healed faster than HD-SRT lesions.

One-Year Functional and Anatomical Outcomes After Selective Retina Therapy With Real-Time Feedback-Controlled Dosimetry in Patients With Intermediate Age-Related Macular Degeneration: A Pilot Study

BACKGROUND AND OBJECTIVES

This pilot study sought to evaluate changes in macular function and drusen volume (DV) after selective retina therapy (SRT) in patients with intermediate age-related macular degeneration (iAMD).

STUDY DESIGN/MATERIALS AND METHODS

Twenty participants with bilateral iAMD were included in this prospective interventional case series study. After titrating pulse energy by real-time feedback-controlled dosimetry, SRT with a wavelength of 527 nm was applied around the macula of one eye of each patient. Changes in best-corrected visual acuity (BCVA), DV within the central 5-mm ring (C5), and retinal sensitivity (RS) of the SRT-treated eyes (treated eyes) and untreated fellow eyes (untreated eyes) were evaluated at baseline and then at 3, 6, 9, and 12 months after treatment using linear mixed models.

RESULTS

The mean BCVA did not change significantly between baseline and 12 months in both treated and untreated eyes (P = 0.06, P = 0.24, respectively), whereas the BCVA increase rate was faster for treated than for untreated eyes at the 12-month visit (-0.072 logMAR; 95% confidence interval [CI], -0.085 to -0.059 logMAR; P = 0.006). The mean cube root transformation of DV (cube root DV) within C5 in the untreated eyes increased significantly from 0.278 ± 0.115 at baseline to 0.295 ± 0.132 mm (P = 0.027) at 12 months, whereas the cube root DV change in treated eyes was not significant (P = 0.553). The rate of increase in the cube root DV was lower in treated than in untreated eyes at the 12-month visit (-0.016 mm; 95% CI, -0.018 to -0.011 mm; P = 0.015). The mean RS was increased from 22.49 ± 2.40 dB to 24.09 ± 2.19 dB (P < 0.001) in the treated eyes, whereas the change of mean RS in the untreated eyes was not significant at the 12-month visit (P = 0.18). The treated eyes had a higher rate of increase in RS than untreated eyes at the 12-month visit (1.012 dB; 95% CI, 0.776-1.251 dB; P = 0.037). The RS change was significantly associated with the interaction between SRT treatment and time (P = 0.028), whereas it was not associated with cube root DV change (P = 0.106). No SRT-related adverse effects were observed in all participants during the 1-year follow-up.

CONCLUSION

Since SRT improved the mean RS and reduced the rate of change in drusen load in the treated eyes, as compared to the untreated eyes, SRT might slow the progression of iAMD. However, further large randomized clinical trials are necessary to confirm the efficacy of SRT for iAMD. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Selective retina therapy for subretinal fluid associated with choroidal nevus

Purpose

To report a case of a patient with subretinal fluid (SRF) associated with choroidal nevus (CN), who was treated with selective retina therapy (SRT) and ultimately achieved resolution of the SRF.

Observations

A 41-year-old man with SRF associated with CN in his right eye (RE) underwent ophthalmologic evaluation, including optic coherence tomography, fluorescein angiography (FA) and indocyanine green angiography. The best corrected visual acuity (BCVA) converted to the logarithm of the minimum angle of resolution (logMAR) was 0.00 in the RE. SRT (532 nm, 1.7 μs pulse duration, 30 pulses in 100Hz; Medical Laser Center Lübeck) was performed with the laser spots equally distributed across the FA leakage area. Until 20 months SRT was repeated several times because the SRF decreased every time in response to SRT, but was not completely resolved and sometimes increased with time. After performing 6 times of SRT session, leakage on FA stopped at 21 months follow-up and SRF was resolved at 31 months. At 60 months after the first SRT, there were no signs of malignant transformation, no SRF, and the BCVA in the RE was 0.22.

Conclusions and Importance

SRT seems to be a useful treatment and proper clinical studies are necessary to establish the best treatment protocol for SRF associated with CN.

Selective retina therapy monitoring by speckle variance optical coherence tomography for dosimetry control

SIGNIFICANCE

Selective retina therapy (SRT) selectively targets the retinal pigment epithelium (RPE) and reduces negative side effects by avoiding thermal damages of the adjacent photoreceptors, the neural retina, and the choroid. However, the selection of proper laser energy for the SRT is challenging because of ophthalmoscopically invisible lesions in the RPE and different melanin concentrations among patients or even regions within an eye.

