Foveal Sparing Research Articles

Cross-over in line bisection among stroke patients

Objective To explore possible mechanisms of the cross-over observed in stroke patients comple-ting a line bisection test. Methods Twenty-five stroke patients with left neglect and twenty normal subjects were studied.In the ordinary line bisection test,there are two papers presenting 20 mm and 100 mm lines respectively.On each paper,three lines with the same length are presented at the left,middle and right of the paper.In the line im-age test,the two papers are the same as in line bisection test,but here subjects are asked to set endpoints of each re-al line. Results Replicating earlier findings,length cross-over was observed in the patients with neglect.In the hline image test,those patients neglected lines on both sides but with a much larger proportion on the left.The patientsunderestimated long lines as in previous studies,but they also underestimated very short lines in contrast to earlier findings. Conclusion Foveal neglect sparing may explain these observations.For very short lines,the left end of the line falls into foveal vision and the left part of the line was not neglected.As a result,the crossover effect of line length occurs. Key words: Hemineglect; Line bisection test; Cross-over effect; Stroke

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.

In Vivo Imaging of Foveal Sparing in Geographic Atrophy Secondary to Age-Related Macular Degeneration

To investigate morphologic alterations in geographic atrophy caused by age-related macular degeneration (AMD) in the presence of foveal sparing using high-resolution in vivo imaging. Simultaneous spectral domain optical coherence tomography (SD-OCT, 870 nm, 40,000 A-scans/s) and confocal scanning laser ophthalmoscopy (cSLO; fundus autofluorescence; excitation, 488 nm; emission, 500-700 nm) were performed in 18 eyes with geographic atrophy and foveal sparing using a combined instrument. Anatomic layers were evaluated, and retinal thickness in the fovea and the peripheral macula were measured and compared with those in controls of similar age. Fundus autofluorescence imaging showed an inhomogeneously reduced signal at the residual foveal island. SD-OCT scans disclosed mitigation of the foveal pit in the absence of extracellular fluid accumulation and an increased mean central retinal thickness of 248 +/- 28 microm compared with 225 +/- 12 microm in control eyes (P = 0.005). No difference in retinal thickness in the peripheral macula was observed (245 +/- 16 vs. 253 +/- 11 microm; P = 0.6). Subanalysis revealed marked appearance of swelling and widening of visible structures at the central outer nuclear layer (153 +/- 22 microm vs. 127 +/- 12 microm; P = 0.003). Below the external limiting membrane, a broad band of irregular high reflectivity was detected instead of the normal three separate reflective bands. Thickening at the foveal site may reflect a pre-apoptotic stage of neuronal cellular elements indicating imminent atrophy. Limited structure-function correlation found in our study suggests that future therapeutic intervention may be beneficial in only a subset of AMD patients with foveal sparing.

Reorganization of visual processing in macular degeneration: Replication and clues about the role of foveal loss

We previously reported large-scale reorganization of visual processing (i.e., activation of “foveal” cortex by peripheral stimuli) in two individuals with loss of foveal input from macular degeneration [Baker, C.I., Peli, E., Knouf, N., & Kanwisher, N. G. (2005). Reorganization of visual processing in macular degeneration. Journal of Neuroscience, 25(3), 614–618]. Here, we replicate this result in three new individuals. Further, we test the hypothesis that this reorganization is dependent on complete loss of foveal input. In two other individuals with extensive retinal lesions but some foveal sparing we found no evidence for reorganization. We conclude that large-scale reorganization of visual processing in MD occurs only in the complete absence of functional foveal vision.

