Abstract
Purpose :
To detect early changes of Retinal Nerve Fiber Layer (RNFL) in axons of different diameter using specialized multiwavelength configured fundus imaging in vivo in rats with experimentally elevated Intraocular Pressure (IOP). Previous in vitro experiments demonstrated that reflectance of axons with different size depends on wavelength. Abnormalities of the RNFL thickness have been previously correlated to the reflectance optical characteristic of retinal cylindrical structures by in vitro experiments. However, this knowledge must be transferred into in vivo applications for diagnosis of the diseases like glaucoma. We hypothesize that specialized multiwavelength configured fundus imaging can observe the reflectance of RNFL cylindrical structures based on IOP pressure to correlate low IOP with short wavelengths and high IOP with long wavelengths in vivo.
Methods :
Spectral reflectance in the wavelength range 532nm to 670nm was assessed in 10 healthy female Long Evans rats using a custom-made optical system allowing fine adjustment of animal positioning and retinal focus. IOP was measured using a Tonolab Tomometer. In 5 rats Ocular hypertension (OHT) was induced with intracameral injection of silicon oil, while 5 rats were used as untreated controls. One week later, spectral reflectance was remeasured in both control and OHT, data normalized, and compared with baseline results. Spectral RNFL reflectance vs. IOP was established for both control and OHT groups.
Results :
Both control and OHT group reflectance measurements showed inversely correlated response to changes in wavelength prior to inducing OHT. The control group showed no change in the RNFL reflectance spectral response after one week. Reflectance spectral response of the OHT group showed positive (direct correlation) response at short wavelengths and negative response (inverse correlation) at longer wavelengths with the transition occurring around 600nm.
Conclusions :
Our results show that the RNFL reflectance spectral response in vivo correlates IOP characteristics with wavelength. Mild IOP increase cause changes of the spectra to occur at short wavelengths. Bundles with high IOP have a flat spectral response.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.