The effect of axial length on ocular blood flow assessment in anisometropes

Association of choroidal thickness and blood flow features with asymmetric axial lengths in children with unilateral myopic anisometropia

BACKGROUND

Considering that changes in the choroidal thickness are closely related to ocular growth, we studied the choroidal thickness (CT) and the blood flow features in children with unilateral myopic anisometropia (UMA) as well as investigating the relationship between choroidal changes and myopia.

METHODS

Subjective refractive, axial length (AL), and biometric parameters were measured in 98 UMA children (age: 8-15 years). CT and choroidal blood-flow features, including the choroidal vessel volume (CVV), choroidal vascularity index (CVI), and choriocapillaris perfusion area (CCPA), were measured through swept-source optical coherence tomography angiography. The macular region was categorized into four concentric circles of diameters 0-1 mm (central fovea), 1-3 mm (parafovea), 3-6 mm (perifovea), and 6-9 mm (extended), and further categorized into superior (S), inferior (I), temporal (T), and nasal (N) quadrants.

RESULTS

The aforementioned four regions of myopic eyes displayed significantly lower CT, CVV, and CVI than those of non-myopic eyes. CCPA changes differed across different regions of both the eyes (parts of N and T quadrants). There was an inverse association between CT and the interocular AL difference (central and other regions S, T quadrant). No correlation was noted between CVV and CVI with interocular AL difference. CT and CVV were positively correlated in the 0-6-mm macular region of myopic eyes (Spearman correlation coefficient = 0.763, P < 0.001).

CONCLUSIONS

In UMA children, CCT and blood flow may be related to myopia progression. A robust correlation between CT and CVV in the 0-6-mm macular region and reduced CT and diminished blood flow indicated an association with myopia.

Ocular blood flow evaluation by laser speckle flowgraphy in pediatric patients with anisometropia

Purpose

To determine the differences and reproducibility of blood flow among hyperopic anisometropic, fellow, and control eyes.

Methods

We retrospectively studied 38 eyes of 19 patients with hyperopic anisometropia (8.2 ± 3.0 years of age) and 13 eyes of eight control patients (6.8 ± 1.9 years). We measured the optic nerve head (ONH) and choroidal circulation using laser speckle flowgraphy (LSFG) and analyzed the choroidal mean blur rate (MBR-choroid), MBR-A (mean of all values in ONH), MBR-V (vessel mean), MBR-T (tissue mean), and sample size (sample), which are thought to reflect the ONH area ratio, area ratio of the blood stream (ARBS). We then assessed the coefficient of variation (COV) and intraclass correlation coefficient (ICC) and compared the differences among amblyopic, fellow, and control eyes in MBR, sample, and ARBS.

Results

The ONH, MBR-A, MBR-T, and ARBS of amblyopic eyes were significantly higher than those of fellow eyes (P < 0.01, P < 0.05, and P < 0.05, respectively), and control eyes (MBR-A and ARBS, P < 0.05, for both comparisons). The sample-T (size of tissue component) in amblyopic eyes was significantly smaller than that in fellow and control eyes (P < 0.05). Blood flow in the choroid did not differ significantly between the eyes. The COVs of the MBR, sample, and ARBS were all ≤10%. All ICCs were ≥0.7. The COVs of pulse waveform parameter fluctuation, blowout score (BOS), blowout time (BOT), and resistivity index (RI) in the ONH and choroid were ≤10%.

Conclusion

The MBR value of the LSFG in children exhibited reproducibility. Thus, this method can be used in clinical studies. The MBR values of the ONH in amblyopic eyes were significantly high. It has been suggested that measuring ONH blood flow using LSFG could detect the anisometropic amblyopic eyes.