AIM

We propose and demonstrate SRT monitoring based on speckle variance optical coherence tomography (svOCT) for dosimetry control.

APPROACH

M-scans, time-resolved sequence of A-scans, of ex vivo bovine retina irradiated by 1.7-μs duration laser pulses were obtained by a swept-source OCT. SvOCT images were calculated as interframe intensity variance of the sequence. Spatial and temporal temperature distributions in the retina were numerically calculated in a 2-D retinal model using COMSOL Multiphysics. Microscopic images of treated spots were obtained before and after removing the upper neural retinal layer to assess the damage in both RPE and neural layers.

RESULTS

SvOCT images show abrupt speckle variance changes when the retina is irradiated by laser pulses. The svOCT intensities averaged in RPE and photoreceptor layers along the axial direction show sharp peaks corresponding to each laser pulse, and the peak values were proportional to the laser pulse energy. The calculated temperatures in the neural retina layer and RPE were linearly fitted to the svOCT peak values, and the temperature of each lesion was estimated based on the fitting. The estimated temperatures matched well with previously reported results.

CONCLUSION

We found a reliable correlation between the svOCT peak values and the degree of retinal lesion formation, which can be used for selecting proper laser energy during SRT.

Towards Automatically Controlled Dosing for Selective Laser Trabeculoplasty

Purpose

Selective laser trabeculoplasty (SLT) is a treatment option for open-angle glaucoma; however, it lacks an instant evidence for successful irradiation. So far ophthalmologists use the visible appearance of permanent champagnelike bubbles (macro bubbles) as an indicator for appropriate pulse energy. We hypothesize that micro bubbles, which start energetically far below the appearance of macro bubbles, already trigger the therapeutic benefit. Here we present two methods to capture the onset of these micro bubbles.

Methods

The trabecular meshwork of freshly enucleated porcine eye globes was irradiated with a series of 15 pulses with a pulse duration of 1.7 μs and with increasing energy at a repetition rate of 100 Hz per each spot of 200 μm in diameter. An optical and an optoacoustic method have been developed and appropriate algorithms investigated towards the real-time detection of the onset of micro bubbles.

Results

Both observation methods are capable of detecting micro bubble nucleation. Threshold radiant exposures were found at 310 ± 137 mJ/cm². By combination of both methods a sensitivity and specificity of 0.96 was reached.

Conclusions

In case that the therapeutically demanded pressure reduction is already achieved with these micro bubbles, which needs to be proven clinically, then the methods presented here can be used in an automatic feedback loop controlling the laser irradiation. This will unburden the clinicians from any dosing during SLT.

Translational Relevance

Automatic real-time pulse energy dosing based on the formation of micro bubbles in SLT significantly improves and facilitates the treatment for the physician.

Selective Retina Therapy Reduces Bruch's Membrane Thickness and Retinal Pigment Epithelium Pathology in Age-Related Macular Degeneration Mouse Models

Purpose

To investigate the effect of selective retina therapy (SRT) on age-related macular degeneration (AMD)-like alterations of retinal pigment epithelium (RPE) and Bruch's membrane (BrM) in AMD mouse models as therapeutic approach for the treatment of dry AMD.

Methods

In B6.129P2-Apoe^tm1Unc/J (ApoE^−/−) and B6.129X1-Nfe2I2^tm1Ywk/J (NRF2^−/−), one randomized eye of each mouse in groups of 15 mice was treated by SRT (532 nm, 300 ms, ∼1.4-μs pulse, 100 Hz, 50-μm spot), the fellow eye and healthy C57BL/6J mice served as controls. Clinical examinations were obtained at treatment day and 1 month later, followed by enucleation to analyze BrM thickness and ultrastructural RPE morphology.

Results

Nearly all ApoE^−/− and NRF2^−/− mice showed AMD-like retinal alterations. BrM thickness was increased in both mouse models, RPE had vacuoles within the cell body and shortened apical microvilli. SRT neither affected neuroretinal anatomy nor function. BrM thickness as well as AMD-like ultrastructural alterations of the RPE were significantly reduced in laser-treated eyes compared with fellow control and untreated control eyes.

