Nasotemporal Overlap Research Articles

The Detection of Macular Analysis by SD-OCT for Optic Chiasmal Compression Neuropathy and Nasotemporal Overlap

To assess the diagnostic performance of the macular parameters detected by spectral-domain optical coherence tomography (SD-OCT) in band atrophy (BA) eyes. Forty-nine BA eyes with permanent temporal hemianopia and 89 normal eyes were enrolled. Any patients who had nasal visual field loss were excluded. Each participant was imaged by three-dimensional (3D) OCT-2000, and 10 × 10 grids in the macula were automatically allocated. The thickness of the macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL)+ (GCL+inner plexiform layer [IPL]), and GCL++ (RNFL+GCL+IPL) in both nasal and temporal hemiretina was calculated and compared between the BA and normal eyes. The areas under the receiver operating characteristic curves (AUCs) in these parameters were compared between the nasal hemiretina and the temporal hemiretina. All the parameters in the BA eyes were significantly thinner than those in the normal eyes. The AUCs for the mRNFL, GCL+, and GCL++ thickness in the nasal hemiretina were 0.890, 0.988, and 0.981, respectively. The parameters in the nasal hemiretina showed significantly higher AUCs than those parameters in the temporal hemiretina. In the temporal hemiretina, the damaged grids in the mRNFL were located in the arcuate areas in each hemifield. The inner macular parameters in the nasal hemiretina exhibited high diagnostic abilities to detect BA. The GCL+ was more affected than mRNFL. The characteristic pattern of mRNFL and GCL+ thinning was implicated in the anatomical architecture regarding the nasotemporal overlap of the crossed and uncrossed fibers around the fovea. (www.umin.ac.jp/ctr number, UMIN000006900.).

Evidence of midline retinal nasotemporal overlap in healthy humans: A model for foveal sparing in hemianopia?

The existence of midline retinal nasotemporal overlap in humans is controversial. Here we used the Poffenberger paradigm and monocular vision to assess the existence of a midline retinal area projecting to both hemispheres and of a possible differential contribution of the two hemiretinae. When brief visual stimuli were presented at 1 degrees eccentricity they were responded to equally quickly with either hand while at 6 degrees the hand on the same side as the stimulated hemifield was consistently faster than the contralateral hand. This pattern of results is consistent with a nasotemporal overlap at 1 degrees and a complete lateralization at 6 degrees . Both hemiretinae contribute to the overlap area which can be considered as responsible for foveal sparing in hemianopic patients.

Nasotemporal overlap of retinal ganglion cells in humans: a functional study.

A zone of overlap along the vertical retinal meridian where ipsi- and contralaterally projecting ganglion cells intermingle has been demonstrated histologically in nonhuman primates. The widening of the zone of overlap in the foveal region was thought to produce a foveal sparing extending 1.5 degrees in the blind hemifield in human hemianopia. The functional relevance of the nasotemporal overlap is still unclear and cannot be shown definitely by conventional perimetry, because of insufficient spatial accuracy, light-scattering effects, and insufficient fixation control. Therefore, this study was undertaken to investigate the vertical field border by a perimetric method that does not have these shortcomings. A scanning laser ophthalmoscope (SLO) was used to scan vertical triplets of dots along the vertical field border in 20 patients (36 eyes) with homonymous hemianopia without macular sparing. Stimuli and fundus were imaged simultaneously for fixation monitoring. None of the patients showed a field border that coincided exactly with the vertical midline. In 34 eyes, the seeing area extended from the vertical meridian into the blind hemifield and formed a vertical strip of perception. None of the patients showed additional foveal sparing. Twenty-two eyes showed a concave shape of the seeing area within the foveal region of the blind hemifield. Our results show that the nasotemporal overlap exists in humans. It consists of a strip of intact perception reaching into the blind hemifield. The concave shape can be explained by the size and distribution of the receptive fields of the retinal ganglion cells.

