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. 2015 Dec 4;7(1):13-21.
doi: 10.1364/BOE.7.000013. eCollection 2016 Jan 1.

Retinal safety of near infrared radiation in photovoltaic restoration of sight

H Lorach  1 , J Wang  1 , D Y Lee  2 , R Dalal  3 , P Huie  1 , D Palanker  1
Affiliations

Retinal safety of near infrared radiation in photovoltaic restoration of sight

H Lorach et al. Biomed Opt Express. .

Abstract

Photovoltaic restoration of sight requires intense near-infrared light to effectively stimulate retinal neurons. We assess the retinal safety of such radiation with and without the retinal implant. Retinal damage threshold was determined in pigmented rabbits exposed to 880nm laser radiation. The 50% probability (ED50) of retinal damage during 100s exposures with 1.2mm diameter beam occurred at 175mW, corresponding to a modeled temperature rise of 12.5°C. With the implant, the same temperature was reached at 78mW, close to the experimental ED50 of 71mW. In typical use conditions, the retinal temperature rise is not expected to exceed 0.43°C, well within the safety limits for chronic use.

Keywords: (170.0170) Medical optics and biotechnology; (170.4470) Ophthalmology.

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Figures

Fig. 1
Fig. 1
Damage threshold determination in normal retina. A) NIR fundus of a rabbit retina 1 hour after irradiation with various intensities (1-6: 350-250-200-175-150-125mW). No lesions were visible at locations 5 and 6. B) OCT of the 350mW (1) and 250mW (2) lesions demonstrates severe retinal damage (whitening) and detachment. C) Mild retinal whitening in the 175mW lesion. No retinal changes were observed with OCT after the 150mW and 125mW exposures.
Fig. 2
Fig. 2
Changes in avascular retina after implantation. OCT reveals changes in the retina above the implant starting at 2 hours after the implantation.
Fig. 3
Fig. 3
Retinal damage above the implants after irradiation with increasing power. (A) Implanted retina before irradiation. (B) In the same retina, no damage can be seen at 60mW, but mild whitening is detectable at 90mW (C), pointed by the yellow arrow. (D) Severe damage and detachment occurs at 125mW.
Fig. 4
Fig. 4
Temperature rise in the retina. A) Spatial distribution of the temperature rise in the rabbit eye at the end of the 100s long irradiation. The temperature rise is maximum at RPE, and it rapidly drops with distance. Small absorption of the 880nm radiation in water results in slight elevation of temperature on the beam axis. B) Comparison of the thermal modeling to direct temperature measurements. Optoacoustic measurements of the RPE temperature rise during 810nm illumination by a 2mm wide beam of 129mW (dashed lines, OA1 and OA2) are plotted along the RPE temperature computed with our model using the same beam characteristics (blue curve). Experimental data replotted from (Kandulla, Elsner et al. 2006) with permission. C) Temperature rise as a function of power (dash line) plotted along with the probability of retinal damage (solid line) for the normal (red) and implanted (green) retina. At 175mW, corresponding to the ED50 in normal retina, the temperature rise reaches 12.5°C. With an implant, the same temperature is reached at 78mW (intersection between green and yellow dash lines), matching the experimental thresholds (solid green curve) with ED50 at 71mW.
Fig. 5
Fig. 5
Modeled temperature rise as a function of the beam size, implant size and duty cycle. A) Temperature increases with increasing beam diameter (5mW/mm2) has an inflexion point when beam exceeds the 2mm implant size. B) With a constant beam size of 4.5mm, temperature increases with increasing implant diameter. C-D) Pulsing light (5ms, 40Hz) generates temperature spikes of about 0.05°C, oscillating around the blue line corresponding to the average power.
Fig. 6
Fig. 6
Modular implant and its axio-symmetric model. A) Implant composed of 7 disks in a hexagonal pattern is modeled B) by an axio-symmetric structure composed of a central disk and a ring separated by a 200μm gap. C) A solid implant with same total diameter is used for comparison.
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