Conclusions

SRT reduces BrM thickness and AMD-like RPE alterations in AMD mouse models without damage to structural or functional properties of neuroretina. It may be a prophylactic or therapeutic option for dry AMD.

Translational Relevance

SRT shows therapeutic effectivity in murine AMD models and might therefore become an option for the treatment of dry AMD.

Retinal Laser Therapy Preserves Photoreceptors in a Rodent Model of MERTK-Related Retinitis Pigmentosa

Purpose

We investigated the effects of various retinal laser therapies on preservation of the photoreceptors in an animal model of Mer tyrosine kinase receptor (MERTK)-related retinitis pigmentosa (RP). These modalities included photocoagulation with various pattern densities, selective RPE therapy (SRT), and nondamaging retinal therapy (NRT).

Methods

Laser treatments were performed on right eyes of RCS rats, using one of three laser modalities. For photocoagulation, six pattern densities (spot spacings of 0.5, 1, 1.5, 3, 4, and 5 spot diameters) were delivered in 19-day-old animals, prior to the onset of photoreceptor degeneration, to determine the optimal treatment density for the best preservation of photoreceptors. The left eye was used as control. Rats were monitored for 6 months after treatment using electroretinography, optical coherence tomography, and histology.

Results

Photocoagulation resulted in long-term preservation of photoreceptors, manifested morphologically and functionally, with the extent of the benefit dependent on the laser pattern density. Eyes treated with a 1.5 spot size spacing showed the best morphologic and functional preservation during the 6-month follow-up. SRT-treated eyes exhibited short-term morphologic preservation, but no functional benefit. NRT-treated eyes did not show any observable preservation benefit from the treatment.

Conclusions

In a rodent model of MERTK-related RP, pattern photocoagulation of about 15% of the photoreceptors (1.5 spot diameter spacing) provides long-term preservation of photoreceptors in the treatment area.

Translational Relevance

Availability of retinal lasers in ophthalmic practice enables rapid translation of our study to clinical testing and may help preserve the sight in patients with photoreceptor degeneration.

Selective retina therapy: toward an optically controlled automatic dosing

Selective retina therapy (SRT) targets the retinal pigment epithelium (RPE) with pulsed laser irradiation by inducing microbubble formation (MBF) at the intracellular melanin granula, which leads to selective cell disruption. The following wound healing process rejuvenates the chorio-retinal junction. Pulse energy thresholds for selective RPE effects vary intra- and interindividually. We present the evaluation of an algorithm that processes backscattered treatment light to detect MBF as an indicator of RPE cell damage since these RPE lesions are invisible during treatment. Eleven patients with central serous chorioretinopathy and four with diabetic macula edema were treated with a SRT system, which uses a wavelength of 527 nm, a repetition rate of 100 Hz, and a pulse duration of 1.7 μs. Fifteen laser pulses with stepwise increasing pulse energy were applied per treatment spot. Overall, 4626 pulses were used for algorithm parameter optimization and testing. Sensitivity and specificity were the metrics maximized through an automatic optimization process. Data were verified by fluorescein angiography. A sensitivity of 1 and a specificity of 0.93 were achieved. The method introduced in this paper can be used for guidance or automatization of microbubble-related treatments like SRT or selective laser trabeculoplasty.

Motion-invariant SRT treatment detection from direct M-scan OCT imaging

PURPOSE

Selective retina therapy (SRT) is a laser treatment targeting specific posterior retinal layers. It is focused on inducing damage to the retinal pigment epithelium (RPE), while sparing other retinal tissue compared to traditional photocoagulation. However, the targeted RPE layer is invisible with most imaging modalities and induced SRT lesions cannot be monitored. In this work, imaging scans acquired from an experimental setup that couples the SRT laser beam with an optical coherence tomography (OCT) beam are analyzed in order to evaluate the treatment as they occur.

METHODS

We isolated a small part of the time-resolved scan corresponding to the end of the treatment, for which we have microscopic evidence of the SRT outcome. We then use a convolutional neural network to correspond each scan to the treatment result. We explore which aspects of the scan convey more valuable information for a robust therapy evaluation. By only using this adequately small part, we can achieve an online estimation, while being resilient to eye movement.

