Temporal Crescent Research Articles

Evidence for differential effects of terminal and dendritic competition upon developmental neuronal death in the retina

Retinal ganglion cells with ipsilaterally projecting axons were labelled with horseradish peroxidase injected unilaterally along the optic pathway in adult rats. Unoperated controls were compared with three groups of animals operated at birth, given (a) contralateral enucleation, (b) contralateral lesion to the optic tract or (c) both lesions simultaneously. The numbers of ipsilaterally projecting cells were increased in all three operated groups, presumably because of a reduction in natural neuronal death following diminished terminal and dendritic competition. The pattern of increase of labelled cell density varied with the type of lesion: enucleation led to a major increase within lower temporal retina; optic tract lesion caused its major increase in upper temporal retina, centred at the location of the area centralis; and the double lesion combined both effects above. The distribution of cell-body sizes was differentially affected by the lesions: enucleation led to a shift in the distribution towards the small cell side of the spectrum, when compared with the controls; optic tract lesion shifted the distribution towards the large cell side of the spectrum, but only outside the temporal crescent; and the double lesion led to a shift towards small cells within the temporal crescent and towards large cells outside the crescent, again combining the effects of the single lesions. Large alpha-like neurones with ipsilateral axons were common in the nasal retina of both groups given optic tract lesions but they were rare in the nasal retina of unoperated and, especially, of enucleated rats. The limits of the temporal crescent were unchanged, notwithstanding the large numbers of cells outside the crescent in operated rats. It is suggested that postnatal competitive interactions at the level of terminals and of dendrites control natural neuronal death in the rat retina with different requirements regarding retinal topography and ganglion cell types. The postnatal regulation of neuronal numbers is not responsible for the generation of the nasotemporal division but may be involved in the development of differential distributions of specific ganglion cell types across the retina.

Ipsilaterally projecting retinal ganglion cells in the eastern chipmunk (Tamias sibiricus asiaticus)

Ipsilaterally projecting ganglion cells were studied in whole-mounted retinas of the eastern chipmunk ( Tamias sibiricus asiaticus) by labelling these cells with horseradish peroxidase (HRP) injected into the optic tract. The HRP-labelled cells were distributed exclusively in the temporal crescent which occupied about a quarter of the whole retinal area. The temporal crescent contained contralaterally projecting cells as well as ipsilaterally projecting cells. The soma size of ipsilaterally projecting cells, especially of those in the dorso-temporal crescent, was significantly larger than that of contralaterally projecting cells.

Suppression in strabismus--an update.

Previous reports have described suppression scotomas, suppression varying with the type of strabismus and suppression confined to one half of the retina (hemiretinal suppression). Our findings show that suppression in all varieties of strabismus, with the exception of the monofixation syndrome, involves the whole of the visual field of the deviating eye except for its monocular temporal crescent. In the monofixation syndrome our findings show a small central suppression scotoma involving the fovea but leaving the rest of the visual field of the deviating eye unsuppressed. We could find no evidence to support the concept of hemiretinal suppression but found evidence to support the presence of a trigger mechanism for suppression which operates on a hemiretinal basis.

Ganglion cell death during development of ipsilateral retino-collicular projection in golden hamster.

In rats and hamsters all parts of the superior colliculus (SC) receive a topographically organized projection from the retina of the contralateral eye, and the rostral part also has a direct input from the lower temporal crescent of the ipsilateral retina, which views the central, binocular portion of the visual field. Initially the uncrossed projection covers the entire SC, but over the first 2 weeks of postnatal life it becomes progressively restricted to its adult distribution. However, if the opposite eye is removed at birth there is a persistent widespread uncrossed projection to the SC. We have used short- and long-term retrogradely transported neuronal markers to examine the distribution and fate of the ganglion cells of origin of the uncrossed retino-collicular projection throughout postnatal development. We conclude that the withdrawal of the early exuberant projection to the caudal SC is associated with death of ganglion cells and their virtual elimination outside the temporal crescent of the ipsilateral retina. Early enucleation of the other eye rescues many of these cells.

