Physiological diurnal variability and characteristics of the ocular pulse amplitude (OPA) with the dynamic contour tonometer (DCT-Pascal)

Inventory of Ocular Pulse Amplitude Values in Healthy Subjects and Patients With Ophthalmologic Illnesses: Systematic Review and Meta-analysis

PURPOSE

Many studies have examined the ocular pulse amplitude (OPA) to better understand its physiology and clinical relevance, but the papers are scattered, not consistently indexed, and sometimes difficult to locate. We aimed to identify and summarize the relevant published evidence on OPA and, in a meta-analysis, outline specific differences of this parameter between healthy individual, primary open-angle glaucoma, normal-tension glaucoma, ocular hypertension, and cataract patients.

DESIGN

Systematic review and meta-analysis.

METHODS

A thorough literature search and data extraction were conducted by 2 reviewers independently. Reports on OPA measured by the dynamic contour tonometry in conjunction with different ocular and systemic diseases or potential influencing factors were included.

RESULTS

Of the 527 initially found reports, 97 met the inclusion criteria assessing 31 clinical conditions. A meta-analysis based on 6850 eyes and 106 study arms (68.8%) revealed differences in mean OPA values in millimeters of mercury between various entities. Among healthy eyes, the OPA was 2.58 mm Hg (95% CI: 2.45-2.71), whereas OPA values were higher in glaucoma (unspecified glaucoma 2.73 mm Hg, 95% CI: 2.38-3.08; normal-tension glaucoma 2.66 mm Hg, 95% CI: 2.36-2.97; and primary open-angle glaucoma 2.92 mm Hg, 95% CI: 2.75-3.08). Although ocular hypertension showed the highest OPA values (3.53 mm Hg, 95% CI: 3.05-4.01), the lowest values were found in cataract eyes (2.26 mm Hg, 95% CI: 1.57-2.94).

CONCLUSION

We found different OPA values characteristic of different clinical entities, with above-normal values in glaucoma and ocular hypertension and lower values in cataract patients. Our work is intended for clinicians and researchers who want to get a quick overview of the available evidence or who need statistical data on OPA distributions in individual diseases.

Measuring intraocular pressure with OCT: the first approach

The variability of corneal OCT speckle statistics is indirectly related to changes in corneal microstructure, which may be induced by intraocular pressure (IOP). A new approach is considered, which attempts to estimate IOP based on corneal speckle statistics in OCT images. An area (A) under trajectories of contrast ratio with respect to stromal depth was calculated. The proposed method was evaluated on OCT images from the ex-vivo study on porcine eyeballs and in-vivo study on human corneas. A statistically significant multivariate linear regression model was obtained from the ex-vivo study: IOP = 0.70 · A - 6.11, in which IOP was precisely controlled in the anterior chamber. The ex-vivo study showed good correlation between A and IOP (R = 0.628, at the least) whereas the in-vivo study showed poor correlation between A and clinical air-puff tonometry based estimates of IOP (R = 0.351, at the most), indicating substantial differences between the two studies. The results of the ex-vivo study show the potential for OCT speckle statistics to be utilized for measuring IOP using static corneal imaging that does not require corneal deformation. Nevertheless, further work is needed to validate this approach in living human corneas.

Ocular Pulse Amplitude Correlates With Ocular Rigidity at Native IOP Despite the Variability in Intraocular Pulse Volume With Each Heartbeat

Purpose

The purpose of this study was to assess ocular coat mechanical behavior using controlled ocular microvolumetric injections (MVI) of 15 µL of balanced salt solution (BSS) infused over 1 second into the anterior chamber (AC) via a syringe pump.

Methods

Intraocular pressure (IOP) was continuously recorded at 200 Hz with a validated implantable IOP telemetry system in 7 eyes of 7 male rhesus macaques (nonhuman primates [NHPs]) during 5 MVIs in a series at native (3 trials), 15 and 20 mm Hg baseline IOPs, repeated in 2 to 5 sessions at least 2 weeks apart. Ocular rigidity coefficients (K) and ocular pulse volume (PV) were calculated for each trial. Data were averaged across sessions within eyes; PV was analyzed with a three-level nested ANOVA, and parameter relationships were analyzed with Pearson Correlation and linear regression.