RESULTS

The available dataset consists of time- resolved OCT scans of 98 ex vivo porcine eyes, treated with different energy levels. The proposed method yields high performance in the task of predicting whether the applied energy was adequate for SRT treatment, by focusing on the immediate OCT signal acquired during treatment time.

CONCLUSIONS

We propose a strategy toward online noninvasive SRT treatment assessment, able to provide a satisfying evaluation of a treatment status, that therefore could be used for the planning of the treatment continuation.

Selective Retina Therapy with Real-Time Feedback-Controlled Dosimetry for Treating Acute Idiopathic Central Serous Chorioretinopathy in Korean Patients

PURPOSE

To evaluate short-term treatment outcomes following selective retina therapy (SRT) with real-time feedback-controlled dosimetry in Korean patients with acute idiopathic central serous chorioretinopathy (CSC).

METHODS

Sixteen eyes (16 patients) with acute idiopathic CSC (symptom duration < 3 months) were included in this retrospective study. All patients underwent a single session of SRT with real-time feedback-controlled dosimetry. Best-corrected visual acuity (BCVA) and central foveal thickness (CFT) before and 3 months after treatment were examined and compared.

RESULTS

The logarithm of minimal angle of resolution BCVA was significantly better 3 months after treatment (0.16 ± 0.18) than at the time of diagnosis (0.27 ± 0.18, P = 0.002). Additionally, subretinal fluid had resolved in all 16 eyes 3 months after treatment and CFT was significantly lower 3 months after treatment (215.6 ± 17.9 μm) than at baseline (441.4 ± 124.8 μm, P < 0.001). No notable SRT-related complications were observed during the study period.

CONCLUSION

The results of the present study suggest that SRT is a useful therapeutic option for patients with acute idiopathic CSC. Further studies are required to better understand the long-term efficacy of this treatment. This trial is registered with clinical trial registration number NCT03339856.

Variability of panretinal photocoagulation lesions across physicians and patients. Quantification of diameter and intensity variation

BACKGROUND

Photocoagulation lesion intensity relies on the judgement of retinal blanching. Lesions turn out variable due to observer-dependent judgement and time dependency of blanching. We investigated lesion variability per patient and per physician in clinical routine treatments.

METHODS

In this observational clinical trial, different physicians performed panretinal photocoagulation for diabetic retinopathy. Study eyes received 20-30 study lesions at 20 ms (three physicians, nine eyes) and 200 ms (four physicians, 12 eyes) irradiation time (532 nm continuous wave photocoagulator, 300 μm spot size). Lesions were imaged after 1 hour with photography and optical coherence tomography (OCT). We measured lesion diameters in fundus and OCT images, and graded intensities according to a previously published six-step classifier.

RESULTS

200-ms lesions were larger and more severe (568, 474-625 μm [median, IQR], predominantly class 6) than 20-ms lesions (397, 347-459 μm, predominantly classes 3-4). The impact of laser power was small compared to other factors. Lesion intensities and diameters in fundus and OCT images varied significantly between patients and between physicians. Median photographic lesion diameters varied by up to a factor of 1.61 (20 ms) or 1.5 (200 ms) respectively.

CONCLUSIONS

In this study, the treated area of retina varied by up to a factor of 1.61² = 2.59 for a given spot number. As clinical efficacy depends on the treated area, which is a function of lesion number by area per lesion, our results implicate poor control of the overall treatment effect if treatments are administered according to lesion number or spacing alone. Better ways of laser effect control should be sought.

Automatic assessment of time-resolved OCT images for selective retina therapy

Purpose

In recent years, selective retina laser treatment (SRT), a sub-threshold therapy method, avoids widespread damage to all retinal layers by targeting only a few. While these methods facilitate faster healing, their lack of visual feedback during treatment represents a considerable shortcoming as induced lesions remain invisible with conventional imaging and make clinical use challenging. To overcome this, we present a new strategy to provide location-specific and contact-free automatic feedback of SRT laser applications.

Methods

We leverage time-resolved optical coherence tomography (OCT) to provide informative feedback to clinicians on outcomes of location-specific treatment. By coupling an OCT system to SRT treatment laser, we visualize structural changes in the retinal layers as they occur via time-resolved depth images. We then propose a novel strategy for automatic assessment of such time-resolved OCT images. To achieve this, we introduce novel image features for this task that when combined with standard machine learning classifiers yield excellent treatment outcome classification capabilities.