An albino-like decussation error in the optic chiasm revealed by anomalous ocular dominance columns.

We report a unique anomaly in the ocular dominance column pattern of a single, normally pigmented macaque monkey. The column pattern contained large monocular areas inserted between the normal columns and the dorsal V1 border. These monocular regions received transneuronal input from the contralateral eye, indicating that a small population of temporal ganglion cells erroneously decussated at the optic chiasm. Projection of the column pattern back onto the visual field showed that the monocular wedges represented a approximately 5-deg sector of ipsilateral field. This corresponded to the extent of naso-temporal overlap of ganglion cells in the normal retina, suggesting an error in axon guidance affecting cells close to the vertical midline of the retina. The consequences of the crossing error in this animal were threefold: it produced an anomalous monocular zone near the V1 border, the vertical meridian was not represented at the V1 border, and points near the vertical meridian were represented twice in the brain, once in each hemisphere.

Nasotemporal overlap at the retinal vertical meridian: Investigations with a callosotomy patient

To evaluate nasotemporal overlap at the retinal vertical midline, we asked a callosotomy patient to compare the orientation of square wave gratings that were presented in his opposing visual fields. The gratings were horizontally or vertically oriented and had spatial frequencies ranginf rom 1 to 8 cycles per degree (cpd). Retinal stabilization ensured the gratings remained properly lateralized during sustained presentations. In accord with previous investigations, when the gratings were presented for only 200 msec, or their medial edges were 2° from the vertical meridian, performance was generally at chance. However, when presentations lasted 2 sec and the medial edges of the gratings were 1° from the vertical meridian, above chance performance was obtained. Accuracy rates were highest with 2 and 4 cpd gratings, and dropped at 1 and 8 cpd. Unexpectedly, the subject performed significantly better when the gratings were offset vertically from each other than when both were displayed on the horizontal meridian. Since this improvement did not occur when gratings were presented horizontally aligned above or below the horizontal meridian, it must be attributed to the relative offset between the gratings. The data suggest a narrow zone of nasotemporal overlap at the retinal vertical midline where very limited visual information is encoded by crossed temporal and uncrossed nasal retinal ganglion cells. An experiment in which only one grating in a pair was close to the vertical meridian indicates that this zone may be more pronounced in the nasal hemiretina.

Nasotemporal overlap investigated in a case of agenesis of the corpus callosum

In primates fibres from nasal retinae project contralaterally and those from temporal retinae ipsilaterally. At the border between these two regions an area of overlap where ipsi- and contralaterally projecting ganglion cells intermingle has been demonstrated in monkeys and cats. However, behavioural studies have failed to provide confirmatory evidence in humans. In this experiment simple reaction times to lateralized light flashes at four points of eccentricity (1/2, 1, 2 and 4 degrees) were recorded in an acallosal female. Responses made by the directly stimulated hemisphere were subtracted from those made by the indirectly stimulated hemisphere to arrive at estimates of interhemispheric transmission time. If present, a region of overlap should result in information being available to both hemispheres and consequently alleviate the need for any interhemispheric crossing. However, a large transmission time was found, even with stimuli presented close to fixation, thereby providing no evidence for the existence of such a region in humans.

Topography and extent of visual-field representation in the superior colliculus of the megachiropteran Pteropus.

