Introduction: Microcirculation of optic nerve head (ONH) in open-angle glaucoma (OAG) patients with unilateral visual field (VF) loss has yet to be fully investigated, especially the perimetrically unaffected fellow eyes. Methods: Thirty-eight OAG patients with VF defect in one eye and normal VF in the other eye, and thirty-one healthy participants were analyzed. All participants underwent laser speckle flowgraphy (LSFG), spectral-domain optical coherence tomography (SD-OCT) imaging, and VF test for further analyses. LSFG measurements included mean blur rate in all area of ONH (MA), big vessel area of ONH (MV), and tissue area of ONH (MT). SD-OCT parameters included circumpapillary retinal nerve fiber layer (cpRNFL) thickness and macula thicknesses. The difference of LSFG and SD-OCT indices between glaucoma patients and healthy controls were compared. The diagnostic accuracy was analyzed with the areas under the receiver operating characteristic curves (AROCs). Results: Global cpRNFL thickness and macular thickness in unaffected eyes of OAG patients were higher than their fellow eyes and lower than healthy eyes. MA and MV in healthy eyes and unaffected eyes were significantly higher than in affected eyes. MT in unaffected eyes of OAG patients was higher than in their fellow affected eyes but lower than in healthy eyes. The AROCs were highest for cpRNFL (0.925), followed by macular thickness (0.838), and MT (0.834). Conclusions: ONH microcirculation in perimetrically unaffected fellow eyes was decreased in OAG patients with unilateral VF loss. LSFG can detect changes of ONH in high-risk eyes before detectable VF damage, which may reflect the vascular pathophysiology for glaucoma.

Glaucomatous optic neuropathy is characterized by enlargement of optic disc cup, thinning and notching of neuroretinal rim, progressive retinal nerve fiber layer (RNFL) thinning, and specific visual field (VF) defects. Structural changes of the optic nerve head (ONH) and RNFL often precede VF damage [1, 2]. Clinically, glaucoma is usually bilateral but can be asymmetric. Glaucoma patients could have asymmetric intraocular pressure (IOP) between both eyes, and the higher IOP may occur in the worse eye [3]. Optic disc hemorrhage may be more common in an eye with perimetrical glaucoma than in the fellow perimetrically unaffected eye [3]. The neuroretinal rim, RNFL, macular ganglion cell complex, peripapillary and macular vessel density (VD), and characteristics of the prelamina and lamina cribrosa may change in the fellow eyes of glaucoma patients with unilateral VF loss [4‒10]. As the disease progresses, the perimetrically unaffected eyes may have a higher risk of developing VF damage.

The mechanical theory and vascular theory are the commonly proposed mechanisms for glaucoma development [11, 12]. The mechanical theory suggests that IOP elevation could cause distortion and displacement of the lamina cribrosa, which result in blockade of axonal transport and subsequently axonal death. The vascular theory proposes that vascular dysregulation in ONH and retina could cause glaucomatous optic neuropathy [13, 14]. Primary open-angle glaucoma (POAG) has mainly pressure-dependent mechanism for disease development. Patients with normal tension glaucoma (NTG) are proposed to have abnormal susceptibility to normal IOP. Besides, reduction of ocular blood flow due to vascular dysregulation, systemic hypotension, and abnormal blood coagulation are pressure-independent mechanisms for pathogenesis of NTG.

Previous studies showed that the VD measured by optical coherence tomography angiography (OCT-A) in the ONH, peripapillary retina, and macula were associated with the severity of glaucomatous VF defects [15, 16]. In eyes with single-hemifield VF defects, decreased VD in the peripapillary and macular areas were noted in the perimetrically intact hemiretina [17, 18]. Attenuation of retinal microvasculature before detectable VF defects is present in patients with POAG.

Laser speckle flowgraphy (LSFG) uses the laser speckle phenomenon to noninvasively measure the ocular blood flow. The device is equipped with a diode laser which is applied to the fundus. The light generated in the tissue is scattered to produce speckle patterns on the imaging plane. The reflected light generated by the moving erythrocytes can interfere with the speckle pattern and blur the speckles. The mean blur rate (MBR) is a quantitative index of blood flow velocity in the target tissue and has been used to measure the relative blood flow in ONH, choroid, and retinal vessels [19‒22]. The commercially available LSFG-RetFlow (Nidek Co., LTD, Japan) consists of a fundus camera equipped with an 830-nm diode laser, a digital charge coupled device camera and a fixation target. The devices measure an area of 22 degrees at the retina, and a total of 120 frames are recorded during a 4-s period. The built-in analysis software averages all frames, and the four-heartbeat data are converted into one-heartbeat data after analysis. A composite color-coded map is generated to show the vascular distribution of the ONH and retina (Fig. 1). The LSFG device does not obtain the absolute blood flow velocity in the unit of “mm/s.” It is a quantitative index of erythrocytes velocity for measurement of the relative blood flow and is expressed in arbitrary units. LSFG can also monitor the changes of blood flow in the same retinal or choroidal vessels and tissue over time. In addition, the waveform profiles changing with the heartbeat can also be assessed [20‒22].

Fig. 1.

Color-coded composite map of the optic nerve head (ONH). The elliptical region was set semi-manually at the outer edge of the ONH. The colors represent the time averages of MBR over one heartbeat. Higher numbers indicate faster blood flow.

Fig. 1.