Results

Our approach was evaluated on both ex vivo porcine eyes and human patients in a clinical setting, yielding performances above 95 % accuracy for predicting patient treatment outcomes. In addition, we show that accurate outcomes for human patients can be estimated even when our method is trained using only ex vivo porcine data.

Conclusion

The proposed technique presents a much needed strategy toward noninvasive, safe, reliable, and repeatable SRT applications. These results are encouraging for the broader use of new treatment options for neovascularization-based retinal pathologies.

Half-dose photodynamic therapy followed by diode micropulse laser therapy as treatment for chronic central serous chorioretinopathy: evaluation of a prospective treatment protocol

PURPOSE

To evaluate the outcome of a prospective protocol for the treatment of chronic central serous chorioretinopathy (CSC).

METHODS

Interventional prospective case series in 59 eyes (59 patients) with active chronic CSC. All patients were first treated with indocyanine green angiography (ICGA)-guided half-dose photodynamic therapy (PDT). In case of persistent serous subretinal fluid (SRF) after a follow-up period of at least 6 weeks, ICGA-guided PDT was repeated. If the SRF persisted after two PDT treatments, additional ICGA-guided high-density subthreshold diode micropulse laser (HSML) therapy was performed. Clinical evaluation included best-corrected visual acuity (BCVA), fundoscopy, OCT, fundus autofluorescence, fluorescein angiography and ICGA.

RESULTS

After a single PDT treatment, complete resolution of SRF was seen in 37 of 59 eyes. Of the 22 eyes with no complete resolution of SRF, 19 eyes received a second PDT treatment, after which seven eyes of the 19 eyes showed a complete resolution of SRF. Ten eyes underwent HSML, of which one eye had complete resolution of SRF within 7 weeks. At final follow-up a complete resolution of SRF was present in 80% of all eyes. The mean BCVA improved from 0.28 logMAR at baseline to 0.16 logMAR at final follow-up. Improvement of BCVA was highest after the first treatment (-0.12 logMAR, p < 0.001).

CONCLUSIONS

The proposed treatment strategy using half-dose PDT and HSML in active chronic CSC resulted in an anatomical success rate of 80%. The first half-dose PDT treatment has the highest likelihood of a favourable treatment response on OCT and BCVA increase.

Selective Retina Therapy in Acute and Chronic-Recurrent Central Serous Chorioretinopathy

PURPOSE

Selective retina therapy (SRT), the confined laser heating and destruction of retinal pigment epithelial cells, has been shown to treat acute types of central serous chorioretinopathy (CSC) successfully without damaging the photoreceptors and thus avoiding laser-induced scotoma. However, a benefit of laser treatment for chronic forms of CSC is questionable. In this study, the efficacy of SRT by means of the previously used 1.7-µs and shorter 300-ns pulse duration was evaluated for both types of CSC, also considering re-treatment for nonresponders.

MATERIAL AND METHODS

In a two-center trial, 26 patients were treated with SRT for acute (n = 10) and chronic-recurrent CSC (n = 16). All patients presented with subretinal fluid (SRF) in OCT and leakage in fluorescein angiography (FA). SRT was performed using a prototype SRT laser system (frequency-doubled Q-switched Nd:YLF-laser, wavelength 527 nm) with adjustable pulse duration. The following irradiation settings were used: a train of 30 laser pulses with a repetition rate of 100 Hz and pulse durations of 300 ns and 1.7 µs, pulse energy 120-200 µJ, retinal spot size 200 µm. Because SRT lesions are invisible, FA was always performed 1 h after treatment to demonstrate laser outcome (5-8 single spots in the area of leakage). In cases where energy was too low, as indicated by missing FA leakage, energy was adjusted and the patient re-treated immediately. Observation intervals were after 4 weeks and 3 months. In case of nonimprovement of the disease after 3 months, re-treatment was considered.

