Establishing the Calibration Curve of a Compressive Ophthalmodynamometry Device.

The relationship between externally applied force and intraocular pressure was determined using an ex-vivo porcine eye model (N=9). Eyes were indented through the sclera with a convex ophthalmodynamometry head (ODM). Intraocular pressure and ophthalmodynamometric force were simultaneously recorded to establish a calibration curve of this indenter head. A calibration coefficient of 0.140 ± 0.009 mmHg/mN was established and was shown to be highly linear (r = 0.998 ± 0.002). Repeat application of ODM resulted in a 0.010 ± 0.002 mmHg/mN increase to the calibration coefficient.Clinical Relevance- ODM has been highlighted as a potential method of non-invasively estimating intracranial pressure. This study provides relevant data for the practical performance of ODM with similar compressive devices.

Empirical retinal venous pulse wave velocity using modified photoplethysmography.

OBJECTIVE: Using the novel imaging method of high-speed modified photoplethysmography we measured the retinal venous pulse wave velocity in a single case. RESULTS: A healthy 30-year-old subject underwent high-speed modified photoplethysmography (120 frames per second) with simultaneous ophthalmodynamometry at 26 Meditron units. A video of the optic nerve was analyzed using custom software. A harmonic regression model was fitted to each pixel in the time series and used to quantify the retinal vascular pulse wave parameters. Retinal venous pulsation at the optic disc was observed as a complex dynamic wall motion, whereas contraction commenced at a point in the vein at the center of the optic disc, and progressed centrifugally. The empirically estimated retinal venous pulse wave velocity at this segment was approximately 22.24694 mm/s. This measurement provides an estimate for future studies in the field.

Non-invasive intracranial pressure assessment.

Assessing intracranial pressure (ICP) remains a cornerstone in neurosurgical care. Invasive techniques for monitoring ICP remain the gold standard. The need for a reliable, safe and reproducible technique to non-invasively assess ICP in the context of early screening and in the neurocritical care environment is obvious. Numerous techniques have been described with several novel advances. While none of the currently available techniques appear independently accurate enough to quantify raised ICP, there is some promising work being undertaken.

Trabecular Meshwork Response to Pressure Elevation in the Living Human Eye.

The mechanical characteristics of the trabecular meshwork (TM) are linked to outflow resistance and intraocular pressure (IOP) regulation. The rationale behind this technique is the direct observation of the mechanical response of the TM to acute IOP elevation. Prior to scanning, IOP is measured at baseline and during IOP elevation. The limbus is scanned by spectral-domain optical coherence tomography at baseline and during IOP elevation (ophthalmodynamometer (ODM) applied at 30 g force). Scans are processed to enhance visualization of the aqueous humor outflow pathway using ImageJ. Vascular landmarks are used to identify corresponding locations in baseline and IOP elevation scan volumes. Schlemm canal (SC) cross-sectional area (SC-CSA) and SC length from anterior to posterior along its long axis are measured manually at 10 locations within a 1 mm segment of SC. Mean inner to outer wall distance (short axis length) is calculated as the area of SC divided by its long axis length. To examine the contribution of adjacent tissues to the effect IOP elevations, measurements are repeated without and with smooth muscle relaxation with instillation of tropicamide. TM migration into SC is resisted by TM stiffness, but is enhanced by the support of its attachment to adjacent smooth muscle within the ciliary body. This technique is the first to measure the living human TM response to pressure elevation in situ under physiological conditions within the human eye.

Photoplethysmographic measurement of various retinal vascular pulsation parameters and measurement of the venous phase delay.

PURPOSE: Retinal vein pulsation properties are altered by glaucoma, intracranial pressure (ICP) changes, and retinal venous occlusion, but measurements are limited to threshold measures or manual observation from video frames. We developed an objective retinal vessel pulsation measurement technique, assessed its repeatability, and used it to determine the phase relations between retinal arteries and veins. METHODS: Twenty-three eyes of 20 glaucoma patients had video photograph recordings from their optic nerve and peripapillary retina. A modified photoplethysmographic system using video recordings taken through an ophthalmodynamometer and timed to the cardiac cycle was used. Aligned video frames of vessel segments were analyzed for blood column light absorbance, and waveform analysis was applied. Coefficient of variation (COV) was calculated from data series using recordings taken within ±1 unit ophthalmodynamometric force of each other. The time in cardiac cycles and seconds of the peak (dilation) and trough (constriction) points of the retinal arterial and vein pulse waveforms were measured. RESULTS: Mean vein peak time COV was 3.4%, and arterial peak time COV was 4.4%. Lower vein peak occurred at 0.044 cardiac cycles (0.040 seconds) after the arterial peak (P = 0.0001), with upper vein peak an insignificant 0.019 cardiac cycles later. No difference in COV for any parameter was found between upper or lower hemiveins. Mean vein amplitude COV was 12.6%, and mean downslope COV was 17.7%. CONCLUSIONS: This technique demonstrates a small retinal venous phase lag behind arterial pulse. It is objective and applicable to any eye with clear ocular media and has moderate to high reproducibility. ( http://www.anzctr.org.au number, ACTRN12608000274370.).

