Ocular blood flow study using color doppler imaging: Normative value and its relevance in glaucoma

Pratheeba Devi Nivean; Murali Ariga; M Nivean; Malarchelvi Palani

doi:10.4103/tjosr.tjosr_135_20

ORIGINAL ARTICLE

Year : 2021 | Volume : 59 | Issue : 1 | Page : 10-12

Ocular blood flow study using color doppler imaging: Normative value and its relevance in glaucoma

Pratheeba Devi Nivean¹, Murali Ariga², M Nivean¹, Malarchelvi Palani¹
¹ Department of Ophthalmology, M N Eye Hospital, Chennai, Tamil Nadu, India
² Department of Ophthalmology, Swamy Eye Clinic, Villivakkam, Chennai, Tamil Nadu, India

Date of Submission	12-Sep-2020
Date of Acceptance	30-Jan-2021
Date of Web Publication	27-Mar-2021

Correspondence Address:
Dr. Pratheeba Devi Nivean
M N Eye Hospital, 781 T H Road, Tondiarpet, Chennai - 600 021, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/tjosr.tjosr_135_20

Abstract

Aim: The aim was to study the normative pattern of ocular blood flow (OBF) using color Doppler imaging. Materials and Methods: It was a prospective study including healthy volunteers without any ocular pathology. Results: We analyzed ocular blood flow for 25 eyes of consecutive normal patients. Our study had 14 males and 11 females. The standard deviation of the resistive index of Ophthalmic artery, Central retinal artery and short posterior ciliary artery were 0.07, 0.08 and 0.12 respectively. Discussion: Ischemia to the optic nerve and dysfunctional vascular regulation are likely responsible for glaucomatous damage. Ocular hemodynamics, though complex, can be assessed to an extent by many ways. The quantification of blood flow in these vessels can give great lengths of information with regard to the pathological processes behind retinal and optic nerve head diseases such as glaucoma. Lower ocular perfusion pressure, vascular dysregulation, and lower OBF can worsen glaucoma. Conclusion: To our knowledge, there are no South Indian studies showing the normative data.

Keywords: Color Doppler imaging, glaucoma diagnostics, ocular blood flow

How to cite this article:
Nivean PD, Ariga M, Nivean M, Palani M. Ocular blood flow study using color doppler imaging: Normative value and its relevance in glaucoma. TNOA J Ophthalmic Sci Res 2021;59:10-2

How to cite this URL:
Nivean PD, Ariga M, Nivean M, Palani M. Ocular blood flow study using color doppler imaging: Normative value and its relevance in glaucoma. TNOA J Ophthalmic Sci Res [serial online] 2021 [cited 2021 Jun 16];59:10-2. Available from: https://www.tnoajosr.com/text.asp?2021/59/1/10/312290

Introduction

Glaucoma is a multifactorial optic neuropathy characterized by progressive retinal ganglion cell death and visual field loss. Elevated intraocular pressure (IOP) is the major risk factor for open-angle glaucoma (OAG), however, many individuals with elevated IOP do not develop glaucoma and many individuals with glaucoma progress despite achieving a reasonable level of IOP.^[1],[2],[3]

Growing evidence has shown that ischemia to the optic nerve and dysfunctional vascular regulation are likely responsible for glaucomatous damage in many individuals.^{[4],[5],[6],[7]} In the 2009 World Glaucoma Association report,^[5] a consensus was agreed upon that lower ocular perfusion pressure (OPP), vascular dysregulation, and lower ocular blood flow (OBF) may be involved in OAG.

There are a lot of studies on the evaluation of OBF in the Western world. Unfortunately, there are no Indian studies. We did this study to analyze the trend of OBF in Indian eyes.

Materials and Methods

This investigation was conducted in a tertiary eye hospital. All experimental procedures were confirmed to the tenets of the Declaration of Helsinki and approved by the institutional review board. We included and excluded patients based on inclusion and exclusion criteria. All participants signed informed consent before the procedure.

A study included normal healthy controls with no ocular abnormality, normal optic discs, and IOP below 20 mmHg in both eyes. We excluded patients with glaucoma, cardiovascular disorders, hypertensives, chronic eye disease, any renal or pulmonary disease, using steroids in any form, pregnancy, and lactation. All examinations were performed in both eyes, but one eye (right eye) was analyzed in all patients.

Measurement specifics

Brachial artery blood pressure and pulse were assessed after a 5-min rest period using a calibrated automated sphygmomanometer. IOP was assessed using Goldmann applanation tonometry. OPPs were calculated using the following equation:

(systolic blood pressure [systolic OPP], diastolic blood pressure [diastolic OPP], and IOP).^[8]

Color Doppler imaging

Color Doppler imaging (CDI) was done by a single radiologist in a scan center with a linear probe of frequency 8–10 mmHg in GE Voluson EB ultrasound machine [Figure 1]. CDI measurements were taken in the ophthalmic artery (OA), central retinal artery (CRA), and temporal principal component analysis short posterior ciliary arteries. In each vessel, peak systolic velocity (PSV) and end-diastolic velocity (EDV) was determined, and Pourcelot's resistive index (RI) was calculated (RI = (PSV − EDV)/PSV).