Serpiginous Choroidopathy With Bilateral Foveal Sparing and Good Visual Acuity After 18 Years of Disease

Serpiginous Choroidopathy With Bilateral Foveal Sparing and Good Visual Acuity After 18 Years of Disease

Attentional Modulation of Receptive Field Structure in Area 7a of the Behaving Monkey

Spatial attention modulates the activity of inferior parietal neurons. A statistically rigorous approach to classical retinotopic mapping was used to quantify the receptive fields of area 7a neurons under 2 attentional conditions. Measurements were made with retinal stimulation held constant and the locus of attention manipulated covertly. Both tasks required central fixation but differed in the locus of covert attention (either on the center fixation point or on a peripheral square target in one of 25 locations). The neuron's identity over the recording session was confirmed using chaos theory to characterize unique temporal patterns. Sixty-six percent of the neurons changed prestimulus activity based on task state. Retinotopic mapping showed no evidence for foveal sparing. Attentional factors influenced visual responses for approximately 30% of the neurons. Two types of modulation were equally observed. One group of cells had a multiplicative scaling of response, with equal instances of enhancement and suppression. A second group of cells had a complex interaction of visual and attentional signals, such that spatial tuning was subject to a nonlinear modulation across the visual field based on attentional constraints. These 2 cell groups may have different roles in the shift of attention preceding motor behaviors and may underlie shifts in parietal retinotopic maps observed with intrinsic optical imaging.

Visual acuity loss and clinical observations in a large series of patients with stargardt disease

Purpose To assess visual acuity impairment in Stargardt disease. Design Retrospective clinic-based cross-sectional study. Participants Three-hundred sixty-one patients with Stargardt disease. Methods Clinical findings in 361 patients were analyzed as part of a cross-sectional evaluation. Visual acuity at their most recent visit, fundus photographs, and electroretinographic findings were reviewed, and patients were categorized into four clinical phenotypes. Seventy-three patients with 20/40 or better vision and 38 patients with 20/50 to 20/100 vision in the better seeing eye at their initial visit who were followed for at least 1 year were included in a survival analysis. For analysis purposes, these latter patients were categorized into four 20-year age groups according to their age at initial visit. Main outcome measures Best-corrected visual acuity from the eye with better vision on the most recent visit was used in the cross-sectional analysis. For the survival analysis, best-corrected visual acuity was used from the eye with better vision on the initial visit. Results Eighty-two of the 361 patients (23%) had 20/40 or better acuity in at least one eye, 64 (18%) 20/50 to 20/100, and 199 (55%) 20/200 to 20/400, whereas 16 (4%) had worse than 20/400 in each eye at their most recent visit. In the patients with visual acuity of 20/40 or better, 59 (72%) had foveal sparing visible on ophthalmoscopic examination. The median time to develop visual acuity of 20/200 or worse was 22 years for the patients with 20/40 or better visual acuity at their initial visit. Those seen initially in the first two decades of life with this level of acuity showed a median time of 7 years to reach a visual acuity of 20/200 or worse compared with 22 years and 29 years for those who were initially seen at ages 21 to 40 or 41 to 60, respectively. Analyzing by the four 20-year age groups, the log rank statistic indicated significant differences in the survival experience among the four groups ( P = 0.004). The median time to develop 20/200 vision or worse was 6 years for the patients with 20/50 to 20/100 visual acuity at their initial visit, and this result, based on the log rank statistic, was independent of age group at initial visit ( P = 0.852). Conclusions In a large cohort of Stargardt patients, a cross-sectional analysis showed that almost a quarter had vision of 20/40 or better, whereas 4% had acuity of worse than 20/400. The presence of foveal sparing ophthalmoscopically was associated with a higher prevalence of 20/40 or better visual acuity. Survival analysis showed that the prognosis of patients who initially were seen with visual acuity of 20/40 or better is related to age at initial visit.

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.

Visual Losses in Early Age-Related Maculopathy

Age-related maculopathy (ARM) can be considered a transition from normal retinal changes to pathological processes. It is important to recognize patients who have progressed beyond a normal state in order to provide appropriate clinical management. This pilot study considers the clinical dilemma of diagnosing and monitoring early ARM. We carried out a controlled study and tested the visual functions of 11 pre-ARM (PARM) and 11 early ARM subjects. Apart from compromised visual acuity, losses in central visual field, color vision, and visual adaptation were also recorded in our ARM subjects. We found a low contrast (LC) Amsler grid to be most sensitive to central field defects and that the desaturated panel D-15 gave too many false positives among normal elderly subjects. Our results indicate foveal sparing in early ARM and question the capacity of acuity assessment to reflect early functional changes adequately. A clinical battery is recommended to detect and monitor ARM.

