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Vivek P Vasuki, Puneet Singh Braich, Dane Stewart, Vikram Brar; Stereoscopic infrared imaging of the optic nerve in glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):915.
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Evaluation of cup to disc ratios has not been explored using infrared technology, although it is widely known that infrared light penetrates deeper into the eye than conventional imaging modalities. We aim to evaluate whether stereoscopic infrared (SIR) photography provides an enhanced assessment of the cup to disc ratio compared to stereoscopic color (SC) and red-free (SRF) images.
Seventeen eyes diagnosed with glaucoma or as glaucoma suspects were evaluated. Eyes with concurrent vitreoretinal disease or significant media opacities were excluded. All eyes received SIR, SC, and SRF photos in addition to spectral domain OCT imaging. All data was de-identified and presented randomly before being analyzed to avoid bias by sequential comparison of the same eye. Horizontal and vertical cup to disc ratios were measured by a single ophthalmologist. A pairwise comparison was made between all 3 groups with a stringent Bonferroni correction of the p-value (i.e. p was not 0.05, but 0.0167).
The mean of the differences in vertical cup to disc ratios were 0.07 (SC vs. SRF, p < 0.01), 0.11 (SC vs. SIR, p<0.01) and 0.04 (SIR vs. SRF, p =0.08). The mean differences in horizontal cup to disc ratios were 0.11 (SC vs. SRF, p < 0.01), 0.11 (SC vs. SIR, p<0.01) and 0.006 (SIR vs. SRF, p =0.81). When SC photos revealed a vertical cup to disc ratio of less than 0.45, neither of the other modalities deviated by more than 0.1 of that assessment. However, when vertical cup to disc ratios were larger than 0.5 on SC photos, 40% of the time SRF photos were able to find an additional difference of 0.15 (p<0.01). SIR was able to detect a 0.15 additional difference 50% of the time (p<0.01). When horizontal cup to disc ratios were larger than 0.5 on SC photos, 24% of the time SRF and SIR photos were able to find an additional difference of 0.15 (p<0.01). The range of differences measured between techniques was 0-0.3. The greatest difference in examiner estimation was noted in eyes with cup to disc ratios larger than 0.5.
Our results suggest that a larger estimation of horizontal and vertical cup to disc ratios is possible with stereoscopic infrared imaging compared to color stereoscopic photos. This suggests that more of the optic cup is being visualized with infrared imaging, particularly in eyes with ratios higher than 0.5. A larger sample size may indicate that SIR measures larger vertical cup to disc ratios than SRF imaging.
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