The impact of ocular blood flow in glaucoma.

The multifunctional choroid.

PURPOSE The purpose of the study was to evaluate the choroidal thickness in patients with central serous chorioretinopathy, a disease attributed to increased choroidal vascular hyperpermeability. METHODS Patients with central serous chorioretinopathy underwent enhanced depth imaging spectral-domain optical coherence tomography, which was obtained by positioning a spectral-domain optical coherence tomography device close enough to the eye to acquire an inverted image. Seven sections, each comprising 100 averaged scans, were obtained within a 5 degrees x 30 degrees rectangle to encompass the macula. The subfoveal choroidal thickness was measured from the outer border of the retinal pigment epithelium to the inner scleral border. RESULTS The mean age of subjects undergoing enhanced depth imaging spectral-domain optical coherence tomography was 59.3 years (standard deviation, 15.8 years). Seventeen of 19 patients (89.5%) were men, and 12 (63.2%) patients had bilateral clinical disease. The choroidal thickness measured in 28 eligible eyes of the 19 patients was 505 microm (standard deviation, 124 microm), which was significantly greater than the choroidal thickness in normal eyes (P < or = 0.001). CONCLUSION Enhanced depth imaging spectral-domain optical coherence tomography demonstrated a very thick choroid in patients with central serous chorioretinopathy. This finding provides additional evidence that central serous chorioretinopathy may be caused by increased hydrostatic pressure in the choroid.

Enhanced depth imaging optical coherence tomography of the choroid in central serous chorioretinopathy.

The retinal and cerebral microvasculatures share many morphological and physiological properties. Assessment of the cerebral microvasculature requires highly specialized and expensive techniques. The potential for using non-invasive clinical assessment of the retinal microvasculature as a marker of the state of the cerebrovasculature offers clear advantages, owing to the ease with which the retinal vasculature can be directly visualized in vivo and photographed due to its essential two-dimensional nature. The use of retinal digital image analysis is becoming increasingly common, and offers new techniques to analyse different aspects of retinal vascular topography, including retinal vascular widths, geometrical attributes at vessel bifurcations and vessel tracking. Being predominantly automated and objective, these techniques offer an exciting opportunity to study the potential to identify retinal microvascular abnormalities as markers of cerebrovascular pathology. In this review, we describe the anatomical and physiological homology between the retinal and cerebral microvasculatures. We review the evidence that retinal microvascular changes occur in cerebrovascular disease and review current retinal image analysis tools that may allow us to use different aspects of the retinal microvasculature as potential markers for the state of the cerebral microvasculature.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7580.2005.00395.x

Retinal vascular image analysis as a potential screening tool for cerebrovascular disease: a rationale based on homology between cerebral and retinal microvasculatures

The progress in understanding and treatment of diabetic retinopathy

The retina receives its nutrients from two separate circulations: retinal and choroidal circulation. This short overview describes the determinants in the regulation of these circulations. Retinal circulation is characterized by a low blood flow while flow in the choroid is high. The choroidal circulation is mainly controlled by sympathetic innervation and is not autoregulated. Retinal circulation lacks autonomic innervation, shows an efficient autoregulation and is mainly influenced by local factors. Local mediators released by endothelial cells and surrounding retinal tissue also have a substantial role in the regulation of retinal circulation.

Regulatory Mechanisms in the Retinal and Choroidal Circulation

—The present study provides evidence that retinal tissue may profoundly influence the retinal arterial smooth muscle cell tone by releasing an unknown retinal relaxing factor. Isolated bovine retinal arteries with and without adhering retinal tissue were mounted in a wire myograph for isometric tension recordings. The maximal contraction induced by prostaglandin F 2α was 0.95±0.7 mN (n=6) in the presence and 5.15±0.76 mN (n=6) in the absence of adhering retinal tissue. The contractions induced by U-46619, serotonin, and endothelin-1 were similarly blocked in the presence of retinal tissue. The K + 120 mmol/L-induced contraction was not significantly affected (2.8±0.7 mN, n=6, in the presence and 3.6±0.7 mN, n=6, in the absence of retinal tissue). Placing a piece of bovine retinal tissue in the proximity of a contracted (ie, with prostaglandin F 2α ) retinal artery induced a complete relaxation of the retinal vessel, suggesting the involvement of a diffusible chemical vasorelaxant. Also porcine, canine, and ovine retinal tissue completely relaxed the contracted (with prostaglandin F 2α ) bovine retinal artery. Other smooth muscle preparations, including rat mesenteric and renal arteries and rat main bronchi, also relaxed with the application of a piece of bovine retinal tissue. Incubation of bovine retinas in a Krebs-Ringer bicarbonate solution yielded a solution that relaxed isolated precontracted bovine retinal arteries, confirming the involvement of a diffusible chemical messenger. Hexane extraction, heating the solution to 70°C, or treatment with trypsin did not alter the relaxing properties of the incubation solution. The characteristics of the retinal relaxing factor do not correspond with those of nitric oxide, prostanoids, adenosine, acetylcholine, or any other of the known vasoactive neurotransmitters released from the retina. Our results suggest that retinal arterial tone is controlled by a diffusible, hydrophilic, and heat-stable relaxing factor that does not correspond with a known vasoactive molecule formed within the retina.