Color-coded composite map of the optic nerve head (ONH). The elliptical region was set semi-manually at the outer edge of the ONH. The colors represent the time averages of MBR over one heartbeat. Higher numbers indicate faster blood flow.

Close modal

In this study, we aimed to investigate the microcirculation of OHN with LSFG in open-angle glaucoma (OAG) patients with unilateral VF loss, and compare the differences of LSFG parameters among perimetrically unaffected, perimetrically affected, and healthy eyes. We further determined whether correlations among parameters of LSFG, RNFL thickness, and VF existed. Areas under the receiver operating characteristic curves (AROCs) were calculated to summarize the diagnostic capabilities of various parameters.

This prospective study was approved by the Institutional Review Board (IRB) of Kaohsiung Chang Gung Memorial Hospital (KCGMH) (IRB number: 202201402B0) and was performed according to the principles outlined in the Declaration of Helsinki. Written informed consent was obtained from all the participants in the study.

Study Participants

This cross-sectional study investigated patients with open-angle glaucoma, including POAG and NTG who attended KCGMH for glaucoma medication treatment and received regular follow-up. All the patients had VF loss in one eye and normal VF in the other eye. The control subjects were from hospital staff and patients coming for ophthalmic examinations. POAG was defined as an IOP greater than 21 mm Hg without medication, open anterior chamber angle, a glaucomatous optic disc, and RNFL defects with corresponding VF defects. NTG was defined the same as POAG except the IOP was less than 21 mm Hg on more than two occasions without medication. All the control subjects had no ocular disease and did not receive laser procedures or ocular surgeries. Besides, they had normal anterior segment, ONH, and retina. The IOP was less than 21 mm Hg, and the VF exams were within normal limits.

Systemic evaluation included systolic and diastolic blood pressure (BP) measurements. The mean arterial pressure (MAP) was calculated according to the formula: DBP + 1/3 (SBP − DBP), and the ocular perfusion pressure (OPP) was calculated according to the formula: 2/3 MAP − IOP.

Inclusion and Exclusion Criteria

Participants were included if they had a best-corrected visual acuity better than 20/40 and open angle on gonioscopy. Participants were excluded if they had a history of corneal degeneration, uveitis, secondary glaucoma, optic neuropathy other than glaucoma, retinal degeneration, retinal vessel occlusion, previous ocular trauma, or refractive surgery.

Ophthalmological Examinations

All of the participants underwent comprehensive examinations, including refraction, best-corrected visual acuity, Goldmann applanation tonometry, slit-lamp biomicroscopy, gonioscopy, dilated stereoscopic exam of the ONH and retina, central corneal thickness (CCT), color fundus photography, VF and spectral-domain optical coherence tomography (OCT) and LSFG measurements.

The refraction was measured and denoted as spherical equivalence, which is calculated by sphere plus half of the cylinder. CCT was measured by non-contact specular microscope (SP-3000P, TOPCON, Tokyo, Japan). VF was performed with Swedish Interactive Threshold Algorithm standard 30-2 Humphrey field analyzer (HFA, Carl Zeiss Meditec, Dublin, CA). VF exams were considered reliable if the fixation losses were ≤20% and false-positive and false-negative response rates were ≤15%. A glaucomatous VF defect was defined as a cluster of 3 or more significant (p < 5%) non-edge contiguous points with at least 1 at the p < 1% level on the same horizontal meridian on the pattern deviation plot, a pattern standard deviation of 95% outside the normal limits, and a glaucoma hemifield test outside the normal limits. Glaucomatous VF defects were confirmed by two reliable exams. The definition of OAG with unilateral VF loss was one eye diagnosed with repeatable glaucomatous VF defects, and the other eye showed no VF defects. Contralateral eyes of OAG patients must have consistently normal and reliable VF results based on at least 3 VF tests.

Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) was used to measure circumpapillary retinal nerve fiber layer (cpRNFL) thickness and macular thickness at the same visit. The fast RNFL thickness protocol with scan circle 3.5 mm in diameter was used for measuring the thickness of cpRNFL. The macular thickness was measured as 8 × 8 grid within the central 25° × 30° at the macular area by the posterior pole asymmetry analysis scan. The average macular thickness was automatically generated in the report. Only an image quality of at least 20 was used for this study.

The LSFG evaluation was performed using the LSFG-RetFlow (Nidek Co., LTD, Japan). We assessed the microcirculation at the ONH by semi-manually drawing an elliptical region, which was customized to the ONH borders for all participants. The identification of the ONH borders was compared by using the LSFG composite map with the color fundus photography, and the delineation of the ONH border was performed in all LSFG images by a well-trained operator. The main parameter of LSFG for the quantification of microcirculation at ONH is the MBR. Three MBR parameters were calculated for the ONH microcirculation. MA indicates MBR in all area of ONH, MV indicates MBR in big vessel area of ONH, and MT indicates MBR in tissue area of ONH.