Retrobulbar Blood Flow Parameters in Patients With Anisometropic Amblyopia

Introduction We aim to compare retrobulbar blood flow parameters between the amblyopic eye and the fellow eye in patients with anisometropic amblyopia. Methods Peak systolic velocity (PSV) and end-diastolic velocity (EDV) of the ophthalmic artery (OA), central retinal artery (CRA), and posterior ciliary artery (PCA) were measured by color Doppler imaging (CDI), and the resistivity index (RI) and pulsatility index (PI) were calculated in 62 patients aged 12-40 years with anisometropic amblyopia. Results The mean PSV values of OA, CRA, and PCA in amblyopic and fellow eyes were 30.38 ± 10.34, 8.45 ± 2.27, and 8.03 ± 2.77, and 33.73 ± 14.46, 8.35 ± 2.05, and 8.81 ± 2.77, respectively. The mean EDV values of OA, CRA, and PCA in amblyopic and fellow eyes were 6.86 ± 2.64, 1.47 ± 1.59, and 1.94 ± 2.03, and 8.57 ± 4.30, 1.80 ± 1.73, and 2.32 ± 1.20, respectively. The mean RI values of OA, CRA, and PCA in amblyopic and fellow eyes were 0.77 ± 0.10, 0.85 ± 0.14, and 0.78 ± 0.15, and 0.75 ± 0.07, 0.79 ± 0.20, and 0.74 ± 0.13, respectively. OA-PSV and OA-EDV values were significantly lower in the amblyopic eye than in the healthy eye (p < 0.05). OA-RI values were significantly higher (p < 0.05) in the amblyopic eye than in the healthy eye. Conclusions Considering the decrease in PSV and EDV and the increase in RI, which are the blood flow parameters of the amblyopic eye, our study may provide guidance to focus on increasing blood flow in the treatment of amblyopia.

Association of Ambulatory Blood Pressure and Other Factors With Intraocular Pressure-Related 24-Hour Contact Lens Sensor Profile in Untreated Glaucoma

Purpose

To investigate the association of diurnal blood pressure (BP) and other factors with the intraocular pressure (IOP)–related 24-hour contact lens sensor (CLS) profile of patients with untreated glaucoma.

Methods

The prospective study included 82 patients with untreated normal-tension glaucoma. CLS measurements and ambulatory BP monitoring were performed simultaneously for 24 hours. The association between the mean arterial pressure (MAP) and CLS profile was examined for the daytime and nocturnal periods using linear regression analysis. The associations between other factors and the CLS profile were also examined.

Results

Multivariate analysis of data from 63 eligible patients showed that higher average MAPs were significantly associated with larger average nocturnal CLS values (β coefficient = 0.273; P = 0.023); a larger increase in the last CLS value (β coefficient = 0.366; P = 0.003); larger standard deviations (SDs) of CLS values for the daytime, nocturnal, and 24-hour periods (β coefficient = 0.407, 0.293, and 0.375; P < 0.001, P = 0.032 and 0.002, respectively); and higher average ocular pulse frequencies for the daytime, nocturnal, and 24-hour periods (β coefficient = 0.268, 0.380, and 0.403; P = 0.029, 0.002, and 0.001, respectively). Thicker subfoveal choroids and shorter axial length were significantly associated with larger SDs and larger average CLS values, respectively. Smaller anterior chamber volume and lower corneal hysteresis were associated with larger SDs or larger average ocular pulse amplitude.

Conclusions

Ambulatory BP and several ocular parameters were significantly associated with various parameters of the 24-hour CLS profile.

Translational Relevance

Ambulatory BP and ocular parameters may be modifiers of the 24-hour IOP-related profile of CLS.

Changes in Retinal Optical Coherence Tomography Angiography Indexes Over 24 Hours

Purpose

To evaluate changes in the retinal microvasculature of young adults over 24 hours using optical coherence tomography angiography (OCT-A).

Methods

Participants (n = 44, mean age 23.2 ± 4.1 years, 24 myopes and 20 nonmyopes) with normal ophthalmological findings were recruited. Two macular OCT-A and OCT scans, systemic blood pressure, intraocular pressure (IOP), and biometry measurements were taken every four hours over 24 hours. Superficial and deep retinal layer en face images were analyzed to extract magnification-corrected vascular indexes using image analysis including foveal avascular zone metrics, vessel density, and perfusion density for the foveal, parafoveal, and perifoveal zones.

