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Biomedical subjects

S Ishiko

Publications and source records attributed to S Ishiko.

47 records · Page 3Linked to original sources
PubMed1992

Outward permeability of the blood-retinal barrier.

To characterize quantitatively the active transport mechanism of the blood-retinal barrier (BRB), we estimated the inward (Pin) and outward permeability (Pout) of the BRB in monkey eyes using vitreous fluorophotometry. Pin values for fluorescein (F) and fluorescein glucuronide (FG) were simulated by computer in separate experiments following measurements of intraocular fluorescence at 1 h following the intravenous injection of F or FG. The estimated mean Pin values for F and FG were 4.7 +/- 1.6 and 5.9 +/- 1.7 x 10(-6) cm/min, respectively, in ten eyes of five monkeys. At 1 month thereafter, F was injected into the right vitreous cavity and the same amount of FG was injected into the left vitreous cavity. The intraocular kinetics of fluorescence were measured at 6-24 h postinjection. As estimated by the simulation model, the mean Pout values were 7.7 +/- 2.6 and 1.7 +/- 0.9 x 10(-4) cm/min for F and FG, respectively. The Pout/Pin ratio was 160 +/- 78 for F and 26 +/- 9 for FG. The intraperitoneal injection of probenecid resulted in a significant decrease in the Pout value for F (P less than 0.005) but had no significant effect on that for FG, suggesting that F is excreted from the retina via an active transport mechanism; as characterized by the Pout/Pin ratio, the actual magnitude of the latter is far greater than that previously reported.

Animals↗
PubMed1992

Blood-ocular barrier permeability in monkeys.

The permeability of the blood-ocular barrier was investigated in five monkeys using vitreous fluorophotometry (VFP). Inward permeability (Pin) of the blood-retinal barrier was calculated by a computer simulation method. Kinetic VFP was performed after intravitreal injection of fluorescein (F) or fluorescein monoglucuronide (FG). The estimated mean value of Pin (x10(-6) cm/min) was 4.8 (SD 1.2). The mean rates of loss (per hour) of F from the anterior chamber (Ka) and the vitreous (Kv) were 0.11 (SD 0.01) and 0.13 (SD 0.03), respectively, which were approximately three and four times greater than those of FG (0.04 (SD 0.01) and 0.03 (SD 0.01), respectively). Probenecid administered intraperitoneally decreased both the Ka and the Kv of F significantly but had no effect on the Ka or the Kv of FG, suggesting that F was excreted from the eye with the aid of the active transport mechanism. The results of comparative studies of the rates of loss of F from the anterior chamber (Ka) and from the vitreous (Kv) suggested that active transport was more predominant in the blood-retinal barrier than in the blood-aqueous barrier.

Animals↗
PubMed1992

Ocular circulatory changes following scleral buckling procedures.

The effect of segmental scleral buckling (SB) on ocular circulation was evaluated by measurements of the ocular pulse amplitude (PA) and the ophthalmic artery pressure (OAP). In this study the OAP was defined as the intraocular pressure (IOP) at which the PA disappeared during increasing IOP. Twenty four patients with unilateral rhegmatogenous retinal detachment who underwent SB of varying extent were studied; the unoperated fellow eyes served as controls. Both the OAP and the ophthalmic perfusion pressures (OAP minus IOP) decreased significantly (p < 0.01) as the area of SB treatment increased. Follow-up measurements showed that the OAP was relatively lower up to 3 months postoperatively than after 3 months, and then remained stable. Our results indicated that SB affects the ocular pulse measurements and may decrease ocular blood flow because of decreased ophthalmic perfusion pressure, probably due to increased choroidal vascular resistance, and that the greater the extent of the SB treatment, the greater the possibility of decreased ocular blood flow.

Adult↗
PubMed1991

Oscillatory potentials and permeability of the blood-retinal barrier in noninsulin-dependent diabetic patients without retinopathy.