The waveform parameters of flow velocity were also obtained: the blowout time (BOT) indicates the time that the wave maintained at more than half of the mean of the maximum and minimum MBR during a heartbeat. BOT means the duration of high-volume blood flow. High BOT indicates well-maintained perfusion during the cardiac cycle. The Blowout score (BOS) is calculated from the difference of the maximum and the minimum MBR and the average MBR. It means the amount of blood maintained in the vessels in one heartbeat. A high BOS indicates a high constancy of blood flow during the cardiac cycle. Acceleration time index (ATI) is defined as the ratio of time to reach the peak of MBR and the duration of the heartbeat. ATI is a maximum blood flow index in one heartbeat. Skew indicates the asymmetric distribution of the MBR waveform. A positive value means a leftward distribution, 0 means a perfectly symmetrical waveform, and a negative value means a rightward distribution. A high skew value indicates arteriosclerosis. Fluctuation describes the dimension of the amplitude of the waveform curve [20‒22].

Data Processing and Statistical Analysis

All analyses were performed using the MedCalc® Statistical Software version 22.006 (MedCalc Software Ltd, Ostend, Belgium). Categorical variables were compared using the χ2 test between groups and expressed as numbers. The independent samples t test was used for comparison of continuous variables between glaucoma and healthy participants, and between glaucoma eyes and healthy eyes. The paired samples t test was used to compare measurements between perimetrically affected eyes and unaffected eyes of OAG patients. Correlations between LSFG and VF parameters, and between LSFG and OCT parameters were assessed using the Spearman’s correlation coefficient. AROCs were used to demonstrate the capabilities of LSFG parameters to discriminate between perimetrically affected eyes and healthy eyes. The method of DeLong was used to evaluate statistical differences of AROCs among OCT and LSFG parameters. All the statistical tests were two-sided. A p value <0.05 was considered significant.

A total of 69 participants were enrolled, including 31 healthy subjects (VF mean deviation [MD] −0.27 ± 1.72 decibels [dB]) and 38 patients with OAG with VF defects in one eye (MD −3.32 ± 4.02 dB) and normal VF test in the other eye (MD −0.73 ± 1.64 dB). There were no significant differences between patients with glaucoma and healthy subjects in age, gender, race, and systemic BP measurements (all p values >0.05). There were also no differences among healthy eyes, perimetrically unaffected eyes, perimetrically affected eyes in CCT, IOP, and OPP. The perimetrically unaffected eyes had lower cpRNFL thickness and macular thickness than healthy eyes (both p values <0.001), but there were no differences between perimetrically unaffected eyes and healthy eyes in MD and PSD. The perimetrically affected eyes had worse MD and PSD, and thinner cpRNFL and macular thickness compared with healthy eyes and perimetrically unaffected eyes (all p values <0.001). The demographic data are shown in Table 1.

Table 1.

Demographic data of normal subjects and glaucoma patients

Healthy eyes (n = 31)Glaucoma patientsp value
perimetrically unaffected eyes (n = 38)perimetrically affected eyes (n = 38)
Age, years 55.8±12.2 56.3±12.9 0.869a   
Male/female 17/14 26/12 0.247a   
SBP, mm Hg 136±20 130±12 0.169a   
DBP, mm Hg 91±15 86±9 0.188a   
MAP, mm Hg 106±16 101±9 0.151a   
SE, D −2.87±3.52 −3.79±2.96 −4.38±3.01 0.248b 0.011c 0.064d 
CCT, μm 530±46 524±35 524±33 0.561b 0.989c 0.544d 
IOP, mm Hg 14.3±3.0 14.1±3.2 14.5±3.2 0.761b 0.449c 0.847d 
OPP, mm Hg 53±6 56±11 56±11 0.128b 0.449c 0.186d 
VF 
 MD, dB −0.27±1.72 −0.73±1.64 −3.32±4.02 0.324b 0.0005c 0.002d 
 PSD, dB 2.05±1.14 2.01±0.87 4.99±4.46 0.875b 0.0004c 0.005d 
 cpRNFL thickness, μm 103±10 90±14 76±16 0.0001b <0.0001c <0.0001d 
 Macular thickness, μm 294±15 281±15 273±15 0.0008b <0.0001c <0.0001d 
Healthy eyes (n = 31)Glaucoma patientsp value
perimetrically unaffected eyes (n = 38)perimetrically affected eyes (n = 38)
Age, years 55.8±12.2 56.3±12.9 0.869a   
Male/female 17/14 26/12 0.247a   
SBP, mm Hg 136±20 130±12 0.169a   
DBP, mm Hg 91±15 86±9 0.188a   
MAP, mm Hg 106±16 101±9 0.151a   
SE, D −2.87±3.52 −3.79±2.96 −4.38±3.01 0.248b 0.011c 0.064d 
CCT, μm 530±46 524±35 524±33 0.561b 0.989c 0.544d 
IOP, mm Hg 14.3±3.0 14.1±3.2 14.5±3.2 0.761b 0.449c 0.847d 
OPP, mm Hg 53±6 56±11 56±11 0.128b 0.449c 0.186d 
VF 
 MD, dB −0.27±1.72 −0.73±1.64 −3.32±4.02 0.324b 0.0005c 0.002d 
 PSD, dB 2.05±1.14 2.01±0.87 4.99±4.46 0.875b 0.0004c 0.005d 
 cpRNFL thickness, μm 103±10 90±14 76±16 0.0001b <0.0001c <0.0001d 
 Macular thickness, μm 294±15 281±15 273±15 0.0008b <0.0001c <0.0001d 

SBP, systolic blood pressure; DBP, diastolic blood pressure; MAP, mean arterial pressure; SE, spherical equivalence; CCT, central corneal thickness; IOP, intraocular pressure; OPP, ocular perfusion pressure; VF, visual field; MD, mean deviation; PSD, pattern standard deviation; cpRNFL, circumpapillary retinal nerve fiber layer.