RESULTS

Of 10 patients with active CSC that presents focal leakage in FA, 5 had completely resolved fluid after 4 weeks and all 10 after 3 months. Mean visual acuity increased from 76.6 ETDRS letters to 85.0 ETDRS letters 3 months after SRT. Chronic-recurrent CSC was characterized by less severe SRF at baseline in OCT and weaker leakage in FA than in acute types. Visual acuity changed from baseline 71.6 to 72.8 ETDRS letters after 3 months. At this time, SRF was absent in 3 out of 16 patients (19%), FA leakage had come to a complete stop in 6 out of 16 patients (38%). In 6 of the remaining chronic CSC patients, repeated SRT with higher pulse energy was considered because of persistent leakage activity. After the re-treatment, SRF resolved completely in 5 patients (83.3%) after only 25 days.

CONCLUSION

SRT showed promising results in treating acute CSC, but was less effective in chronic cases. Interestingly, re-treatment resulted in enhanced fluid resolution and dry conditions after a considerably shorter time in most patients. Therefore, SRT including re-treatment if necessary might be a valuable CSC treatment alternative even in chronic-recurrent cases.

Tissue response of selective retina therapy by means of a feedback-controlled energy ramping mode

BACKGROUND

The purpose of the study was to evaluate the safety and selectivity of the retinal pigment epithelium lesions by using automatic energy ramping and dosimetry technique for selective retina therapy and to investigate the healing response.

METHODS

Ten eyes of Chinchilla Bastard rabbits were treated with an automatic dosage controlled selective retina therapy laser (frequency doubled Q-switched Nd:YLF, wavelength: 527 nm, pulse duration: 1.7 μs, repetition rate: 100 Hz, pulse energy: linear increasing from pulse to pulse up to shut down - maximal 110 μJ, max. number of pulses in a burst: 30, retinal spot diameter: 133 μm). After treatment, fundus photography, optical coherence tomography and fluorescein angiography were performed at three time points from 1 h to 3 weeks. Histological analysis was performed.

RESULTS

A total of 381 selective retina therapy laser spots were tested (range 13-104 μJ).Typical fundus photographs obtained at 1 h after irradiation showed that 379 out of 381 lesions produced by selective retina therapy were not visible ophthalmoscopically and the lesions could be detected by angiography only. Optical coherence tomography images revealed that the structure of photoreceptors was preserved, but a disrupted retinal pigment epithelium layer was observed as was expected. By 3 weeks, histology showed selective retinal pigment epithelium damage without any effect on the inner retina and focal proliferation of the retinal pigment epithelium layer.

CONCLUSIONS

Automatically controlled selective retina therapy is a significant improvement in this innovative treatment. It could be demonstrated that the non-contact, reflectometric technique with a controlled pulse energy ramp is safe and selective.

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.

Online optical coherence tomography during subthreshold laser irradiation

PURPOSE

To investigate the role of real-time optical coherence tomography (OCT) in the detection of standard and nonvisible subthreshold laser irradiation.

METHODS

We used an integrated platform consisting of a slit-lamp, a digital camera, a slit-lamp mounted OCT, and a 532-nm laser photocoagulator (Topcon Inc., Tokyo, Japan). The laser aiming beam and the OCT scan were aligned to obtain real-time tomographic imaging of the irradiated area during laser exposure. Standard and subthreshold laser irradiation and simultaneous OCT acquisition were tested in artificial and biological samples. Laser testing cards were chosen as artificial samples. Freshly enucleated pig eyes were used for iris irradiation.

RESULTS

Ophthalmoscopically visible reference burns were placed on the laser testing card in 2 parallel lines. Then, a series of laser spots with the same size and duration but different power were placed between the reference burns. Online OCT during laser irradiation detected changes in the reflectivity profile of the artificial sample at a power of 200 mW, in absence of ophthalmoscopically visible lesions. Similarly, reference burns were placed on pig iris and between them various laser spots were performed at ranging powers. Changes in the iris optical properties, as detected with online OCT, were produced with a power of 860 mW in absence of visible endpoint.

CONCLUSIONS

Online OCT is able to identify non-ophthalmoscopically visible lesions during subthreshold laser irradiation either in artificial samples or in pig iris.

Selective retina therapy (SRT) in patients with geographic atrophy due to age-related macular degeneration

BACKGROUND

For geographic atrophy (GA) due to age-related macular degeneration (AMD) there is so far no approved treatment option. Usually, increased autofluorescence (AF) levels of different patterns adjacent to the atrophic area indicate lipofuscin-laden retinal pigment epithelium (RPE) cells at a high risk for apoptosis. Herein, SRT was used to selectively treat these cells to stimulate RPE proliferation, in order to reduce or ideally stop further growth of the atrophic area.