A minute fraction of Syrian golden hamster retinal ganglion cells project bilaterally

Bilaterally projecting retinal ganglion cells (BPRGCs) in the adult Syrian golden hamster were identified through the use of two retrogradely transported neuronal labels, horseradish peroxidase and Nuclear Yellow, placed separately in each optic tract. The distribution and size of doubly labeled retinal ganglion cells were characterized and their numbers were determined. Strict criteria were used to exclude artifactual doubly labeled cells. This work revealed that: (a) BPRGCs comprise less than 0.01% of the entire retinal ganglion cell population, averaging 7.4 (SD = 3) cells per retina; (b) BPRGCs are found primarily in the upper, peripheral retina and not along the vertical meridian or in the temporal crescent; and (c) BPRGCs correspond in size to ordinary retinal ganglion cells in their immediate vicinity, thus providing no evidence that they comprise a separate population of cells. Electrophysiological collision experiments were also performed, with stimulating electrodes in the two brachia of the superior colliculi and a recording electrode in one optic nerve. A collision effect was not detected, thus supporting the anatomical findings of rare bilateral branching of optic nerve axons. The occurrence of BPRGCs may reflect occasional ambiguities in the cues that guide axons through the chiasm.

Projection lines and the ipsilateral retino-geniculate pathway in the hooded rat

The organization of the hooded rat's dorsal lateral geniculate nucleus was studied with anatomical techniques, with particular regard to the representation of temporal retina and the binocular field. The ipsilateral and contralateral retinal terminal fields were examined in three stereotaxic planes following injections of horseradish peroxidase into the eye. Projections arising from the temporal crescent of the retina were studied with silver staining techniques for anterograde degeneration products. Following discrete retinal lesions there was clear evidence that the temporal retina projects in a topographic fashion both ipsilaterally and contralaterally. The orientation of the lines of projection in the dorsal lateral geniculate nucleus was assessed by retrograde labelling of cells after cortical implants of horseradish peroxidase. Although both the lines of projection and the ipsilateral terminal field extend rostro-caudally in the dorsal lateral geniculate nucleus, their paths are oblique rather than parallel. Their intersection appears to correspond to the representation in this nucleus of conjugate retinal points. This was confirmed by administering horseradish peroxidase by iontophoresis in either the binocular or monocular representation of the primary visual cortex, while one eye received an injection of [ 3H]proline. Only those cortical injections in the binocular region gave rise to labelled projection lines passing through the autoradiographically-labelled ipsilateral terminal field. The rat's dorsal lateral geniculate nucleus displays none of the cytoarchitectural lamination which is so prominent in the primate and cat. Even after labelling the input to the nucleus from one eye, there is still no obvious laminar relationship between the terminal fields from the two eyes. Despite the absence of lamination, the current results suggest that the principle of apposing the representation of conjugate retinal points in the dorsal lateral geniculate nucleus is the same in the rat as in cat and monkey.

Crossed and uncrossed visual topography in dorsal lateral geniculate nucleus of the pigmented rat.

1. The representation of the retinocentric visual field within the dorsal lateral geniculate nucleus (dLGN) was assessed electrophysiologically by recording multicellular responses from anesthetized pigmented rats. Separate experiments examined the representation through either the contralateral or ipsilateral eye along the dorsoventral, mediolateral, and rostrocaudal dimensions of the nucleus. 2. The crossed projection displays an orderly representation of the visual field, mapping eccentricities out to 100 degrees from the optic disk. There is, however, a marked absence of eccentricities greater than 60 degrees representing upper nasal visual space. The uncrossed projection also displays an orderly representation of the visual field but is limited in extent to upper nasal visual space at far eccentricities of 50-90 degrees. 3. The ipsilateral projection, which represents far eccentric upper nasal visual space, occupies a region in the contralateral representation corresponding with upper nasal visual space at reduced eccentricity. It is these two regions that are considered binocularly conjugate: the temporal crescent of each eye with another crescent (the conjugate central crescent) lying between the optic disk and the temporal crescent of the opposite eye. It is suggested that the crossed and uncrossed representations are aligned in the dLGN so that projection lines for discrete regions of the binocular visual field course through the nucleus from rostroventral to caudodorsal. Although the dLGN of the rat lacks the cytoarchitecturally distinct laminae associated with the regions of afferent input from each eye, as is seen in the primate and cat dLGN, the organizing principle of apposing the representation of the visual field through each eye is similar.

Suppression in strabismus and the hemiretinal trigger mechanism.