Subhyaloid Hemorrhage Illustrating a Mechanism of Macular Hole Formation

In Reply. —We thank Dr Foos for his helpful comments regarding our recent Photo Essay. Subhyaloid hemorrhage 1 and preretinal hemorrhage 2 are terms commonly used to describe such lesions. Neither term is optimal for identifying the ultrastructural location of the extravasated blood. The former is imprecise, and the latter is incorrect because the internal-limiting membrane is usually considered to be part of the retina. The anatomically (if not grammatically) correct subinternal limiting membrane hemorrhage is sometimes used as well, 3 although it is rather cumbersome. As Dr Foos points out, sublaminar retinal hemorrhage or submembranous retinal hemorrhage might be preferable terms. Whichever descriptive term is used, we believe that our conclusion is correct, ie, that the foveal sparing in this case illustrates an anatomical feature that could be important in the pathogenesis of macular hole formation.

Age related maculopathy with foveal sparing

Visual loss from age related maculopathy (ARM) is thought to involve foveal regions but in this case foveal sparing is reported consistent with a paradoxical performance and symptoms. The fundus view, manifest foveation, better than expected acuity, a blue-yellow colour loss and an intact central visual field support the likelihood of foveal sparing. We suggest that the detection and classification of ARM patients should consider parafoveal integrity by assessing colour vision, contrast sensitivity to medium and low spatial frequencies, and macular perimetry as well as acuity and fundus changes. The prognosis for continued foveal survival greater than four years is poor and patients with foveal sparing should be given a guarded prognosis.

Spatial and temporal contrast sensitivity in hemianopia. A comparative study of the sighted and blind hemifields.

Spatial and temporal contrast sensitivity was measured, under identical test conditions using spatially and temporally localized stimuli, in 4 normally sighted human subjects and in 3 healthy hemianopic subjects whose stable visual field loss exhibited foveal sparing. Testing was undertaken at central fixation and at a variety of eccentric loci along the horizontal meridian of the sighted and perimetrically blind field. In comparison with the normal (control) sensitivities obtained in this study, spatial and temporal sensitivities in the sighted hemifield in subjects with striate cortical lesions were both reduced; in addition, we were unable to demonstrate greater-than-chance performance at any extrafoveal locations in the blind hemifield.

Correlation between visual evoked potentials and pet neuroimaging in normals and subjects with retrochiasmatic lesions

This chapter explains eye and head reading path in hemianopic patients. In hemianopic patients, visual information is available only in one hemifield; thus, to compensate for hemianopia, it is necessary to have appropriate ocular motor strategies for efficient use of the remaining half of the visual field. The purpose of a study described in the chapter was to analyze the qualitative and quantitative changes of the ocular motor scanning behavior during reading, that is, the reading path. The hemianopic patients had to read aloud four different short texts as accurately and quickly as possible, in an experiment where the head was fixed and second, in a more natural head-free-to-move condition. In one of the four texts presented, the distances between the letters and words were decreased. The results indicate that patients with pure hemianopia and foveal sparing optimally learn to compensate their visual handicap by active and motivated visual training. Characteristically, two of the four hemianopic subjects that did not produce any acoustical reading errors were the best adapted ones. In daily life, they had developed a consistent set of ocular motor strategies to compensate for their specific visual handicap.

The functional properties of the light-sensitive neurons of the posterior parietal cortex studied in waking monkeys: foveal sparing and opponent vector organization