MATERIAL AND METHODS

Six eyes of six patients with bilateral equally pronounced GA were treated by SRT, while the fellow eye served as control. Irradiation was performed using a prototype SRT laser (Medical Laser Center Lübeck, Nd:YLF laser; 527 nm; 200 ns/1.7 micros pulse duration; 30 repetitive pulses at 100 Hz). Test lesions with increasing energies were applied at the lower vessel arcade to determine the individual angiographic and ophthalmoscopic threshold radiant exposures. Treatment was then performed in the area of increased AF adjacent to the GA using energies between both thresholds. The GA progression rates of treated and fellow eyes were evaluated.

RESULTS

After a 1-year follow-up, a progression of the atrophic area was observed in the treated eyes (0.7-8.0 mm(2)/yr, mean 3.0 mm(2)/yr; 46%/yr) whereas the progression rates of the fellow eyes were insignificantly lower (0.46-4.04 mm(2)/yr, mean 1.9 mm(2)/yr; 30%/yr; p = 0.134). The progression rate in the treated eyes of two patients increased significantly, while in the other four patients, the progression rates were nearly the same between both eyes. Moreover, one of these two eyes showed an unexpected RPE reaction after treatment, since all laser lesions led to RPE atrophy and thus an accelerated enlargement of the GA occurred.

CONCLUSION

SRT in the hyperautofluorescent areas of GA was not able to stop or slow down the progression of GA. However, modified treatment strategies might be more promising, e.g. placing the spots outside the hyperautofluorescent areas where RPE apoptosis is postulated. Moreover, SRT studies on GA might be more successfully performed on specific subgroups of GA, based on autofluorescence and other findings.

Selective retina therapy (SRT) of chronic subfoveal fluid after surgery of rhegmatogenous retinal detachment: three case reports

BACKGROUND

Shallow subfoveal fluid accumulation after successful surgery for retinal detachment can be the reason for compromised visual acuity. To date, therapeutical options to tackle this problem have not been established. Selective retina therapy (SRT) is a new laser technology that uses a train of mus-laser pulses to selectively damage retinal pigment epithelial (RPE) cells while sparing retinal structures.

METHODS

We treated three patients with chronic subfoveal fluid accumulation after retinal detachment surgery. The median period between retinal surgery and SRT treatment was 7 months. For SRT, we used a prototype frequency-doubled, Q-switched Nd:YLF laser (lambda = 527 nm). Each laser exposition contained 30 pulses (t = 1,7 micros, 100 Hz, E = 100-400 microJ). Two of the three patients were treated subfoveally. OCT III (optical coherence tomography) examinations were performed to evaluate changes in subretinal fluid accumulation.

RESULTS

In all three patients, we observed complete resolution of subfoveal fluid within 1-5 months. Follow-up has been 16 months to 2 years. Visual acuity improved in all patients. In one patient, cystoid macular edema developed 3 months after treatment. Additional SRT treatments were not necessary.

CONCLUSION

SRT is a safe treatment. Visual acuity improved after SRT, even in subfoveal irradiations. SRT is an option to support subretinal fluid reabsorption. In this situation where no other therapeutical options are established, SRT may be a beneficial treatment for chronic subfoveal fluid accumulation after retinal detachment surgery.

Selective retina therapy in patients with central serous chorioretinopathy

BACKGROUND

Central serous chorioretinopathy (CSC) is a disease with a localized breakdown of the outer blood-retinal barrier located within the retinal pigment epithelium (RPE) causing subretinal fluid accumulation. Selective retina therapy (SRT) is a new, minimally invasive laser technology that has been designed to selectively target the RPE. SRT spares retinal tissue.

METHODS

Twenty-seven eyes of 27 patients with active CSC were treated with SRT using a pulsed double-Q-switched Nd-YLF prototype laser (lambda=527 nm, t=1.7 micros). At baseline, best-corrected visual acuity was determined and fluorescein angiography and optical coherence tomography were performed. The patients were followed for up to 3 months.