Results

After MVI at native baseline IOP of 10.4 ± 1.6 mm Hg, IOP increased by 9.1 ± 2.8 mm Hg (∆IOP) at a 9.6 ± 2.7 mm Hg/s slope, ocular pulse amplitude (OPA) was 0.70 ± 0.13 mm Hg on average; the average K was 0.042 ± 0.010 µL-1 and average PV was 1.16 ± 0.43 µL. PV varied significantly between trials, days, and eyes (P ≤ 0.05). OPA was significantly correlated with K at native IOP: Pearson coefficients ranged from 0.71 to 0.83 (P ≤ 0.05) and R2 ranged from 0.50 to 0.69 (P ≤ 0.05) during the first trial.

Conclusions

The MVI-driven ∆IOP and slope can be used to assess ocular coat mechanical behavior and measure ocular rigidity.

Translational Relevance

Importantly, OPA at native IOP is correlated with ocular rigidity despite the significant variability in PV between heartbeats.

Changes in intraocular pressure and ocular pulse amplitude of rhesus macaques after blue light scleral cross-linking

BACKGROUND

Scleral cross-linking can enhance the biomechanical strength of the sclera and is expected to be a new operative method for the prevention of myopia. However, studies investigating the changes in intraocular pressure (IOP) and ocular pulse amplitude (OPA) after blue light-riboflavin induced scleral collagen cross-linking (SXL) in rhesus monkeys are limited. This study aimed to investigate the changes in IOP and OPA in three-year-old rhesus macaques 1 week, 1 month, and 3 months after blue light-riboflavin SXL.

METHODS

Seven three-year-old rhesus macaques (14 eyes) were randomly divided into two groups, with 4 monkeys in group A (8 eyes) and 3 monkeys in group B (6 eyes). The right eye of each rhesus macaque was used as the experimental eye, whereas the left eye was used as the control. In group A, one quadrant of each right eye was irradiated. In group B, two quadrants of each right eye and one quadrant of each left eye were irradiated. The IOP and OPA of both eyes were measured in all seven rhesus macaques before SXL and 1 week, 1 month, and 3 months postoperatively, and differences in the IOP and OPA between the experimental and control eyes were evaluated via the paired t test.

RESULTS

In groups A and B, there were no significant differences between the experimental and control eyes in the IOP or OPA before SXL or 1 week, 1 month, or 3 months postoperatively (P > 0.05).

CONCLUSIONS

The IOP and OPA are not significantly affected in 1 vs 0 or in 1 vs 2 quadrants of blue light SXL.

IOP, IOP Transient Impulse, Ocular Perfusion Pressure, and Mean Arterial Pressure Relationships in Nonhuman Primates Instrumented With Telemetry

Purpose

To characterize relationships between intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP), IOP transient impulse, and IOP baseline impulse using continuous telemetry in nonhuman primates.

Methods

We used our validated implantable telemetry system to wirelessly record bilateral IOP and arterial BP at 500 Hz in 7 eyes of 4 male rhesus macaques, aged 4 to 5 years. IOP, MAP, OPP, IOP transient impulse, and IOP baseline impulse were averaged into 1-hour periods over 20 days for each NHP. IOP transient impulse was defined as the portion of total IOP due to transient IOP fluctuations <0.5 seconds duration alone and IOP baseline impulse as the remaining area under the IOP versus time curve. OPP was defined as arterial BP-IOP (calculated continuously), and MAP was the hourly average of the continuous BP curve. Relationships between the variables were analyzed for each 24-hour period using either multivariate linear regression or Spearman Correlation Coefficients as appropriate.

Results

Over twenty 24-hour periods, IOP transient impulse and OPP showed significant positive relationship in all eyes, which was driven largely by the data during waking hours. There was no significant relationship between IOP and MAP, IOP transient impulse and MAP, or IOP baseline impulse and IOP transient impulse.

Conclusions

There are significant positive relationships between the frequency and/or size of transient IOP fluctuations (IOP transient impulse) and OPP. A possible explanation of this finding is that higher OPP, as well as a greater number of blinks and saccades (the primary sources of IOP transients), are associated with increased activity.