Results

Significant diurnal variations (P < 0.001) were observed in the vessel and perfusion density in the three superficial retinal layer regions, with acrophase between 4:30 PM and 8:30 PM. Only foveal and parafoveal regions of the deep retinal layer exhibited significant diurnal variations with acrophase between 9 AM and 3 PM. Myopes and nonmyopes had different acrophases but not amplitudes in the parafoveal perfusion density of superficial retinal layer (P = 0.039). Significant correlations were observed between diurnal amplitudes or acrophases of superficial retinal layer indexes and systemic pulse pressure, IOP, axial length and retinal thickness.

Conclusions

This study shows, for the first time, that significant diurnal variation exists in OCT-A indexes of macular superficial and deep retinal layer over 24 hours and were related to variations in various ocular and systemic measurements. Myopes and nonmyopes showed differences in the timing but not in amplitude of the superficial retinal layer parafoveal perfusion density variations but not in deep retinal layer.

Choroidal thickness and choriocapillaris vascular density in myopic anisometropia

BACKGROUND

This study aims to examine interocular differences in the choroidal thickness and vascular density of the choriocapillaris in anisometropic myopes and to further explore the relationship between choroidal blood flow and myopia.

METHODS

The sample comprised 44 participants with anisometropic myopia, aged 9 to 18 years, with normal best-corrected visual acuity. All participants underwent a series of examinations, including spherical equivalent refraction (SER) and axial length (AL), measured by a Lenstar optical biometer and optical coherence tomography angiography (OCTA) scanner. OCT measured the choroidal thickness, vascular density, and flow voids of the choriocapillaris, and a customized algorithm was implemented in MATLAB R2017a with the post-correction of AL. The choroidal thickness was measured at the fovea and 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm nasally, temporally, inferiorly, and superiorly to the fovea. The vascular density and the flow voids of the choriocapillaris were measured at a 0.6-mm-diameter central circle, and the 0.6-2.5 mm diameter circle in the nasal, temporal, inferior, and superior regions. Repeated-measured ANOVAs were used to analyze the interocular differences. Partial correlations with the K value and age adjustments were used to study the relationships between the choroidal thickness, the choriocapillaris vascular density and flow voids, the SER and AL.

RESULTS

The choroidal thickness of the more myopic eyes was significantly thinner than less myopic eyes (P ≤ 0.001), and the flow voids in the more myopic eyes were more than less myopic eyes (P = 0.002). There was no significant difference in the vascular density of the choriocapillaris between the more and less myopic eyes (P = 0.525). However, when anisometropia was more than 1.50 D, the vascular density of choriocapillaris in the more myopic eyes was significantly less than the less myopic eyes (P = 0.026). The interocular difference of the choroidal thickness was significantly correlated with the interocular difference in SER and AL in the center, superior, and inferior regions but not in the nasal or temporal regions. The interocular differences of the vascular density and the flow voids of the choriocapillaris were not correlated with the interocular difference of SER and AL.

CONCLUSIONS

The choroidal thickness is thinner in the more myopic eyes. The flow void is increased, and the vascular density of the choriocapillaris is reduced in the more myopic eyes of children with anisometropia exceeding 1.50 D.

Ocular Anatomical and Functional Characteristics in Anisometropic Chinese Children

SIGNIFICANCE

This research found that anterior and posterior biometrics differ in many aspects between fellow eyes of anisometropic children. This might shed light on the mechanisms underlying the onset and progression of anisometropia and myopia.

PURPOSE

This study aimed to investigate the ocular biometric parameters, peripheral refraction, and accommodative lag of fellow eyes in anisometropic children.

METHODS

Anisometropic children were recruited. Axial length (AL), vitreous chamber depth (VCD), central corneal thickness, anterior chamber depth (ACD), lens thickness (LT), simulated K readings, central and peripheral refractive errors, and accommodative lag were measured in both eyes. The subfoveal choroidal thickness, average choroidal thickness, and choroid vessel density of the 6 × 6-mm macular area were measured by optical coherence tomography.

