Temperature-Controlled Retinal Photocoagulation Reliably Generates Uniform Subvisible, Mild, or Moderate Lesions

Abstract

Purpose: Conventional retinal photocoagulation produces irregular lesions and does not allow reliable control of ophthalmoscopically invisible lesions. We applied automatically controlled retinal photocoagulation, which allows to apply uniform lesions without titration, and aimed at five different predictable lesion intensities in a study on rabbit eyes.Methods: A conventional 532-nm photocoagulation laser was used in combination with a pulsed probe laser. They facilitated real-time fundus temperature measurements and automatic exposure time control for different predefined time/ temperature dependent characteristics (TTC). We applied 225 control lesions (exposure time 200 ms) and 794 TTC lesions (5 intensities, exposure times 7-800 ms) in six rabbit eyes with variable laser power (20-66.4 mW). Starting after 2 hours, we examined fundus color and optical coherence tomographic (OCT) images over 3 months and classified lesion morphologies according to a seven-stage OCT classifier.Results: Visibility rates in funduscopy (OCT) after 2 hours were 17% (68%) for TTC intensity group 1, 38% (90%) for TTC group 2 and greater than 94% (.98%) for all consecutive groups. TTC groups 1 through 4 correlated to increasing morphological lesion intensities and increasing median funduscopic and OCT diameters. Group 5 lesions were as large as, but more intense than group 4 lesions.Conclusions: Automatic, temperature controlled photocoagulation allows to apply predictable subvisible, mild, or moderate lesions without manual power titration.Translational Relevance: The technique will facilitate standardized, automatically controlled low and early treatment of diabetic retinopathy study (ETDRS) intensity photocoagulation independently of the treating physician, the treated eye and lesion location.

Visualization of Changes in the Choriocapillaris, Choroidal Vessels, and Retinal Morphology After Focal Laser Photocoagulation Using OCT Angiography

“…Strategies such as micropulse laser have been developed that may minimize tissue damage, especially in the macula. 12,35 Recently, Koinzer and associates 36 demonstrated in an animal model that automatic, temperature-controlled laser photocoagulation can predictably induce subvisible, mild, or moderate lesions without manual power titration. Application of fundus temperature measurements during laser photocoagulation would enable clinicians to perform laser photocoagulation while minimizing damage to retinal tissue.…”

Lesion strength control by automatic temperature guided retinal photocoagulation

“…Although these lesions were mostly funduscopically invisible, damage could be seen by the OCT evaluation in the outer retinal layers. 25 This result demonstrates the possibility of temperature/time guided irradiation control for clinically increasingly important subvisible thermal treatments as published. 13,15 Studies on rabbits and patients showed that OCT lesion classes are suitable as endpoint criteria during photocoagulation.…”

“…20 Furthermore, it was shown that the temperature measurement is suitable for an automatic irradiation control by using the measured temperature-dependent optoacoustic pressure amplitudes for a feedback algorithm that shuts off the treatment laser automatically after the desired lesion strength is achieved. 21,24,25 The aim of this work was the further development and investigation of the automatic irradiation time control during photocoagulation toward different degrees of coagulation. Figure 8 shows that for φ A ¼ 1.1 and φ B ¼ 1.12 the lesions are ophthalmoscopically visible on less than 30% of the irradiations.…”

Evolution of Concepts and Technologies in Ophthalmic Laser Therapy

“…The probing laser pulses are applied simultaneously with application of a therapeutic laser to detect temperature rise in tissue during the exposure. Precision of this method is on the order of 1 • C, and this feedback is then used to adjust laser power or pulse duration to ensure predictable outcome of photocoagulation (Koinzer et al 2015).…”