Polarimetric calibration of a spectropolarimeter instrument with high precision: Sunrise chromospheric infrared spectropolarimeter (SCIP) for the sunrise iii balloon telescope.

The Sunrise chromospheric infrared spectropolarimeter (SCIP) installed in the international balloon experiment sunrise iii will perform spectropolarimetric observations in the near-infrared band to measure solar photospheric and chromospheric magnetic fields simultaneously. The main components of SCIP for polarization measurements are a rotating wave plate, polarization beam splitters, and CMOS imaging sensors. In each of the sensors, SCIP records the orthogonal linearly polarized components of light. The polarization is later demodulated on-board. Each sensor covers one of the two distinct wavelength regions centered at 770 and 850 nm. To retrieve the proper circular polarization, the new parameter R, defined as the 45° phase shifted component of Stokes V in the modulation curve, is introduced. SCIP is aimed at achieving high polarization precision (1σ<3×10-4 of continuum intensity) to capture weak polarization signals in the chromosphere. The objectives of the polarization calibration test presented in this paper are to determine a response matrix of SCIP and to measure its repeatability and temperature dependence to achieve the required polarization precision. Tolerances of the response matrix elements were set after considering typical photospheric and chromospheric polarization signal levels. We constructed a feed optical system such that a telecentric beam can enter SCIP with the same f-number as the light distribution instrument of the sunrise iii telescope. A wire-grid linear polarizer and achromatic wave plate were placed before SCIP to produce the known polarization. The obtained response matrix was close to the values expected from the design. The wavelength and spatial variations, repeatability, and temperature dependence of the response matrix were confirmed to be smaller than tolerances.

Light-absorbing properties and osmolarity of indocyanine-green depending on concentration and solvent medium.

PURPOSE: To evaluate the absorption spectrum and osmolarity of three currently used indocyanine green (ICG) products at different concentrations and with different solvent media. METHODS: The absorption spectrum and osmolarity of three different ICG products (Pulsion, Munich, Germany; Akorn, Buffalo Grove, IL; and Laboratoires SERB, Paris, France) were analyzed. Each ICG was further diluted with balanced salt solution or glucose 5%. Four different concentrations were evaluated: 0.005%, 0.0025%, 0.001%, and 0.00025%. ICG (Pulsion) diluted in viscoelastic material (Healon; Pharmacia, Stockholm, Sweden) was analyzed at a concentration of 0.0025%. The following parameters were measured: absorption spectrum between 400 and 1000 nm, osmolarity, and the emission spectrum of the light source of a commonly used vitrectomy machine (Megatron; Geuder, Heidelberg, Germany). RESULTS: Independent from the manufacturer, concentrations of 0.005%, 0.0025%, and 0.001% ICG diluted in balanced salt solutions (BSS and BSS Plus; Alcon Pharmaceuticals, Fort Worth, TX) and glucose 5% showed two maxima, one at approximately 700 nm and a second one at 780 nm. There was an increase from zero to maximum absorption between 600 and 700 nm and a return to zero between 800 and 900 nm. The absorption band of ICG diluted in the viscoelastic material was similar to the saline solution (BSS or BSS Plus)-diluted ICG. At lower concentrations of 0.001% or 0.00025%, the peak at 700 nm decreased, forming a shoulder in the curve, whereas the peak at 780 nm remained stable. Osmolarity was in the range of 302 to 313 mOsM for BSS Plus-diluted ICG. When glucose 5% was used for ICG dilution, absorption between 600 and 700 nm decreased, and osmolarity was lower (between 292 and 298 mOsM). The light source emission was between 380 and 760 nm. CONCLUSIONS: Dilution of ICG using the balanced salt solutions BSS or BSS Plus resulted in a steep increase of absorption starting at 600 nm. In clinical practice, there is an overlap between the absorption band of ICG and the emission curve of the light source, resulting in a possible photosensitizing effect, especially at higher ICG concentrations. This effect becomes less likely with decreasing ICG concentrations or when glucose 5% is used as a solvent medium.

Retinal damage from indocyanine green in experimental macular surgery.

PURPOSE: Previous work has shown that indocyanine green (ICG)-assisted peeling of the inner limiting membrane (ILM) may cause retinal damage. In this study, a toxic and a photodynamic effect of ICG at the vitreoretinal interface was assumed. METHODS: Ten human donor eyes were hemisected, and 0.05 mL of 0.05% ICG was poured over the trephined macula in eight eyes. After 1 minute, the dye was drained by irrigation. The macula in each of two eyes was illuminated for 3 minutes with wavelengths of 380 to 760, 380 to 620, or 620 to 760 nm. Two eyes were treated with ICG only, and two eyes were illuminated only. Retinal specimens from the macula and the untreated retina were processed for light and electron microscopy. The irradiance of the light source and the absorption properties of ICG were measured. RESULTS: Exposure of the ICG-stained ILM to wavelengths beyond 620 nm resulted in severe damage to the inner retina, including loss of ILM, cellular disorganization, and fragmentation of the cytoplasm. ICG staining alone or in combination with wavelengths of 380 to 620 nm disclosed rupture of Müller cells with detachment of the ILM, but no other cellular disorganization. Eyes subjected to illumination only showed no abnormalities. CONCLUSIONS: The spectral absorption properties of ICG may account for a possible photodynamic effect of ICG at the vitreoretinal interface. ICG alone induces ILM detachment and disruption of Müller cells even without intentional peeling of the membrane. It is assumed that accumulation of the dye at the vitreomacular interface may enhance the concentration and osmolarity of ICG at the retina beyond intravitreous values and critical limits.