The organization of nerve fiber bundles in the primate optic nerve head

Horseradish peroxidase was injected into various areas of the optic disc of monkeys to label retrograde axoplasmic transport and permit identification and mapping of ganglion cells projecting through the areas of injection. Peripheral ganglion cell axons project through the deeper layers of the peripapillary nerve fiber layer (NFL) and enter the peripheral optic nerve. Peripapillary ganglion cell axons project through those coming from peripheral locations to superficial positions in the NFL, then to the central optic nerve. The Bjerrum portion of the optic nerve head includes approximately the central 30 degrees of the superior and inferior temporal quadrants of the disc. The course of nerve fiber bundles corresponding to those most susceptible to glaucoma (Bjerrum area) is regularly and predictably organized horizontally and vertically in the nerve head.

Historical summary of visual fields methods

A brief historical progression of visual field testing is presented. The time period is from ancients who had no instrumentation to moderns who employ sophisticated diagnostic methods.

Perception at the blind spot and tilt aftereffect

Black and white stripes were used to induce a tilt aftereffect near the blind spot. Stripe fragments on either side of the blind spot were seen as being completed across the blind spot, but the magnitude of the tilt aftereffect they induced suggested that the perceptually "filled-in" portions of the stripes did not contribute to the aftereffect. So perceptually filled-in lines seem not to be fully potent percepts.

Rescaling of the retinal map of visual space during growth of the kitten's eye

We have measured the angle between the visual axis and the axis projected from the center of the optic disk in 35 cats ranging in age from two weeks to adulthood. Our results show that this angle, a, declines from around 27 degrees in very young kittens to about 16 degrees in adult cats, with most of the change occurring during the first 6 weeks after birth. We interpret this change as reflecting a progressive contraction of the area of object space projected onto the retina. For this to occur, the posterior nodal distance of the eye's optical system must increase by a larger factor than the transverse extent of the retina. This process undoubtedly contributes to maturation of the kitten's visual function, causing a reduction of the size of neuronal receptive fields and an enhancement of spatial resolution.

Gray crescent in the optic nerve head

Twenty-nine patients had a slate-gray crescent within the peripheral tissue of the optic nerve head. Twenty-five of the patients were black; an examination of 100 consecutive black patients revealed the gray crescent in 12 cases. The gray crescents were usually bilateral and were most often located along the temporal or inferotemporal disk margin. Failure to recognize the anatomic location of the gray crescent may lead to misdiagnosis of disk cupping.

Excitation of units in the lateral geniculate and contiguous nuclei of the cat by stretch of extrinsic ocular muscles

In cats, anaesthetized with chloralose and paralysed, the responses of units in the right lateral thalamus were recorded while the extrinsic ocular muscles (EOM) of the right eye were stretched in the dark. Phasic responses were found in all layers of the dorsal lateral geniculate nucleus (LGNd) and in the perigeniculate nucleus (PGN). A given unit usually responded to stretch of more than one EOM and thus to more than one direction of rotation of the eye in the orbit. LGNd. Of a sample of 76 units in LGNd, 55 (72%) gave visula but no muscle responses and 21 (28%) responded to EOM stretch. In all, 40 units with EOM responses were examined and 25 of the 27 tested (93%) also had visual responses. Of the 40 units, 32 could be allocated to layers, thus; layer A, 8 (25%); layer A1, 20 (63%); layer B, 3 (9%); central interlaminar nucleus, 1 (3%). It is interesting that most of the EOM responses were found in layer A1 which recieves the excitatory visual input from the eye whose EOM were stretched. Muscle responsive units occurred with ON- and OFF-centre visual responses of sustained and transient types. PGN. In PGN, 21 units gave EOM responses and most of them were also excited by visual input. The conclusion is that the LGNd and PGN receive an extraretinal proprioceptive signal which should be present during at least large saccadic eye movements. The anatomical pathways which may be involved and the significance of the signal are discussed briefly.

Turnover of mouse photoreceptor outer segments in constant light and darkness

Pigmented mice differ from frogs in that lighting regime has only a small effect on rod outer segment turnover. During 8 days in constant light or darkness, disc addition measured as total displacement of a radioactive band in rod outer segments of mice which has received injections of tritiated amino acids was never modified by more than 7% compared to cyclic light controls. Disc shedding continued in each lighting regime, and as judged from outer segment dimensions, disc shedding approximately balanced disc addition.

An estimate of image quality in the rat eye

The point spread function on the optic axis of the rat eye is indirectly estimated to increase from a half-height width no greater than 12.5' to not less than 36' after dilation of a 0.33 mm pupil diameter to 3.0 mm.

