Transscleral visible/near-infrared spectroscopy for quantitative assessment of haemoglobin in experimental choroidal tumours.

Purpose: To study the feasibility of using transscleral visible/near-infrared spectroscopy (Vis/NIRS) to estimate the content of haemoglobin in choroidal tumour phantoms of ex vivo porcine eyes. Methods: Thirty enucleated porcine eyes were prepared with a tumour phantom made by injecting a suspension of gelatine, titanium dioxide and human blood into the suprachoroidal space. The blood concentrations used were 2.5%, 25% and 50%, with 10 eyes in each group. Alternating Vis/NIRS measurements were taken over the phantom inclusion and on the opposite (normal) side of each eye. For statistical analysis, a genetic algorithm was utilized to suppress insignificant wavelengths in the spectra. The processed spectra were then used to build a regression model based on partial least squares regression and evaluated by twofold cross-validation. Results: Ultrasonography revealed that all phantoms were localized within the suprachoroidal space with no penetration through the retina. The largest mean diameters of the phantoms with 2.5%, 25% and 50% blood were 15.5, 15.2 and 15.7 mm, respectively (p > 0.05). The largest mean thicknesses were 4.5, 4.5 and 4.8 mm, respectively (p > 0.05). Statistical analysis of the spectral data showed that it was possible to correctly discriminate between the normal side and the tumour phantom side of the eyes in 99.88% of cases. The phantoms could be correctly classified according to their blood concentrations in 99.42% of cases. Conclusions: This study demonstrates that transscleral Vis/NIRS is a feasible and accurate method for the detection of choroidal tumours and to assess the haemoglobin content in such lesions.