A flexible photoacoustic retinal prosthesis

Abstract

Retinal degenerative diseases of photoreceptors are a leading cause of blindness with no effective treatment. Retinal prostheses aim to restore sight by stimulating residual retinal cells. Here, we present a photoacoustic retinal stimulation technology. We designed a polydimethylsiloxane and carbon-based flexible film that converts near-infrared laser pulses into a localized acoustic field with 51-µm lateral resolution, allowing precise stimulation of mechanosensitive retinal cells. This photoacoustic stimulation robustly and locally modulated retinal ganglion cell activity in both wild-type and degenerated ex vivo rat retinae. In animals subretinally implanted with a millimeter-sized photoacoustic film, pulsed laser stimulation generated neural modulation along the visual pathway to the superior colliculus, as measured by functional ultrasound imaging. The biosafety of the film was confirmed by the absence of short-term adverse effects, while local thermal increases were measured below 1 °C. These findings demonstrate the potential of photoacoustic stimulation for high-acuity visual restoration in blind patients.

Abstract via europepmc.

Flags from extraction

• n_subjects — The paper reports separate group sizes for different sub-experiments rather than one grand total: ex vivo LE retinae n=4 rats, ex vivo P23H retinae n=4 rats, in vivo biocompatibility P23H n=8, in vivo photoacoustic-stimulation LE n=7. These are not necessarily non-overlapping and are given as a list rather than summed.
• exposures[0] — Ultrasound is generated photoacoustically (laser-driven film), not by a conventional piezoelectric transducer; 'fundamental frequency' is the intrinsic acoustic centre frequency of the film (42.2 MHz) rather than a driven electrical frequency, and 'pulse duration'/'PRF'/'duty cycle' map onto the single ~36-ns photoacoustic pulse and laser repetition rate rather than a conventional TUS tone-burst; recorded with a flag given the unusual mapping onto the standard TUS timing fields.
• exposures[0].timing.sonication_duration_s — Combines the ex vivo swept burst-duration range (db=5-30 ms) with the very different in vivo train structure (eight 125-ms bursts within a 2-s train, repeated 15 times); these come from different experiments and are listed together for one target/frequency per the exposure-grouping rule.
• exposures[0].free_field.pressure_kpa — 146.2 kPa is a hydrophone characterisation value at a non-stimulation laser condition (7 µJ/pulse, measured 0.9 mm from the film) and its measurement medium (water vs. tissue) is not explicitly stated; placed in free_field as the best-available characterisation value, distinct from the in-situ (at-target) stimulation pressures (0.05-0.15 MPa) reported elsewhere.
• exposures[0].in_situ.ispta_w_cm2 — ISPTA values (below 0.06 and 0.9 mW/cm2) are stated as upper bounds ('below'), not exact values.
• sham_type — Controls used were stimulus-matched but non-photoacoustic (direct 1030-nm laser on the retina without the film; continuous 595-nm laser light on the retina), which does not match any listed sham_type category cleanly; coded as 'other'.
• adverse_events — Effects observed (photoreceptor thinning, microglial activation) are attributed by the authors to mechanical implantation rather than to the acoustic/photoacoustic stimulation itself.