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Biomedical subjects

G T Feke

Publications and source records attributed to G T Feke.

At least 37 records · Page 2Linked to original sources
PubMed1991

Preretinal pH changes in the rabbit under conditions of light and dark.

Preretinal pH was measured in the avascular region of 19 rabbit retinas during alternating cycles of light and dark, using a miniature, needle-type pH electrode. In 14 experiments with the rabbits breathing room air, cyclic changes in pH, decreasing in the dark and increasing in the light, were observed. The transition from light to dark caused a mean pH decrease of 0.047 +/- 0.029 U (n = 14). An inversion of the light/dark pH response was observed in five experiments. In three of these, the effect was induced by having the rabbits breathe 100% O2. In the five rabbits showing a reversed response, a mean pH increase of 0.034 +/- 0.025 pH U was observed in the dark; light-ON caused a decrease of 0.035 +/- 0.025 pH U. The direction of the preretinal pH change is thought to be the net effect of light/dark-induced changes in the metabolism of the photoreceptors and inner retinal layers (defined for the purpose of this paper as the region between the outer synaptic layer and the inner limiting membrane). In six separate experiments, retinal metabolism was assessed by measuring preretinal PO2 during alternating cycles of light and dark while the rabbits breathed room air. Oxygen tension declined from a mean of 14.5 +/- 6.2 (S.D.) mmHg in the light to 10.1 +/- 5.4 (S.D.) mmHg in darkness, and increased from a mean of 10.9 +/- 5.1 (S.D.) mmHg in darkness to 15.4 +/- 5.8 (S.D.) mmHg in the light. The time courses of the pH and the PO2 changes were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effect of timolol on human retinal, choroidal and optic nerve head circulation.

In a double-masked, randomized, placebo-controlled study, we evaluated the effect of topical timolol maleate 0.5% on the retinal, choroidal, and optic nerve head circulation in 5 healthy volunteer subjects. Changes in the pulsatile component of choroidal blood flow (PCBF) were determined from measurements of the ocular pulse wave. Changes in the retinal arterial blood flow rate (RBF) and optic nerve head capillary blood speed (CBS) were determined by laser Doppler velocimetry and monochromatic photography. In timolol-treated eyes, PCBF decreased by 32 +/- 12% (p = 0.0007). Changes in RBF and CBS were not statistically significant. In the contralateral placebo-treated eyes, PCBF decreased by 15 +/- 8% (p = 0.006) and RBF increased by 18 +/- 10% (p = 0.002). The change in CBS was not statistically significant.

Administration, Topical↗
PubMed1991

Optic nerve head blood speed as a function of age in normal human subjects.

We used the laser Doppler technique to determine the relation between age and the speed of blood cells moving through the capillaries of the optic nerve head. We studied 22 normal human volunteers ranging in age from 16-76 years. The results were best described by a statistically significant quadratic relationship between capillary blood speed and age. Blood speeds were lowest in the youngest and oldest subjects and highest in subjects between 27 and 35 years old. A two-phase linear model showed a statistically significant 20% decrease in blood speed in volunteers between the ages of 31 and 76. The results were not affected by gender, degree of refractive error, systemic blood pressure, intraocular pressure, cup/disc ratio of the optic nerve head, or by site-to-site differences in the light scattering properties of the optic nerve head tissue. Capillary blood speed was, on average, 15% greater from temporal sites than from nasal sites, corresponding to the equally greater distribution of ganglion cell axons within the same area. The results provide a baseline of normal age-controlled data that can be compared to measurements obtained from patients with disorders of the optic nerve head thought to have a vascular etiology.

Adolescent↗
PubMed1989

Effects of optic atrophy on retinal blood flow and oxygen saturation in humans.

Retinal blood flow and oxygen saturation were evaluated in patients with unilateral inner retinal degeneration secondary to neurogenic optic atrophy. Arteriovenous O2 saturation for temporal and nasal vascular segments of the affected eyes, evaluated by retinal vessel oximetry, was 12% +/- 9% higher than in the fellow eyes (seven patients). Blood flow in the temporal retinal arteries of the affected eyes, measured by the laser Doppler technique, was 48% +/- 20% lower than in the fellow eyes (four patients). The combination of these results indicated a 40% +/- 29% reduction in O2 delivery in the affected eyes (four patients), thereby quantifying the decrease in retinal metabolism that resulted from inner retinal degeneration.

Adolescent↗
PubMed1989

Blood flow in the normal human retina.

The laser Doppler technique was used to measure the blood flow rate in 41 major vessels in ten eyes of healthy volunteer subjects. The specific relationship between blood flow rate, F, and vessel diameter, D, was determined for both retinal arteries and retinal veins. On average, F increased with increasing D at a power of 4.1, consistent with the presence of Poiseuille flow. In six eyes of six subjects, measurements on individual vessels were combined to yield the total retinal blood flow rate. The mean and standard deviation of the total retinal blood flow was 80 +/- 12 microliter/min. The blood flow rate per unit mass of retinal tissue was calculated and found to be in good agreement with that reported for macaque monkeys. Blood flow to the temporal side of the retina was approximately three times larger than to the nasal side. There was no significant difference between blood flow to the superior and the inferior retina.

Adult↗
PubMed1988

Evaluation of micrometric and microdensitometric methods for measuring the width of retinal vessel images on fundus photographs.

