Temporal Hemifield Research Articles

Visual field defects in cats with neonatal or adult immunological loss of retinal ganglion cells

Behavioral perimetry methods were used to assess the monocular visual fields of 12 cats that had received intraocular injections of antibodies against large (alpha/Y) retinal ganglion cells. The antibodies produced defects in head and eye orientation responses to stimuli presented in the nasal visual field of the treated eye; responses to stimuli in the temporal visual hemifield were normal. Similar results were seen in cats that received antibody injections at 4 weeks of age or as adults. In the context of previous results, these findings suggest that a loss of Y cells in the lateral geniculate nucleus is sufficient to reduce geniculocortical function for head and eye orientation to visual stimuli in the nasal visual field.

The eye of the humboldt penguin, Spheniscus humboldti: visual fields and schematic optics.

Construction of a schematic eye indicates that the eye of Spheniscus humboldti is aquatic in design. The lens has a power of 100 dioptres (D) while (in air) the cornea has a power of 29 D. In air, the eye is myopic (approximately 28 D) but in water it is emmetropic. Minimum pupil size would seem insufficient to allow the pupil to function as a stenopaic aperture and increase depth of focus sufficiently to overcome the eye's aerial myopia. Entry into water reduces maximum image brightness by approximately three times. In air, the maximum width of the retinal binocular field is 45 degrees and this occurs approximately 10 degrees above the line of the bill. The bill intrudes into the retinal field and binocular field width in the plane containing the bill and the optic axes is 28 degrees. The vertical extent of the binocular field is 125 degrees. In the plane containing the optic axes the cyclopean field equals 282 degrees and the optic axes diverge by 116 degrees. In this plane the mean uniocular field is 155 degrees with the temporal hemifield approximately 11 degrees larger than the nasal hemifield. Entry into water reduces the widths of the visual fields such that maximum binocular field width is only 17 degrees and the vertical extent is reduced to about 80 degrees. Binocular vision is lost in the plane of the bill, and the uniocular retinal field is reduced by 32 degrees and the cyclopean field by 36 degrees.

Removal of the more-experienced eye decreases visual field deficits in cats reared with unequal alternating monocular exposure

Unequal alternating monocular exposure produces a nasal field deficit for the less-experienced eye, which persists despite prolonged unrestricted binocular exposure. We now report that this deficit decreases after the more experienced eye is removed. Prior to enucleation, the visual field of the less-experienced eye was restricted to the temporal hemifield; 5 months after enucleation of the more-experienced eye, this field extended into the nasal field. Our results are consistent with those in monocularly-deprived cats, and with the occasional recovery of human amblyopes after loss of the fixating eye.

A simple technique for lateralizing visual input that allows prolonged viewing

A simplified technique is described for obtaining lateralization of visual input with prolonged viewing. This technique is based on the presence of constant normal lateral limits for horizontal rotation of the eyes with reference to the head. With head movement prevented by use of a standard bite bar, and the eyes rotated to the left and held at their lateral limit, the temporal half of the visual field of the left eye may be used for lateralized input to the right hemisphere or vice versa for input to the left hemisphere. Any form of visual stimuli or visually monitored task can be used if confined within one of the extreme temporal hemifields. In comparison to previous methods, this technique is technically simple, inexpensive, without significant risk or discomfort to the subject, readily applicable to normal and various brain-lesioned subjects, and permits prolonged in-depth viewing. An alternative version of this technique uses a stabilized spectacle frame fitted with adjustable central occluders set to allow vision through only one or both of the extreme temporal hemifields.

Pattern evoked potentials in human albinism: Evidence of two different topographical asymmetries reflecting abnormal retino-cortical projections

In fifteen subjects with oculo-cutaneous or ocular albinism pattern-reversal visual evoked potentials (VEP) were recorded to monocular whole-field (16° radius) and right and left vertical half-field (16° radius) stimulation from an array of occipital electrodes. In all 15 subjects the VEP was of low amplitude and the monocular response to whole-field stimulation showed abnormal asymmetry in scalp topography. This asymmetry was similar to that produced by stimulation of the temporal half-field in the same eye. Two distinct types of VEP asymmetry were readily identified in different subjects. In 5 the major positivity of the response ( P100 ) was distributed in the channels ipsilateral to the stimulated eye or temporal half-field, being similar in distribution to the P100 from the temporal hemifield of normal individuals. In 9 other subjects the converse occurred; the P100 was distributed contralaterally. The remaining subject was unique in that the responses from each eye had a distribution that resembled one of the two main groups. The nasal half-field responses also differentiated the two groups. On stimulation of the nasal field in the first group the P100 was usually absent or attenuated and when present it had the same topography as the temporal half-field P100 . In contrast the nasal half-field P100 from the second group was always present and, although almost invariably smaller than the temporal half-field P100 , it had an identical distribution. There was no correlation between these two patterns of VEP asymmetry and clinical or known genetic features. The findings confirm that in human albinos each hemisphere receives a predominantly monocular input from the contralateral eye; i.e. in addition to the temporal half-field, approximately 20° of the nasal half-field is projected to the hemisphere contralateral to each eye and not, as in normal subjects, to the ipsilateral hemisphere. Furthermore, the finding of two distinct and in some respects opposite types of VEP topographical asymmetry raises the possibility of two variants of the geniculo-cortical projection patterns existing in human albinos similar to those described in the Siamese cat.