Retinal Arterial Tone Is Controlled by a Retinal-Derived Relaxing Factor

The aim of this study was to investigate the contribution of stereo vision to the acquisition of a natural interception task. Poor catchers with good (N = 8; Stereo+) and weak (N = 6; Stereo-) stereo vision participated in an intensive training program spread over 2 weeks, during which they caught over 1,400 tennis balls in a pre-post-retention design. While the Stereo+ group improved from a catching percentage of 18% to 59%, catchers in the Stereo- group did not significantly improve (from 10 to 31%), this progress being indifferent from a control group (N = 9) that did not practice at all. These results indicate that the development and use of of compensatory cues for depth perception in people with weak stereopsis is insufficient to successfully deal with interceptions under high temporal constraints, and that this disadvantage cannot be fully attenuated by specific and intensive training.

/pdf/stereo-vision-enhances-the-learning-of-a-catching-skill-14egbpcm40.pdf

Stereo vision enhances the learning of a catching skill.

PURPOSE: To investigate whether a pressure-induced myogenic vasoconstriction can be demonstrated in isolated bovine retinal arteries and to determine the cellular mechanisms involved. METHODS: Isolated bovine retinal arteries were mounted on a pressure myograph without flow and exposed to stepwise increases in intraluminal pressure. Changes in internal diameter were monitored continuously using an inverted microscope video system. RESULTS: Bovine retinal arteries showed myogenic tone at pressures higher than 10 mm Hg. This pressure-induced contraction was absent in calcium-free Krebs-Ringer bicarbonate solution. Inhibition of L-type voltage-operated calcium channels with nifedipine (1 microM) suppressed the myogenic contraction. After depolarization of the vascular smooth muscle cells with a K+ 120 mM solution, a pressure-induced contraction was still observed, indicating that besides stimulation of voltage-operated calcium channels, depolarization-independent mechanisms contribute to the pressure-induced myogenic vasoconstriction. CONCLUSIONS: Isolated bovine retinal arteries spontaneously contract when exposed to raised intraluminal pressure. This response depends on extracellular calcium and is blocked by nifedipine. In addition, depolarization-independent mechanisms seem to be involved.

Pressure-induced myogenic responses in isolated bovine retinal arteries.

Purpose To investigate the mechanisms involved in hypoxic vasodilation using an in vitro setup. Methods Retinal arteries with and without retinal tissue were mounted on a wire myograph. The segments were contracted with prostaglandin (PG)F(2alpha) (30 microM) or 120 mM K(+). Hypoxia was induced by replacement of O(2) by N(2) in the gas used to bubble the Krebs-Ringer bicarbonate organ bath solution. Results Hypoxia induced complete relaxation of preparations with adherent retinal tissue contracted with PGF(2alpha). Preparations without retinal tissue were not affected by the change in oxygenation. When the retinal arteries were contracted with 120 mM K(+), hypoxia no longer induced relaxation of the preparation with adherent retinal tissue. The presence of an NO-synthase inhibitor (L-NA, 0.1 mM), a cyclooxygenase inhibitor (indomethacin, 50 microM), or an adenosine receptor antagonist (8-sulfophenyltheophylline, 1 mM) did not affect hypoxic vasodilation. Excitatory amino acids and lactate had no or only a limited effect on the PGF(2alpha)-induced contraction and are therefore unlikely mediators of hypoxic vasodilation. HCl (10 mM) reduced the pH to 6.1 +/- 0.08 (n = 4) and induced a pronounced but transient relaxation of the retinal artery contracted with PGF(2alpha) or 120 mM K(+), whereas hypoxia induced relaxation of the retinal artery contracted with PGF(2alpha) only in the presence of adherent retinal tissue. Conclusions Adherent retinal tissue mediates the hypoxic vasodilatation of bovine retinal arteries in vitro. Neither NO, prostanoids, adenosine, excitatory amino acids lactate or changes in pH seem to be involved in this hypoxic response.

Christophe Delaey

Papers

Regulatory Mechanisms in the Retinal and Choroidal Circulation

Retinal Arterial Tone Is Controlled by a Retinal-Derived Relaxing Factor

Stereo vision enhances the learning of a catching skill.

Pressure-induced myogenic responses in isolated bovine retinal arteries.

A retinal-derived relaxing factor mediates the hypoxic vasodilation of retinal arteries.