RESULTS

Thirty-two children aged 11.1 ± 1.7 years were enrolled. The average degree of anisometropia was 2.49 ± 0.88 D. The AL, VCD, ACD, and simulated K reading values were significantly larger in the more myopic eyes, whereas the LT value was significantly smaller. Subfoveal choroidal thickness (P = .001) and average choroidal thickness (P = .02) were smaller in the more myopic eyes than in the contralateral eyes, whereas choroid vessel density (P = .03) was larger. The amount of anisometropia had a significant positive correlation with the difference in AL (r = 0.869, P < .001), VCD (r = 0.853, P < .001), and ACD (r = 0.591, P < .001) and a negative correlation with the difference in LT (r = -0.457, P = .009).

CONCLUSIONS

Ocular biometrics differ in many aspects between the fellow eyes of anisometropic Chinese children, and the difference is correlated with the degree of anisometropia.

Correlation between retrobulbar blood flow parameters and retinal nerve fiber, ganglion cell and inner plexus layer thickness in myopia

PURPOSE

To assess the thickness of the retinal nerve fiber layer (RNFL), ganglion cell and inner plexus layer (GCIPL) and blood flow parameters in retrobulbar vessels, and to analyze correlations between these parameters in myopes.

METHODS

The study included forty myopic and 20 healthy eyes. Standard eye examination was supplemented with OCT of the optic nerve and macula (GCIPL, RNFL, RNFL in each quadrant and rim area of the optic nerve) and color Doppler imaging of retrobulbar arteries [peak systolic and end-diastolic velocities, pulsatile index and resistance index (RI) in the ophthalmic (OA), central retinal (CRA), nasal posterior ciliary and temporal posterior ciliary arteries].

RESULTS

Significant correlations were found between blood flow parameters in the CRA, RNFL and GCIPL thickness, and axial length (AL) and spherical equivalent (SE). There were significant positive correlations between RNFL with PSV and EDV in the CRA and negative correlations between RNFL and RI in the CRA. GCIPL was positively correlated with PSV and EDV in the CRA. The decrease in RA was associated with reduced blood flow velocities in the CRA, TPCA and NPCA.

CONCLUSION

The reduced retrobulbar blood flow in healthy young myopes is correlated with increasing AL and refractive value, and thinning of the RNFL and GCIPL. Reduction of the rim-area of the optic disc is associated with vascular and retinal circulatory disorders. These phenomena indicate the vascular basis of the described changes. To the best of our knowledge, this is the first study which correlates ocular circulation with retinal structure.

Should Pearson's correlation coefficient be avoided?

PURPOSE

To survey the use of Pearson's correlation coefficient (r) and related statistical methods in the ophthalmic literature, to consider the limitations of r, and to suggest suitable alternative methods of analysis.

RECENT FINDINGS

Searching Ophthalmic and Physiological Optics (OPO), Optometry and Vision Science (OVS), and Clinical and Experimental Optometry (CXO) online archives using correlation and Pearson's r as search terms resulted in 4057 and 281 hits respectively. Coefficient of determination, r square, or r squared received fewer hits (65, 8, and 22 hits respectively). The assumption that r follows a bivariate normal distribution was rarely encountered (3 hits) although several studies applied Spearman's rank correlation (70 hits). The intra-class correlation coefficient (ICC) was widely used (178 hits), but fewer hits were recorded for partial correlation (43 hits) and multiple correlation (13) hits. There was little evidence that the problem of sample size was addressed in correlation studies.

SUMMARY

Investigators should be alert to whether: (1) the relationship between two variables could be non-linear, (2) the data are bivariate normal, (3) r accounts for a significant proportion of the variance in Y, (4) outliers are present, the data are clustered, or have a restricted range, (5) the sample size is appropriate, and (6) a significant correlation indicates causality. In addition, the number of significant digits used to express r and the problems of multiple testing should be addressed. The problems and limitations of r suggest a more cautious approach regarding its use and the application of alternative methods where appropriate.

Interocular Difference of Peripheral Refraction in Anisomyopic Eyes of Schoolchildren

Purpose

Refraction in the peripheral visual field is believed to play an important role in the development of myopia. The purpose of this study was to investigate the differences in peripheral refraction among anisomyopia, isomyopia, and isoemmetropia for schoolchildren.

