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Randomized Controlled Trial
. 2023 Mar 23;18(3):e0283387.
doi: 10.1371/journal.pone.0283387. eCollection 2023.

Estimating pulsatile ocular blood volume from intraocular pressure, ocular pulse amplitude, and axial length

Ryan H Somogye  1 , Cynthia J Roberts  1   2 , Eberhard Spoerl  3 , Karin R Pillunat  3 , Lutz E Pillunat  3 , Robert H Small  1   4
Affiliations
Randomized Controlled Trial

Estimating pulsatile ocular blood volume from intraocular pressure, ocular pulse amplitude, and axial length

Ryan H Somogye et al. PLoS One. .

Abstract

The purpose of this study was to develop a method of estimating pulsatile ocular blood volume (POBV) from measurements taken during an ophthalmic exam, including axial length and using a tonometer capable of measuring intraocular pressure (IOP) and ocular pulse amplitude (OPA). Unpublished OPA data from a previous invasive study was used in the derivation, along with central corneal thickness (CCT) and axial length (AL), as well as IOP from the PASCAL dynamic contour tonometer (DCT) and intracameral (ICM) measurements of IOP for 60 cataract patients. Intracameral mean pressure was set to 15, 20, and 35 mmHg (randomized sequence) in the supine position, using a fluid-filled manometer. IOP and OPA measurements were acquired at each manometric setpoint (DCT and ICM simultaneously). In the current study, ocular rigidity (OR) was estimated using a published significant relationship of OR to the natural log of AL in which OR was invasively measured through fluid injection. Friedenwald's original pressure volume relationship was then used to derive the estimated POBV, delivered to the choroid with each heartbeat as a function of OR, systolic IOP (IOPsys), diastolic IOP (IOPdia), and OPA, according to the derived equation POBV = log (IOPsys/IOPdia) / OR. Linear regression analyses were performed comparing OPA to OR and calculated POBV at each of the three manometric setpoints. POBV was also compared to OPA/IOPdia with all data points combined. Significance threshold was p < 0.05. OR estimated from AL showed a significant positive relationship to OPA for both DCT (p < 0.011) and ICM (p < 0.006) at all three manometric pressure setpoints, with a greater slope for lower IOP. Calculated POBV also showed a significant positive relationship to OPA (p < 0.001) at all three setpoints with greater slope at lower IOP, and a significant negative relationship with IOPdia. In the combined analysis, POBV showed a significant positive relationship to OPA/ IOPdia (p < 0.001) in both ICM and DCT measurements with R2 = 0.9685, and R2 = 0.9589, respectively. POBV provides a straight-forward, clinically applicable method to estimate ocular blood supply noninvasively. Higher IOP in combination with lower OPA results in the lowest values of POBV. The simplified ratio, OPA/ IOPdia, may also provide a useful clinical tool for evaluating changes in ocular blood supply in diseases with a vascular component, such as diabetic retinopathy and normal tension glaucoma. Future studies are warranted.

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Conflict of interest statement

Dr. C. Roberts is a consultant to Ziemer Ophthalmic Systems AG.(relevant) and Oculus Optikgeräte GmbH (not relevant). This does not alter adherence to PLOS ONE policies on sharing data and materials. The remaining authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Positive correlation of OPA to estimated OR (K) for DCT measurements.
Fig 2
Fig 2. Positive correlation of OPA to estimated OR (K) for ICM measurements.
Fig 3
Fig 3. Positive correlation of POBV to OPA for DCT measurements.
Fig 4
Fig 4. Positive correlation of POBV to OPA for ICM measurements.
Fig 5
Fig 5. Negative correlation of POBV to IOP for DCT measurements.
Fig 6
Fig 6. Negative correlation of POBV to IOP for ICM measurements.
Fig 7
Fig 7. Strong correlation of the Calculated POBV to the Factor OPA/IOP for DCT Measurements.
Fig 8
Fig 8. Strong correlation of the Calculated POBV to the Factor OPA/IOP for ICM Measurements.
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