Development of X- and Y-cells in kittens

A contrast reversal stimulus was used to classify the retinal ganglion cells of kittens 3--12 weeks of age. At 3 and 4 weeks of age, the majority of the units were classified as Y-cells. The percentage of X-cells was similar to that of the adult at 5--6 weeks of age although other response properties were not adult-like. The angular size of the receptive field center was significantly larger than that of the adult through 5--6 weeks of age. An estimate of the position of the vertical meridian was obtained from the positions of the receptive fields in the visual field which permitted the calculation of the posterior nodal distance in kittens of various ages. From the posterior nodal distance, the linear extent of the receptive field center was determined. This showed that there is only a very slight increase in the linear size of the receptive field center from 3 weeks to adulthood.

Importance of corpus callosum for visual receptive fields of single neurons in cat superior colliculus

1. Section of the posterior two-thirds of the corpus callosum eliminates almost completely the response of superior colliculus (SC) neurons to stimulation of the contralateral eye in split-chiasm cats. On the contrary, the responsiveness of SC neurons to stimulation of the contralateral eye is not abolished by a transection of the posterior and tectal commissures leaving the corpus callosum intact. The callosal section also reduces the number of SC receptive fields abutting the vertical meridian in the ipsilateral eye of split-chiasm cats. 2. In cats with intact optic pathways, a similar callosal section abolishes the SC representation of the ipsilateral visual field in the ipsilateral eye and also reduces the number of receptive fields adjoining the vertical meridian in the same eye. In the contralateral eye, the SC representation of the ipsilateral visual field is reduced in extension to about one-fifth of that seen in cats with intact commissures. 3. The results suggest that the corpus callosum is the main pathway for cross-midline communication of visual information at not only the cortical, but also the midbrain level. The corpus callosum may subserve this function because it contains uninterrupted crossed corticotectal projections or because it transmits visual information from one hemisphere to contralateral cortical areas projecting ipsilaterally to SC. The latter hypothesis is more likely but, in any case, the findings imply that the lack of interhemispheric transfer of visual learning in cats with a chiasmatic and callosal section may depend on a midline disconnection of both subcortical and cortical visual centers. 4. The corpus callosum is also responsible for the representation of the ipsilateral visual field of the ipsilateral eye in the cat SC. The SC representation of the ipsilateral visual field in the contralateral eye is due, in minimal part, to direct retinotectal connections from temporal retina and, for the largest part, to the corpus callosum. 5. Finally, the corpus callosum contributes to the representation of the contralateral visual field near the vertical meridian of the temporal retina in both split-chiasm and normal cats. This is probably due to the scarcity of direct retinotectal projections from this part of the retina and to their supplementation by corticotectal neurons influenced by the callosal afferents.

On the light-stimulated coupling between rhodopsin and its disk membrane environment

Disks from bovine ROS undergo a rapid shrinkage when flash illuminated with green light (Uhl, R., et al. (1977) Biochim. Biophys. Acta 469. 113-122). This can be monitored as a light scattering transient, referred to as the P signal. In this paper the P signal is studied at various temperatures and pH. The temperature dependence of the kinetics reveals that "P" consists of two sequential reaction steps. Both appear to occur within the receptor molecule rhodopsin. The actually observed event, the shrinkage of the disk, is therefore not rate limiting under the tested conditions. Both steps of "P" take place while there is only one spectroscopically detectable reaction of the rhodopsin molecule, the metarhodopsin I-metarhodopsin II transition. This implies that there are intermediates of the rhodopsin photolytic cycle which are not evident as spectroscopically separate species. The amplitude of "P", i.e., the extent of the disk shrinkage, is independent of the state of the equilibrium between the two photoproducts absorbing at 478 and 380 nm respectively and called MI and MII. A scheme is suggested in which the irreversible decay of MI (478) triggers the disk shrinkage (and maybe transduction), and in which there is an equilibrium between MII (380) and a proposed isochromic photoproduct MI' (478).

Efferent system in the retina of the frog, Rana catesbiana

Single units were recorded through glass microelectrodes placed on the optic disk or on the retina of the opened eye of the frog (Rana catesbiana). Units were classified as A-, B-, and C-fibers according to conduction velocities. By the method of collision between naturally elicited and electrically elicited impulses, many of the B-fibers and some A- and C-fibers, which showed unusual behavior to photic stimulation, were found to be efferent fibers. Retinal effects of the efferent nerves were studied by repetitive stimulation and cooling of the optic nerve. The effects were found to be both inhibitory and excitatory.

