Biomedical subjects
Publications and source records attributed to C L Schepens.
(1) In owl monkeys, where no yellow staining of the media is present, there are clear-cut ophthalmoscopic and histologic differences in the lesions produced by equal amounts of argon green and blue light. (2) The yellow staining of the macula causes differences in lesion intensity and depth when different wavelengths are used for photocoagulation. (3) In humans the influence of age on this difference is apparent.
A newly designed mechanical phacofragmentator powered by compressed air was tested on 200 human hard nuclear cataracts and ten traumatic owl monkey cataracts. The device, which consists of a turbine-driven diamond burr, successfully fragmented hard human cataracts, both in vitro and when implanted in the anterior chamber of rabbits and monkeys. Iatrogenic damage to the iris was noted in the early cases, but no collapse of the anterior chamber or gross damage of the cornea occurred. Iris damage can be avoided, once the operator gains sufficient skill in manipulating the instrument. The ten traumatic monkey cataracts were all removed without complication, except for one case in which the posterior lens capsule was ruptured with subsequent vitreous prolapse.
An improved instrument for removing vitreous tissue consists of a replaceable cutting tip and a micromotor that powers the cutting tip. The cutting tip consists of a helical cutter and a metallic tube housing the cutter. An automated power-control unit is also available to control evacuation, infusion, and speed of rotation of the instrument. Several devices for monitoring the outflow of evacuation material and pressure in the eye and in the evacuation line are included. The cutting tip is illuminated by a fiber-optic system, which provides an additional factor of safety. The instrument contains a cleaning mechanism that eliminates the need for disassembling the cutting tip. When an automated control unit is not available, the vitreous nibbler may be used with manual suction, gravity-controlled infusion, and a simplified control unit.
In 375 scleral buckling procedures, an absorbable gelatin implant (Retina Gelfilm) was used. This series included 192 trapdoor and scleral pouch procedures, and 183 operations in which a gelatin implant was used beneath a silicone rubber implant. Two thicknesses of gelatin implants were used, 0.5 mm and 0.75 mm. Absorption time varied from 2 to 24 months, depending on the thickness of the implant and whether it was used alone or beneath a silicone rubber implant. Gelatin is an excellent absorbable implant when used alone or under a silicone rubber implant in selected patients with retinal detachment to produce a temporary elevation or posterior extension of the buckle, or both.
The effects of an incision through the pars plana ciliaris for open-sky subtotal vitrectomy were evaluated in four groups of monkeys, with incisions ranging from 170 degrees to 240 degrees. The nasal long ciliary artery and nerve and the anterior ciliary arteries from the inferior and medial recti were left intact in all cases. Follow-up observation ranging from three to 24 months indicates that the 170 degrees incision and the longer incisions in which the temporal ciliary artery and nerve were sacrificed do not cause severe anterior segment necrosis. The advantages of the incision through the pars plana ciliaris are (1) easier approach to the vitreous cavity, (2) preservation of the crystalline lens and an intact iris, and (3) circumvention of the corneal and chamber angle complications sometimes associated with the transcorneal approach.
The power density at the retina provided by presently available laser photocoagulators is subject to variation. Three factors contribute to making the retinal image of the laser beam substantially different from the spot size indicated on the selector of the photocoagulator. These are the operator's variable accommodation, the astigmatism introduced by the contact lens, and the depth of focus of the observation system. The assumption that the same setting on the instrument regularly produces the same power density at the retina will lead to errors in comparing lesions. The safest procedure is to start from the threshold in every location.
Six owl monkeys were exposed intravitreally for 6 to 28 months to Dow Corning Medical Fluid 350 in a morphologic study of silicone retinopathy. Fellow eyes of each silicone-injected animal and six eyes from three normal untreated monkeys served as controls. In addition, two eyes were treated post-mortem with silicone oil to insure that no artefact redistribution occurred. Each case was studied histochemically in frozen sections, with electron microscopy of Epon-embedded materials. All silicone-injected eyes showed numerous empty spaces in the inner segment of the retina adjacent to the vitreoretinal interface, corresponding to the intercellular spaces between Müller's filbers. These spaces contained numerous spherical bodies encircled by a homogeneous electron-opaque material, suggesting a silicone-phospholipid complex. Marked degeneration of small ganglion cells was seen. Müller's fibers appeared to be shrivelled. The lack of phospholipids in the inner segment of the visual receptors was marked, although no significant morphologic lesions were detectable. Abnormally high ATPase activity was found in both plexiform layers. There were no such lesions in the untreated control eyes, nor any detectable artefactual redistribution of silicone oil in the eyes treated post-mortem with Medical Fluid 350.
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The prognosis in complicated retinal detachments has improved with advances in vitreous surgery. Different types of vitreous membranes require different instrumentation and different surgical techniques. This presentation describes the indications, instrumentation and surgical techniques for the management of various types of vitreous membranes. An exhibit on vitreous surgery illustrates various instrumentation.
The properties of radio frequency (RF) diathermy currents are briefly reviewed. The inadequacy of damped currents is stressed. The recommended machine generates a frequency of 13.56 MHz. It has a power amplifier, crystal control, coaxial lead from machine to handle, and an impedance of 200 ohms. The two types of electrodes and handles described are shielded from the electrode tip to the diathermy machine. One has a short handle, and an electrode angulated at 35degrees, used in open-sky vitrectomies. The other has a longer handle and straight probe, and is provided with a system for saline infusion. It is used in closed transscleral operations. Electrodes require 35 to 50% more current when used underwater than when used on dry sclera. If charring of tissue is to be avoided, it is advisable to keep the intensity near the level at which gas bubbles form at the electrode tip. Blood vessels can be closed reliably and safely with these electrodes.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.