Method: χ2 test for categorical data.

aIndependent samples t test for comparisons between mean values of healthy subjects and glaucoma patients.

bIndependent samples t test for comparisons between mean values of healthy eyes and perimetrically unaffected eyes.

cPaired samples t test for comparisons between mean values of perimetrically unaffected eyes and perimetrically affected eyes.

dIndependent samples t test for comparisons between mean values of healthy eyes and perimetrically affected eyes.

Boldface indicates statistical significance.

The MBR and waveform parameters for ONH microcirculation in healthy eyes, perimetrically unaffected eyes, perimetrically affected eyes are presented in Table 2. For the MBR parameters, MA and MV were significantly lower in perimetrically affected eyes compared with healthy eyes and perimetrically unaffected eyes (all p values <0.01). Besides, MT was significantly different among healthy eyes, perimetrically unaffected eyes, and perimetrically affected eyes. The waveform parameters of LSFG revealed no differences among healthy eyes, perimetrically unaffected eyes, and perimetrically affected eyes.

Table 2.

Waveform parameters of LSFG in healthy, perimetrically unaffected and perimetrically unaffected eyes

Healthy eyes (n = 31)Glaucoma patientsp value
perimetrically unaffected eyes (n = 38)perimetrically affected eyes (n = 38)
MA 25.3±5.2 23.1±5.0 19.8±4.7 0.079a <0.0001b <0.0001c 
MV 51.7±11.5 48.1±11.2 42.7±10.5 0.196a 0.002b 0.001c 
MT 16.2±3.8 14.3±3.3 11.6±3.1 0.033a <0.0001b <0.0001c 
BOT 50.6±5.6 50.9±4.6 51.4±5.9 0.842a 0.608b 0.534c 
BOS 76.8±6.5 76.4±5.9 76.4±8.4 0.755a 0.997b 0.817c 
Skew 11.4±2.0 11.6±1.9 11.2±3.0 0.630a 0.463b 0.815c 
ATI 30.7±5.1 31.5±4.0 32.4±6.3 0.470a 0.371b 0.222c 
Fluctuation 12.9±3.7 13.2±3.5 13.2±4.7 0.737a 0.882b 0.822c 
Healthy eyes (n = 31)Glaucoma patientsp value
perimetrically unaffected eyes (n = 38)perimetrically affected eyes (n = 38)
MA 25.3±5.2 23.1±5.0 19.8±4.7 0.079a <0.0001b <0.0001c 
MV 51.7±11.5 48.1±11.2 42.7±10.5 0.196a 0.002b 0.001c 
MT 16.2±3.8 14.3±3.3 11.6±3.1 0.033a <0.0001b <0.0001c 
BOT 50.6±5.6 50.9±4.6 51.4±5.9 0.842a 0.608b 0.534c 
BOS 76.8±6.5 76.4±5.9 76.4±8.4 0.755a 0.997b 0.817c 
Skew 11.4±2.0 11.6±1.9 11.2±3.0 0.630a 0.463b 0.815c 
ATI 30.7±5.1 31.5±4.0 32.4±6.3 0.470a 0.371b 0.222c 
Fluctuation 12.9±3.7 13.2±3.5 13.2±4.7 0.737a 0.882b 0.822c 

MA, mean blur rate in all area of optic nerve head; MV, mean blur rate in big vessel area of optic nerve head; MT, mean blur rate in tissue area of optic nerve head; BOT, blowout time; BOS, blowout score; ATI, acceleration time index.

Method: χ2 test for categorical data.

aIndependent samples t test for comparisons between mean values of healthy eyes and perimetrically unaffected eyes.

bPaired samples t test for comparisons between mean values of perimetrically unaffected eyes and perimetrically affected eyes.

CIndependent samples t test for comparisons between mean values of healthy eyes and perimetrically affected eyes.

Boldface indicates statistical significance.

The cpRNFL thickness significantly correlated with MA (ρ = 0.527, p < 0.0001), MV (ρ = 0.458, p < 0.0001), and MT (ρ = 0.566, p < 0.0001). The macular thickness also significantly correlated with MA (ρ = 0.487, p < 0.0001), MV (ρ = 0.436, p < 0.0001), and MT (ρ = 0.491, p < 0.0001). The correlations between MBR and OCT parameters are shown in Figure 2a–f. The MD of VF also significantly correlated with MA (ρ = 0.272, p = 0.0001), MV (ρ = 0.249, p = 0.0140), and MT (ρ = 0.335, p = 0.0008).

Fig. 2.

Correlations between cpRNFL thickness and MBR parameters and between macular thickness and MBR parameters. a MA versus cpRNFL. b MV versus cpRNFL. c MT versus cpRNFL. d MA versus macular thickness. e MV versus macular thickness. f MT versus macular thickness. cpRNFL, circumpapillary retinal nerve fiber layer; MBR, mean blur rate; MA, mean blur rate in all area of optic nerve head; MV, mean blur rate in big vessel area of optic nerve head; MT, mean blur rate in tissue area of optic nerve head.

Fig. 2.