Figure 1: Picture of color Doppler imaging machine

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Examination technique

Ocular color Doppler imaging was conducted in a scan center by a single radiologist. This study was done after a pilot study to evaluate OBF to eliminate the learning curve by the same radiologist. Scanning was done on all participants in supine position with eyes closed and gaze directed at the ceiling. A thick layer of acoustic gel was applied to the closed upper eyelid, and a linear probe of frequency 8–10 mmHg was placed on the temporal part of the closed upper eyelid with examiners hand resting on the orbital margin to minimize pressure on the globe.

The Doppler sample gate (<2 mm) is then placed at the center of the detected vessel to image the spectral pattern. As orbital vessels are frequently parallel to the ultrasound bean, an angle convection of <60 is required when needed and color box steering is sometimes required to attain this. To examine OA, the sample volume is oriented nasally and superior to the optic nerve. CRA is identified next to the central retinal vein as two parallel vascular structures with opposite flow sense included in the hypoechoic central band of the conal region. Short posterior ciliary arteries are visualized in the posterolateral region of the papilla, on both sides, temporal and nasal, respectively. PSV and EDV values are obtained by taking the velocity reading at the peak of the spectral wave pattern and that at the wave trough, respectively. RI was calculated for OA, CRA, and short posterior ciliary arteries as

Results

We analyzed OBF for 25 eyes of consecutive normal patients. Our study had 14 males and 11 females. Our participants were divided into three groups based on their age. There were 3, 17, and 5 people in the age group of 20–40, 41–60, and above 60, respectively. The average pulse rate was 74.2. The average IOP measured in that visit by applanation tonometry was 13.5 mmHg. The mean OPP was 50.2. The standard deviation of the RI of OA, CRA, and short posterior ciliary artery is 0.07, 0.08, and 0.12, respectively [Table 1].

Table 1: Normative data of color doppler imaging in our population

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Discussion

Although it is widely accepted that elevated IOP is the important factor in the progression of glaucoma, local and systemic vascular factors have also been cause for the progressive glaucomatous damage. A population-based study has shown that the risk of progression is more when there is a reduction in diastolic blood pressure below 40 mmHg.^[9] Measurement of systolic BP through 24-h diurnal cycle has shown that progression of the glaucoma is more in patients who have greater nocturnal dips.^[10] Several local vascular alterations such as OA stenosis, decreased blood flow velocities, and increased resistance in the central retinal and short posterior ciliary arteries also cause the progression of the disease.

Chronic optic nerve ischemia has been shown to induce retinal ganglion cell damage independent of IOP. Chronic ocular ischemia may be due to faulty vascular autoregulation and the inability of the vasculature to overcome elevated IOP to maintain adequate perfusion.

Evaluation of ocular perfusion is a challenge. There is no single method to quantitatively determine the total OBF, but a combination gives a better approximation.^[11] Color Doppler imaging measures the blood flow velocities and is the most reliable method for detecting the hemodynamics of the posterior ciliary arteries.^[12] Our study finds the trend of velocities in the vessels responsible for autoregulation and nerve health.

On analysis of the data of our population with another study with normative data, we found that the PSV of our patients was slightly lesser compared to the Western world but the RI is slightly higher in our population in all the three tested vessels.^[13]

A normal wave pattern in a Doppler imaging is biphasic with a peak and trough [Figure 2]a and [Figure 2]b. However, this normal pattern is lost in vascular occlusions and in glaucoma patients. An increase in the RI of retrobulbar vasculature, particularly CRA and short posterior ciliary artery, causes glaucoma according to many studies.

Figure 2: (a and b) Normative picture of the color Doppler imaging showing peak and trough

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CDI has been used for the study of various retinal diseases^[14] including diabetic retinopathy, retinal vascular occlusions, ocular ischemic conditions, retinopathy of prematurity, and also glaucoma.^[15] Limitations of CDI are that it does not provide quantitative information on vessel diameter and it depends on probe placement and further standardization of this technique is required.^[16]

Conclusion

We started doing this study as we did not find any normative values in our population. We found that the PSV of our patients was slightly lesser than the Western world. The RI was higher in all the three vessels than the Western population. Our aim was to obtain normative data before conducting studies on glaucoma patients and to further study the effect of drugs on OBF (this is an ongoing study).

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

This study was funded by Cipla.

Conflicts of interest

There are no conflicts of interest.

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