Shin-ichiro Kawano

Photothermal, cryogenic, and diathermic effects of retinal adhesive force in vivo.

Abstract: Argon laser photocoagulation, cryoretinopexy, and diathermy of moderate intensity is applied to 140 rabbit eyes. Retinal adhesive force is measured from 1 day to 6 months following the treatment, using the authors’ new in vivo method. A small retinal detachment is induced within the area surrounded by the burns. At the moment when the detachment starts to expand beyond the burns, subretinal pressure is measured using a resistance servo‐nulling method. Retinal adhesive force is then calculated according to Laplaces law and compared with that of untreated eyes. Both photocoagulation and diathermy enhanced adhesiveness within 24 hours to 128% and 122%, respectively, of normal levels. Cryoretinopexy reduced the retinal adhesiveness during the first week, but afterwards generated as much adhesiveness as the other two methods. Beyond 6 months, under the conditions described here by the authors, the adhesive force was stronger after diathermy (279%) than after cryoretinopexy (214%) or laser photocoagulation (220%).

EFFECTS OF BIOLOGICAL STIMULI ON THE VISCOSITY OF THE VITREOUS

Changes in the physical properties of the vitreous induced by various biological stimuli were investigated with Cannon‐Fenske kinematic and cone‐plate rotary viscometers. Heating greatly decreased the viscosity of the human vitreous, the critical temperature being between 50°C and 60°C. Freezing also affected the viscosity, but less so than heating. Viscosity of hyaluronic acid was also decreased by heating to approximately 60°C. Preliminary incubation with hyaluronidase made the viscosity of both the vitreous and hyaluronic acid heat‐stable. Lens extraction decreased vitreous viscosity markedly, suggesting a decrease of hyaluronic acid concentration and/or a lowering of hyaluronic acid molecular weight. Vitreous haemorrhage resulted in decreased vitreous viscosity. Cryoretinopexy at the level employed in this study induced little change in vitreous viscosity, while retinal diathermy caused a moderate decrease. In the course of vitreous haemorrhage and retinal diathermy, a return towards normal of the viscosity was observed, suggesting the presence of local hyaluronic acid production.

Effects of Intraocular Irrigating Solutions on The Electroretinographic b-Wave

We studied the effects of physiologic saline, lactated Ringers solution, and BSS (balanced salt solution) on the electroretinogram of the rabbit in vitro. The b-wave amplitudes decreased when the retina was incubated in lactated Ringers solution or BSS. These amplitudes recovered to 60% to 70% of the original level when the retina was re-immersed in the control medium. With physiologic saline, the b-wave amplitude recovered only to about 30% after 20 minutes of incubation, and recovery was nil after 60 minutes of incubation time. Extended contact with physiologic saline produced permanent damage to the retina. Bicarbonate ion and glucose were shown to be essential for maintaining the ERG amplitude.

Vector Analysis of Corneal Astigmatism after Scleral Buckling Surgery

We conducted a short-term prospective study of 125 eyes with retinal detachment to examine changes of corneal astigmatism about 2 weeks after scleral buckling surgery, using a vector method on 2-fold-angle rectangular coordinates. Segmental buckles of one to less than two quadrants produced significantly greater changes in astigmatism (1.65 +/- 0.97 dptr) than those of less than one quadrant (0.88 +/- 0.75 dptr) and those spanning two quadrants or more (1.09 +/- 0.38 dptr) (p = 0.0005, Kruskal-wallis test; n = 73). The amplitude of differential vectors after explant buckling surgery (1.33 +/- 0.89 dptr, n = 24) was significantly greater than after implant buckling surgery (0.65 +/- 0.45 dptr, n = 15) (p = 0.009, Mann-Whitney U-test) with buckles of one quadrant or less. Differential vectors tended to direct toward the buckles. There was no obvious directional tendency in the case of encircling procedures (n = 52).

Axial length of eyes with rhegmatogenous retinal detachment

We conducted a prospective study of 226 eyes with nontraumatic rhegmatogenous retinal detachment; we examined patient characteristics as well as changes in axial length and corneal curvature induced by scleral buckling surgery. Eyes with a round hole in lattice degeneration were characterized by axial length that was longer than that of eyes with retinal tears with and without lattice degeneration. Sex and age also correlated significantly with axial length. Surgically induced changes in axial length depended upon the procedures performed, but the retinal detachment surgery primarily caused a change in the refractive status.

Pressure Profile of Ophthalmic Surgical Procedures: An Experimental Study on the Rabbit Eye

A balloon sensor was implanted in the posterior wall of the rabbit eye, and pressure fluctuation during several surgical procedures was monitored. Temporary IOP increase during digital massage sometimes reached near 100 mm Hg. Pressure increase during incision on the cornea was quite high, while corneal suturing, lens extraction, iridectomy, and open-sky vitrectomy induced minor fluctuating pressure on the posterior wall. Diathermy coagulation and scleral incision during simulated retinal detachment surgery increased IOP, exceeding 50 mm Hg and sometimes reaching 100 mm Hg.

Some experimental data concerning the safety of vitrectomy

Abstract Several reasons why vitrectomy does not compromise retinal functions are shown, based on closed and open‐sky vitrectomy on the rabbit eye. We observed that ERG b‐ and c‐waves were stable during and after open‐sky vitrectomy. The c‐wave disappeared when the retina was detached. Function of the retinal ganglion cells after vitrectomy was shown to be almost normal by electrophysiological studies and by measured amounts of axonally transported radioactive proteins.

Why Do Corticosteroids Increase the ERG Amplitude? an Experimental Study in Rabbits

Effects of betamethasone and dexamethasone (which have no mineralocorticoid action) on the visual function of adult albino rabbits were studied in in vitro and in vivo. In in vitro study, betamethasone and dexamethasone had no effects on ERG at a concentration of 4x 10-5 g/ml or below. Concentration of 8x 10-5 g/ml increases the amplitudes of in vitro ERGs, but the concentration was considered too high to be a possible level in vivo. An intravenous injection (single shot) of betamethasone 0.5 mg/kg body weight did not change ERGs and VECPs within 5 hours observations. In chronic in vivo study (daily intravenous injections of betamethasone 0.1 mg/kg and 0.3 mg/kg body weight for 15 days), ERGs did not change so much.