Ocular pulse amplitude in different types of glaucoma using dynamic contour tonometry: Diagnosis and follow-up of glaucoma

The aim of the present study was to compare the ocular pulse amplitude (OPA) in patients with different types of glaucoma using dynamic contour tonometry (DCT), to evaluate ocular and systemic factors associated with the OPA and to verify whether OPA measured by DCT is an independent predictor for glaucoma diagnosis. A total of 217 eyes of 217 participants in the following five groups were included in this cross-sectional study: Chronic angle closure glaucoma (CACG), primary open angle glaucoma, normal tension glaucoma (NTG), suspected open angle glaucoma (SOAG) and normal control (NC). The following tests were simultaneously performed during a single visit: Intra-ocular pressure (IOP), OPA, cup-to-disk (C/D) ratio, mean damage (MD) and loss variance (LV). OPAs were compared in each group. The association between OPA and IOP, age, C/D ratio, MD and LV was detected. OPA analysis prior to and after trabeculectomy was also performed to assess its prognostic value. Among the 217 individuals, the OPA was consistent with the IOP, both measured by DCT, along with the MD and LV. Patients with CACG and SOAG had higher OPA values than those with NTG and normal controls. Compared with patients aged >30 years, the OPA was significantly lower in younger patients, while they may not have been affected by different C/D ratios. After trabeculectomy, the OPA had significantly decreased compared with the values prior to surgery. In conclusion, the present study showed that the OPA is correlated with the IOP determined by DCT. CACG and SOAG patients had higher OPA values than patients with other types of glaucoma. OPA measured by DCT may be a predictor for glaucoma diagnosis and prognosis.

Evaluation of ocular pulse amplitude in non-arteritic anterior ischaemic optic neuropathy

BACKGROUND

To evaluate the ocular pulse amplitude (OPA) in patients with chronic non-arteritic anterior ischaemic optic neuropathy (NAION).

METHODS

This cross-sectional study comprised a study group of 30 eyes from 30 patients with NAION and a control group of 31 eyes from 31 age and gender-matched healthy subjects. Bilateral OPA was measured with dynamic contour tonometry (DCT) and was compared between the study and control groups.

RESULTS

No statistically significant difference was found between the study and control groups in terms of hypertension, diabetes mellitus, ischaemic heart disease and hyperlipidemia. The mean intraocular pressure (IOP) measured with Goldmann Applanation Tonometry and DCT in the study and control groups was not statistically different (p₁ = 0.094, p₂ = 0.240). The mean OPA in the study group and the control group were 2.01 ± 0.69 mmHg and 1.97 ± 0.68 mmHg (p = 0.839).

CONCLUSION

No significant difference was determined in the OPA levels of eyes with NAION at the chronic stage and eyes in the control group.

Review on Dynamic Contour Tonometry and Ocular Pulse Amplitude

Intraocular pressure (IOP) measurement is the cornerstone of the management of glaucoma patients. The gold standard for assessing IOP is Goldmann applanation tonometry (GAT). Recently, the dynamic contour tonometer (DCT) has become available. While both devices provide reliable IOP measurements, the results are not interchangeable. DCT has the advantage of measuring an additional parameter: ocular pulse amplitude (OPA). OPA is defined as the difference between systolic and diastolic IOP and represents the pulsatile wave front produced by the varying amount of blood in the eye during the cardiac cycle. It has been shown to vary with ocular structural parameters, such as axial length, corneal thickness, and ocular rigidity, as well as with systemic variables like heart rate, blood pressure, and left ventricular ejection fraction. Although the existence of some of these associations is still controversial, the clinical relevance of OPA has been consistently suggested, especially in glaucoma. Further research on this intriguing parameter could not only provide insight into glaucoma pathophysiology but also help integrate this variable into clinical practice.

Age-Related Changes in Corneal Deformation Dynamics Utilizing Scheimpflug Imaging

Purpose

To study age-related changes in corneal deformation response to air-puff applanation tonometry.

