Retinal blood flow after superior cervical ganglionectomy: a laser Doppler study in the cynomolgus monkey

Role of the retinal vascular endothelial cell in ocular disease

Retinal endothelial cells line the arborizing microvasculature that supplies and drains the neural retina. The anatomical and physiological characteristics of these endothelial cells are consistent with nutritional requirements and protection of a tissue critical to vision. On the one hand, the endothelium must ensure the supply of oxygen and other nutrients to the metabolically active retina, and allow access to circulating cells that maintain the vasculature or survey the retina for the presence of potential pathogens. On the other hand, the endothelium contributes to the blood-retinal barrier that protects the retina by excluding circulating molecular toxins, microorganisms, and pro-inflammatory leukocytes. Features required to fulfill these functions may also predispose to disease processes, such as retinal vascular leakage and neovascularization, and trafficking of microbes and inflammatory cells. Thus, the retinal endothelial cell is a key participant in retinal ischemic vasculopathies that include diabetic retinopathy and retinopathy of prematurity, and retinal inflammation or infection, as occurs in posterior uveitis. Using gene expression and proteomic profiling, it has been possible to explore the molecular phenotype of the human retinal endothelial cell and contribute to understanding of the pathogenesis of these diseases. In addition to providing support for the involvement of well-characterized endothelial molecules, profiling has the power to identify new players in retinal pathologies. Findings may have implications for the design of new biological therapies. Additional progress in this field is anticipated as other technologies, including epigenetic profiling methods, whole transcriptome shotgun sequencing, and metabolomics, are used to study the human retinal endothelial cell.

Sympathetic activities influence blood-flow velocity and resistance in the rabbit ophthalmic artery

PURPOSE

The aim of this study was to investigate sympathetic influences on blood-flow velocity and resistance in the rabbit ophthalmic artery during the transition period from the light to the dark phase.

METHODS

Eight (8) New Zealand albino rabbits were entrained to a daily 12-h light and 12-h dark cycle. Blood-flow velocities in the ophthalmic artery were determined at -2 (baseline), 0, 2, and 4 h after the onset of darkness. Pulsed and color Doppler images of the ophthalmic artery were recorded using a 12-MHz linear ultrasound transducer. Resistive index of blood flow was calculated using the peak systolic velocity and the end diastolic velocity. Measurements of intraocular pressure (IOP) were taken, using a pneumatonometer at the same time points. Blood-flow velocity, resistive index, and IOP were also determined in the same rabbits after surgical decentralization of the ocular sympathetic nerves.

RESULTS

Compared with the baseline at -2 h, a significant increase in the resistive index of blood flow in the ophthalmic artery occurred at 2 and 4 h after the onset of darkness. Parallel elevations of IOP were observed. After the sympathetic decentralization, peak systolic and end diastolic velocities decreased and resistive indexes increased from the presurgical values in the ophthalmic artery. In the postsurgical rabbits, elevation of IOP was absent during the light-dark transition period. There was also no time-dependent increase of resistive index in the ophthalmic artery.

CONCLUSIONS

During the light-dark transition period, resistance to blood flow in the rabbit ophthalmic artery increases in parallel to IOP elevation. The removal of sympathetic activities decreases blood-flow velocity, but increases blood-flow resistance. Like the endogenous elevation of IOP, the time-dependent increase of resistance to blood flow in the rabbit ophthalmic artery during the light-dark transition period depends upon, at least partially, ocular sympathetic activities.

Increases in Central Retinal Artery Blood Flow in Humans Following Carotid Artery and Stellate Ganglion Irradiation with 0.6 to 1.6.MU.m Irradiation

The authors applied near-infrared low-level laser irradiation (LLLI) directed to the stellate ganglion (SG) and to the common carotid artery (CCA), and compared the effects on central retinal artery blood flow using color pulse Doppler sonography. In 10 healthy volunteers, LLLI (0.92 W, 1 : 1 duty cycle, 10 min) to both the SG and CCA significantly increased peak systolic blood velocity in the ophthalmic artery (p<0.001, each) and central retinal artery (p<0.001, each) without changes in vessel resistance. Irradiation to the CCA produced a stronger effect than that to the SG in the ophthalmic artery (p=0.007) and central retinal artery (p=0.031). These data suggest that LLLI to the SG or to the CCA is a useful therapy for increasing the retrobulbar blood flow, with irradiation directed to the CCA being more effective than that directed to the SG in clinical settings.

The acute effects of stellate ganglion block on circulation in human ocular fundus

PURPOSE

To study the acute effects of local-anesthetic stellate ganglion block (SGB) on tissue circulation in the human fundus.

METHODS

Eleven patients with Bell's palsy (age 56+/-6 y, mean+/-SD) who underwent SGB for its treatment participated in the study. Using the laser speckle method, normalized blur (NB) value, a quantitative index of tissue blood velocity, was measured every 0.125 s over an area located halfway between the macula and the optic nerve head (ONH) with no discrete visible vessels and averaged over 3 pulses when fixation was satisfactory (NB(ch-ret)). NB(ch-ret) and intraocular pressure (IOP) in both eyes, blood pressure (BP), and pulse rate (PR) were measured before, and 10, 20, 30, and 60 min after SGB. SGB was induced by injecting 1% mepivacaine hydrochloride (5 ml) into the vicinity of the seventh cervical vertebra on the paralyzed side.

RESULTS

The IOP in the blocked side significantly decreased between 20 and 60 min following SGB, compared to the baseline, while IOP in the unblocked side remained unchanged. The NB(ch-ret) was significantly increased after 10 min by about 8% in the blocked side, but its effect almost disappeared at 60 min. There was no significant change in NB(ch-ret) in the unblocked side, BP or PR throughout the experimental period.

CONCLUSION

SGB increased tissue circulation in the fundus in the blocked side, but its effect was thought to be small and transient.