Correlations between cpRNFL thickness and MBR parameters and between macular thickness and MBR parameters. a MA versus cpRNFL. b MV versus cpRNFL. c MT versus cpRNFL. d MA versus macular thickness. e MV versus macular thickness. f MT versus macular thickness. cpRNFL, circumpapillary retinal nerve fiber layer; MBR, mean blur rate; MA, mean blur rate in all area of optic nerve head; MV, mean blur rate in big vessel area of optic nerve head; MT, mean blur rate in tissue area of optic nerve head.

Close modal

The AROC of cpRNFL, macular thickness, and LSFG parameters for distinguishing perimetrically affected eyes from healthy eyes was highest for cpRNFL (AROC = 0.925, 95% CI: 0.834–0.975), followed by macular thickness (AROC = 0.838, 95% CI: 0.728–0.917) and MT (AROC = 0.834, 95% CI: 0.723–0.914). However, the differences did not reach statistical significance by DeLong test (all p values >0.05). The data are shown in Table 3.

Table 3.

Area under the receiver operator characteristic curves (AROCs) for differentiating between affected eyes and healthy eyes

AROC curve (95% CI)p values
cpRNFL thicknessmacular thicknessMTcpRNFL versus macular thicknessmacular thickness versus MTcpRNFL thickness versus MT
Affected eyes 0.925 (0.834–0.975) 0.838 (0.728–0.917) 0.834 (0.723–0.914) 0.081 0.941 0.107 
AROC curve (95% CI)p values
cpRNFL thicknessmacular thicknessMTcpRNFL versus macular thicknessmacular thickness versus MTcpRNFL thickness versus MT
Affected eyes 0.925 (0.834–0.975) 0.838 (0.728–0.917) 0.834 (0.723–0.914) 0.081 0.941 0.107 

AROC, area under the receiver operating characteristic; cpRNFL, circumpapillary retinal nerve fiber layer thickness; MT, mean blur rate in tissue area of optic nerve head.

Method: DeLong test.

This study investigated the microcirculation of ONH in OAG patients with unilateral VF loss. The results showed that the cpRNFL thickness and macular thickness in perimetrically unaffected eyes were lower than healthy eyes but higher than perimetrically affected eyes. The structural damage was detectable in perimetrically unaffected eyes in glaucoma patients with unilateral VF loss. Besides, the MBR parameters, including MA, and MV, were significantly lower in perimetrically affected eyes than the healthy and perimetrically unaffected eyes. The MBR parameter of MT in perimetrically unaffected eyes was higher than perimetrically affected eyes; besides, MT in perimetrically unaffected eyes was lower than healthy eyes. In addition, MBR parameters significantly correlated with both structure and visual function. These results implied that the structural damage and microcirculation impairment were present not only in the perimetrically affected eyes but also the perimetrically unaffected eyes.

Structural damages of the ONH and cpRNFL often precede VF loss in glaucoma patients [23, 24]. Previous studies had reported the asymmetric changes of neuroretinal rim, cpRNFL, and macular ganglion cell complex in fellow eyes of glaucoma patients with unilateral VF damage [4‒7]. Our results also showed decreased cpRNFL and macular thickness in perimetrically unaffected eyes in glaucoma patients with unilateral VF loss.

The vascular networks of the optic disc, peripapillary retina, macula, and choroidal structures in patients with preperimetric and perimetric glaucoma have been quantitatively evaluated by OCT angiography. In eyes with preperimetric glaucoma, the perifoveal VDs and radial peripapillary capillary VD were lower than normal control eyes. The peripapillary and macular VD were decreased in early glaucomatous eyes compared with normal eyes. The damage of macular microvasculature was more prominent in the perifoveal area than in the parafoveal region [15]. Yarmohammadi et al. assessed VD of POAG patients with unilateral VF loss and found the mean whole image VD in unaffected eyes was higher than in their fellow affected eyes but lower than in healthy eyes [25]. The changes of retinal microvasculature in perimetrically affected and unaffected eyes may compromise the blood supply to ONH and retina, and cause further VF damage.

Dysregulation of ocular blood flow has an important role in the development of glaucoma. When assessing the ocular blood flow in asymmetric or unilateral glaucoma, Fontana et al. [26] evaluated the pulsatile ocular blood flow in NTG patients with unilateral VF loss. They found the pulsatile ocular blood flow was significantly lower in the eyes of NTG patients with and without VF loss than in normal subjects; besides, the pulsatile ocular blood flow in NTG eyes with VF loss was lower than in the contralateral eyes with normal VF. They suggested that hemodynamic difference between both eyes may lead to the occurrence of glaucoma in eye with lower blood flow. Nicolela et al. [27] used color Doppler imaging to assess blood flow velocities in patients with asymmetric glaucoma and unilateral VF loss. They found that the blood velocity of central retinal artery was lower in the more affected eye than in the less affected eye. Additionally, even eyes with normal VF had decreased blood velocities in the retrobulbar vessels, which suggested that the circulatory changes probably preceded detectable VF damage.