Methods

Fifty healthy subjects were recruited for a prospective study and divided into two equal age groups (≤ 28 and ≥ 50 years old). Up to three measurements by a corneal deformation analyser based on the Scheimpflug principle were performed on the left eye of each subject. Raw Scheimpflug images were used to extract changes in anterior and posterior corneal profiles, which were further modelled by an orthogonal series of Chebyshev polynomial functions. Time series of the polynomial coefficients of even order exhibited a dynamic behavior in which three distinct stages were recognized. A bilinear function was used to model the first and the third stage of corneal dynamics. Slope parameters of the bilinear fit were then tested between the two age groups using Wilcoxon rank sum test and two-way non-parametric ANOVA (Friedman) test.

Results

Statistically significant changes (Wilcoxon test, P<0.05) between the age groups were observed in the phase of the second applanation dynamics for the posterior corneal profile. In a two-way comparison, in which the corneal profile was used as a dependent variable, statistically significant changes (ANOVA/Friedman test, P = 0.017) between the groups were also observed for that phase.

Conclusion

Corneal biomechanics depend on age. The changes in corneal deformation dynamics, which correspond to mostly free return of the cornea to its original shape after the air pulse, indicate that the age related differences in corneal biomechanics are subtle but observable with high speed imaging.

IOP telemetry in the nonhuman primate

This review is focused on continuous IOP monitoring using telemetry systems in the nonhuman primate (NHP), presented in the context that IOP fluctuations at various timescales may be involved in glaucoma pathogenesis and progression. We use glaucoma as the primary framework to discuss how the dynamic nature of IOP might change with age, racial heritage, and disease in the context of glaucoma susceptibility and progression. We focus on the limited work that has been published in IOP telemetry in NHPs, as well as the emerging data and approaches. We review the ongoing efforts to measure continuous IOP, and the strengths, weaknesses and general pitfalls of the various approaches.

Assessing subject-related variations of the Ocular Response Analyzer parameter calculation

BACKGROUND

The aim was to study the relationships between the output parameters of the Ocular Response Analyzer (ORA) and those calculated from the raw ORA data and to ascertain the subject-related variations of ORA parameter calculation procedures.

METHOD

Six subjects were recruited for a prospective study. Up to 32 measurements by ORA were performed in series on the dominant eye of each subject. A relationship was examined between Goldmann-correlated intraocular pressure values (IOPg) obtained from the standard ORA output and IOPg' calculated from raw ORA data with a custom-written procedure. The same analysis was carried out for the parameters of corneal hysteresis (CH and CH'). Data and statistical analysis included Epanechnikov kernel smoothing, orthogonal linear regression, hypothesis testing and bootstrap techniques.

RESULTS

The group average (mean ± standard deviation) IOPg and CH values were 11.6 ± 1.8 mmHg and 10.7 ± 1.7 mmHg, respectively. A strong correlation was found between IOPg and IOPg' and also between CH and CH' parameters. There was a significant (Behrens-Fisher test, p < 0.001) difference between subjects for both IOPg and CH calculations, in terms of the regression slope parameter.

CONCLUSIONS

Subject-related variations of ORA parameter calculation were demonstrated. This could indicate that currently employed estimators of IOP parameters include unreported algorithmic procedures that may lead to biased results.

Ocular pressure waveform reflects ventricular bigeminy and aortic insufficiency

Ocular pulse amplitude (OPA) is defined as the difference between maximum and minimum intraocular pressure (IOP) during a cardiac cycle. Average values of OPA range from 1 to 4 mmHg. The purpose of this investigation is to determine the source of an irregular IOP waveform with elevated OPA in a 48-year-old male. Ocular pressure waveforms had an unusual shape consistent with early ventricular contraction. With a normal IOP, OPA was 9 mmHg, which is extraordinarily high. The subject was examined by a cardiologist and was determined to be in ventricular bigeminy. In addition, he had bounding carotid pulses and echocardiogram confirmed aortic insufficiency. After replacement of the aortic valve, the bigeminy resolved and the ocular pulse waveform became regular in appearance with an OPA of 1.6–2.0 mmHg. The ocular pressure waveform is a direct reflection of hemodynamics. Evaluating this waveform may provide an additional opportunity for screening subjects for cardiovascular anomalies and arrhythmias.

