Year : 2003 | Volume
: 51 | Issue : 2 | Page : 133--138
Pulsatile ocular blood flow among normal subjects and patients with high tension glaucoma
Harish C Agarwal, V Gupta, R Sihota, K Singh
Dr. R P Centre for Ophthalmic Sciences, All Institute of Medical Sciences, New Delhi, India
Harish C Agarwal
Dr. R P Centre for Ophthalmic Sciences, All Institute of Medical Sciences, New Delhi
Purpose: To estimate pulsatile ocular blood flow (POBF) among normal subjects and to compare various parameters in eyes of primary open angle glaucoma with high intraocular pressure (IOP).
Methods: POBF was estimated in 95 eyes of 95 normal subjects above the age of 40 years and in 35 eyes of 35 primary open angle glaucoma patients using the OBF system (OBF Labs Ltd., UK). Correlation of age, gender, IOP, pulse amplitude, pulse volume and pulse rate with POBF was studied. POBF values were measured in glaucomatous patients before IOP control and one month later after control of IOP to <22mmHg.
Results: The mean POBF among normal subjects was 1382.2 + 413ml/min (range 636-2291m/min). Females had a significantly higher mean POBF (1512 + 347ml/min) than males (1193 + 312ml/min). The mean IOP among normal subjects was 12.6mmHg and in glaucoma patients, 29.1mmHg. Mean POBF in glaucomatous eyes with initially elevated IOP was 718.9 + 322.6 ml/min, which improved after IOP control to 1129 + 291ml/min. IOP had a strong (P<.01) negative correlation with POBF
(r = -0.667)
Conclusions: POBF among eyes of normal subjects in this study is higher than reported among Caucasian eyes. Primary open angle glaucoma eyes with high IOP have significantly reduced ocular blood flow. Therapy aimed at lowering IOP has a positive effect on ocular haemodynamics.
|How to cite this article:|
Agarwal HC, Gupta V, Sihota R, Singh K. Pulsatile ocular blood flow among normal subjects and patients with high tension glaucoma.Indian J Ophthalmol 2003;51:133-138
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Agarwal HC, Gupta V, Sihota R, Singh K. Pulsatile ocular blood flow among normal subjects and patients with high tension glaucoma. Indian J Ophthalmol [serial online] 2003 [cited 2020 Sep 22 ];51:133-138
Available from: http://www.ijo.in/text.asp?2003/51/2/133/14715
Pulsatile ocular blood flow (POBF) is due to the pulsatile waveform created as blood passes through the eye with each heart beat. Pulsatile ocular blood flow measures 70% of the total blood flow to the eye and it is known that 85% of the total blood flow is choroidal circulation., Since it is the choroidal flow which supplies the optic nerve, POBF assumes importance in the evaluation of glaucomatous damage. POBF can also be affected by systemic and local drugs and in conditions like retinitis pigmentosa, diabetic retinopathy and carotid artery stenosis.,, The OBF system calculates the ocular blood flow based on the amplitude of IOP variation. Several studies have been done to assess POBF in normal subjects among Caucasian eyes, ,, including testing of its reproducibility., However, there are limited reports of POBF values among Asians. In this study we estimated POBF values among normal Indian subjects and in primary open angle glaucoma patients with high IOP and again after IOP control.
Material and Methods
Ninety-five normal subjects who reported for routine presbyopic check up and satisfied the inclusion criteria were enrolled in the study, which was carried out over 6 months. Inclusion criteria were age above 40 years, IOP + 2 DSph, relatives of glaucoma patients, those with any fundus pathology and those with systemic diseases or on systemic drugs. Only one eye of each subject was selected randomly (computerised randomisation) for inclusion in the study.
Thirty five patients of bilateral primary open angle glaucoma (POAG) reporting to the glaucoma clinic for the first time were included. Diagnostic criteria for POAG was a record of IOP > 22mmHg on two successive occasions, optic disc cupping greater than 0.5 in the presence of glaucomatous field defects, and open angles on gonioscopy. Visual field examination was performed with central 30-2 full threshold program of the Humphrey field analyser 645 (Humphrey Instruments, San Leandro, CA, USA). The minimum criterion for defining a glaucomatous field defect was the presence of a cluster of 3 abnormal points in the expected area of the same hemifield with pattern deviation probability less than 2% and at least one point less than 1% or at least 2 adjacent points with a pattern deviation less than 1% and glaucoma hemifield outside normal limits. Patients had similar exclusion criteria as normal subjects. Patients were recruited only if their IOP readings on previous occasions was >22mmHg without antiglaucoma therapy and was confirmed high on applanation tonometry and OBF tonography. Only one eye of each patient was selected randomly (by computer generated randomisation) for inclusion in the study. Glaucoma patients and normal subjects were matched for comparison by age, gender and refraction. All patients were re-examined after control of IOP to less than 22mmHg one month later.