A perimeter and a modified Lees screen were used to determine the area of visual field that is suppressed in strabismus. Strabismic patients without fusion suppress the whole area of the visual field of the deviating eye that could have correspondence with the dominant eye. In the monofixation syndrome, suppression only involves the fovea and the diplopic point of the deviating eye. Diplopia, if present, is appreciated throughout the visual field shared by the two eyes, except for the blind spots. No evidence of hemiretinal suppression was found in any type of horizontal strabismus, including exotropia. However, there is a hemiretinal trigger mechanism for suppression. Once suppression has been triggered by this mechanism, it involves the whole visual field of the deviating eye, except for the monocular temporal crescent.

Ganglion cell death within the developing retina: A regulatory role for retinal dendrites?

The effects of neonatal midbrain lesions on populations of retinal ganglion cells with ipsilateral or contralateral projections were investigated in hooded rats with the use of horseradish peroxidase. After bilateral lesions of the superior colliculus performed at birth, the number of contralaterally projecting ganglion cells is reduced but the number of ipsilaterally projecting cells is increased. Bilateral tectal lesions performed 5 days after birth reduce the number of both contralaterally and ipsilaterally projecting ganglion cells. Unilateral tecto-pretectal lesions performed at birth lead to extensive retrograde degeneration of contralaterally projecting ganglion cells in the opposite retina; but both the ipsilateral terminal fields of the same retina and its population of ipsilaterally projecting ganglion cells are increased. Cells located at the border between the temporal crescent and the nasal areas of the retina opposite an unilateral tecto-pretectal lesion were found to have their dendrites pointing towards the severely depleted nasal areas more frequently than in normal rats. These observations suggest that competitive interactions between retinal dendrites may play a role in regulating ganglion cell death in the developing retina. The increased population of ipsilaterally projecting ganglion cells would reflect the survival of neurones which would otherwise normally degenerate, resulting from reduced local interactions as a consequence of the massive removal of neighbouring contralaterally projecting cells.

Sparing of the temporal crescent in homonymous hemianopia and its significance for visual orientation

Eleven patients with homonymous hemianopia of acute onset, and without any improvement within two months or more, were investigated for the disability caused by their visual field defect. Nine of them, with a complete and dense hemianopia (in four cases due to a purely occipital lesion), indicated that they were moderately to severely handicapped, at least initially. Two patients, however, were never really disabled by their visual field loss. From the beginning they never had collisions with people or objects, either in known or in unknown surroundings. Only when stationary, they sometimes 'overlooked' static objects immediately in front of them. In both patients the unpaired portion of the visual field, the 'temporal crescent', was partially preserved. The importance of this monocular visual field area for visual orientation, especially movement perception. will be discussed.

Metabolic mapping of the primary visual system of the monkey by means of the autoradiographic [14C]deoxyglucose technique.

An autoradiographic technique that employs 2-[14-C]deoxyglucose to measure the local rates of glucose utilization within the brain has been applied to the binocular visual system of the Macaque monkey. This method, which pictorially displays the relative rates of glucose consumption in the component structures of the brain, delineates the regions of altered functional activity because of the close relationship between functional activity and energy metabolism. Bilateral retinal stimulation results in the delineation of different rates of glucose consumption in at least four cytoarchitectural layers of the striate cortex. The most intense metabolic activity appears to be in Layer IV, the locus of the termination of the geniculocortical pathway. Bilateral visual occlusion lowers the rates of glucoes consumption in striate cortex and markedly reduces the metabolic differentiation of the various layers. Unilateral visual deprivation delineates the laminae of the lateral geniculate body and the ocular dominance columns of the striate cortex. It also results in the autoradiographic visualization of regions with normally monocular input in the striate cortex, such as the rostral portions of the mushroom-like configurations in the calcarine cortex, which represent the extreme temporal crescents of the visual fields, and small regions in the most caudal part of the mushroom configurations, which are believed to represent the cortical loci of the blind spotsof the visual fields.

Aberrant visual projections in the Siamese cat.

Aberrant visual projections in the Siamese cat.

A study of normal and congenitally abnormal retinogeniculate projections in cats.

