Abstract
Purpose: :
The purpose of this study is to compare the vascular pulsatility of the Optic Nerve Head (ONH) in normal subjects, versus treated and non treated glaucoma groups.
Methods: :
Twenty normal subjects (IOP 11–21 mmHg) and 45 glaucoma subjects in three categories based on IOP: Low IOP: 5 to 11 mmHg; Moderate IOP: 11 to 30 mmHg; and High IOP: >30 mmHg. Subjects were monitored with a single point Laser Doppler Flowmeter to measure pulsatility for 60 seconds. The probing laser, emitting at 785 nm, was focused on the ONH neuroretinal rim with special care to avoid major vessels and monitored with an infrared CCD camera to visualize the fundus structures. For the Velocity we determined the pulsatility as a unitless coefficient from 0 to 1 according to the formula: Pulsatility = (Vmax–Vmin ) / Vmax
Results: :
In our series , we examined two situations: Protocol A: This protocol measured the pulsatility in all four groups. The normal group showed a mean of 0.429 ± 0.08. The mean values among glaucoma patients was: Low IOP: 0.421 ± 0.13; Moderate IOP: 0.447 ± 0.11; and High IOP: 0.598 ± 0.11.
The Low and Moderate IOP groups were not significantly different when compared to normal (p=0.85 and 0.65 respectively).The High IOP group showed a statistically significant difference from normals (p=0.02)and borderline significant difference from the Moderate group (p=0.08).
Protocol B: We compared the ONH pulsatility in 5 patients while their pressure was >30mmHg (mean 34.2±8.1 mmHg) and again when their pressure was <22mmHg (mean 19.6±4.6 mmHg) . In these patients pulsatility changed from 0.600 ± 0.07 to 0.480 ± 0.07 (p=0.03).
Conclusions: :
The pulsatility of blood velocity in the ONH neuroretinal rim was significantly greater in uncontrolled glaucoma than in normal subjects. In general, this pulsatility appears to be greater at IOPs greater than 30mmHg. Possible mechanisms by which such pulsatility might contribute to glaucomatous optic atrophy will be discussed.
Keywords: intraocular pressure • blood supply