It has been proposed that flying foxes (genus Pteropus) have a primate-like pattern of representation in the superficial layers of the superior colliculus (SC), whereby the visual representation in this structure is limited by the same decussation line that limits the retino-geniculo-cortical projection (Pettigrew, 1986). To test this hypothesis, visual receptive fields were plotted based on single- and multi-unit recordings in the SC of ten flying foxes. A complete representation of the contralateral hemifield was observed in the SC. Although the binocular hemifield of vision in Pteropus is 54 deg wide, receptive-field centers invaded the ipsilateral hemifield by only 8 deg, and the receptive-field borders by 13 deg. This invasion is similar to that observed at the border between visual areas V1 and V2 in the occipital cortex. The extent of the ipsilateral invasion was not affected by a lesion that completely ablated the occipital visual areas, thus suggesting that this invasion may be consequence of a zone of nasotemporal overlap in the retinal projections to the two colliculi. Neurones located in the superficial layers typically responded briskly to stimulation of both eyes, with a bias towards the contralateral eye. After cortical lesions the neuronal responses to the ipsilateral eye were depressed, and the ocular-dominance histograms shifted towards an even stronger dominance by the contralateral eye. However, cells located in the rostral pole of the SC remained responsive to the ipsilateral eye after cortical lesions. Responses in the stratum opticum and stratum griseum intermediale were more severely affected by cortical lesions than those in the stratum griseum superficiale. Our results demonstrate that the SC in flying foxes retain some generalized mammalian characteristics, such as the stronger direct projections of the contralateral eye and the location of the upper, lower, central, and peripheral representations in the SC. Nonetheless, the extent of visual representation in the SC demonstrates a specialized, primate-like pattern. These observations are consistent with the hypothesis that megachiropterans are members of a group that branched off early during the differentiation of primates from basal mammals.

Interhemispheric transfer and the processing of foveally presented stimuli

Two arguments are commonly given in favor of a nasotemporal overlap along the vertical meridian of the visual field: anatomical findings and the existence of macular sparing in hemianopia. A review of the literature, however, points to the weakness of the evidence. The anatomical indications are exclusively based on horseradish peroxidase studies, which can not give an unequivocal answer to the amount of overlap in central vision, and which were not supported by a recent study that made use of the more direct [ 14C]2-deoxy- d-glucose technique. The argument of macular sparing in hemianopia appears to be derived evidence that depends on the validity of the anatomical findings. In addition, behavioral studies consistently failed to find functional confirmation of the overlap. To further test the possibility of bilateral representation in central vision, a new paradigm is proposed. It is argued that if interhemispheric transfer is needed for the processing of foveally presented stimuli, the world-beginning superiority effect should be larger for subjects with left hemisphere dominance than for subjects with right hemisphere dominance. Results are in line with the hypothesis and point to the fact that interhemispheric transfer of visual information may be involved in more processing than usually accepted. It is also noted that transfer time seems to depend on the amount of information that must be transferred, and is significantly shorter than the estimates obtained in visual half field studies.

Single retinal ganglion cells projecting bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals in the cat.

In most mammals with frontalized eyes, retinal ganglion cells in the nasal or temporal retina send their axons to the contralateral or ipsilateral half, respectively, of the brain. Previous studies in the cat, however, have indicated a retinal region of "nasotemporal overlap" from which arise the retinal projections to both the contralateral and ipsilateral halves of the brain. The present study thus examined in the cat whether any retinal ganglion cells give rise to bifurcating axons that innervate both halves of the brain. By employing fluorescent retrograde double labeling, we investigated whether or not single retinal ganglion cells project bilaterally to the lateral geniculate nuclei or superior colliculi by way of axon collaterals. After Fast Blue was injected into the lateral geniculate nucleus on one side and Diamidino Yellow was injected contralaterally into the lateral geniculate nucleus, 100-200 ganglion cells in each retina were double labeled with both tracers. These double-labeled cells were distributed primarily in the temporal retina, including the region around the vertical meridian and, additionally, in the nasal retina. About 60-80% of the double-labeled cells had large cell bodies (more than 25 microns in diameter), and the others had medium-sized ones (15-25 microns in diameter). The pattern of distribution of double-labeled cells, which was observed after the combined injection into both superior colliculi, was similar to that seen after the combined injection into both lateral geniculate nuclei; more than 90% of double-labeled cells, however, were large.(ABSTRACT TRUNCATED AT 250 WORDS)

Single retina ganglion cells sending axon collaterals to the bilateral superior colliculi: a fluorescent retrograde double-labeling study in the Japanese monkey ( Macaca fuscata)

Single retinal ganglion cells projecting bilaterally to the superior colliculi (SC) by way of axon collaterals were revealed in the Japanese monkey ( Macaca fuscata). After injecting Fast blue into the SC on one side and Diamidino yellow into the SC on the opposite side, some retinal ganglion cells were double-labeled with both tracers. Most of them were large cells (more than 25 μm in diameter), and were localized in a narrow strip around the vertical meridian of the retina on each side. This retinal area roughly corresponds to the reported strip of nasotemporal overlap, where both crossed and uncrossed retinofugal projections arise.