Noninvasive assessment of intracranial pressure with venous ophthalmodynamometry. Clinical article.

OBJECT: Venous ophthalmodynamometry is a technique used to register the pressure within the central retinal vein. Because the outflow of the central retinal vein is exposed to the intracranial pressure (ICP), the pressure of the central retinal vein may be correlated with the ICP. In the absence of adequate statistical evidence, the authors compared the pressure of the central retinal vein with results of simultaneous invasive monitoring of ICP in neurosurgical patients. METHODS: The pressure within the central retinal vein was recorded in 102 patients, in whom invasive continuous monitoring of ICP had become necessary for various reasons, mostly because of suspected hydrocephalus and intracranial hemorrhage. RESULTS: A highly significant correlation of the pressure in the central retinal vein and the intracranial cavity was confirmed statistically. An increased pressure of the central retinal vein indicated an elevated ICP, with a probability of 84.2%, whereas a normal pressure of the central retinal vein indicated a normal ICP in 92.8% of patients. Conclusions Venous ophthalmodynamometry is a valuable technique for the noninvasive assessment of ICP.

Ophthalmodynamometry for ICP prediction and pilot test on Mt. Everest.

BACKGROUND: A recent development in non-invasive techniques to predict intracranial pressure (ICP) termed venous ophthalmodynamometry (vODM) has made measurements in absolute units possible. However, there has been little progress to show utility in the clinic or field. One important application would be to predict changes in actual ICP during adaptive responses to physiologic stress such as hypoxia. A causal relationship between raised intracranial pressure and acute mountain sickness (AMS) is suspected. Several MRI studies report that modest physiologic increases in cerebral volume, from swelling, normally accompany subacute ascent to simulated high altitudes. OBJECTIVES: 1) Validate and calibrate an advanced, portable vODM instrument on intensive patients with raised intracranial pressure and 2) make pilot, non-invasive ICP estimations of normal subjects at increasing altitudes. METHODS: The vODM was calibrated against actual ICP in 12 neurosurgical patients, most affected with acute hydrocephalus and monitored using ventriculostomy/pressure transducers. The operator was blinded to the transducer read-out. A clinical field test was then conducted on a variable data set of 42 volunteer trekkers and climbers scaling Mt. Everest, Nepal. Mean ICPs were estimated at several altitudes on the ascent both across and within subjects. RESULTS: Portable vODM measurements increased directly and linearly with ICP resulting in good predictability (r = 0.85). We also found that estimated ICP increases normally with altitude (10 ± 3 mm Hg; sea level to 20 ± 2 mm Hg; 6553 m) and that AMS symptoms did not correlate with raised ICP. CONCLUSION: vODM technology has potential to reliably estimate absolute ICP and is portable. Physiologic increases in ICP and mild-mod AMS are separate responses to high altitude, possibly reflecting swelling and vasoactive instability, respectively.

Measurement of ophthalmodynamometric pressure with the vented-gas forced-infusion system during pars plana vitrectomy.