Informed consent was obtained from each healthy volunteer and from patients after explaining the procedure. A detailed history to rule out any systemic illness or intake of systemic drugs was taken. Blood pressure was recorded in all subjects. Slitlamp and fundus examination were performed. Axial length was measured with the Sonomed Inc (Lake Success, NY, USA). POBF was recorded in sitting position after instillation of 4% topical lignocaine. The subjects were tested twice over a period of one hour and the mean of the two readings was considered for data analysis
We used an OBF system (OBF Labs Ltd, UK) which has a pneumotonometer that transmits IOP change signals as changes in ocular blood flow. The POBF measurements are derived assuming a standard scleral rigidity and assuming that the outflow of blood from the eye is nonpulsatile. The signals can be recorded over a period of 5-20 seconds; we used the 20-second cycle. The attached computer automatically selects 5 representative pulses; other pulses which do not approximate these are discarded. The IOP, pulse amplitude, pulse volume, pulse rate and the POBF are recorded and stored in a database.
The Shapiro-Wilks test was used to determine whether POBF values among healthy subjects conformed to a normal distribution. Mean and standard deviation were calculated for males and females in both the groups. Multiple stepwise linear regression analysis was performed to determine the influence of age, IOP, pulse amplitude, pulse volume and pulse rate on POBF among normal subjects. The 't' test was used to compare whether differences between the normal and glaucoma subjects were statistically significant. A p-value of + 9.7 years. The mean IOP was 29.1 + 6.8 mmHg and mean axial length was 22.72 + 1.2 mm. The mean PA, PV and PR were 3.4 + 1.46mmHg, 4.3 + 1.9ml, and 77.9 + 17 per minute respectively. The mean POBF among glaucoma subjects was significantly lower [719.9 + 322ml/min (range 139-1504ml/min)] than among normal subjects (P + 8.6 years and mean IOP was 12.6 + 4 mmHg. Mean axial length was 22.84 + 1.1mm. The mean values of PA, PV, PR were 3.5 + 1.3mmHg, 8.5 + 3ml, and 79 + 13 per minute respectively. The mean POBF among the normal subjects was 1382.2 + 387ml/min (range 636-2291ml/min). The histogram [Figure 1] of POBF among normal subjects assumes a normal distribution curve (Shapiro-Wilks test, P=0.09). Univariate and multivariate regression analysis was done with POBF as the dependent variable; and age, IOP, mean blood pressure, pulse amplitude (PA), pulse volume (PV) and pulse rate (PR) as independent variables. Age did not show correlation with POBF. IOP had a statistically significant (P also did not show correlation with POBF (r=0.012). Both PA and PR had weak correlation with POBF (r=0.11) which was statistically not significant (P=0.45). However, PV had a significantly ( P + 6.8 mmHg to 16.2 + 2.3mmHg after therapy. Mean POBF increased from 719.9 + 322ml/min to 1129 + 291.4ml/min after therapy (P 6sub and 16.3 mmHg 7sub ) compared to ours. [Table 3] compares the values of pulsatile ocular blood flow in normal subjects by previous authors with ours. The latest version of the OBF tonometer used in our study is different from the Langham tonometer used in two reports, and the older version of the OBF system used in another study, which could also account for differences in POBF measurements seen.
Axial length is shown to have a significant negative correlation with POBF. This is because the pulse wave depends on the volume of choroidal vascular bed and the relationship between volume and pressure changes in the individual eye. A similar volume of blood entering the eye will thus produce greater pressure change in smaller hyperopic eyes than in larger myopic eyes. Axial length of the normal subjects was within normal range as we had excluded patients with refractive error of greater than ± 2D. This was probably the reason we did not find an association of this parameter associated with POBF.
Primary open angle glaucoma patients with high IOP underwent POBF measurement before IOP control measures were undertaken. Mean POBF was significantly lower in this group than in normal subjects. It has been experimentally confirmed that blood supply to the optic disc and peripapillary choroid is most susceptible to raised IOP., After IOP was controlled by antiglaucoma therapy in our study , POBF improved in each eye though the mean ocular blood flow in treated eyes of glaucoma patients remained lower than the normal subjects. Although the IOP of these eyes after treatment was higher than the mean IOP in the normal subjects, it is known that despite similar eye pressure, eyes of open angle glaucoma patients have lower perfusion than ocular hypertensives., The mode of treatment was not used for analysis. Nor did we aim to correlate the POBF with degree of glaucomatous defect in these eyes. It is possible that other forms of medical therapy can bring changes in POBF to a different extent.
Till date no direct method of clinically measuring the optic nerve circulation exists. The observations in this study, however, confirm the possibility of IOP rise contributing to optic nerve damage by reducing the blood flow. This study also assumes importance in providing reference values at different IOP ranges in normal and glaucomatous subjects and would be useful in evaluating further studies using the OBF tonograph.
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