Metastable motion anisotropy

The phenomenon of apparent motion can arise when two spatially separated visual tokens are presented in temporal sequence. If tokens at opposite corners of a hypothetical square are presented simultaneously followed by simultaneous presentation of tokens at the remaining two corners, an apparent motion percept may occur along either the vertical or horizontal axis. The display is perceptually metastable since most observers will perceive motion along only one axis at a time. The metastable display, however, produces anisotropic results, in that with central fixation, vertical motion is seen more frequently than horizontal motion. The ratio of the vertical to horizontal length of the sides of a rectangle needed to achieve equal frequencies of motion judgments along the respective axes falls in the range of 1.18-1.92 for different observers in our experiments. It appears that signal transmission across the vertical midline is a major determinant of the vertical bias, since the anisotropic effects disappear when the fixation point is sufficiently offset along the horizontal meridian so as to cause a fully homonymous representation of all of the metastable tokens. One of the factors may be signal degradation or delay in callosal transmission which could reduce the strength of the motion signal along the horizontal axis. In addition, there appears to be a strip along the vertical midline with a width of 30-50 min arc within which reduced levels of anisotropy are found. The possibility that this strip is a consequence of a zone of naso-temporal overlap in the projection of the retina to the brain along the vertical meridian will be discussed.

The nasotemporal division of retinal ganglion cells with crossed and uncrossed projections in the fetal rhesus monkey

The development of the partial decussation pattern in the primate retina was studied in fetal rhesus monkeys of known gestational ages. Retinal ganglion cells with either crossed or uncrossed projections were identified by labeling with HRP following unilateral injections of this tracer into the optic tract. At all fetal ages, very few cells (less than 0.5% of the total ganglion cell population) were found to project to the inappropriate hemisphere. The nasotemporal overlap zone, defined as the retinal region along the vertical meridian containing cells with either crossed or uncrossed projections, also appeared equivalent to that described for the adult animal. A temporal offset in the decussation pattern of large ganglion cells, similar to that of the mature retina, could be recognized as early as 50 d before birth. These results indicate that an adultlike retinal decussation pattern is evident in the fetal primate at a stage when projections from the 2 eyes are completely intermingled within retinorecipient nuclei, and prior to the onset of retinal ganglion cell loss. Moreover, the primate visual system exhibits a degree of precision in the specification of the nasotemporal division unrivaled among the mammalian species studied to date. The developmental specificity evident in the decussation pattern of the fetal rhesus monkey appears to reflect the specialized organization of this primate's retina for binocular focal vision.

Nasotemporal overlap of crossed and uncrossed retinal ganglion cell projections in the Japanese monkey (Macaca fuscata)