Methods

Thirty-eight anisomyopic children were recruited and divided into two groups: (1) both eyes were myopic (anisomyopic group, AM group) and (2) one eye was myopic and the contralateral eye was emmetropic (emmetropic anisomyopic group, EAM group). As controls, 45 isomyopic and isoemmetropic children were also recruited with age and central spherical equivalent (SE) matched to those of the AM and EAM groups. The controls were divided into three groups: (1) intermediate myopia group (SE matched to the more myopic eye of AM group), (2) low myopia group (SE matched to the less myopic eye of AM group and the more myopic eye of EAM group), and (3) emmetropia group (SE matched to the less myopic eye of EAM group). Peripheral refraction at 7 points across the central ±30° on the horizontal visual field with a 10° interval was measured with an autorefractor. Axial length (AL), corneal curvature (CC), and anterior chamber depth (ACD) were also determined by using the Zeiss IOL-Master.

Results

The relative peripheral spherical equivalent [RPR(M)] and relative peripheral spherical value [RPR(S)] of the more myopic eye was shifted more hyperopically than the contralateral eye in both the AM and the EAM groups (both p<0.0001). The RPR(M, S) of the less myopic eyes in the AM and EAM groups showed a relatively flat trend across the visual field and were not significantly different from the emmetropia group. The RPR(M, S) of less myopic eyes in the AM group were shifted less hyperopically than in the isomyopic low myopia group and the more myopic eye of the EAM group [RPR(M), p = 0.007; RPR(S), p = 0.001], although the central SEs of the three groups were not significantly different from each other. However, RPR(M, S) of the more myopic eyes were not different from the corresponding isomyopic groups. There was also no significant difference in the relative peripheral astigmatism [RPR(J0, J45)] between the more and the less myopic eyes in either the AM or the EAM group.

Conclusion

Refraction of anisomyopia differs between the two eyes not only at the central visual field but also at the off-axis periphery. The relative peripheral refraction of the more myopic eye of anisomyopia was shifted hyperopically, as occurs in isomyopia with similar central subjective SE values. Less myopic eyes were much less hyperopically shifted in relative peripheral refraction than the corresponding isomyopic eyes, but are comparable to emmetropic eyes. This emmetropia-like relative peripheral refraction in less myopic eyes might be a factor responsible for slowing down the progression of myopia.

[Effects of blood flow properties on ocular hemodynamics]

AIM

to study the effects of blood rheology on ocular blood flow (OBF) parameters and estimated individual normal range of intraocular pressure (IOP).

MATERIAL AND METHODS

A total of 15 patients (15 eyes) taking warfarin were enrolled. Volumetric parameters and linear velocity of OBF under warfarin treatment and after its cessation were obtained by means of flowmetry (Paradigm's Blood Flow Analyzer) and color Doppler flow mapping (Voluson 730), respectively. On the basis of flowmetry results an individual normal range of IOP was calculated in all patients.

RESULTS

Pulsatile OBF does not appear to correlate with warfarin-induced changes in blood rheology (p = 0.09), however, depends on IOP fluctuations (p = 0.02). Resistance index of retinal vessels is found to rise significantly with increasing blood viscosity (p < 0.05).

CONCLUSION

The use of warfarin, an indirect thrombin inhibitor, has no effect on estimated individual normal range of IOP, which is crucial for glaucoma diagnosis and monitoring.

The effect of anisometropic amblyopia on retrobulbar blood flow parameters. Anisometropic amblyopia and retrobulbar blood flow