RESULTS

After 4 weeks 85.2% of patients showed complete resolution of subretinal fluid and in 96.3% there was no leakage visible on fluorescein angiography. After 3 months 100% of patients demonstrated no subretinal fluid and 100% of patients had no leakage activity on fluorescein angiography. Visual acuity, 20/40 at baseline, improved to 20/28 after 4 weeks and to 20/20 after 3 months.

CONCLUSION

SRT is a safe and effective treatment for active CSC. Especially if the RPE leak is located close to the fovea, SRT is the favoured therapeutic option. We recommend earlier treatment of patients with acute CSC in order to prevent development of chronic changes due to CSC with irreversible anatomical and functional damage. SRT might be considered as a first-line treatment for active CSC.

[Selective Retina Therapy (SRT)]

Selective Retina Therapy (SRT) is a new and very gentle laser method developed at the Medical Laser Center Lübeck. It is currently investigated clinically in order to treat retinal disorders associated with a decreased function of the retinal pigment epithelium (RPE). SRT is designed to selectively effect the RPE while sparing the neural retina and the photoreceptors as well as the chorioidea. Aim of the therapy is the rejuvenation of the RPE in the treated areas, which should ideally lead to a long term metabolic increase at the chorio-retinal junction. In contrast to conventional laser photocoagulation, which is associated with a complete thermal necrosis of the treated site, SRT completely retains full vision. This paper reviews the methods and mechanisms behind selective RPE effects and reports the first clinical results. An online dosimetry technique to visualize the ophthalmoscopically invisible effects is introduced.

[Selective retina therapy in patients with diabetic maculopathy]

Selective Retina Therapy (SRT) is a new laser treatment that selectively targets the retinal pigmen epithelium (RPE). In this study, we treated 39 patients presenting with nonischemic, focal and focal-diffuse diabetic maculopathy with SRT. In the main. the results indicate that SRT had stabilizing effects on visual acuity, angiographic leakage, lipid exudation, and foveal retinal thickness. SRT is safe and is especially useful for treating pathologies that are located close to the fovea, which cannot be treated with conventional argon laser photocoagulation.

Selektive Retinatherapie

Selective retina therapy (SRT) is currently under evaluation, as a new and very subtle laser method, for the treatment of retinal disorders associated with a degradation of the retinal pigmentary epithelium (RPE). SRT makes it possible to selectively effect the RPE, sparing the adjacent neural retina with the photoreceptors and also the choroid below the RPE. In the best case, the therapy leads to regeneration of the RPE and a long-term metabolic increase at the chorio-retinal junction. In contrast to conventional laser photocoagulation, which is associated with complete thermal necrosis of and around the treated site, absolutely no scotoma occurs in SRT. This paper reviews the methods and mechanisms behind the selective effects of the RPE. In vitro and preclinical results are used to describe the bandwidth of selective effects with respect to different irradiation settings. An optoacoustic technique is introduced to visualize effects that cannot be seen by ophthalmoscopy and to facilitate dosimetry control without recourse to angiography completes the report.

Cell disintegration by laser-induced transient microbubbles and its simultaneous monitoring by interferometry

Selective retina treatment (SRT) is a novel short pulsed laser therapy of several retinal diseases associated with a decreased metabolism at the retinal pigment epithelium (RPE). The range of laser pulse energies is small, in which the desired selective RPE disintegration is achieved without adverse effects to the neural retina. Thus, a real-time dosimetry control is required. We investigated a noninvasive interferometric technique able to monitor microbubble formation around the intracellular melanin granula, which is the origin of the desired RPE damage. A porcine ex vivo RPE model was irradiated by single pulses (350 ns1.7 mus) of a neodymium: yttrium lithium fluoride laser (527 nm). The specimen was simultaneously probed by a Michelson interferometer (helium neon-laser: 633 nm) and by a hydrophone. Cell viability assays (Calcein-AM) were performed after irradiation. At threshold radiant exposure for cell death (ED(50)=129+/-5 mJ cm2 for 350 ns; ED50=180+/-5 mJ cm2 for 1.7 mus), the interferometric transients changed due to microbubble formation. No major differences in the bubble dynamics were observed between both pulse durations. An algorithm to determine cell death from the interferometric transients showed less than 10% false positive or false negative results for the applied laser expositions compared to the viability assay. Interferometry is a reliable noncontact technique to monitor RPE disintegration and may serve as real-time dosimetry control during SRT.