PURPOSE: To measure ophthalmodynamometric pressure (ODP) with the vented-gas forced-infusion (VGFI) system during vitrectomy in patients with various vitreoretinal disorders and to investigate factors related to ODP. METHODS: This study included 169 eyes of 169 patients undergoing pars plana vitrectomy. After core vitrectomy, the intraocular pressure was gradually raised by using the VGFI system. When the central retinal artery or its branches on the optic nerve head showed pulsations, the pressure was recorded as ODP. Diastolic blood pressure (DBP) and systolic blood pressure (SBP) were measured simultaneously with ODP. Multiple regression analysis was performed to investigate the relationship between ODP and various explanatory variables: DBP, SBP, age, presence of diabetic mellitus (DM) and hypertension (HT), body mass index, and serum total cholesterol. RESULTS: ODP was 66.9 +/- 12.5 mm Hg (range, 15.5-103.7), and it correlated significantly with DBP (r = 0.60, P < 0.0001) but not with SBP (r = 0.12, P = 0.12). ODP in DM patients who had proliferative diabetic retinopathy and diabetic macular edema was lower than that in non-DM patients, whereas DBP was not significantly different between the two groups. Similar results were obtained in HT patients. Multiple regression analysis revealed that ODP had a significant correlation with DBP (P < 0.0001), presence of DM (P = 0.02), and presence of HT (P = 0.03). CONCLUSIONS: VGFI is a new method of determining ODP. ODP was significantly associated with DBP and was lower in patients with DM and HT.

[Ophthalmodynamometry of diastolic retinal arterial collapse pressure: correlation with systemic blood pressure]. / Ophthalmodynamometrie des diastolischen retinalen arteriellen Kollapsdruckes: Korrelation mit dem systemischen Blutdruck.

BACKGROUND: The aim of the study was to examine whether estimations of the central retinal artery collapse pressure obtained by corneal contact lens ophthalmodynamometry are correlated with measurements of the systemic blood pressure. PATIENTS AND METHODS: The clinical observational case series study included 168 eyes (from 111 patients) without retinal vascular diseases. The mean age was 65.6+/-13.6 years (mean +/- standard deviation) and the mean refractive error was 0.31+/-2.89 diopters (-13.75 to +6,50 diopters). After conventional measurement of the diastolic arterial blood pressure at the upper arm, Goldmann contact lens ophthalmodynamometry was non-invasively performed with the patient under topical corneal anesthesia. Ten measurements were taken, the mean of which were taken for statistical analysis. RESULTS: The ophthalmodynamometric estimations of the retinal central artery collapse pressure obtained in arbitrary units, showed a correlation coefficient of r=0.40 (P<0.001) with systemic diastolic arterial blood pressure measurements, with or without taking the intraocular pressure into account. The correlation coefficients were slightly higher for the measurements on the left eyes (r=0:47; P<0.001) than on the right eyes (r=0.43; P<0.001). CONCLUSION: Estimations of the central retinal artery collapse pressure in arbitrary units did not show a strong linear correlation with measurements of the systemic blood pressure. There were signs of an autoregulation mechanism of the ophthalmic artery.

Central retinal artery and vein collapse pressure in giant cell arteritis versus nonarteritic anterior ischaemic optic neuropathy.

Arteritic anterior ischaemic optic neuropathy and nonarteritic anterior ischaemic optic neuropathy are acute optic neuropathies, which have to be differentiated from each other. It was the purpose of this study to assess whether ophthalmodynamometry with an assessment of the collapse pressure of the central retinal artery (CRA) and vein (CRV) is helpful for that. Using a Goldmann contact lens-associated ophthalmodynamometer, the diastolic collapse pressure of the CRA and CRV were measured in six patients (eight eyes) with giant cell arteritis-induced anterior ischaemic optic neuropathy (GC-AION) and in 10 patients (12 eyes) with acute non-arteritic anterior ischaemic optic neuropathy (NAION). CRA collapse pressure was significantly (P=0.001; 95% confidence interval (CI): -68.7, -20.0) lower in the GC-AION group (52.7+/-24.6 arbitrary units) than in the NAION group (97.0+/-25.8 arbitrary units). CRV collapse pressure did not vary significantly (P=0.47). As measured by ophthalmodynamometry, CRA pressure is significantly lower in GC-AION than in NAION. CRV pressure does not vary markedly. These finding may be helpful for the clinical differentiation between GC-AION and NAION, and may give hints for the pathogenesis.

[Ophthalmodynamometry in the diagnostics of Grave's ophthalmopathy]. / Ophthalmodynamometrie in der Diagnostik der endokrinen Orbitopathie.