To look for a correlation between or the effect of anisometropia amblyopia on retrobulbar blood flow parameters. Peak systolic velocity (PSV) and end-diastolic velocity (EDV) of the ophthalmic artery (OA), central retinal artery (CRA), and temporal posterior ciliary artery (tPCA) were measured with color Doppler imaging, and systolic/diastolic ratio, resistivity index (RI), and pulsatility index (PI) were computed in 42 patients with anisometropic amblyopia. The mean PSV of OA, CRA, and tPCA in amblyopic and fellow eyes were 62.69 ± 24.04, 62.64 ± 20.18; 9.28 ± 3.71, 10.27 ± 4.18; 10.81 ± 4.59, 11.28 ± 4.91, respectively. The mean EDV of OA, CRA, and tPCA in amblyopic and fellow eyes were 15.87 ± 11.31, 14.52 ± 6.54; 2.48 ± 1.17, 2.62 ± 2.06; 3.04 ± 2.34, 3.14 ± 2.18, respectively. The mean RI of OA, CRA, and tPCA in amblyopic and fellow eyes were 0.76 ± 0.08, 0.76 ± 0.08; 0.72 ± 0.08, 0.74 ± 0.95; 0.72 ± 0.09, 0.72 ± 0.08, respectively. The mean PI of OA, CRA, and tPCA in amblyopic and fellow eyes were 1.77 ± 0.42, 1.81 ± 0.46; 01.58 ± 0.42, 1.59 ± 0.43; 1.54 ± 0.43, 1.58 ± 0.49, respectively. There was no statistically significant difference in any of the measured parameters between the amblyopic and fellow eyes. Anisometropic amblyopia did not cause any change in retrobulbar blood flow in amblyopic eyes.

Significant correlations between optic nerve head microcirculation and visual field defects and nerve fiber layer loss in glaucoma patients with myopic glaucomatous disk

BACKGROUND

Eyes with glaucoma are characterized by optic neuropathy with visual field defects in the areas corresponding to the optic disk damage. The exact cause for the glaucomatous optic neuropathy has not been determined. Myopia has been shown to be a risk factor for glaucoma. The purpose of this study was to determine whether a significant correlation existed between the microcirculation of the optic disk and the visual field defects and the retinal nerve fiber layer thickness (RNFLT) in glaucoma patients with myopic optic disks.

METHODS

Sixty eyes of 60 patients with myopic disks were studied; 36 eyes with glaucoma (men:women = 19:17) and 24 eyes with no ocular diseases (men:women = 14:10). The mean deviation (MD) determined by the Humphrey field analyzer, and the peripapillary RNFLT determined by the Stratus-OCT were compared between the two groups. The ocular circulation was determined by laser speckle flowgraphy (LSFG), and the mean blur rate (MBR) was compared between the two groups. The correlations between the RNFLT and MBR of the corresponding areas of the optic disk and between MD and MBR of the optic disk in the glaucoma group were determined by simple regression analyses.

RESULTS

The average MBR for the entire optic disk was significantly lower in the glaucoma group than that in the control group. The differences of the MBR for the tissue in the superior, inferior, and temporal quadrants of the optic disk between the two groups were significant. The MBR for the entire optic disk was significantly correlated with the MD (r = 0.58, P = 0.0002) and the average RNFLT (r = 0.53, P = 0.0008). The tissue MBR of the optic disk was significantly correlated with the RNFLT in the superior, inferior, and temporal quadrants.

CONCLUSIONS

Our study suggests that there is a causal relationship between the thinner RNFLT that led to the MD and reduction in the microcirculation in the optic nerve head.

A study comparing ocular pressure pulse and ocular fundus pulse in dependence of axial eye length and ocular volume

PURPOSE

There is a long-standing discussion about whether myopia is associated with decreased choroidal blood flow, as suggested by pneumotonometric measurements of pulsatile ocular blood flow (POBF). However, it has been noted previously that calculations of POBF depend on intraocular volume.

METHODS

In the present study we investigated this volume dependence through the comparison of ocular pressure pulse and ocular fundus pulse. Fifty-one healthy participants with different refractive errors participated in the study. Pulse amplitude (PA) and POBF were measured using pneumotonometry. Fundus pulsation amplitude (FPA) was measured with laser interferometry. Axial eye length (AEL) was measured with partial coherence interferometry. A mathematical model was used to calculate choroidal volume changes based on FPA. The ocular pressure pulse was converted into pulse volume (PV) according to the standard procedure used for pneumotonometry.

RESULTS

PA and POBF were found to decrease with increasing axial length (r = -0.55, p < 0.001 and r = -0.57, p < 0.001, respectively). A similar relationship existed for PV (r = -0.57, p < 0.001) and FPA (r = -0.46, p = 0.001). In addition, there was a significant association between PV and choroidal volume change during the cardiac cycle (r = 0.61, p < 0.001).

