Development of a prototype of laser Doppler flowmeter for the measurement of blood flow of retinal vessels and optic nerve head tissue in small animals (rats)

Abstract

 

Purpose

 

The aim of the present study was to validate a new laser Doppler flowmeter (LDF) device, specifically designed to measure retinal and optic nerve head blood flow in the rat. We investigated the reproducibility of blood flow parameters measurements on optic nerve head and retinal arteries in Wistar rats along with the effects of hyperoxia.

 

Methods

 

Rats were immobilized on a modified stereotactic table, which allows free rotation of the instrument around the eye, in order to aim the probing beam on the fundus. The fundus is illuminated with a green light and an image is captured with a CCD for easy targeting (measurement diameter about 60 μm). In vivo validation consisted of: (1) Study of linearity of the instrument with a rotating diffusing wheel. (2) Measurement reproducibility during a single experimental session (n = 5 rats, 1 hour, 4 measurements of 5-min duration) by calculation of intra-individual Variation Coefficients (VC) and Intra-class Correlation Coefficient (ICC). (3) Blood Flow (BF), velocity (Vel) and volume (Vol) (mean ± SD) were evaluated in response to 100% oxygen breathing (n = 8 rats).

 

Results

 

Vel varied linearly with the rotating speed (R2=0.9806) while Vol did not change (standard deviation/mean = 2.9%). Short-term reproducibility of retinal arterial Vel shows strong agreement (ICC=0.9, IC 95%=0.7-0.99), associated with low intra-individual VC (7.8 ± 6.6 %). After 2 minutes of 100% oxygen breathing, retinal arterial Vel was significant decreased by 17.0 ± 13.7 % (p=0.012), and optic nerve head BF by 11.0 ± 9.7 % (p=0.018).

 

Conclusions

 

This new LDF device allows repeatable measurements of ocular blood flow in small animals. Rat optic nerve head and retinal blood flow measurements are of crucial interest in physiological and pathophysiological studies. This prototype will be used to investigate various animal models (diabetes mellitus, glaucoma, vascular disorders) and for therapeutic evaluation.

 

 

Optical scheme of the laser Doppler flowmeter prototype (LDF), based on the Schlieren arrangement of the laser delivery and detection system, and rat fundus image.

 

 

Typical rat posture for ocular LDF recording. LDF is held on a horizontal movable stereotatic table with a special mechanical device permitting three-dimensional movements (θ,φ,z) and micrometric positioning of the probing beam on the rat's fundus.

 

Keywords: 436 blood supply