BACKGROUND: Since endocrine orbitopathy is characterised by exophthalmos and increased orbital tissue pressure which may lead to a compression of and damage to the optic nerve, it was the purpose of this study to evaluate whether the increased orbital tissue pressure in endocrine orbitopathy is associated with an elevated central retinal vein pressure as estimated by ophthalmodynamometry, and whether the central retinal vein pressure changes in the course of the disease. PATIENTS AND METHODS: The prospective clinical study included 7 patients (13 eyes) with endocrine orbitopathy. They were screened for the prevalence of a spontaneous pulsation of the central retinal vein. In case of a missing spontaneous pulse, the collapse pressure of the central retinal vein was estimated by a modified ophthalmodynamometry using a corneal contact lens associated ophthalmodynamometric device. A group of 122 patients (156 eyes) without orbital or retinal diseases served as control group. RESULTS: The frequency of a spontaneous pulse of the central retinal vein was significantly lower in the study group (1/13 or 8%) than in the control group (121/156 or 78% p<0.001; odds ratio: 41.5). The central retinal vein collapse pressure as determined by ophthalmodynamometry was significantly higher in the study group (22.7+/-19.5 arbitrary units) than in the control group (4.7+/-12.8 arbitrary units) (p=0.002). For one patient with 7 examinations during a follow-up of 16 months, the central retinal vein pressure increased from 17 arbitrary units to 56 units, and decreased to 14 to 19 arbitrary units after initiation of a systemic therapy and regression of the exophthalmos. Three years later a spontaneous pulsation of the central retinal vein was detectable. CONCLUSION: Ophthalmodynamometry may be a useful examination for the indirect assessment of the orbital tissue pressure in patients with endocrine orbitopathy.

[Ophthalmodynamometry of central retinal vein collapse pressure in idiopathic intracranial hypertension]. / Retinaler Zentralvenenkollapsdruck in der Diagnostik der idiopathischen intrakraniellen Hypertension.

BACKGROUND: The diagnosis of idiopathic intracranial hypertension results from a synopsis of standardised examinations including MRI. Since the cerebrospinal fluid pressure influences the pressure of the central retinal vein, it was the purpose of the present study to evaluate whether the ophthalmodynamometric estimation of the central retinal vein collapse pressure is helpful for the diagnosis of idiopathic intracranial hypertension. PATIENTS AND METHODS: The study included 5 patients with idiopathic intracranial hypertension with a mean age of 38.3+/-10.8 years and 88 subjects of a control group with a mean age of 66.8+/-13.1 years. Using a modified corneal contact lens-associated ophthalmodynamometry, the collapse pressure of the central retinal vein was estimated. RESULTS: The central retinal vein collapse pressure was significantly higher in the study group (33.0+/-27.3 relative units) than in the control group (2.0+/-6.7 relative units) (p<0.006; 95 % confidence interval: -11.5, 50.5). The central retinal artery collapse pressure did not vary significantly between the two groups (52.7+/-15.3 relative units versus 65.6+/-20.4 relative units; p=0.19; 95 % confidence interval: -36.6, 10.5). CONCLUSIONS: The corneal contact lens-associated ophthalmodynamometry can be helpful for the monitoring of patients with intracranial idiopathic hypertension.

Ophthalmodynamometric differences between ischemic vs nonischemic retinal vein occlusion.

PURPOSE: To estimate the central retinal vein pressure in patients with ischemic vs nonischemic central retinal vein occlusion (CRVO). DESIGN: Prospective clinical observational comparative study. METHODS: The study included 28 patients with CRVO, either of the ischemic type (n = 7) or the nonischemic type (n = 21). The control group consisted of 38 subjects without retinal disease. A new ophthalmodynamometer consisting of a Goldmann contact lens fitted with a pressure sensor into the holding grip of the contact lens, was used to indirectly estimate the central retinal artery and vein pressure. RESULTS: Central retinal vein pressure was significantly higher in the ischemic CRVO group than in the nonischemic CRVO group (91.5 +/- 30.1 arbitrary units vs 52.4 +/- 32.5 arbitrary units; P = .014), in which it was significantly (P < .001) higher than in the control group (4.8 +/- 8.1 arbitrary units). Central retinal vein pressure was higher than the diastolic central retinal artery pressure significantly (P = .039) more frequently in the ischemic CRVO group (7/7 or 100%) than in the nonischemic CRVO group (8/21 or 38%) or the control group (0/38; P < .001). Central retinal artery pressure was significantly (P = .017) lower in the ischemic CRVO group (46.0 +/- 10.6 arbitrary units) than in the nonischemic CRVO group (64.5 +/- 22.8 arbitrary units), in which it was significantly (P = .016) lower than in the control group (79.9 +/- 22.3 arbitrary units). CONCLUSIONS: Ophthalmodynamometric estimation of the retinal vein pressure may be helpful for the differentiation between the ischemic vs nonischemic type of CRVO. In the ischemic type, vein pulsations were usually observed at supradiastolic arterial values.