CONCLUSION

The present study confirms experimentally that PA, FPA and POBF are dependent on ocular volume and indicates that the pulsatile component of ocular blood flow is not reduced in myopic patients. Accordingly, the relationship between AEL and POBF described previously appears to be a consequence of different ocular volumes. Our findings have important implications for studies using PA or POBF.

Correlation among choroidal, parapapillary, and retrobulbar vascular parameters in glaucoma

PURPOSE

To study and compare the correlation among choroidal, parapapillary, and retrobulbar vascular parameters in healthy subjects, glaucoma suspects, and open-angle glaucoma (OAG) patients.

DESIGN

Prospective observational clinical study.

METHODS

The study included one randomly selected eye from 21 normal subjects, 30 glaucoma suspects based on optic disc appearance, and 22 OAG patients. The pulsatile ocular blood flow (POBF), a measure of choroidal blood flow, was assessed using ocular blood flow analyzer whereas parapapillary blood flow and blood velocity of retrobulbar blood vessels were measured using scanning laser Doppler flowmetry and color Doppler imaging, respectively. All vascular parameters along with blood pressure and intraocular pressure measurements were obtained within a 2-hour period. Univariate regression analyses were used to evaluate the correlation of POBF values with parapapillary blood flow values, retrobulbar blood flow velocities, and resistive index, which represents vascular resistance, in each group. Two multiple linear regression models were created based on results of univariate analyses and included POBF, mean parapapillary blood flow, age, and mean ocular perfusion pressure; and POBF, temporal short posterior ciliary artery resistive index, age, and mean ocular perfusion pressure.

RESULTS

POBF was significantly associated with parapapillary blood flow (r2 = 0.54; P < .001, positive correlation) and temporal short posterior ciliary artery resistive index (r2 = 0.39; P < .001, negative correlation) in normal subjects. Results were consistent when corrected for age, intraocular pressure, and blood pressure parameters. POBF values did not correlate with parapapillary blood flow values or temporal short posterior ciliary artery resistive index in glaucoma suspects or OAG patients.

CONCLUSION

The relationships of POBF with parapapillary blood flow and calculated retrobulbar vascular resistance differs among normal subjects, glaucoma suspects, and OAG patients. This provides further evidence of vascular dysregulation in OAG.

Pulsatile ocular blood flow: relationship with flow velocities in vessels supplying the retina and choroid

BACKGROUND

Although ocular tonography measures a pulsatile component of the ocular perfusion, the retinal and/or choroidal components of this pulsatile flow remain undefined.

AIM

To compare ocular tonography with the assessment of flow velocities in arteries supplying the retina, choroid and entire orbit.

METHODS

22 normal eyes from 11 subjects were studied. Pulsatile ocular blood flow (POBF) was measured using the ocular blood flow tonograph, and flow velocities in the ophthalmic, central retinal (CRA) and temporal short posterior ciliary arteries (TSPCA) using colour Doppler imaging. The correlation between POBF and retrobulbar flow velocities was determined.

RESULTS

POBF correlated significantly with peak systolic velocity (PSV) of the CRA (r = 0.56, p = 0.007) and the TSPCA (r = 0.48, p = 0.02), and with the resistive index of the TSPCA (r = 0.45, p = 0.04). Additionally, pulse amplitude (PSV-end diastolic velocity) in the CRA and the TSPCA correlated significantly with POBF measurements (each p<0.05). However, POBF did not correlate with any flow velocity indices in the ophthalmic artery.

CONCLUSION

POBF is associated with systolic and pulsatile components of blood flow velocities in both the CRA and the TSPCA. This result suggests that POBF determinations are influenced by the pulsatile components of both choroidal and retinal perfusion.

Pulsatile ocular blood flow in patients with asymmetric internal carotid artery stenosis

BACKGROUND

The pulsatile ocular blood flow (POBF) of patients with asymmetric internal carotid artery (ICA) stenosis was measured bilaterally. The purpose of this study was to investigate the sensitivity of POBF assessments in screening for ICA stenosis.

