Spectral Domain OCT in Experimental Glaucoma

Abstract

Purpose: To evaluate retinal nerve fiber layer (RNFL) and macular thickness values in monkeys with experimentally induced glaucoma (ExpG), using Spectralis (Heidelberg Engineering, Heidelberg, Germany, s.v. 5.4.6) and Cirrus (Carl Zeiss Meditec, Dublin, CA, s.v. 6.0.1) spectral domain optical coherence tomography (SD OCT) instruments.

Methods: Six female cynomolgus macaques with ExpG OD, induced via laser scarification of the trabecular meshwork, were used. Untreated OS served as the control. RNFL, optic nerve, macula and single line scans were collected, 2 to 4 of each, using both instruments. Thickness (um) and volume (um3) values, auto-segmented by the instruments (ASeg) and/or manually segmented (MSeg), are shown as mean±sem; significance is p≤0.05, students t test.

Results: Spectralis: ASeg values in ExpG eyes were significantly lower than in controls for RNFL (53±3.4 vs 101±3.0) and macular volume (MV) (8.8±0.22 vs 9.4±0.26). ASeg central macular thickness (CMT) in ExpG eyes was not meaningfully different from controls (263±12.7 vs 245±9.6). Comparison of ExpG and control eye values following Mseg showed the same trend. Aseg overestimated Mseg average RNFL, MV and CMT more in ExpG eyes (27, 10 and 11 % ) than in controls (2, 5 and 4%). Cirrus: ASeg values in ExpG and control eyes for RNFL (52±2.4 vs 94±2.9), MV (9.6±0.25 vs 10.5±0.28) and CMT (228±7.6 vs 223±6.1) showed differences similar to Spectralis data. Macular retinal ganglion cell-inner plexiform layer (GCIPL) thickness in ExpG eyes (53±2.6) was significantly lower than in controls (84±2.8). Average control Aseg values from Spectralis were higher than values from Cirrus for RNFL (108%) and CMT (110%) but lower for MV (90%). Enhanced depth imaging (EDI) improved visualization of the choroid and optic nerve structures: the magnitude of posterior displacement of the lamina cribrosa, as well as prelaminar and laminar tissue thickness. Spectralis image quality averaged 27 for MV and CMT scans and 37 for RNFL scans. Cirrus signal strength averaged 9.6 for optic nerve and 10.0 for mac cube scans.

Conclusions: Both instruments showed significantly lower RNFL, MV and GCIPL values in ExpG eyes than controls, and comparable CMT between eyes. EDI and GCIPL features were useful in the ExpG model. Aseg, was more variable in the ExpG eyes, did not show a consistent instrument bias for all parameters, highlighting the importance of comparing treatments with the same equipment.

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 551 imaging/image analysis: non-clinical • 610 nerve fiber layer