Impaired microcirculation in the ONH is related to the development and progression of glaucoma. Previous studies showed that the ONH microcirculation assessed by LSFG was reduced in NTG eyes [20, 21]. In the present study, we investigated the ONH microcirculation in patients with unilateral glaucoma, and found that MA and MV were decreased in perimetrically affected eyes. Moreover, decreased MT was found in both perimetrically unaffected and affected eyes. MV is related to the circulation of major retinal vessels and reflects the blood flow in the inner retina. MT is related to the microcirculation of prelaminar region and lamina cribrosa, and is considered a quantitative index of blood flow in the ONH tissue. Decreased MV and MT indicated that the perimetrically affected eyes had compromised microcirculation in the inner retina and ONH. Decreased MT in perimetrically unaffected eyes may indicate early damage of microcirculation in ONH. These results imply that structural changes and vascular insufficiencies can precede detectable functional damage in perimetrically unaffected eyes in OAG patients with unilateral VF loss.

In analysis of the waveform parameters, blowout time and blowout score are related to the stiffness of large arteries, left ventricular function, and systemic vascular resistance [28, 29]. ATI is related to left ventricular function. Skew is associated with the stiffness of large arteries. In our study, we did not find significant differences in the waveform parameters among healthy eyes, perimetrically unaffected eyes, and perimetrically affected eyes.

Previous studies reported that MBR parameters were correlated with cpRNFL thickness and MD of the VF [30‒32]. Lower MBR levels were associated with thinner cpRNFL thickness and worse VF function. Yokoyama et al. [32] found that global cpRNFL thickness positively correlated with MA (r = 0.532, p < 0.001) and MT (r = 0.571, p < 0.001), and MD significantly correlated with MA (r = 0.58, p = 0.0002). In our study, we noted that MA, MV, and MT all positively correlated with cpRNFL thickness, macular thickness, and MD of VF, which may imply that decreased microcirculation of ONH was significantly associated with structural and functional damage in glaucoma.

While analyzing the diagnostic capabilities of MBR parameters for glaucoma, Aizawa et al. [31] reported that the diagnostic capabilities of MBR (AROC = 0.86) and cpRNFL thickness (AROC = 0.91) were statistically similar (p = 0.25). On the contrary, the diagnostic capabilities of MA (AROC = 0.79), MV (AROC = 0.60), and MT (AROC = 0.60) were significantly lower than that of cpRNFL thickness (AROC = 0.91, p < 0.05) in Takeyama’s study [33]. In our study, the cpRNFL thickness had the highest AROC (0.925) for discriminating perimetrically affected eyes from healthy eyes, however, MT (AROC = 0.834) and macular thickness (AROC = 0.838) had comparable diagnostic capabilities (p > 0.05) for detection of glaucoma. Therefore, combining evaluation of cpRNFL thickness, macular thickness, and MT of ONH microcirculation may provide better diagnostic accuracies for early detection of glaucoma.

The present study has some limitations. First, the sample size is relatively small; however, we found decreased microcirculation of ONH and thinning of cpRNFL in the fellow eyes of glaucoma patients with unilateral VF damage. The results suggest that structural damage and vascular insufficiency can precede functional damage. Early detection of vascular changes may predict further glaucomatous progression in the perimetrically unaffected eyes. Larger prospective studies for longitudinal follow-up of VF progression would address the importance of lower blood flow in perimetrically unaffected eyes. Second, the effects of topical antiglaucomatous medications on ONH microcirculation remain controversial. Some studies showed that topical dorzolamide and timolol had no effects on blood flow in ONH; however, other studies showed that topical latanoprost and tafluprost eyedrops may increase blood flow in ONH [34‒37]. Because this study was cross-sectional and observational, and the glaucoma patients did not discontinue the use of antiglaucomatous medications, the possible impact of topical medications on MBR may exist. Besides, personal history of systemic hypertension or antihypertensive medication use might have certain effects on blood flow measurements. Further prospective investigations with a similar background are needed to clarify this issue.

In conclusion, our study showed that ONH microcirculation in perimetrically unaffected fellow eyes was decreased in OAG patients with unilateral VF loss. LSFG can noninvasively detect microvascular changes of ONH in eyes at high risk of developing glaucoma before detectable VF damage. Longitudinal studies are needed to clarify whether LSFG measurements can predict or early detect progression of glaucomatous damage.

We thank Dr. Hsin-Ching Lin and Dr. Chung-Wei Lin for assistance in the manuscript preparation.

This prospective study was approved by the Institutional Review Board (IRB) of Kaohsiung Chang Gung Memorial Hospital (KCGMH) (IRB number: 202201402B0) and was performed according to the principles outlined in the Declaration of Helsinki. Written informed consent was obtained from all the participants in the study.

The authors have no conflicts of interest to declare.

This study was not supported by any sponsor or funder.

Pei-Wen Lin: design the study; data acquisition; conduct the analysis; data interpretation; drafting the manuscript; and revision of the manuscript. Li-Wen Chiu: data interpretation and drafting the manuscript.

The data that support the findings of this study are not publicly available since the containing information may compromise the privacy of research participants, but the de-identified data are available from the corresponding author (P.W.L.) upon reasonable request.