[Temporal change of the disc in normal adults (author's transl)]

We have recently proposed a procedure called stereochronoscopy which allows the detection of temporal changes in the disc by stereoscopic observation of exactly centered fundus pictures. We show that this procedure can also be applied in a slightly modified form to fundus pictures that are not specially centered, although with less precision. Using this technique we were able to show on material covering 10 years (50 eyes) that the discs of healthy adults do not as a rule change over a period of at least 8 years. This is valid for observation of the pictures with an overall magnification of X 14.

Myelin sheath thickness and conduction latency groups in the cat optic nerve

In many animals, the optic nerve has multiple conduction latency groups of fibres yet displays a unimodal frequency distribution of fibre sizes. An attempt has been made to resolve this discrepancy in the cat. Examination of teased preparations of fixed cat optic nerve fibres by polarizing interference light microscopy indicated that a fibre's size may change abruptly along its length. Furthermore, the diameters of single nerve fibres followed for distances of up to 30 mum in serial transverse sections of cat optic nerve showed variations of up to 100% of a fibre's average diameter over that distance. On the other hand, the myelin sheath thickness of these fibres appeared to be relatively constant along any one fibre. A population of cat optic nerve fibres which had a unimodal axon diameter frequency distribution was found to have a myelin sheath thickness frequency distribution with five modes. These modes have been interpreted as indicating the existence of five groups of fibres in the cat optic nerve. Four of these groups may be related to four negative peaks seen in the antidromic compound action potential recorded at the margin of the cat optic disc following stimulation of the optic chiasm. The fifth myelin thickness group appears to represent the slowly conducting fibres which do not make an obvious contribution to the antidromic compound action potential. It is concluded that for the cat optic nerve, the conduction latency groups seen in the compound action potential may be more directly correlated with the frequency distribution of fixed nerve myelin thickness than with the frequency distribution of fixed nerve fibre diameter.

The effect of blood on ocular fundus reflectance and determination of some optical properties of retinal blood vessels

Light reflected from 50 micrometer diameter spots on the fundi of two adult rhesus monkeys was measured as a function of wavelength in 10 nm jumps from 400 to 900 nm. The areas measured were a retinal artery and vein, areas of the disk, macula, and retina devoid of visible blood vessels, and the foveola. The eyes of the two monkeys were then exsanguinated, the blood vessels were filled with normal saline, and reflectances of the same spots on the fundi were again measured. The pairs of reflectance curves were compared and demonstrated that blood is not the major determinant of the characteristic shapes of the retinal tissue spectral reflectance curves. From the pre-exsanguination and postexsanguination data, the isolated retinal artery and vein wall reflectances were determined to be 0.020 and 0.009, respectively, their transmittances 0.837 and 0,977, and the fractions of light absorbed by them 0.143 and 0.014, respectively, in the visible spectral region below 500 nm.

Rapid detection of changes in the optic disc: stereochronoscopy. II. Evaluation technique, influence of some physiologic factors, and follow-up of a case of choked disc

A simple device for viewing stereochronoscopic (Sc) picture pairs under any azimuth is described. The influence of pulse, irradiation, time, and ocular pressure on disc configuration of some healthy and affected subjects is investigated. To test the sensitivity of Sc as compared to that of conventional steroscopy (St), a case of choked disc in which pictures of both kinds had been taken was followed up. This material also served to test 10 observers as to their ability to detect St and Sc effects in fundus pictures. Despite good stereo vision in all observers as tested by the Titmus charts, considerable differences were found in the analysis of fundus pictures. Detailed instruction resulted in improved results. Two cases of glaucoma simplex incipiens are presented in which a change of disc configuration could be detected by SC while ocular pressure and visual field remained normal in one case and did not change in the other.

Intracellular recording and staining of cat's lateral geniculate neurons

Intracellular staining with recording micropipettes filled with a Procion yellow solution was attempted on 11 lateral geniculate neurons of chloralose-anesthetized cats for the purpose of correlating electrophysiologically identified cell types with morphologically identified cell types. Five neurons were successfully stained: one was located in lamina A and the others in lamina A1. They were all identified as P-cells on the basis of their responsiveness to electrical stimulation of optic disc, optic chiasm and visual cortex. The conduction velocities and synaptic delays for specific optic nerve fibers concerned with these P-cells were estimated from the relationship between latency and conduction distance. Intracellular staining has revealed that a neuron located in lamina A and three of four neurons located in lamina A1 had multipolar configuration, with their main dendrites oriented parallel to the plane of the laminae; while one neuron located in lamina A1 had a configuration similar to that of a class II-type neuron described by Guillery in his Golgi preparations. In these experiments no neurons located in lamina B, central interlaminar nucleus and medial interlaminar nucleus were stained. No interneurons were obtained, either.

