A new method for determining the blood quantity in the eye in a unit of time

Lack of association between glaucoma and macular choroidal thickness measured with enhanced depth-imaging optical coherence tomography

PURPOSE

To compare choroidal thickness measurements among normal eyes, eyes with normal tension glaucoma (NTG), and those with primary open-angle glaucoma (POAG), and to correlate choroidal thickness with demographic and clinical ocular parameters.

METHODS

Choroidal thickness was measured with enhanced depth-imaging (EDI) optical coherence tomography (OCT) in one eye of 38 normal, 20 NTG, and 56 POAG subjects and compared among groups. The mean age was 69.3 ± 13.6 years (60.1 ± 13.4 years for normal subjects and 73.8 ± 11.3 years for glaucoma subjects; P < 0.001). Measurements were made at the fovea and in the temporal and nasal choroid every 0.5 mm up to 3 mm away from the fovea. Univariate and multivariate linear regression analyses were performed to assess the association between choroidal thickness and demographic and ocular parameters.

RESULTS

There were no differences in foveal, temporal, or nasal choroidal thickness between normal, NTG, and POAG subjects (all P > 0.05) after adjusting for age, axial length, and intraocular pressure. Similarly, glaucoma severity groups did not differ from each other in all choroidal thickness measurements (all P > 0.05). Age (β = -1.78; P < 0.001) was the most significant factor associated with subfoveal choroidal thickness in the entire group, followed by axial length (β = -11.8; P = 0.002).

CONCLUSIONS

Choroidal thickness does not differ among normal, NTG, and POAG subjects, suggesting a lack of relationship between choroidal thickness and glaucoma based on EDI OCT measurements.

Ocular hypertension in primary glaucoma: a new hypothesis

Some considerations of the vascular events occurring the uvea during the course of glaucoma are reported and a mathematical model is adopted to clarify the interdependence between intraocular pressure, rate of blood flow, blood pressure gradient, and the number of unobstructed capillary vessels in the uveal membrane. By means of this mathematical model the physiopathological vascular cause of the rise in intraocular pressure is confirmed (also independently of an obstacle to aqueous outflow), and the clinical implications in relation to visual sensory impairment are emphasized.

Pressure lowering effect of timolol with reference to its topical vascular action

The hemodynamic effect of timolol maleate in open angle glaucoma was studied rheo-oculographically. Increase in the ocular pulse which reaches maximal amplification 2 h after the instillation of the drug was observed. The maximal pressure lowering effect appeared 3 h after instillation, as if the hemodynamic effect were the trigger for the pressure lowering effect.

Relationship between blood flow velocity in the choroid and intraocular pressure in rabbits

By using thermistors for calorimetry to monitor blood flow velocity in the choroid of the anaesthetized rabbit, it was found that an elevation of intraocular pressure reduced the choroidal blood flow. The relationship between the ratio of perfusion pressure to intraocular tension (x) and the reciprocal value of the percentage of blood flow velocity (l/y) showed a curve convex towards the pressure axis. On a log-lin scale the graph was linear. A significant linear correlation with a coefficient of 0.965 was obtained. The regression equation was found to be log l/y = 0.48x-1.98 +/- 0.29. From the present experiments it is concluded that the vascular bed of the choroid in the rabbit is a passive one with no sign of autoregulation. The observations are discussed from the point of view of blood supply and possible damage to the optic disc.