Corneal deformation dynamics in normal and glaucoma patients utilizing scheimpflug imaging

The purpose of this study was to explore the corneal deformation dynamics recorded in raw Scheimpflug images of CorVis ST tonometer to evaluate age- and glaucoma-related changes in corneal biomechanics. This was a prospective study in which 18 subjects were recruited and divided into three equal groups (healthy young, healthy older and older glaucoma group). Up to three measurements by CorVis ST tonometer were acquired on the left eye of each subject. Raw Scheimpflug images of CorVis ST were used to extract changes in anterior and posterior corneal profiles, which were further modeled by a Chebyshev polynomial expansion of optimally determined order. Corneal deformation dynamics were studied via time-varying series of Chebyshev polynomial coefficients, in which three phases of corneal deformation were determined. The first and the last phase of corneal dynamics were fitted with bilinear functions. Further, the slope of each linear trend in the model was tested between the groups. Statistically significant differences were observed in the final return phase of corneal dynamics between the older group of subjects and those of glaucoma subjects indicating possible biomechanical differences in their tissues that could only be observed with minimum applied pressure.

Can dynamic contour tonometry and ocular pulse amplitude help to detect severe cardiovascular pathologies?

We demonstrate the close relationship between a conspicuous ocular pulse amplitude and severe underlying cardiovascular disease. Two otherwise symptom-free glaucoma patients without any previously diagnosed underlying cardiovascular pathology but with a conspicuous ocular pulse amplitude and who underwent routine examinations in our glaucoma department were referred to the appropriate specialty for further diagnostic procedures. In both patients, the diagnosis of a tachyarrhythmia was made as suspected on dynamic contour tonometry measurements. In addition to medical treatment, one patient underwent electric cardioversion and the second patient was scheduled for pacemaker implantation. A third patient with an unexpected high ocular pulse amplitude despite severe cardiovascular pathology underwent major surgery due to an aortic aneurysm. Carotid stenosis was diagnosed due to side differences in ocular pulse amplitude as well. Ocular pulse amplitude might be a noninvasive and affordable screening tool and could be used to detect severe cardiovascular disease. A prospective study including a larger number of patients is needed to prove this hypothesis.

Ocular pulse amplitude as a dynamic parameter and its relationship with 24-h intraocular pressure and blood pressure in glaucoma

Abnormal ocular blood flow (OBF) has been suspected as one of the underlying mechanisms of glaucoma. The ocular pulse amplitude (OPA) is considered a possible surrogate parameter for ocular blood flow (OBF) measurement and has been studied in its association with glaucoma. Although there have been several studies that reported various ocular and systemic factors in association with OPA, all of these studies were based on a single measurement of these factors as well as OPA. The purpose of this study was to determine the 24-h (h) dynamic variability and any associations between OPA and intraocular pressure (IOP) and blood pressure (BP) variables using 24-h data collected from untreated patients with normal-tension glaucoma (NTG). One hundred and forty-four patients with NTG were consecutively enrolled. All patients underwent 24-h monitoring of IOP, OPA, and BP variables. A cosinor model was used to describe the patterns and statistical significance of the 24-h OPA rhythm, as well as the IOP and BP variables. Associations between 24-h OPA data, IOP and BP variables, and ocular and demographic factors were also assessed using the generalized estimating equation. Over the course of 24-h, OPA (p = 0.007) demonstrated significant dynamic diurnal rhythms that were similar to the other dynamic variables (all p < 0.05). Based on the 24-h data, IOP (p < 0.001), arterial pulse pressure (p = 0.034), and the spherical equivalent (p < 0.001) positively correlated with the OPA, whilst male sex (p < 0.001) negatively correlated with the OPA. These results indicate that OPA is primarily influenced by IOP as well as arterial pulse pressure, spherical equivalent, and gender. In conclusion, OPA is a dynamic ocular parameter that demonstrates a 24-h short-time fluctuation in NTG patients.

Dynamic contour tonometry in primary open angle glaucoma and pseudoexfoliation glaucoma: factors associated with intraocular pressure and ocular pulse amplitude

Purpose:

To compare the intraocular pressures (IOP) and ocular pulse amplitudes (OPAs) in patients with primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PXG), and to evaluate ocular and systemic factors associated with the OPA.