1.
Sommer
A
,
Katz
J
,
Quigley
HA
,
Miller
NR
,
Robin
AL
,
Richter
RC
, et al
.
Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss
.
Arch Ophthalmol
.
1991
;
109
(
1
):
77
83
.
2.
Quigley
HA
,
Katz
J
,
Derick
RJ
,
Gilbert
D
,
Sommer
A
.
An evaluation of optic disc and nerve fiber layer examinations in monitoring progression of early glaucoma damage
.
Ophthalmology
.
1992
;
99
(
1
):
19
28
.
3.
Cho
HK
,
Suh
W
,
Kee
C
.
Visual and structural prognosis of the untreated fellow eyes of unilateral normal tension glaucoma patients
.
Graefes Arch Clin Exp Ophthalmol
.
2015
;
253
(
9
):
1547
55
.
4.
Zeyen
TG
,
Raymond
M
,
Caprioli
J
.
Disc and field damage in patients with unilateral visual field loss from primary open-angle glaucoma
.
Doc Ophthalmol
.
1992
;
82
(
4
):
279
86
.
5.
Caprioli
J
,
Miller
JM
,
Sears
M
.
Quantitative evaluation of the optic nerve head in patients with unilateral visual field loss from primary open-angle glaucoma
.
Ophthalmology
.
1987
;
94
(
11
):
1484
7
.
6.
Kim
DM
,
Hwang
US
,
Park
KH
,
Kim
SH
.
Retinal nerve fiber layer thickness in the fellow eyes of normal-tension glaucoma patients with unilateral visual field defect
.
Am J Ophthalmol
.
2005
;
140
(
1
):
165
6
.
7.
Zangalli
CS
,
Ahmed
OM
,
Waisbourd
M
,
H Ali
M
,
Cvintal
V
,
Affel
E
, et al
.
Segmental analysis of macular layers in patients with unilateral primary open-angle glaucoma
.
J Glaucoma
.
2016
;
25
(
4
):
e401
407
.
8.
Yarmohammadi
A
,
Zangwill
LM
,
Manalastas
PIC
,
Fuller
NJ
,
Diniz-Filho
A
,
Saunders
LJ
, et al
.
Peripapillary and macular vessel density in patients with primary open-angle glaucoma and unilateral visual field loss
.
Ophthalmology
.
2018
;
125
(
4
):
578
87
.
9.
Kim
DW
,
Jeoung
JW
,
Kim
YW
,
Girard
MJA
,
Mari
JM
,
Kim
YK
, et al
.
Prelamina and lamina cribrosa in glaucoma patients with unilateral visual field loss
.
Invest Ophthalmol Vis Sci
.
2016
;
57
(
4
):
1662
70
.
10.
Kwun
Y
,
Han
JC
,
Kee
C
.
Comparison of lamina cribrosa thickness in normal tension glaucoma patients with unilateral visual field defect
.
Am J Ophthalmol
.
2015
;
159
(
3
):
512
8.e1
.
11.
Nakazawa
T
,
Fukuchi
T
.
What is glaucomatous optic neuropathy
.
Jpn J Ophthalmol
.
2020
;
64
(
3
):
243
9
.
12.
Weinreb
RN
,
Aung
T
,
Medeiros
FA
.
The pathophysiology and treatment of glaucoma: a review
.
JAMA
.
2014
;
311
(
18
):
1901
11
.
13.
Shields
MB
.
Normal-tension glaucoma: is it different from primary open-angle glaucoma
.
Curr Opin Ophthalmol
.
2008
;
19
(
2
):
85
8
.
14.
Bojikian
KD
,
Chen
CL
,
Wen
JC
,
Zhang
Q
,
Xin
C
,
Gupta
D
, et al
.
Optic disc perfusion in primary open angle and normal tension glaucoma eyes using optical coherence tomography-based microangiography
.
PLoS One
.
2016
;
11
(
5
):
e0154691
.
15.
Lu
P
,
Xiao
H
,
Liang
C
,
Xu
Y
,
Ye
D
,
Huang
J
.
Quantitative analysis of microvasculature in macular and peripapillary regions in early primary open-angle glaucoma
.
Curr Eye Res
.
2020
;
45
(
5
):
629
35
.
16.
Chen
HSL
,
Liu
CH
,
Wu
WC
,
Tseng
HJ
,
Lee
YS
.
Optical coherence tomography angiography of the superficial microvasculature in the macular and peripapillary areas in glaucomatous and healthy eyes
.
Invest Ophthalmol Vis Sci
.
2017
;
58
(
9
):
3637
45
.
17.
Uchida
N
,
Ishida
K
,
Anraku
A
,
Takeyama
A
,
Tomita
G
.
Macular vessel density in untreated normal tension glaucoma with a hemifield defect
.
Jpn J Ophthalmol
.
2019
;
63
(
6
):
457
66
.
18.
Yarmohammadi
A
,
Zangwill
LM
,
Diniz-Filho
A
,
Saunders
LJ
,
Suh
MH
,
Wu
Z
, et al
.
Peripapillary and macular vessel density in patients with glaucoma and single-hemifield visual field defect
.
Ophthalmology
.
2017
;
124
(
5
):
709
19
.
19.
Sugiyama
T
,
Araie
M
,
Riva
CE
,
Schmetterer
L
,
Orgul
S
.
Use of laser speckle flowgraphy in ocular blood flow research
.
Acta Ophthalmol
.
2010
;
88
(
7
):
723
9
.
20.
Shiga
Y
,
Omodaka
K
,
Kunikata
H
,
Ryu
M
,
Yokoyama
Y
,
Tsuda
S
, et al
.