Scotopic retinal sensitivity in man as determined with visually evoked cortical potentials

Scotopic properties of the peripheral retina in man was studied by recording visually evoked cortical potentials (VECPs). The intensity required for a criterion latency of the scotopic VECP was compared with the sensory threshold in a number of situations where the stimulating retinal site and the area of the stimulus were altered. With circular spot stimulation, the VECT amplitude attenuated greatly as the stimulus site moved to peripheral 10 degrees and was almost null when stimulation was made outside it. However, within the retinal area from the fovea to peripheral 10 degrees, the VECP sensitivity was found to vary according to the rod distribution, as suggested from the sensory threshold. Stimulation with annular patterns revealed that the parallelism between the VECP sensitivity and the rod distribution holds good within up to 30 degrees from the fovea. A strong summation was proved to be operative for eliciting VECPs by stimulation of the peripheral retina.

An attempt to assess the effects of monocular deprivation and strabismus on synaptic efficiency in the kitten's visual cortex

The relative effectiveness of the two eyes in exciting cells in the visual cortex was assessed, using both natural stimulation and electrical stimulation of the optic discs. It is is argued that supramaximal electrical stimulation of the optic nerve could possibly reveal 'subliminal' synaptic inputs even after monocular deprivation or artificial strabismus has caused a loss of natural input from that eye, if such 'silent' synaptic input still survives. However, in kittens monocularly deprived for various periods of time or made artificially strabismic, there was usually excellent agreement between the relative visual excitability in the two eyes and their relative electrical excitability. In one animal, monocularly deprived continuously until 23 weeks of age, we examined the effect of reversibly turning off signals from the normal eye by pressure blinding. There was no evidence of a very rapid return of sensitivity to either electrical or natural stimulation of the deprived eye.

Reflection of light by small areas of the ocular fundus

Light reflected from 50 micrometer spots on the fundi of two rhesus monkeys and three human volunteers was measured as a function of wavelength in 10 nm. jumps from 400 to 900 nm. The areas measured were a retinal artery and vein, areas of the disk, macula, and retina devoid of visible blood vessels, and the fovea.

The dorsomedial cortical visual area: a third tier area in the occipital lobe of the owl monkey (Aotus trivirgatus)

In the owl monkey, microelectrode mapping of Brodmann's area 19 indicates that this region contains part or all of at least 5 separate representations of the visual field, each of which adjoins the anterior border of V II and collectively are termed the third tier of cortical visual areas (V I is the first tier; V II is the second tier). Described in detail in this report is one of the third tier areas which is located on the dorsal surface and the adjacent medial wall of the occipital lobe and corresponds to a densely myelinated zone of cortex. In this dorsomedial area (DM), the representation of the horizontal meridian is partially split, and thus, like V II (see ref. 4) and the dorsolateral crescent5, DM is a second order transformation of the visual hemifield. In one abnormal owl monkey, a portion of the upper quadrant was represented twice in DM. This abnormal case may provide some clues as to how the normal pattern of visuotopic organization is established in the developing brain.

The function of the retina in the perfused eye

The data show that the enucleated eye of the cat can be maintained in apparently physiologically functioning condition by appropriate arterial perfusion. Under appropriate conditions, photically evoked electrical mass responses can be recorded from various parts of the isolated, perfused eye for 8 to 10 hours. ERGs as well as responses from axonal bundles of the optic nerve exhibit shapes, amplitudes and time courses comparable to their counterparts in vivo. Homeostasis of the perfusion ensures the stability of these light-evoked electrical responses. Transient changes in biophysical parameters of the perfusate rapidly induce marked, although reversible, changes in the amplitudes of b-waves of the ERGs. Increases or decreases in the flow rate of the perfusate induce parallel increases or decreases in the amplitudes of the b-waves as well as of the optic nerve responses. Similar alterations in the oxygen concentration of the perfusate induce similar and proportional changes in the amplitudes of the b-waves. It is concluded, that low flow rates of hemoglobin-free perfusate induce hypoxia; consequently, acceleration of the flow can compensate for hypoxia in a certain range. Previous studies on the effects of and recovery after transient hypoxia in mammalian retina are in concordance with the present data. Progressive decrease of temperature induces gradual and reversible reductions in the amplitudes of the b-waves and increases their latencies and peak-times. It is suggested, that initial hypothermia, which occurs during the period of cannulation, reduces the deliterious effects of the coincident unavoidable hypoxia on retinal neuronal elements. Since light-evoked electrical responses can be maintained for many hours in these preparations and since movements of cardiovascular and respiratory origin, invariably present to varying extent in the in vivo experiments, are eliminated, this preparation is suitable for intracellular recordings from neuronal elements of the retina. Potentials were recorded from cells in various layers of the retina of the cat; intracellular recordings from horizontal cells (S-potentials) are described in detail. Spectral analysis of S-potentials allowed to distinguish between three types according to their inputs: a mixed, rod-cone type, which was most frequently encountered, a pure cone- and a pure rod-type. Light- and electronmicroscopic investigation of the retina after perfusion revealed that (1) the extent of cellular damage depends on the flow rate of the perfusate; (2) little cellular damage is observed if medium flow rates, which maintain physiologic responsiveness of the isolated eye to light, were applied for two hours; (3) high flow rates applied for two hours, or medium flow rates applied for 7 hours appear to induce cystic changes in the pigment epithelium, but only minor changes in the cells of the inner nuclear layer.