Materials and Methods:

In this prospective study, on 28 POAG and 30 PXG patients, IOP was measured with the Goldmann applanation tonometry (GAT) and the Pascal dynamic contour tonometry (DCT). Other measurements included central corneal thickness (CCT), vertical cup-to-disc ratio (CDR), and systolic and diastolic blood pressure. Statistical significance was defined as P < 0.05.

Results:

In each of the POAG and PXG groups, GAT IOP was correlated with CCT (r = 0.40, P = 0.03 and r = 0.35, P = 0.05, respectively), whereas DCT IOP and CCT were not correlated. In all patients and in the POAG group, OPA was positively correlated with DCT IOP (r = 0.39, P = 0.002). OPA was not correlated with CCT in the POAG (P = 0.80), nor in the PXG (P = 0.20) group, after adjusting for DCT IOP. When corrected for DCT IOP and CCT, there was a significant negative correlation between OPA and vertical CDR in all patients (r = −0.41, P = 0.002). There was no significant difference in OPA between groups (P = 0.55), even when OPA was adjusted for IOP and systolic and diastolic pressure (P = 0.40), in a linear regression model.

Conclusion:

DCT IOP and OPA are not correlated with CCT. There is no significant difference between the OPA of PXG and POAG eyes. OPA is correlated with DCT IOP, and is lower in eyes with more advanced glaucomatous cupping.

Decreased Ocular Pulse Amplitude and Retinal Nerve Fibre Layer in Multiple Sclerosis

This study was conducted to assess ocular pulse amplitude and retinal nerve fibre layer in patients with multiple sclerosis and their correlation with disease duration and with severity. Retinal nerve fibre layer thickness was measured by Heidelberg Retinal Tomography II (HRT-II; Heidelberg Engineering, Dossenheim, Germany) and ocular pulse amplitude was measured by dynamic contour tonometry (Ziemer Ophthalmic Systems, Port, Switzerland) in 37 multiple sclerosis patients and 72 age- and gender-matched controls. Ocular pulse amplitude was significantly reduced and retinal nerve fibre layer was significantly thinner in temporal, superotemporal, and nasal sectors in patients with multiple sclerosis regardless of having an optic neuritis attack. The retinal nerve fibre layer was thinner in eyes with a previous optic neuritis attack compared with the eyes without an attack, but the difference was not significant. Ocular pulse amplitude showed a positive correlation with visual evoked potential amplitude and a negative correlation with visual evoked potential latency. Retinal nerve fibre layer thickness showed a significant negative correlation with the disease duration but not with visually evoked potential, disease severity, nor previous optic neuritis. These findings indicate that the process of degeneration starts in the early period of the disease, as our study group is composed of early-middle-stage multiple sclerosis patients, and is independent of relapses.

Relationship between ocular pulse amplitude and glaucomatous central visual field defect in normal-tension glaucoma

PURPOSE

To investigate the relationship between central visual field (VF) defects and ocular pulse amplitude (OPA) in early normal-tension glaucoma (NTG).

PATIENTS AND METHODS

This retrospective study included 100 eyes of 100 subjects: 54 NTG patients whose mean deviations were better than -7.00 dB and 46 normal subjects. OPA was measured by dynamic contour tonometry. NTG patients were divided into 2 subgroups according to VF tests: the central VF-invading and the central VF-sparing groups. Ocular parameters including OPA, intraocular pressure (IOP), and indices of VF tests were analyzed in glaucoma patients and normal subjects.

RESULTS

There was no difference in the OPA between the NTG and normal groups. However, IOP and OPA of the central VF-invading group (14.4 ± 2.87 and 2.9 ± 0.78 mm Hg) were higher than those of the central VF-sparing group (12.7 ± 2.52 and 2.0 ± 0.80 mm Hg; P = 0.025 and P < 0.001, respectively). OPA, but not IOP, showed a positive correlation with the VF test indices that represented central field defects (r = 0.494, P < 0.001).

CONCLUSIONS

Increased OPA was related to more centrally located VF defects in NTG patients with mild VF defects.

Effects of body mass index on intraocular pressure and ocular pulse amplitude

AIM

To investigate the effects of body mass index (BMI) on intraocular pressure (IOP) and ocular pulse amplitude (OPA).