The nasotemporal overlap of crossed and uncrossed retinal ganglion cell projections were studied in 11 Japanese monkeys (Macaca fuscata) using HRP and fluorescent dyes (DAPI and RITC) as retrograde tracers and by physiological recordings of antidromic field potentials. A strip of nasotemporal overlap ran orthogonal to the horizontal meridian in all the whole-mount retinas studied. In HRP-labeled retinas of 6 monkeys, the width of the overlap gradually increased from 0.6 degrees in the central retina up to 5 degrees at eccentricity of 5 mm, and to 15 degrees at the extreme periphery. We also noted a clear asymmetric distribution of crossed and uncrossed retinal ganglion cell projections particularly in the perifoveal region; ipsilaterally projecting cells encircled the nasal edge of the fovea, whereas few contralaterally projecting cells were observed in the temporal edge. Soma-size analysis revealed that crossed projections in the temporal portion of the overlap arose mainly from large and small cells (presumably P alpha and P gamma cells, respectively); uncrossed projections in its nasal portion arose from medium-sized cells (presumably P beta cell). Direct evidence of the overlap as well as of the asymmetry was obtained in subsequent fluorescent dye experiments in 3 monkeys. Physiological studies on 2 additional monkeys confirmed the widening of the nasotemporal overlap towards the upper and lower parts of the retina. Moreover, in the nasal portion of the overlap, only slow potentials, which presumably reflect activities of P beta cells, were recorded after stimulation of the ipsilateral LGN as expected from the morphological study. The findings are discussed in relation to clinical observations of macular sparing and splitting, and with regard to the functional differences between P alpha and P beta cell systems on which binocular stereoscopic vision along the midsagittal plane may be based.

Evidence of foveal splitting in a commissurotomy patient

A bilateral projection of the central fovea, produced by naso-temporal overlap at the retinal vertical meridian, has been proposed as the anatomical basis of macular sparing. To evaluate this claim, a commissurotomy patient was required to compare target figures presented 1° or less from the retinal midline with reference figures presented 2.5° from the midline in the same or opposite visual field. The subject judged whether the target and reference were the same or different. It was found that the subject's fovea was effectively split with respect to the cerebral hemispheres; targets in the same visual field as the reference were readily matched with the reference, but accuracy dropped to chance for targets in the opposite field. Ways of reconciling this data with anatomical evidence of nasotemporal overlap and reports of macular sparing are discussed.

Functional dissociation of the hemispheres in the discrimination of complex gratings near the vertical meridian

It was previously shown that the discrimination of complex gratings differing in the spatial phase of their harmonic components is performed more accurately when the stimuli are presented in the left than in the right visual hemifield, provided that the stimuli are separated at least 2deg from the vertical meridian (VM) and/or their spatial frequency exceeds 2 c/deg. Here we report measurements of reaction times (RT) for the discrimination of complex gratings presented laterally at various distances from the VM. The (choice) RTs are found to be longer in the right than in the left hemifield even for stimuli of low spatial frequency at 1 deg from the VM. This rules out the possibility that a naso-temporal overlap in the retino-cortical projection in man is exploited in “bridging the gap” between the two hemispheres in the discrimination of complex gratings.

Cat medial interlaminar nucleus: retinotopy, relation to tapetum and implications for scotopic vision.

The medial interlaminar nucleus (MIN) of the cat was electrophysiologically mapped in sufficient detail to resolve individual laminae and to allow reconstruction of isoazimuth and isoelevation lines in coronal, sagittal, and horizontal planes. The electrophysiologically defined laminar pattern was in agreement with that revealed anatomically in the same animal, as well as with the general pattern revealed by anatomical methods in several unmapped nuclei. The MIN is made up of three distinct layers, each receiving inputs from one hemi-retina but none representing an entire hemifield. We confirm the findings of Guillery et al. (19) that the contralateral hemifield is represented in layers 1 and 2 through the contralateral and ipsilateral eyes, respectively, and that layer 3 represents the ipsilateral hemifield through the contralateral eye. Elevation and absolute value of azimuth are represented continuously through the MIN. When an isoazimuth line crosses the border between layer 3 and either layer 1 or 2, the absolute value of azimuth is maintained but the sign of the azimuth changes. Adjacent points on either side of this border represent mirror symmetrical visual directions on opposite sides of the vertical meridian. This indicates that the distance from the vertical meridian is an independently coded parameter within the geniculate complex. There is virtually no nasotemporal overlap in any layer of the MIN. The function relating magnification (mm3 per steradian) to eccentricity is strikingly similar to the function relating retinal ganglion cell density to eccentricity, suggesting that a constant fraction of retinal ganglion cells project to the MIN at all eccentricities. Most of the volume of each MIN layer is devoted to lower visual fields. Analysis of the geniculate retinotopic maps of Sanderson (46) reveals no equivalent bias toward lower visual fields in the dorsal lateral geniculate nucleus. The MIN represents a region of retina roughly coincident with the tapetum, suggesting a role of the MIN in dim-light vision.