Unequal alternating monocular deprivation causes asymmetric visual fields in cats.

Kittens were reared so that each eye received normal patterned vision on alternate days. If the eyes received equal periods of stimulation, the visual fields were normal. If one eye received much more experience than the other, the field of the less experienced eye was restricted to the temporal hemifield. This change, which differs from that observed when one or both eyes are deprived continuously of patterned input, suggests that an imbalance in the duration of stimulation can influence the outcome of the normal competitive interaction between pathways from the two eyes and can cause a selective suppression of a portion of the input from the less experienced eye. This suppression may involve the ipsilateral retino-geniculo-cortical pathways or it may involve the entire cortical pathway from the less experienced eye, leaving the colliculus to control responses to visual targets.

The organization of the visual hyperstriatum in the domestic chick. I. Topology and topography of the visual projection

The organization of the visual projection to the hyperstriatum, or Wulst, in the domestic chick has been investigated using extracellular recording with microelectrodes. The entire visual field of the contralateral eye projects retinotopically into the Wulst. The superior and inferior margins of the visual field are represented, respectively, in the posterior and anterior regions of the visual projection area. The projection of the nasal and temporal margins of the visual field is more complex, the superior and inferior parts of the temporal hemi-field being represented in the superficial and deep regions of the Wulst respectively, with an intervening projection of the nasal hemi-field at an intermediate depth. Visually responsive units appear to be restricted to the accessory hyperstriatum (HA) and possibly also to a narrow, medial region of the intercalated nucleus (HIS). Visual-evoked activity was never detected in the dorsal hyperstriatum (HD) or ventral hyperstriatum (HV). The organization found in the chick is discussed in relation to the previous physiological and anatomical findings of other workers in the visual Wulst of the pigeon and the owl.

Demonstration of peripheral hemiopic border steps by static perimetry.

10 normal eyes were examined by static perimetry along a horizontal line 60 degrees below the fixation point. All showed a greater sensitivity in the temporal hemifield. The study confirmed the previously reported existence of a step and indicated a greater threshold specifically at the hemiopic border.

VERTICAL STEPS IN ISOPTERS AT THE HEMIOPIC BORDER — IN NORMAL AND GLAUCOMATOUS EYES

Careful perimetry disclosed small steps in peripheral isopters corresponding to the vertical meridan in about 50% of normal eyes as well as eyes with glaucomatous field defects. Most steps were found inferiorly. The contraction of the isopter was always found on the nasal side of the field apart from a few of the glaucomatous eyes, all of which also showed central field defects. The findings suggest that no significance with regard to pathology can be attached to small peripheral steps at the vertical meridan provided that the temporal hemifield is the greater. Steps showing preponderance of the nasal half of the field, however, should arouse suspicion of an existing pathology. The reported observation as well as findings in the literature concerning function, anatomy and pathology suggest that the nasal hemiretina is dominant over the temporal one.

The ocular following reflex elicited from the retinal periphery in the cat

Cats with pretrigeminal brainstem transection were used for experiments. In such cats only vertical eye movements are present. A light slit or a black stick (1° × 4°) were moved with 10°/cm speed along the vertical meridian or parallel up to 40° in the nasal or temporal hemifield. The following movements were evoked from the whole area, but at the periphery their latency was longer and their velocity lower than in the center of the retina. The ocular following reflex can be controlled by the retinal periphery in the cat.

Crossed and uncrossed representation of the visual field by brisk-sustained and brisk-transient cat retinal ganglion cells

The projection of the cat'smonocular visual fieldto the contralateral and ipsilateral optic tractsdiffered for thebrisk-sustainedand brisk-transientclasses of retinal ganglion cell. For both types all units recorded with receptive field centres more than about 0.5° into the temporal visual hemifield hadcrossedaxons. The transition from crossed coverage of temporal hemifield to uncrossedcoverage of nasal hemifield was complete at about 0.5° nasal for the brisk-sustained units but crossed brisk-transient units were found with receptive fields as far nasal as 15.8°. The 50% crossed/50% uncrossed zone for brisk-transient units was located 1–2° nasal of that for brisk-sustained units.

The crossed or uncrossed destination of axons of sluggish-concentric and non-concentric cat retinal ganglion cells, with an overall synthesis of the visual field representation

Two distinct patterns of representationof the visual fieldby the slowly conducting ganglion cellsof the cat's retinawere observed. Both differed from the classical arrangement ofcrossedcells for temporal hemifield and uncrossedfor nasal hemifield. The first, exemplified by sluggish-sustained cells, involved a limited spread of crossed units into the nasal hemifield. The second, found with sluggish-transient units, local-edge-detectors and direction-selective units involved a preponderant representation of the entire nasal hemifield by crossed units.