Biomedical subjects
Publications and source records attributed to G Eisner.
After changing the position of the eye, intravitreal structures demonstrate a gravitary position at rest. As an exception the detached vitreous shows an irreversible position at rest. The vitreous tractions on retinal adhesions are therefore irregular. This could explain the asymmetric distribution of retinal tears and has to be considered for the operation techniques.
Posterior vitreous detachments (PVDs) are common. Their complications--retinal detachment--however, are comparatively rare. PVDs without complications and those prone to complications can be differentiated biomicroscopically by morphological signs, that is by examining the posterior hyaloid and its insertion at the posterior border of the vitreous base. PVD without complications is a rhegmatogenous detachment which has been completed temporarily as well as anatomically. It has the shape of a collapsed bag whose posterior wall has been perforated and whose contents have been emptied through the hole. All other shapes of PVD are prone to complications: either an incomplete rhegmatogenous PVD with persistent vitreoretinal adhesions; or a non-rhegmatogenous PVD whose complications depend on the retinal or vascular disease which caused it.
The different rheological properties of viscous and viscoelastic substances indicate different uses in surgical practice. Purely viscous substances solve manly surface-tactical problems. The stronger the elastic component, the better the substances are suitable also for space-tactical and tissue-tactical purposes. A new field of interest is the neutralization of the buoyancy of silicone oil and gas bubbles. The latter can be used for the insertion of posterior chamber lenses in cases where the lens capsule is lacking (air sandwich). The main disadvantage is the postoperative rise of intraocular pressure: but this can be managed by a release of the substance through a preplaced keratotomy.
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The examination in optical section of sheep eyes, photocoagulated several months previously, shows a disturbed vitreous growth above the destroyed retinal areas (Figs. 2-4). The shape of the resulting deficiencies of vitreous structure (holes) suggests that the vitreous is produced by retinal elements and develops by appositional growth. Holes above lesions due to photocoagulation in an early developmental stage are longer (Fig. 1a; Fig. 2) than those above photocoagulations in later stages (Fig. 1b; Fig. 4). Holes above lesions with intensive retinal destruction (Fig. 2a; Fig. 4a) produce more important vitreous deficienceis than do weaker coagulations (Fig. 2b). Structural deficiencies, though extensive at first, become less important during further growth (Fig. 1c; Fig. 2c; Fig. 3 shows transverse sections at a deep and superficial level through the holes of Figure 2c), which is a sign that in the retinal scars a regeneration of elements producing vitreous occurs. Apart from the theoretical implications concerning the development of the vitreous, the results of our experiments should be considered when photocoagulating children.
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This is the first description of the biomicroscopic appearance of reticular cystoid degeneration (RCD). The case with exceptionally large RCD illustrates the difficulties of diagnosis in the living eye of this rather common condition. There is no scotoma in the visual field and the pillars transgressing the cystoid spaces obviously contain nervous elements. Morphologically the RCD are not very conspicious and are easily confounded with typical cystoid degenerations. Differential diagnosis between these two cystoid alterations of the retina is therefore difficult and possible only if vessels on the outer layer of the cystoid spaces are found.
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Delayed full-thickness skin grafts present an alternative means of treatment to flaps for the closure of deep defects in the lid region. They are indicated wherever there is a risk of recurrence of the causative process which might lead to the loss of the transposed skin.
The anatomical arrangement of vitreous structures in human and animal eyes is described on the basis of coinciding findings of histological examinations, biomicroscopy and the "optical dissection" of unfixed vitreous specimens. The "funnel" of the primary vascular vitreous disappears completely during development. The vitreous cavity is filled with secondary vitreous. Its structure in nearly homogeneous, containing "holes" of low density at all sites where the structure of a normal inner retinal surface is altered. During postnatal development the secondary vitreous forms a new funnel system, consisting of zones of different density and of membranelles (vitreous tracts). Before completion of this funnel system, destruction of the vitreous gel begins and confuses the typical arrangement. Postnatal vitreous structures include: zones of different density: preretinal zone, intermediary zone, retrolental zone; holes (of low density): prepapillary hole, prefoveal hole, prevascular fissures, vitreous tracts (of high density): preretinal tract, median tract, coronary tract, retrolental tract ("hyaloid" tract). The pattern of the "holes" strongly suggests that the framework is formed by retinal elements.
The ability of the immature kidney to autoregulate blood flow was investigated. Renal blood flow was measured by electromagnetic flowmeter. In six puppies, selective blockade of the intrarenal effects of angiotensin II (AII) by [1-sarcosine, 8-alanine]angiotensin II (anti-AII) administered into the renal artery did not change renal blood flow. During selective renal AII blockade, intravenous AII raised perfusion pressure from 76 +/- 2 to 100 +/- 6 mmHg. Renal blood flow increased from 1.59 +/- 0.29 to 1.98 +/- 0.59 ml/g kidney per min, but returned to control levels within 40 s in spite of persistent arterial pressure elevation. In another group of seven puppies, renal blood flow remained constant despite reduction of renal perfusion pressure by aortic constriction to 60 mmHg. In two of these seven puppies intrarenal anti-AII did not abolish autoregulation. Autoregulation of renal blood flow occurs in the puppy and is not influenced by inhibition of angiotensin. The renin-angiotensin system does not appear to be involved in the normal regulation of renal blood flow in the puppy.
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