Waveform analysis of ocular blood flow and the early detection of normal tension glaucoma

Abstract

Purpose: To investigate waveform changes in blood flow (BF) in the optic nerve head (ONH) and to evaluate their usefulness in identifying normal tension glaucoma (NTG).

Methods: Sixty-one eyes of 61 patients with NTG and 21 eyes of age-matched healthy control subjects were included in this study. The NTG eyes were divided into the following three groups based on the progression of their visual field defects: mild (mean deviation [MD] greater than -6.0 decibels [dB]), moderate (MD between -6.0 and -12.0 dB), and severe (MD less than -12.0 dB). The ONH BF analysis was performed with laser speckle flowgraphy (LSFG) and included waveform variables such as skew, acceleration time index (ATI), and blowout time.

Results: In the ONH, LSFG skew variables were significantly lower in the NTG eyes than in the control eyes (P < 0.001), and ATI was significantly higher (P < 0.01), despite similar systemic characteristics in the four groups. The differences were most marked in the mild NTG group. Multiple linear regression analysis showed that MD, average thickness of the circumpapillary retinal nerve fiber layer, and pulse rate were predictive factors for both skew and ATI. A receiver operating characteristic (ROC) curve analysis also revealed that skew (area under the ROC curve, 0.89) and ATI (area under the ROC curve, 0.80) had the greatest power to differentiate normal eyes from eyes with mild NTG.

Conclusions: These results suggest that LSFG measurements of waveform changes in ONH BF can differentiate healthy eyes from eyes with NTG, particularly those with mild NTG.

Keywords: glaucoma; laser speckle flowgraphy; ocular blood flow; optic nerve head; waveform analysis.