METHODS

Totally 140 healthy individuals without any systemic diseases were included in the study. BMI (kg/m(2)) was calculated for every individual. IOP and OPA were measured with Pascal Dynamic contour tonometer (DCT). Blood pressure was also measured along with the DCT. The patients were divided into three groups according to BMI as: Group1, BMI<25; Group2, 25≤BMI<30; Group3, BMI≥30. Mean values of IOP, OPA, systolic blood pressure (SBP) and diastolic blood pressure (DBP) were used in statistical analysis.

RESULTS

In Group1, the means of IOP, OPA, were 16.8±2.3mmHg, 2.7±0.7mmHg respectively; and SBP, DBP were 120.0±6.1mmHg, and 77.4±5.6mmHg respectively. In group2, the mean IOP, OPA, SBP, and DBP were found to be 16.6±2.1mmHg, 2.4±0.7mmHg, 121.7±5.3mmHg, and 79.5±4.9mmHg respectively. In group3, the mean IOP, OPA, SBP, and DBP were found to be 17.3±1.7mmHg, 2.1±0.7mmHg, 122.4±5.7mmHg, and 79.7±5.2mmHg respectively. There were no statistically significant difference between groups in terms of IOP, SBP and DBP, while OPA values were significantly lower in group3 (P=0.001).

CONCLUSION

Decreased OPA values in individuals with higher BMI may indicate that subjects with higher BMI have lower choroidal perfusion and lower ocular blood flow.

24-hour IOP telemetry in the nonhuman primate: implant system performance and initial characterization of IOP at multiple timescales

PURPOSE

IOP is the most common independent risk factor for development and progression of glaucoma, but very little is known about IOP dynamics. Continuous IOP telemetry was used in three nonhuman primates to characterize IOP dynamics at multiple time scales for multiple 24-hour periods.

METHODS

An existing implantable telemetric pressure transducer system was adapted to monitoring anterior chamber IOP. The system records 500 IOP, ECG, and body temperature measurements per second and compensates for barometric pressure in real time. The continuous IOP signal was digitally filtered for noise and dropout and reported using time-window averaging for 19, 18, and 4 24-hour periods in three animals, respectively. Those data were analyzed for a nycthemeral pattern within each animal.

RESULTS

Ten-minute time-window averaging for multiple 24-hour periods showed that IOP fluctuated from 7 to 14 mm Hg during the day, and those changes occurred frequently and quickly. Two-hour time-window averages of IOP for multiple 24-hour periods in three animals showed a weak nycthemeral trend, but IOP was not repeatable from day-to-day within animals.

CONCLUSIONS

The measured IOP was successfully measured continuously by using a new, fully implantable IOP telemetry system. IOP fluctuates as much as 10 mm Hg from day to day and hour to hour in unrestrained nonhuman primates, which indicates that snapshot IOP measurements may be inadequate to capture the true dynamic character of IOP. The distributions, magnitudes, and patterns of IOP are not reproducible from day to day within animals, but IOP tends to be slightly higher at night when IOP data are averaged across multiple 24-hour periods within animals.

Ocular pulse amplitude and retrobulbar blood flow change in dipper and non-dipper individuals

PURPOSE

To evaluate ocular pulse amplitude (OPA), IOP values, and hemodynamic changes in the ophthalmic artery, central retinal artery, and short posterior ciliary artery in dipper and non-dipper patients.

METHODS

A total of 59 right eye measurements of healthy subjects with normotensive were included to the study. Ambulatory blood pressure (BP) monitoring measurement (ABPM), Doppler imaging, and OPA measurements were performed in the same day. The patients in which systolic BP decreased during the nocturnal time by 10% of the diurnal BP or more were called dippers. A patient whose nocturnal systolic BP fell by <10% or even rose was defined as non-dipper. Color Doppler imaging was used for blood flow velocity assessment of ophthalmic, central retinal, and posterior ciliary arteries. For each artery, peak systolic and end-diastolic velocities (PSV and EDV, respectively), resistive index (RI), and pulsalite index (PI) were automatically calculated by the machine. Mean IOP and OPA values were calculated after three consecutive measurements.