Waveform analysis of ocular blood flow and the early detection of normal tension glaucoma
.
Invest Ophthalmol Vis Sci
.
2013
;
54
(
12
):
7699
706
.
21.
Mursch-Edlmayr
AS
,
Luft
N
,
Podkowinski
D
,
Ring
M
,
Schmetterer
L
,
Bolz
M
.
Laser speckle flowgraphy derived characteristics of optic nerve head perfusion in normal tension glaucoma and healthy individuals: a Pilot study
.
Sci Rep
.
2018
;
8
(
1
):
5343
.
22.
Enomoto
N
,
Anraku
A
,
Tomita
G
,
Iwase
A
,
Sato
T
,
Shoji
N
, et al
.
Characterization of laser speckle flowgraphy pulse waveform parameters for the evaluation of the optic nerve head and retinal circulation
.
Sci Rep
.
2021
;
11
(
1
):
6847
.
23.
Sommer
A
,
Katz
J
,
Quigley
HA
,
Miller
NR
,
Robin
AL
,
Richter
RC
, et al
.
Clinically detectable nerve fiber atrophy precedes the onset of glaucomatous field loss
.
Arch Ophthalmol
.
1991
;
109
(
1
):
77
83
.
24.
Quigley
HA
,
Katz
J
,
Derick
RJ
,
Gilbert
D
,
Sommer
A
.
An evaluation of optic disc and nerve fiber layer examinations in monitoring progression of early glaucoma damage
.
Ophthalmology
.
1992
;
99
(
1
):
19
28
.
25.
Yarmohammadi
A
,
Zangwill
LM
,
Manalastas
PIC
,
Fuller
NJ
,
Diniz-Filho
A
,
Saunders
LJ
, et al
.
Peripapillary and macular vessel density in patients with primary open-angle glaucoma and unilateral visual field loss
.
Ophthalmology
.
2018
;
125
(
4
):
578
87
.
26.
Fontana
L
,
Poinoosawmy
D
,
Bunce
CV
,
O’Brien
C
,
Hitchings
RA
.
Pulsatile ocular blood flow investigation in asymmetric normal tension glaucoma and normal subjects
.
Br J Ophthalmol
.
1998
;
82
(
7
):
731
6
.
27.
Nicolela
MT
,
Drance
SM
,
Rankin
SJ
,
Buckley
AR
,
Walman
BE
.
Color Doppler imaging in patients with asymmetric glaucoma and unilateral visual field loss
.
Am J Ophthalmol
.
1996
;
121
(
5
):
502
10
.
28.
Rina
M
,
Shiba
T
,
Takahashi
M
,
Hori
Y
,
Maeno
T
.
Pulse waveform analysis of optic nerve head circulation for predicting carotid atherosclerotic changes
.
Graefes Arch Clin Exp Ophthalmol
.
2015
;
253
(
12
):
2285
91
.
29.
Shiba
T
,
Takahashi
M
,
Hashimoto
R
,
Matsumoto
T
,
Hori
Y
.
Pulse waveform analysis in the optic nerve head circulation reflects systemic vascular resistance obtained via a Swan-Ganz catheter
.
Graefes Arch Clin Exp Ophthalmol
.
2016
;
254
(
6
):
1195
200
.
30.
Kuroda
F
,
Iwase
T
,
Yamamoto
K
,
Ra
E
,
Terasaki
H
.
Correlation between blood flow on optic nerve head and structural and functional changes in eyes with glaucoma
.
Sci Rep
.
2020
;
10
(
1
):
729
.
31.
Aizawa
N
,
Kunikata
H
,
Shiga
Y
,
Yokoyama
Y
,
Omodaka
K
,
Nakazawa
T
.
Correlation between structure/function and optic disc microcirculation in myopic glaucoma, measured with laser speckle flowgraphy
.
BMC Ophthalmol
.
2014
;
14
:
113
.
32.
Yokoyama
Y
,
Aizawa
N
,
Chiba
N
,
Omodaka
K
,
Nakamura
M
,
Otomo
T
, et al
.
Significant correlations between optic nerve head microcirculation and visual field defects and nerve fiber layer loss in glaucoma patients with myopic glaucomatous disk
.
Clin Ophthalmol
.
2011
;
5
:
1721
7
.
33.
Takeyama
A
,
Ishida
K
,
Anraku
A
,
Ishida
M
,
Tomita
G
.
Comparison of optical coherence tomography angiography and laser speckle flowgraphy for the diagnosis of normal-tension glaucoma
.
J Ophthalmol
.
2018
;
2018
:
1751857
.
34.
Tamaki
Y
,
Araie
M
,
Muta
K
.
Effect of topical dorzolamide on tissue circulation in the rabbit optic nerve head
.
Jpn J Ophthalmol
.
1999
;
43
(
5
):
386
91
.
35.
Ishii
K
,
Araie
M
.
Effect of topical timolol on optic nerve head circulation in the cynomolgus monkey
.
Jpn J Ophthalmol
.
2000
;
44
(
6
):
630
3
.
36.
Tamaki
Y
,
Nagahara
M
,
Araie
M
,
Tomita
K
,
Sandoh
S
,
Tomidokoro
A
.
Topical latanoprost and optic nerve head and retinal circulation in humans
.
J Ocul Pharmacol Ther
.
2001
;
17
(
5
):
403
11
.
37.
Tsuda
S
,
Yokoyama
Y
,
Chiba
N
,
Aizawa
N
,
Shiga
Y
,
Yasuda
M
, et al
.
Effect of topical tafluprost on optic nerve head blood flow in patients with myopic disc type
.
J Glaucoma
.
2013
;
22
(
5
):
398
403
.