The width of retinal vessel images on fundus photographs was determined by projection micrometry and microdensitometry. These methods were evaluated on 12 retinal vessels using the negatives of 570-nm monochromatic fundus photographs. For projection micrometry, the intraobserver reproducibility of vessel width measurements was 1.6%-2.9%, depending upon the experience of the observer. Significant interobserver differences in the measured widths were demonstrated. For microdensitometry, three distinct measurement criteria were used. Significant differences in width as measured by the three criteria were found, but there were no interoperator differences for each criterion. The intraoperator reproducibility of vessel width measurements by microdensitometry was 2.1%-2.5%. Significant differences were found in the vessel widths determined by the micrometry and densitometry methods, and results obtained by micrometry are discussed in terms of edge-detection phenomena.

Adult↗
PubMed1986

Anterior optic nerve blood flow decreases in clinical neurogenic optic atrophy.

Anterior optic nerve blood flow was studied in nine patients with unilateral neurogenic optic atrophy using noninvasive techniques. Disk reflectometry measurements from temporal sites demonstrated a significant reduction in the index of blood volume in atrophic optic nerves as compared with the contralateral optic nerves (P less than 0.00001). Laser Doppler measurements from the same temporal sites detected a significant reduction in the speed of blood (P less than 0.002). On average, blood volume was decreased by 49% +/- 11% and blood speed by 30% +/- 17%. Combining the results of these two techniques yielded a relative index of blood flow that showed a significant reduction in the atrophic nerves (P less than 0.0001), averaging 64% +/- 14% temporally. Nasally there was less reduction in blood flow. The results correlated well with clinical assessment of the degree of optic nerve damage (rho = 0.92, P less than 0.002). This study demonstrates that clinical neurogenic optic atrophy induces significant reductions in overall anterior optic nerve blood flow that are detected by these noninvasive techniques.

Adolescent↗
PubMed1986

[Effect of neurogenic optic atrophy on papillary blood flow].

Anterior optic nerve blood flow was measured in 9 patients with unilateral neurogenic optic atrophy. The noninvasive techniques of reflectometry and laser Doppler detected a decrease in capillary blood flow of the affected eyes as compared with the control fellow eyes as compared with the control fellow eyes (p less than 0.002) that averaged about 64% +/- 14%. There was a good correlation between the decrease in blood flow and the clinical severity of disease (p = 0.92, p less than 0.002). These noninvasive techniques provide a sensitive, safe, and accurate evaluation of the anterior optic nerve that is useful in both clinical research and patient care.

Humans↗
PubMed1985

Retinal circulatory changes related to retinopathy progression in insulin-dependent diabetes mellitus.

To quantify the vascular deterioration of the diabetic retina, retinal circulatory changes in 45 insulin-dependent diabetic patients, and in 17 normal controls, were measured and divided into four groups according to severity of retinopathy. The noninvasive laser Doppler technique was used to measure the systolic/diastolic variation of red blood cell velocity (V) at sites along temporal retinal arteries. Flow pulsatility [V (systole)/V (diastole)] was 18% lower (P less than 0.00001) in the mild-retinopathy group than in normal controls, but 35% higher (P less than 0.001) in the severe-retinopathy group than in the mild-retinopathy group. Repeated measurements in three eyes during the progression from mild or moderate to severe retinopathy showed progressive increases in both flow pulsatility and mean retinal blood flow. Altered flow pulsatility appears to be a sensitive indicator of vascular alterations during the progression of diabetic retinopathy.

Adult↗
PubMed1985

Anterior optic nerve blood flow in experimental optic atrophy.

This study attempts to establish whether neurogenic optic atrophy induces changes in anterior optic nerve circulation and to determine how noninvasive techniques of measuring blood flow in vivo compare to microsphere distribution. Five cats underwent unilateral optic nerve transection in the orbital apex and a sham procedure in the contralateral eye. Two to three months later, no abnormalities were detected by fluorescein angiography. Laser Doppler measurements demonstrated a 53% decrease in red blood cell speed through the capillaries of the atrophic optic nerve heads in vivo. Optic disk reflectance measurements of anterior optic nerve blood volume in vivo demonstrated a 51% decrease in the estimated blood volume of the capillaries in atrophic optic nerve heads. Flow was calculated on the basis of these noninvasive measurements and demonstrated an average decrease of 74% in optic atrophy. Histologic studies of microsphere distribution demonstrated an average decrease of 80% in flow to the anterior optic nerve in optic atrophy. These results suggest that anterior optic nerve blood flow is significantly reduced in primary neurogenic optic atrophy. This study also demonstrates that the noninvasive measurements of blood flow are substantiated by histologic evaluation of microsphere distribution.

Animals↗
PubMed1983

Retinal blood flow alterations during progression of diabetic retinopathy.

Alterations in retinal blood flow during the progression of diabetic retinopathy were studied using the dye-dilution technique. Mean fluorescein circulation times were measured in retinal arteriovenous segments with a two-point fluorophotometer in 48 diabetic patients and 20 normal controls. Monochromatic fundus photographs were used to determine vessel diameters. Segmental blood flow (SBF) increased with the progression of background diabetic retinopathy. In patients with distinct capillary closure, SBF was significantly higher than normal values.

Adult↗
PubMed1983

Retinal circulatory changes after scleral buckling procedures.

The noninvasive laser Doppler technique was used to study retinal circulatory characteristics in five patients who underwent uncomplicated scleral buckling procedures. In each patient, the systolic/diastolic variation of the red blood cell speed in the retinal arteries (flow pulsatility ratio) was lower in the eye that had received an intrascleral implant and an encircling band than in the fellow eye. In one patient, an increase in flow pulsatility ratio accompanied an increase in retinal blood flow after removal of the scleral buckling elements. In another patient, the flow pulsatility ratio in the eye that had received a solid implant and an encircling band was less than the ratio in the fellow eye that had received an absorbable implant alone. Our results indicated that reduced retinal blood flow may be common after scleral buckling procedures, and may be a significant factor in otherwise inexplicable postoperative complications.

Adult↗