RESULTS

The mean OPA in non-dipper patients was significantly lower compared with that of dipper patients (P=0.011). There was no significant difference in IOP levels between groups. There was no significant difference in the PSV, EDV, RI, and PI in the ophthalmic, posterior ciliary, and central retinal arteries between the groups.

CONCLUSION

Our study demonstrated that OPA level in non-dippers is lower than dippers. This may give additional information about the effect of BP changes on OPA values.

Ocular pulse amplitude and associated glaucomatous risk factors in a healthy Hispanic population

BACKGROUND

With increasing evidence that vascular risk factors play a role in the development of glaucoma, it is critical to be familiar with factors related to intraocular blood flow, such as the ocular pulse amplitude (OPA). This study evaluates OPA and factors related to it in a healthy, Hispanic population.

METHODS

Refractive error, corneal curvature, Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), OPA, axial length, and central corneal thickness (CCT) measurements were obtained on 104 Hispanic subjects recruited from the community.

RESULTS

OPA ranged from 0.7 to 4.7 mmHg (mean, 2.1 +/- 0.8 mmHg) and showed a significant correlation with refractive error, axial length, GAT, and DCT (r=0.250, -0.358, 0.460, 0.378; P=0.011, <0.001, <0.001, and <0.001, respectively). Mean intraocular pressure with GAT was 15.6 mmHg. Mean CCT was 541.2 microm. The average refractive error was 0.75 diopters (D) of myopia, with 25% having >1.00 D myopia.

CONCLUSION

Normal OPA values have not been studied in Hispanic populations. OPA is thought to provide information regarding ocular blood flow; however, more studies are needed to determine its significance in glaucoma treatment.

A clinical comparison of dynamic contour tonometry versus Goldmann applanation tonometry

BACKGROUND AND OBJECTIVE

To compare the intraocular pressures (IOP) obtained with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) and to determine the dependency of both devices on corneal structure.

PATIENTS AND METHODS

One hundred forty eyes of 70 patients were included. Cases with corneal pathologies, former glaucoma diagnosis, and systemic diseases were excluded. All eyes underwent measurements of central corneal thickness (CCT) and corneal curvature. IOP measurements were obtained with GAT and DCT. The agreement of measurements was statistically analyzed.

RESULTS

The correlation of IOP values obtained with DCT and GAT was statistically significant. The mean DCT values were 0.46 ± 2.55 mm Hg higher than those of GAT, but this difference was statistically insignificant. Bland-Altman plots showed reasonable inter-method agreement between DCT and GAT measurements. GAT readings were significantly affected by CCT, but DCT measurements were affected by age and corneal curvature.

CONCLUSION

DCT is a reliable method of assessing IOP and is less dependent on central corneal thickness. This new technology may be a promising step forward in the management of glaucoma. Further studies are required to validate these observations.

Relationship of intraocular pulse pressure and spontaneous venous pulsations

PURPOSE

To determine the influence of intraocular pulse pressure (IOPP) on the presence of spontaneous venous pulsations (SVP) in patients with normal intracranial pressure.

DESIGN

Clinic-based cross-sectional study.

METHODS

Forty-seven patients without signs and symptoms of elevated intracranial pressure were recruited from a general ophthalmology clinic. Patients with glaucoma or retinal vascular disease were excluded from the study. IOP was determined by applanation, and IOPP was measured with the Pascal Dynamic Contour Tonometer (Ziemer Group, Port, Switzerland). SVP were assessed by undilated (direct) and dilated indirect ophthalmoscopy. Other variables assessed included age, cup-to-disc ratio, and refractive error (spherical equivalent). The main outcome measure was the presence of SVPs with normal IOPP.

RESULTS

The incidence of SVPs declined with increasing age in a nonlinear manner. Dilated examinations yielded the greatest sensitivity for detecting SVPs, with 91.5% of subjects having SVPs. However, in subjects with IOPP of 1.2 mm Hg or more in at least one eye, the incidence of SVPs was 100%.

CONCLUSIONS

A significant correlation exists between the amplitude of IOPP and the presence of SVPs, with SVPs detected in one or both eyes of all patients with IOPP of 1.2 mm Hg or more. When IOPP is 1.2 mm Hg or more, absent SVPs may be more predictive of elevated intracranial pressure than previously recognized.