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

Purpose:

The Pascal Dynamic Contour Tonometer (DCT) allows measuring of the intraocular pressure (IOP) independently of corneal properties. It records simultaneously the haemodynamic IOP fluctuations and the difference between the systolic and the diastolic IOP corresponding to the Ocular Pulse Amplitude (OPA). The OPA indirectly reflects the choroidal perfusion and could be considered as an independent risk factor in glaucoma.

We aimed to establish the physiological diurnal variability of the OPA and its correlations with other biophysical parameters because its characteristics remain partly unclear.




Method:

Prospective randomized study including 52 eyes of 28 normal subjects with Goldmann Applanation Tonometry (GAT) IOPs <22 mmHg. Subjects treated by systemic medications that could interfere with blood pressure or heart rate were excluded. IOP was measured at 9:00 am, 1:00 pm and 4:00 pm by GAT and DCT. 2 consecutive GAT followed by 3 consecutive DCT measurements were performed on each session by the same clinician (SP). Only DCT measurements with quality 1 and 2 were taken into account. Blood pressure, pulse rate and central corneal thickness (CCT) were recorded after the last IOP measurements.

Spearman correlation coefficient was used for correlations assessment.




Results:

Mean age was 40 ± 14 years. Mean DCT values were significantly higher than GAT readings (mean=16.8+2.0 vs 15.2+2.8 mmHg, p<0.02).

The mean OPA was 2.2± 0.7 mmHg (range: 1 to 3.4 mm Hg). The mean amplitude of diurnal OPA fluctuations was 0.4 mmHg. There was no significant difference in the mean OPA values at each time of the diurnal curve. The intraclass correlation (ICC) of only one OPA measurement in relation to part of total variance due to inter-measurement variation was 78%. Averaging over three independent readings of OPA improved ICC to 91%.

The OPA was correlated with GAT (r=0.31 P<0.0001) and DCT IOP measurements (r=0.49 P <0.0001). It was correlated neither with blood pressure nor with age. OPA values of both eyes of the same individual were highly correlated (r=0.89, p<0.0001).




Conclusion:

In normal healthy eyes, the ocular pulse amplitude remains stable during the usual outpatient office hours and was not correlated with blood pressure or age of patients.

To study the physiological diurnal variability of the OPA and its correlations with other biophysical parameters.

N/A

A prospective study including fifty two eyes of twenty eight healthy subjects (15 female, 13 male) with GAT IOP measurements lower than 22 mmHg. The oral consent was obtained from each patient. The IOP measurements by dynamic contour tonometer (SMT Swiss Microtechnology, Switzerland) were performed under topical anaesthesia (oxybuprocaine hydrochloride 0.4mg/ml, Thea Pharma).

The same experienced ophthalmologist performed all the examinations in a non masked fashion. The measurements were taken on the same day at 9:00 am, 1:00 pm and 4:00 pm. To reduce biases due to prior knowledge of the IOP, the examinations were performed as per this following pattern: two consecutive GAT followed by three consecutive DCT IOP measurements(Results are digitaly shown).
A 10 minute break was taken between GAT and DCT to minimize a tonographic effect. Only the DCT measurements with quality 1 and 2 were taken into account.

The CCT, the blood pressure (BP) and pulse rate were recorded at 4:00 pm after the last IOP measurements with Tensoval® blood pressure meter (Hartmann AG, Heidenheim, Germany).

The CCT was measured by ultrasound pachymetry Pachette™(DGH 500 Technology, Inc, Philadelphia, PA).

The mean of five readings was considered for the measurement of CCT.

Mean IOP and OPA values were calculated for each time session.