The visibility of retinal blood vessels.

The plexus of retinal blood vessels was made visible by moving the shadow across the retina in a controlled manner. Frequency of scanning, amplitude of shadow movement, illuminance, contrast and other parameters were varied while flicker was minimised. Reciprocity between diameter and frequency of scanning (to give a constant speed of shadow movement) was not found. Other results were consistent with the view that the shadows normally form a low-contrast, diffuse, stationary image, and that smooth movements similar to the natural drift movements are adequate for making such a stationary image visible.     

Rat retinal blood vessels.

The largest arteries in the rat retina are the arterioles in the nerve fiber layer adjacent to the optic papilla. They are 50 to 100 micrometer in diameter, have an incomplete internal elastic lamina and usually a single layer of smooth muscle. Smaller arterioles of 10 to 50 micrometer have no internal elastic lamina and the media is formed by one or two layers of slender smooth muscle cells. In these vessels, myoendothelial junctions and close contact areas between smooth muscle cells are numerous. Capillaries are present in all layers of the rat retina and from plexuses in the nerve fiber, outer plexiform and exterior part of the inner plexiform layers. In nearly all capillaries, pericytes and their processes from a single layer external to the endothelium with numerous contact points or zones between endothelium and pericytes without any intervening basal laminar material. Areas of close contact between adjacent pericyte processes are frequent. The possible functions of myoendothelial junctions and pericyte-endothelial contacts in relation to vessel tone, mechanical stabilization and metabolic exchange are discussed.     

Permeability of iridial blood vessels.

The permeability properties of rat iridial vessels were examined using fluorescein angiography combined with light and electron microscopic marker studies. Results show that while control iridial vessels of some young rats are permeable to fluorescein, a marked permeability to this dye is commonly seen in older animals. Following paracentesis there is a marked increase in permeability of the radially arranged iridial vessels of older animals to fluorescein while angiograms on the younger animals were inconclusive. When carbon is injected intravenously following completion of the angiography study, both light and electron microscopic observations show that iridial vessels of control eyes are impermeable to carbon. However, following paracentesis an inflammatory reaction occurs. Carbon is seen leaving the lumen of iridial vessels in enlarged spaces between adjacent endothelial cells. This inflammatory reaction is age-related; the increase in permeability to carbon is greatest in older animals. There is little or no carbon labeling in the choroid or ciliary body of these experimental eyes.Thus, in the rat, paracentesis causes a breakdown in the blood-aqueous barrier by specifically inducing an inflammatory reaction in iridial blood vessels. This inflammatory reaction is age-related.     

X-ray elemental analysis differentiates blood vessels and lymphatic vessels in the chick choroid.

PURPOSE: Chick choroidal lymphatics swell rapidly during recovery from form-deprivation occlusion, leading to the question of functional significance. To date, analysis of lymph in initial lymphatics has been problematic because of the difficulties of access. However, elemental composition can be determined using scanning electron microscope (SEM) X-ray microanalysis. This study investigated whether cryo-fixation would permit vascular fluids to be analysed in situ. METHODS: Two chicks were raised normally and seven were raised with monocular occlusion for 12 days before varying periods of normal visual experience. The eyes were rapidly frozen, fractured and X-ray spectra obtained from the lumina of lymphatic and blood vessels in a Cambridge S360 SEM. RESULTS: The elemental signatures of Na/Cl/K/P/S distinguished the two vessel types. CONCLUSIONS: These results suggest this bulk-frozen tissue technique can quantify relative changes in elemental species present in various ocular compartments in response to light-induced changes in the retina.     

The effect of blood on ocular fundus reflectance and determination of some optical properties of retinal blood vessels.

Light reflected from 50 micrometer diameter spots on the fundi of two adult rhesus monkeys was measured as a function of wavelength in 10 nm jumps from 400 to 900 nm. The areas measured were a retinal artery and vein, areas of the disk, macula, and retina devoid of visible blood vessels, and the foveola. The eyes of the two monkeys were then exsanguinated, the blood vessels were filled with normal saline, and reflectances of the same spots on the fundi were again measured. The pairs of reflectance curves were compared and demonstrated that blood is not the major determinant of the characteristic shapes of the retinal tissue spectral reflectance curves. From the pre-exsanguination and postexsanguination data, the isolated retinal artery and vein wall reflectances were determined to be 0.020 and 0.009, respectively, their transmittances 0.837 and 0,977, and the fractions of light absorbed by them 0.143 and 0.014, respectively, in the visible spectral region below 500 nm.     

The influence of the estrogens on a retinal blood vessels

PURPOSE: To define the influence of the estrogens on a retinal blood vessels. MATERIAL AND METHODS: 20 healthy women, mean age 23.5 +/- 1.55 with normal laboratory investigations and with regular fundus and blood vessels appearance, participated in our study. Fundus examination was performed with fundus camera Canon NF 505 and with HRT II. The measurements were made before estrogens application (300 microg dermal plasters) and 36 hours after the application in 4th and 6th day of a period. RESULTS: The difference between the size of the retinal vessels before and after estrogens application was significant in all cases. In the main branches the increase of a vessel's diameter was 4.4% to 11.22% (mean 7.61% +/- 3.210%), p<0.05. The increase in a smaller branches of central retinal artery balanced from 1.2% to 9.2% (mean 5.47 +/- 4.11%), p<0.05. CONCLUSIONS: Estrogens have a great vasodilatation effect on a retinal blood vessels. The level of the dilatation after the estrogens' application is about 8% in main branches and about 5% in a smaller vessels.     

Pulsatile ocular blood flow: relationship with flow velocities in vessels supplying the retina and choroid

BACKGROUND: Although ocular tonography measures a pulsatile component of the ocular perfusion, the retinal and/or choroidal components of this pulsatile flow remain undefined. AIM: To compare ocular tonography with the assessment of flow velocities in arteries supplying the retina, choroid and entire orbit. METHODS: 22 normal eyes from 11 subjects were studied. Pulsatile ocular blood flow (POBF) was measured using the ocular blood flow tonograph, and flow velocities in the ophthalmic, central retinal (CRA) and temporal short posterior ciliary arteries (TSPCA) using colour Doppler imaging. The correlation between POBF and retrobulbar flow velocities was determined. RESULTS: POBF correlated significantly with peak systolic velocity (PSV) of the CRA (r = 0.56, p = 0.007) and the TSPCA (r = 0.48, p = 0.02), and with the resistive index of the TSPCA (r = 0.45, p = 0.04). Additionally, pulse amplitude (PSV-end diastolic velocity) in the CRA and the TSPCA correlated significantly with POBF measurements (each p<0.05). However, POBF did not correlate with any flow velocity indices in the ophthalmic artery. CONCLUSION: POBF is associated with systolic and pulsatile components of blood flow velocities in both the CRA and the TSPCA. This result suggests that POBF determinations are influenced by the pulsatile components of both choroidal and retinal perfusion.