[Non-invasive determination of intracranial pressure. Physiological basis and practical procedure]. / Die nicht-invasive Bestimmung des Hirndruckes durch den Augenarzt: physiologische Grundlagen und Vorgehen in der Praxis.

It has been shown in some recently published papers that the intracranial pressure can be determined by dynamometric measurement of the outflow pressure of the central retinal vein (VOP). The knowledge gained by the basic experiments of Baurmann in 1925 has been forgotten by the ophthalmic community for many years. In this paper the basic phenomena of venous collapse are outlined which are fundamentally different from the biomechanics of the arterial collapse phenomenon observed by ophthalmodynamometry. A practical guideline is given for the dynamometric measurement of venous outflow pressure which equals the intracranial pressure. Performing dynamometry of the central retinal vein enables the ophthalmologist to determine intracranial pressure in a non-invasive way.

Central retinal artery and vein collapse pressure in eyes with chronic open angle glaucoma.

AIMS: To determine central retinal vessel collapse pressure in chronic open angle glaucoma. METHODS: For 19 eyes with chronic open angle glaucoma and 27 eyes of a control group, central retinal vessel collapse pressure was measured by a Goldmann contact lens fitted with a pressure sensor in its holding grip. RESULTS: Central retinal vein collapse pressure was significantly (p=0.001) higher in the glaucoma group than in the control group (26.1 (SD 26.4) relative units versus 6.1 (8.4) relative units). CONCLUSIONS: Measured by a new ophthalmodynamometer, central retinal vein collapse pressure measurements may be abnormally high in eyes with chronic open angle glaucoma.

Reproducibility of ophthalmodynamometric measurements of central retinal artery and vein collapse pressure.

BACKGROUND: To assess the reproducibility of ophthalmodynamometric measurements using a new, Goldmann contact lens associated, device allowing biomicroscopic visualisation of the optic disc. METHODS: The prospective clinical study included 87 eyes of 58 subjects presenting with a normal fundus (n=40), or ocular diseases (n=47). With topical anaesthesia, a Goldmann contact lens, fitted with a pressure sensor mounted into the holding ring of the contact lens, was placed onto the cornea. Pressure was applied onto the globe through the contact lens, and the pressure values obtained when the central retinal vessels started pulsating were noted. The measurements were performed 10 times. RESULTS: The mean coefficients of variation for redeterminations of the collapse pressure of the central retinal vein and artery were 16.3% (SD 11.4%), and 8.5% (4.1%), respectively. CONCLUSIONS: A simple and new, Goldmann contact lens associated, ophthalmodynamometer allows central retinal artery and vein collapse pressure measurements which are reproducible in a clinical setting.

Ophthalmodynamometric assessment of the central retinal vein collapse pressure in eyes with retinal vein stasis or occlusion.

PURPOSE: Using a new Goldmann contact lens associated ophthalmodynamometric device, it was the purpose of the present study to determine the central retinal vein collapse pressure in eyes with retinal vein occlusions or retinal venous stasis. METHODS: The prospective clinical non-interventional comparative study included 19 patients with central retinal vein occlusion ( n=8), branch retinal vein occlusion (n=4), or retinal venous stasis (n=7) and 42 subjects of a control group. With topical anesthesia, a Goldmann contact lens fitted with a pressure sensor was put onto the cornea. Pressure was exerted on the globe by pressing the contact lens, and the pressure value at the time when the central retinal vein started pulsating was noted. RESULTS: Central retinal vein collapse pressure measured 103.6+/-25.4 arbitrary units (AU) in eyes with central retinal vein occlusion what was significantly higher than in the eyes with retinal venous stasis (58.1+/-37.5 AU; p=0.02) and the eyes with branch retinal vein occlusion (43.8+/-25.5 AU; p=0.004). In the latter two groups, the measurements of the central retinal vein collapse pressure were significantly (p<0.001) higher than the measurements in the eyes of the control group (4.2+/-7.8 AU). CONCLUSION: As measured by a new ophthalmodynamometer with direct biomicroscopic visualization of the central retinal vessels during examination, central retinal vein collapse pressure is significantly higher in eyes with central retinal vein occlusion, followed by eyes with branch retinal vein occlusion, eyes with retinal venous stasis and, finally, normal eyes. These findings may have diagnostic and therapeutic implications.