Primary Application of Time-Domain Analysis of Dynamic Blood Flow Autoregulation in the Optic Nerve of Glaucomatous Monkeys

Abstract

Purpose: : The purpose of the study was to use laser speckle flowgraphy (LSFG) to study dynamic autoregulation of optic nerve head (ONH) in 3 monkeys with unilateral experimental glaucoma (EG).

Methods: : In both normal and EG eyes (laser-induced chronic IOP elevation) of 3 monkeys under pentobarbiture anesthesia, IOP was manometrically controlled. While BP was continuously registered via a cannulated tibial aretry (91±7 mmHg, n=3), IOP was rapidly increased from 10 to 40 mmHg Meanwhile, laser speckle images in the ONH were captured (30 maps/sec) for 2 minutes with the LSFG (Softcare, Japan). Blood flow (BF) of the entire area of the ONH were computed offline from the images and analyzed to extract the time-domain parameters: T_r (time to the maximal BF change), BF_max (maximal BF change, %) and K₂₀ (BF recovering rate 20 seconds after BF_max) and compared between the normal and the EG eyes.

Results: : Cumulative IOP exposures in the EG eyes varied as follows: IOP elevation maximum (38±9, 24±11, 32±11 mmHg) and duration (3, 4.5, 6 months) for M1, M2, M3, respectively; the average IOP in normal eyes was 11±2.5 mmHg (n=3). The general pattern of the dynamic autoregulation in all 3 control eyes was similar including a rapid BF decrease and a slower return to near the normal level. In the EG eyes, the pattern was different from the normal eyes, but varied individually (Fig 1). M1 had a smaller BF_max, but the BF recovered to a higher level; The BF in M2 & M3 responded passively to the IOP change, i.e., the BF did not return at all. In average, the T_r increased by 2.5±0.7 times in EG eyes: 16.2, 7.6, 17.9 sec vs. 7.8, 3.5, 5.4, respectively, for M1, M2, M3; BF_max(%) were 10.4, 15.2, 19.0 for EG eyes and 26.1, 17.2, 11.9% for control. K₂₀ was reduced by 50±19% in EG eyes: 0.064, 0, 0.015 vs. 0.10, 0.047, 0.041 per sec in control. None of the parameters had statistically significant difference between the EG and normal (P>0.05).

Conclusions: : The data suggest that individual-eye alterations in the dynamic autoregulation are present in these three animals. The delayed responding and recovering times to the IOP change are likely due to weakened vascular smooth muscles in the ONH and can be used to quantify the autoregulation dysfunction.

Keywords: optic nerve • intraocular pressure • blood supply