We describe in this paper the results of a new study of the inferior parietal lobule in 10 waking monkeys combining the methods of behavioral control, visual stimulation, and single neuron analysis. In this study, 1682 neurons were identified; 804 were studied in detail. Neurons insensitive to visual stimuli comprise the fixation, oculomotor, and projection-manipulation classes thought to be involved in initiatives toward action. The largest group of the light-sensitive (LS) neurons were activated from large and frequently bilateral response areas that excluded the foveal region; we term this foveal sparing. The remaining cells subtended areas including the fovea, when tested with large stimuli (6 degrees X 6 degrees), but only 8 of 216 cells studied in detail responded to the small fixation target light. We propose that a dynamic central neural process associated with the acts of fixation and visual attention suppresses responses to foveal stimuli. Parietal LS neurons are sensitive to stimulus movement and direction over a wide range of velocities. The vectors point either inward toward the center or outward toward the perimeter of the visual field, and for neurons with bilateral response areas, the vectors commonly point in opposite directions in the two half-fields; we term this opponent vector organization. The functional properties of area 7 LS neurons are such that they could signal motion in the immediate surround and the apparent motion accompanying head movements and forward locomotion. We surmise that they contribute to a central neural image of immediately surrounding space and to the perceptual constancy of that space obtaining during bodily movement. These properties are suitable for the attraction of gaze and attention to objects and events in the peripheral visual fields. It is this system, together with the classes of parietal neurons concerned with action initiatives, whose destruction is thought to account for the hemi-inattention and neglect of the parietal lobe syndrome in primates.

Foveal Sparing

The pattern of retinal ganglion cell projections to the dorsal lateral geniculate nuclei has been demonstrated with horseradish peroxidase neuronography. A 1 degree-wide strip centered on the vertical meridian has been found in which ipsilaterally and contralaterally projecting ganglion cells intermingle. This strip expands to a width of 3 degrees at the fovea, since mixing of horseradish peroxidase-labeled and unlabeled ganglion cells was found in a band approximately 0.5 degrees wide along both the nasal and temporal rims of the foveola. These labeled ganglion cells rimming the foveal pit in its entirety represent a possible anatomical basis for "foveal sparing".

Demonstration of bilateral projection of the central retina of the monkey with horseradish peroxidase neuronography

In the primate, ganglion cells of the temporal retina project ipsilaterally and those of the nasal retina, contralaterally into the optic tract. The vertical meridian passing through the fovea defines the border between these two populations of ganglion cells and has been demonstrated in four Macaque monkeys after unilateral injection of horseradish peroxidase into the dorsal lateral geniculate nucleus and examination of the pattern of retrograde labeling of those ganglion cells projecting to the injected side. A median 1 degree vertical strip in which ipsi- and contralaterally projecting ganglion cells intermingle was found, confirming the report by Stone et al. ('73). In addition, occasional extrafoveal labeled ganglion cells were found as far as 2 degrees from the vertical midline in the otherwise unlabeled hemiretinae. These ganglion cells were not numerous and had somata of all sizes, suggesting that they do not constitute a separate class of ganglion cells as found in the temporal retina of the cat. In contrast to the description by Stone et al. ('73), the strip of vertical overlap did not show a constant width through the fovea, since mixing of labeled and unlabeled ganglion cells was found in a band approximately 1/2 degree wide along both the nasal and temporal rims of the foveal pit which is 500 mum (2 degrees) in diameter. Beyond these 1/2 degree arcs, the appropriate hemiretina was either completely unlabeled, or contained virtually every ganglion cell labeled on the side projecting to the injected dorsal lateral geniculate nucleus. The scattered labeled ganglion cells rimming an otherwise unlabeled hemifovea represent a possible anatomical basis for the phenomenon of "macular" or "foveal sparing" in which unilateral damage to the occipital cortex produces homonymous hemianopsia with sparing of a small island of centralmost vision extending about 1 degree from the foveal center. From this study, it is not possible to define the receptive fields or specific photoreceptor connections of the ganglion cells labeled with horseradish peroxidase, so that at the present time quantitative correlations cannot be made between the numbers of ganglion cells remaining on the affected side of the fovea and the extent of preservation of visual function in the spared zone. The presence of labeled ganglion cells rimming the fovea in its entirety is compatible with the sequence of foveal development in late prenatal life. After lateral displacement both nasally and temporally of ganglion cells which initially lay in the median vertical overlap strip of 1 degree, in the adult retina a strip approximately 1/2 degree wide around the perimeter of the foveola should contain a mixture of ipsi- and contralaterally projecting ganglion cells. The total population of ganglion cells beyond this 1/2 degree band should be completely ipsi- or contralateral in their projection patterns, as is observed...