Richard L. Purple

Ocular Changes in the Mucopolysaccharidoses after Bone Marrow Transplantation: A Preliminary Report

Metabolic correction and physiologic response were evaluated after bone marrow transplantation in mucopolysaccharidosis. Eleven patients were prospectively evaluated to determine the effect of bone marrow transplantation on the progressive ocular manifestations of these disorders. Follow-up of 0.6 to 2.8 years after successful donor stem cell engraftment showed that some patients had slow clearing of the corneal clouding, reduction of intracytoplasmic inclusions in the conjunctiva, resolution of optic nerve edema, and stabilized or improved retinal function as determined by electroretinography. These preliminary results suggest that early bone marrow transplantation may alter some of the progressive ophthalmic characteristics of the mucopolysaccharidoses. Long-term follow-up is necessary to determine if these early alterations in the ocular features are predictive of a prolonged functional improvement in the visual status.

Afferent fibers with multiple encoding sites.

Abstract A primary afferent fiber with the capability for initiating impulses at more than one sensory terminal belongs to one of two classes. The first, termed simultaneous reset, appears to be more common in nature, including most, if not all myelinated afferents. Analysis of this class shows that multiple encoding sites increase mean discharge and produce significantly less variability in discharge rate of the parent axon. The second class, termed non-simultaneous reset, is far more difficult to analyze, although multiple encoding sites belonging to this class would appear to be limited to C fibers with large areas of innervation. Some possible utilities of the simultaneous reset class include the allowance for both non-disruptive multiplexing of information from different transducers, and for trophic activities of growth and repair without interfering with ongoing function.

A paired comparison of two models of experimental retinal ischemia

Increased intraocular pressure and vascular ligation models are often used in studies of global ocular ischemia. The purpose of this study is to perform a paired comparison of retinal recovery in these paradigms. Our data indicate that ERG b-wave recovery profiles, following identical periods of ischemia, differ significantly between models. We propose that increased intraocular pressure models induce greater retinal injury than vascular ligation models. We suggest that pressure or another aspect of the increased intraocular pressure model induces injury beyond that caused by ischemia alone and caution against direct comparison of results obtained using these two models.

Involutional Diabetic Retinopathy

The end-stage or involutional phase of proliferative diabetic retinopathy may result in stabilization of vision for long periods of time. However, the clinical resemblance to the progressive tapetoretinal degenerations suggests that marked functional impairment of the retina is present in such eyes. We studied 19 eyes with involutional retinopathy to document the status of the retinal function. Studies included fluorescein angiography, visual field examination, dark adaptation testing, color vision testing, electro-oculography and electroretinography (ERG). The results indicated marked functional abnormalities in all eyes. The ERG tracings showed uniformly subnormal responses and delayed implicit times, similar to those of dominantly inherited retinal pigment degeneration, and indicative of a progressive retinal disorder. In two patients, color vision testing showed defects similar to those seen in inherited tritanopia; and in the remaining patients, defects were indicative of an acquired blue-yellow dyschomatopsia.

Retinal ganglion cell activity in the ground squirrel under halothane anesthesia.

Abstract Retinal ganglion cell activity in the predominantly cone retina of the ground squirrel was studied under conditions of light halothane anesthesia with intensive controls and/or monitors of the animals physiological state. Maintained dark discharge was comparable to what has been found in other mammalian retina. Only one kind of color opponent retinal ganglion cell—designated the BG-G unit—was found when the preparation was physiologically normotensive. The BG-G units converted into two other forms of color opponents when the preparations blood pressure became hypotensive. The change was reversible.

Synaptic organization in the neuropile of the lateral eye of Limulus

Abstract Serial sections of the lateral plexus and neuropile of the compound eye of Limulus reveal apparent synaptic structures near the center of the neuropile at sites where three axon collaterals meet. The possibility of reciprocal synaptic action is suggested by the frequent occurrence of apparent synaptic contacts in at least two of the three apposed processes. Synaptic contacts have been observed directly opposite each other, and we speculate that the membrane around the synaptic contacts may contain both release and receptor sites for transmitter.

Dense peripheral corneal clouding in Scheie syndrome.

A 28-year-old woman with Scheie syndrome (MPS I-S) presented with the unusual feature of extremely dense peripheral corneal clouding, allowing maintenance of good central visual acuity. Characteristic systemic features, an abnormal electroretinogram result, and absent alpha-L-iduronidase activity confirmed the diagnosis despite the unusual corneal pattern of clouding.

The ultrastructure of cones in the walleye retina

The ultrastructure of single and twin cone photoreceptors in the retina of the walleye was analyzed by scanning and transmission electronmicroscopy. The outer segment disks resemble those of other vertebrates. An accessory outer segment arises from the inner segment, makes frequent contacts with the outer segment proper, and may thus provide a bridge for signal transmission from outer to inner segment. A palisade of some 30 calycal processes surrounds and may provide structural support for the outer segment. The region of apposition between the inner segments of twin cones consists of a space of some 28 nm with no indication of gap junctions. The proximal quarter of the inner segment displays a profusion of some 50 lateral fins which increase the inner segment surface by 3-4 X and do not contact fins of neighboring cones. The fins surround a profusion of Müller cell microvilli and probably promote metabolic exchange between cones and Müller cells. Apart from differences in size and the presence of apposed inner segments, twin and single cones appear to be morphologically similar.

Some temporal output properties of color opponent units in the ground squirrel retina

Responses of BG-G units to equal energy stimuli of different wavelengths reveal a tonic to phasic pattern of responses in which short wavelengths (blue) evoke tonic activity, medium wavelengths (green to yellow) evoke phasic activity and intermediate wavelengths evoke in-between patterns. The patterns correlate with wavelength but are relatively insensitive to intensity. Output patterns of BG-G cells to white and to monochromatic light at the animals neutral point are almost identical, and the pattern identities may be a neural correlate to the behavioral phenomenon of the neutral point.

Effects of using the oxygen-carrying fluorocarbon, FC43, on the ERG of the arterially perfused cat eye

Arterial perfusion of the isolated cat eye with a perfusate augmented with a 20% (wt/vol) emulsion of the oxygen carrying-fluorocarbon, FC43, produces a much larger b-wave in the electroretinogram than use of the same perfusate lacking FC43. The c-wave is either unchanged or slightly reduced by use of this solution. Halving the oxygen content of the FC43-augmented perfusate also reversibly reduces the b-wave. The use of perfusates with and without FC43 but containing similar amounts of oxygen produces b-waves of similar amplitude. The large b-wave recorded during use of a well-oxygenated, FC43-augmented perfusate suggests that the use of perfusates containing less oxygen produces retinal hypoxia. The b-wave recorded in vivo is considerably smaller than that recorded from the isolated eye during perfusion with a well-oxygenated, FC43-augmented perfusate, but the waveforms are very similar. In particular, the ratios of the b-wave to a-wave are almost identical. The larger ERG recorded in vitro is a result of increasing the shunt resistance to ground upon enucleation. Histological examination of retinas perfused for two hours with the FC43-augmented and standard perfusate reveal no clear signs of tissue hypoxia in either retina. However, even two hours of complete ischemia produces limited inner retinal deterioration and virtually no outer retinal damage, suggesting that the histological state of the retina may not be a reliable indicator of its physiological state. Despite the improved electrophysiological state of the retina produced by increasing its oxygen supply, the survival time of the isolated eye was not increased.