Electroretinography and vitreous fluorophotometry were performed in 36 eyes of 36 noninsulin-dependent diabetic patients and in 32 eyes of 32 healthy control subjects between the ages of 30 and 59 years. Fluorescein fundus angiograms showed no abnormalities in either group. Peak implicit time of the first deflection of the oscillatory potential, interpeak interval between the first and second deflections, and the sum of the amplitudes of the upward deflections were analyzed. Inward permeability of the blood-retinal barrier was calculated by vitreous fluorophotometry and computer simulation. The peak implicit time of the first deflection and the interpeak interval between the first and second deflections of the oscillatory potential were significantly longer in diabetic patients than in control subjects (P less than 0.01). No significant difference in inward permeability of the blood-retinal barrier existed between the two groups. These results indicate that a selective delay in the peak implicit time of the oscillatory potential (neurosensory retinal abnormality) may be present in noninsulin-dependent diabetic patients, representing retinal functional changes before changes in blood-retinal barrier permeability are apparent.

Adult↗
PubMed1991

[Changes in ocular structure and in blood-ocular barrier permeability of experimental myopia induced in monkeys].

We induced myopia by eyelid suturing in one eye each of six 9-month-old cynomolgus monkeys to elucidate the condition by studying changes in the ocular structure and the blood-ocular barrier (BOB) permeability. Optical elements were measured by A-mode ultrasonography; vitreous fluorophotometry was carried out to document BOB permeability before eyelid suturing and 3, 10, 16, and 28 months after suturing. The axial length of the sutured eyes increased significantly compared with that of the non-sutured contralateral eyes at 10 months after suturing and continued to lengthen with time. The dioptric power (D) of the sutured eyes changed in the same way. (mean, -3.08D 28 months after suturing). The permeability of the blood-retinal barrier of the sutured eyes significantly increased from 10 months after suturing compared with that of the fellow eyes, and continued to increase over the period of observation. The permeability index of the blood-aqueous barrier also increased significantly from only 16 months after suturing further increasing as the period of observation lengthened. We hypothesize that in the transition from emmetropia to myopia, the permeability of the BOB rises, and continue to rise as myopia develops. Thus, the breakdown of the BOB, i.e., the breakdown of the ocular homeostasis, is considered to be closely related to the occurrence and the development of myopia.

Animals↗
PubMed1990

Blood-ocular barrier permeability in experimental myopia.

Vitreous fluorophotometry (VFP) was performed for myopic eyes induced by unilateral eyelid suturing of six young cynomolgus monkeys in order to study the permeability of the blood-ocular barrier. The eyelid fusion was temporarily cut and opened at about five-month intervals, and the dioptric power and axial length of test and control eyes were measured. VFP was carried out before and after intravenous injections of fluorescein-Na. The inward permeability of the blood-retinal barrier (P(in)) was estimated by our computer simulation method, and the index of permeability of the blood-aqueous barrier (AQ) was also obtained. Significant prolongation of the length of the vitreous cavity was first seen 10 months after suturing, with the degree of myopia progressing subsequently. P(in) and AQ values increased as myopia progressed: significant increases were observed at 10 and 16 months after suturing, respectively. These results indicate a close relationship between the occurrence and progress of myopia and increased permeability of the blood-ocular barrier.

Animals↗
PubMed1990

Estimation of permeability in blood-retinal barrier.

Permeability of the blood-retinal barrier (BRB) can be determined by vitreous fluorophotometry and computer analysis. In this study, we characterize our eye model and apply it to normal human subjects. In this investigation of BRB permeability, we employed four parameters for the eye model: the inward permeability (Pin) and outward permeability (Pout) of the BRB; the diffusion coefficient in the posterior vitreous gel (D-p); and the plasma fluorescein concentration. The values of Pin, D-p, and plasma fluorescein concentration significantly affected the fluorescein concentration in the posterior vitreous 60 minutes after intravenous fluorescein injection. The value of Pout had little influence on the fluorescein kinetics in the posterior vitreous 60 minutes after injection. The results of experiments on humans indicate that the estimated values obtained by simulation fit satisfactorily the measured values. It is suggested that our computer simulation method in conjunction with vitreous fluorophotometry can effectively estimate permeability of BRB in normal and pathological eyes.

Adolescent↗
PubMedDate not supplied

Abnormal vitreous structure in optic nerve pit.

A 37-year-old man presented with an optic nerve pit and serous macular detachment of the left eye. Scanning laser ophthalmoscopy revealed a cyst-like structure terminating at the pit in the premacular vitreous. During ocular movement, this structure moved vigorously and seemed to exert traction on the pit. We believe that it is part of an anomalous Cloquet's canal, and that traction on the pit may be a significant factor in the development of serous macular detachment in this patient.

Adult↗