Detection and characterization of glaucoma-like canine retinal tissues using Raman spectroscopy.

Early detection of pathological changes and progression in glaucoma and other neuroretinal diseases remains a great challenge and is critical to reduce permanent structural and functional retina and optic nerve damage. Raman spectroscopy is a sensitive technique that provides rapid biochemical characterization of tissues in a nondestructive and noninvasive fashion. In this study, spectroscopic analysis was conducted on the retinal tissues of seven beagles with acute elevation of intraocular pressure (AEIOP), six beagles with compressive optic neuropathy (CON), and five healthy beagles. Spectroscopic markers were identified associated with the different neuropathic conditions. Furthermore, the Raman spectra were subjected to multivariate discriminate analysis to classify independent tissue samples into diseased/healthy categories. The multivariate discriminant model yielded an average optimal classification accuracy of 72.6% for AEIOP and 63.4% for CON with 20 principal components being used that accounted for 87% of the total variance in the data set. A strong correlation (R2>0.92) was observed between pattern electroretinography characteristics of AEIOP dogs and Raman separation distance that measures the separation of spectra of diseased tissues from normal tissues; however, the underlining mechanism of this correlation remains to be understood. Since AEIOP mimics the pathological symptoms of acute/early-stage glaucoma, it was demonstrated that Raman spectroscopic screening has the potential to become a powerful tool for the detection and characterization of early-stage disease.

Spectral domain optical coherence tomography (SD-OCT) assessment of the healthy female canine retina and optic nerve.

OBJECTIVE: To provide normative data for canine whole retinal thickness (WRT), nerve fiber layer thickness (NFL), photoreceptor layer thickness (PR), and outer nuclear layer thickness (ONL) using spectral domain optical coherence tomography. ANIMAL STUDIED: Twelve healthy adult intact female beagles. PROCEDURE: Horizontal volume scans through the area dorso-temporal from the optic nerve (superior retina), and the area ventro-temporal from the optic nerve (inferior retina) were used to evaluate the thickness of retinal NFL, PR, ONL, and WRT. Peripapillary circular scans were used to evaluate NFL thickness. Statistical analyses were performed to compare the thickness of the individual layers between the superior and inferior retina (paired t-test). One-way analysis of variance (ANOVA) was used to compare the thickness of peripapillary NFL between the superior, inferior, temporal and nasal quadrants of the circle scan. RESULTS: The WRT, PR, and NFL thickness were greater in the superior than in the inferior retina (198.7 ± 9.6 µm vs. 164.4 ± 6.4 µm, P < 0.0001; 95.5 ± 6.5 µm vs. 78.8 ± 7.4 µm, P < 0.0001; and 26.4 ± 1.6 µm vs. 25.0 ± 1.9 µm, P = 0.0236, respectively). No statistical difference was found between the ONL thickness of the superior and inferior retina (50.1 ± 6.4 µm vs. 44.3 ± 3.6, P = 0.0578). Peripapillary NFL thickness showed a similar tendency as the linear scans, with the superior quadrant having the greatest thickness (91.26 ± 7.0 µm) and the inferior quadrant being the thinnest (76.42 ± 9.2 µm) (P < 0.001). CONCLUSIONS: Results of our in vivo studies showed significant differences between thickness values for the superior (tapetal) and inferior (nontapetal) retinal regions.