Relationship between nocturnal blood pressure dip and β-parapapillary atrophy zone choroidal vessel density in normal-tension glaucoma patients

Abstract

Purpose: To investigate the relationship between nocturnal blood pressure (BP) dip and parapapillary choroidal vessel density (pCVD) in patients with normal-tension glaucoma (NTG).

Methods: This study analyzed 267 eyes of 267 untreated NTG patients who underwent 24-hour (h) intraocular pressure (IOP) and ambulatory BP monitoring in the habitual position. Patients were classified into 3 groups [non-dippers (nocturnal BP dip < 10%), dippers (nocturnal BP dip between 10% and 20%, and over-dippers (nocturnal BP dip > 20%)], and pCVDs were measured by using optical coherence tomography angiography (OCTA) images. Logistic regression analyses were performed to identify clinical factors associated with "over-dipper" cases. Linear regression analyses were conducted to determine the correlation between various clinical variables and pCVD.

Results: In clinical characteristics, over-dippers exhibited lower pCVD values compared to non-dippers or dippers (P = 0.004). High diurnal intraocular pressure (IOP) fluctuation (P = 0.031), high diurnal mean arterial pressure (MAP) fluctuation (P = 0.001), and low pCVD (P = 0.002) were identified as predictors of being "over-dipper" in multivariable logistic regression analyses. Moreover, peripapillary retinal vessel density (P = 0.040), presence of choroidal microvasculature dropout (P = 0.039), and nocturnal MAP dip % (P = 0.002) showed significant correlations with pCVD according to multivariable linear regression analyses.

Conclusion: Over-dippers presented with lower pCVD than non-dippers or dippers as measured by OCTA choroidal images. Low pCVD was a predictor of "over-dipper" cases and associated with a greater percentage of nocturnal MAP dip in NTG patients. 24-h ambulatory BP monitoring may provide further information for detecting low pCVD in NTG patients with nocturnal BP dip.

Fig 1. Measurement of parapapillary choroidal vessel density (pCVD).

The boundaries of the optic disc and β-parapapillary atrophy margins, excluding large retinal vessels, were manually demarcated (yellow outline) using ImageJ software on en-face images obtained by using optical coherence tomography angiography scanning laser ophthalmoscopy (A and D). The demarcation lines are also shown above on en-face images of OCTA choroidal layer (B and E). The selected area of interest was converted to range of interest and 8-bit binary slab was created according to the mean threshold algorithm of ImageJ software of choroidal en-face image to measure pCVD (C and F). The orange demarcation outline shows choroidal microvascular dropout (CMvD) in figure E.

Fig 2. 24-hour mean arterial pressure (MAP) patterns of upper and lower parapapillary choroidal vessel density (pCVD) quartile groups.

The 2 dashed horizontal lines indicate diurnal MAP mean (upper panel) and diurnal MAP mean minus 10 mmHg (lower panel). Dark area represents nocturnal dip below diurnal MAP mean minus 10 mmHg.

Fig 3. A representative case showing the relationship between parapapillary choroidal vessel density and nocturnal blood pressure dip.

A 55-year-old over-dipper normal-tension glaucoma patient with axial length 23.49 mm and nocturnal blood pressure dip of 23.90% showed superotemporal and inferotemporal neural rim loss on optic disc photography and retinal nerve fiber layer (RNFL) loss on red-free RNFL photography. According to spectral-domain optical coherence tomography, RNFL and macular ganglion cell-inner plexiform thickness loss corresponding to the same locations of neural rim loss on optic disc photography were also evident. Visual field exam revealed corresponding central scotoma with a mean deviation of -5.13 dB. Parapapillary choroidal vessel density measurement using choroidal layer en-face images showed vessel density of 48.80%.

Fig 4. A representative case showing the relationship between parapapillary choroidal vessel density and nocturnal blood pressure dip.

A 61-year-old non-dipper normal-tension glaucoma patient with axial length 23.54 mm and nocturnal blood pressure dip of 7.21% showed superotemporal neural rim loss on optic disc photography and retinal nerve fiber layer (RNFL) loss on red-free RNFL photography. Upon spectral-domain optical coherence tomography imaging, RNFL and macular ganglion cell-inner plexiform thickness loss corresponding with superotemporal location were also noted. Visual field exam showed corresponding inferonasal scotoma with a mean deviation of -5.22 dB. Parapapillary choroidal vessel density measurement by choroidal layer en-face images showed vessel density of 58.76%.