Nasotemporal overlap investigated in a case of agenesis of the corpus callosum

In primates fibres from nasal retinae project contralaterally and those from temporal retinae ipsilaterally. At the border between these two regions an area of overlap where ipsi- and contralaterally projecting ganglion cells intermingle has been demonstrated in monkeys and cats. However, behavioural studies have failed to provide confirmatory evidence in humans. In this experiment simple reaction times to lateralized light flashes at four points of eccentricity ( 1 2 ,1,2 and 4°) were recorded in an acallosal female. Responses made by the directly stimulated hemisphere were subtracted from those made by the indirectly stimulated hemisphere to arrive at estimates of interhemispheric transmission time. If present, a region of overlap should result in information being available to both hemispheres and consequently alleviate the need for any interhemispheric crossing. However, a large transmission time was found, even with stimuli presented close to fixation, thereby providing no evidence for the existence of such a region in humans.

Nasotemporal overlap in retinal projections in man

In humans, the nasal retina projects to the contralateral hemisphere, whereas the temporal retina projects ipsilaterally. The nasotemporal line that divides the retina into crossed and uncrossed parts coincides with the vertical meridian through the fovea. This normal projection of the retina is severely altered in albinism, in which the nasotemporal line shifted into the temporal retina with temporal retinal fibers cross the midline at the optic chiasm. This study proposes the loss of binocular vision as direct cause for misrouting of temporal retinal fibers and shifting of the nasotemporal line temporally in albinism. It is supported by many observations that clearly indicate that loss of binocular vision causes uncrossed retinal fibers to cross the midline.This hypothesis may alert scientists and clinicians to find ways to prevent or minimize the loss of binocular vision that may occur in some diseases such as albinism and early squint. Hopefully, this will minimize the misrouting of temporal fibers and improve vision in such diseases.

The projection of the fovea to the superior colliculus in rhesus monkeys

Horseradish peroxidase was injected into the superior colliculus of seven Rhesus monkeys to determine whether retinal ganglion cells concerned with the fovea project to the superior colliculus or whether, as results of several experiments using other methods suggest, only the parafoveal retina projects directly to this region. The retinal distribution of ganglion cells labelled by retrograde transport showed unequivocally that there is a direct projection from the fovea to the superior colliculus. However, there was no convincing evidence that the nasotemporal overlap that exists in the retinogeniculate projections also occurs in the projection to the superior colliculus. The results cast serious doubt on schemes that attribute little or no role to the superior colliculi in foveal vision and which emphasize the projection of the fovea to the visual cortex and the peripheral retina to the superior colliculi.

The decussation of the retinothalamic pathway in the cat, with a note on the major meridians of the cat's eye.

We have studied the naso-temporal division of the retinothalamic pathway of the cat by making large unilateral injections of horseradish peroxidase into the lateral geniculate nucleus. In confirmation of previous work, our retinal whole-mounts show a distinct vertical decussation line separating the contralaterally projecting nasal retina from the ipsilaterally projecting temporal retina. The ipsilateral decussation line is quite sharp, while the contralateral decussation is somewhat more diffuse, with numbers of large cells extending a few degrees into the temporal retina. However, in contrast to the results of optic tract section, our material (demonstrating the thalamic component only) does not reveal any significant population of contralaterally projecting small cells across most of the temporal retina. The previous observation of approximately 200 micrometer of naso-temporal overlap in the area centralis is confirmed here, and evidence is presented that this overlap may increase at eccentricities above the horizontal meridian. Taken together with previously published data, this demonstration of the vertical decussation line has allowed us to estimate the relative inclinations of the major meridians of the cat's eye.