METHODS

Seventeen subjects with asymmetric ICA stenosis confirmed with carotid duplex ultrasound were recruited. The diagnoses of ICA stenosis were categorised into less than 50 per cent, 50 to 69 per cent and 70 per cent or greater. Their POBF and ocular dimensions were measured after local anaesthesia. Twenty-three normal healthy subjects were recruited as the control. All of the subjects had an inter-ocular axial length difference of less than one millimetre.

RESULTS

There were 14 males and three females in the patient group with a median age of 74 years. Fourteen patients had reduced POBF to the eye ipsilateral on the side with greater ICA stenosis. The reduction in POBF ranged from 3.1 to 49.2 per cent. Two patients had reduced POBF contralateral to the side with greater ICA stenosis. One patient had similar POBF between the eyes. The control group included six males and 17 females with a median age of 65 years. The difference in their POBF between the eyes ranged from 0.3 to 13.0 per cent.

CONCLUSIONS

Stenosis of the internal carotid artery was found to reduce the POBF ipsilateral to the side with greater stenosis. The overlap in the difference in inter-ocular POBF between the patient and control groups led to a low sensitivity (calculated as 41.2 per cent) for screening ICA stenosis from an assessment of POBF. Therefore, POBF assessment is not a good diagnostic tool for screening for ICA stenosis.

Effect of breath-holding on pulsatile ocular blood flow measurement in normal subjects

BACKGROUND

The Valsalva maneuver is known to affect intraocular pressure (IOP). Simple breath-holding may cause IOP elevation. A recent study demonstrated a decrease in pulsatile ocular blood flow (POBF) during forcible exhalation. This study investigated whether breath-holding could affect POBF measurement.

METHODS

Thirty-eight healthy young adults were recruited. Their POBF's were measured with an ocular blood flow pneumatonometer. The first set of measurements was made using normal measurement protocol. Three consecutive readings were obtained, and the mean was used for analysis. The second set of measurements was taken after 5-min rest, and the subjects were required to hold their breath during the acquisition period.

RESULTS

As previously reported, POBF reduced with increasing myopia. There was no significant change in IOP, pulse rate, POBF, and pulse amplitude between normal protocol and breath-holding condition. POBF and pulse amplitude demonstrated a greater variation, shown by coefficient of variation, when subjects held their breath.

CONCLUSIONS

This study found a greater variation in consecutive POBF measurements during breath-holding condition. There was no significant difference in either POBF or pulse amplitude during breath-holding session, probably because of the use of three consecutive measurements, and averaged results were generated from them. It is advised to measure the POBF by taking consecutive readings, and subjects should not hold their breath.

The Validity of a New Noncontact Tonometer and Its Comparison with the Goldmann Tonometer

PURPOSE

This study compared a new noncontact tonometer (NCT), the Nidek NT-4000 (Nidek Co., Ltd., Aichi, Japan), with a pulse detection feature; an earlier model, the Nidek NT-2000, without this pulse detection facility; and Goldmann tonometry.

METHODS

Thirty-one young subjects had their intraocular pressure (IOP) in one eye randomly measured by two NCT's, followed by a Goldmann tonometer. The pulse detection mode used by the NT-4000 included synchronizing the IOP with the peak of the pulse (P-P), the middle of the pulse (P-M), or the bottom of the pulse (P-B). The order of measurements from these three modes was also random. Three consecutive readings were obtained from each mode/tonometer, and the mean was used for analysis.

RESULTS

Goldmann tonometry demonstrated the smallest variation from consecutive measurements (coefficient of variation, <4%), followed by the NT-4000 (coefficient of variation, <5% in various modes) and the NT-2000 (coefficient of variation, >5%). For the NT-4000, the mean IOP decreased from the highest in the P-P mode (16.1 mm Hg) to the lowest in the P-B mode (14.7 mm Hg), with the P-M mode in the middle. A significant difference was found among the IOP readings using the NT-4000 (in various modes), NT-2000, and Goldmann tonometry (repeated-measures analysis of variance, p < 0.01). More than 80% of the results from the NT-4000 were within 3 mm Hg of those from the Goldmann tonometry.

CONCLUSIONS

The pulse detection feature from this new NCT could capture and monitor pulse waves, thus reducing the variations in the consecutive measurements. The NT-4000 also performed better than the NT-2000 when compared with the Goldmann tonometry.