AbstractRetinogeniculate terminations have been studied by fiber degeneration and microelectrode mapping methods in normal cats and in Siamese cats in which the retinogeniculate pathway is congenitally abnormal. The normal representation of the visual field, including the monocular temporal crescent, has been determined. It has also been shown that there is a cellular discontinuity in lamina A which corresponds to the blind spot or optic disc. In normal cats four geniculate layers receive retinogeniculate terminals; two layers (A and C) receive contralateral and two layers (A1 and C1) receive ipsilateral afferents.In Siamese cats laminae A and C are normal. Lamina A1 is broken up into four main cell segments. Two of these receive a normal input from the ipsilateral temporal hemiretina; two receive an abnormal projection from the contralateral temporal hemiretina. The abnormal projection originates primarily from a vertical strip of retina about 20°–25° in width that lies just temporal to the area centralis. Within this abnormal projection a normal retinotopic sequence is maintained but, since this projection goes to the contralateral instead of the ipsilateral lamina A1, the abnormal segments of lamina A1 receive a mirror‐image of the normal representation.Lamina C1 and the medial interlaminar nucleus receive an abnormal contralateral input from the temporal hemiretina similar to that found in lamina A1.

Acquired Hole in the Disk

An Army officer, 21 years of age, was first seen by me in December, 1929. He had 6/5 vision in each eye, with no appreciable error of refraction, and his media and fundi were found to be perfectly normal. In March, 1933, he came back complaining that a month previously, with his right eye, people's faces looked as if they had a bulge on the right side. He had seen an Army oculist who reported that at first the disk looked slightly oedematous and the veins engorged, but that this had rapidly subsided. He had had a general examination, including a blood test which was negative, and his teeth, sinuses, etc., had been passed as normal. Vision in the right eye was 6/6, and there was a relative scotoma for colours-objects looked dull instead of bright, and linear objects had a kink in them. There was no pain on movement, or tenderness on pressure over the the globe. The right disk is shown in Fig. 1 (overleaf). There seemed to be a hollowing out of the temporal side, with what appeared to be a newly-formed temporal crescent (not present in the other eye), and two faint ridges enclosing an area of slight swelling. Involvement of the macula at the apex of the inner bulge would account for the metamorphopsia. It looked as if there must be something in the temporal edge of the nerve head just outside the globe, causing a retraction of the temporal side of the nerve head, and a bulging forward of the sclerotic and other tissues with some dragging away of these tissues from the nerve head (Fig. 2, overleaf). The appearance suggested a gumma or tuberculoma, or possibly a vascular tumour or neurofibroma. It was unlikely that a plaque of disseminated sclerosis could produce such an effect. A further full investigation revealed nothing, and he was given no treatment. One month later the condition was almost unchanged though there seemed to be some faint whitish dots on the raised area. Vision was 6/6. The vitreous was perfectly clear, and there was slight enlargement of the blind spot.

LOCALIZING VALUE OF TEMPORAL CRESCENT DEFECTS IN THE VISUAL FIELDS

The fact that the most peripheral portion of the temporal field has an unpaired representation in the optic pathways and visual cortex has been well recognized. The field of the two eyes, together, or the binocular field, is the combination of the right and the left uniocular field. These partly overlap, so that the nasal field of one eye covers the greater portion, the paired portion, of the other, leaving an outer, crescentic, uniocular area unpaired. This unpaired portion is called the temporal crescent or half-moon (fig. 1). The paired portion has a diameter of approximately 120 degrees; the unpaired portion extends for 30 to 40 degrees on each side beyond the paired portion. The fibers of the peripheral portion of the nasal retina pass in the medial portion of the optic nerve.1However, the most distal point of the visual pathway at which the fibers of the temporal

DEFECTS IN VISUAL FIELD OF ONE EYE ONLY IN PATIENTS WITH A LESION OF ONE OPTIC RADIATION

Lesions of the optic radiation cause contralateral homonymous defects in the fields of vision. The defect may be quadrantic or hemianopic, with or without sparing of central vision. Sometimes, however, careful perimetric determinations reveal partial and unpaired blind areas, i. e., a defect in one section of the field of vision of one eye but not in the corresponding field of the other eye. The commonest type of unpaired defect in cases of lesions of the optic radiation is known as the temporal crescent or half moon defect. The terms temporal crescent and half moon have reference to either one of the two areas which are temporal and peripheral to the binocular field of vision (fig. 1). Each of these areas is projected on the retina of one eye only (on the nasal retina) and therefore represents the uniocular field of vision. It corresponds to the phylogenetically oldest monocular