Receptive-field characteristics of single neurons in lateral suprasylvian visual area of the cat

The visual receptive fields of 213 cells in the lateral suprasylvian visual cortex (LS, or Clare-Bishop area) were studied in cats anesthetized with nitrous oxide. Eighty-one percent of the cells were directionally selective. They responded poorly to stationary stimuli flashed on or off, but gave a directionally selective response to stimuli moving through the receptive field. Most of these had a single preferred direction and an opposite null direction. They typically responded to a range of directions of stimulus movement from 45 to 90 degrees to either side of the preferred direction. Small stimuli (1-2 degrees or smaller) typically were effective and 87% of the directionally selective cells showed spatial summation. About 32% had inhibitory mechanisms which decreased the response of the cell if the stimulus exceeded a maximum size. There was little or no evidence that LS area cells were orientation selective or sensitive to variations in stimulus shape independent of size.

[The relationship of the collapse-phenomenon on the disc to the pulsatory variations of the intraocular pressure (author's transl)]

The collapse-phenomenon of the central retinal artery induced by compression of the eyeball and the pulsatory variations of the intraocular pressure were recorded simultaneously. The collapse-phenomenon indicating the systolic pressure of the ophthalmic artery was correlated to the peak and that indicating the diastolic pressure of the ophthalmic artery to the through of the pulsewave. This finding has to be taken into account when evaluating the curves delivered by Stepanik's ophthalmic artery-tonography.

The representation of the visual field in the lateral geniculate nucleus of Macaca mulatta

Microelectrode recording techniques were used to investigate the projection of the visual field into the lateral geniculate nucleus (LGN) of Macaca mulatta. The data were used to construct charts plotting visual direction, designated in terms of azimuth and elevation, onto sections of the nucleus cut in coronal, sagittal and horizontal Horsley-Clarke planes. The projection of the horizontal meridian divides the LGN along its plane of symmetry into a medial-superior half having negative elevations and a lateral-inferior half having positive elevations. Elevations become more positive or negative with distance from this plane. Azimuths closest to the vertical meridian are located posteriorly, while the most peripheral azimuths are found at the anterior pole. Two families of surfaces representing visual directions of constant azimuth and elevation are described. Visual field zones of increasing eccentricity are represented serially along the posterior-anterior axis of the LGN, with the foveal area restricted to the posterior pole and the monocular crescent projecting to the anterior pole. The mapping is completely continuous across the horizontal meridian. The edges of the stacked cell laminae exposed around the periphery of the LGN form an oval band which receives the projection of the perimeter of the contralateral hemifield. The vertical meridian is represented by the posterior two-thirds of this band, while the periphery of the hemifield projects to the anterior third. The central visual field out to the optic disc is represented by six cell layers, while the rest of the binocular field projects to four layers only (2 parvocellular and 2 magnocellular). The monocular crescent is represented by one parvocellular and one magnocellular layer. Features associated with the projection column of the optic disc are integrated into the transition from six to four layers. Details of the receptive field topography in the vicinity of the optic disc discontinuities indicate that these gaps are produced by intralaminar mechanisms. The magnification factor (mm-3/steradian) increased monotonically from peripheral visual fields to the foveal center, varying over a range of three decades. This range is intermediate between those derived from data reported in the literature for the retina and the striate cortex. The ratio of LGN magnifications at any two angular eccentricities is a power function, with an exponent of 1.34, of the corresponding ratio of retinal ganglion cell densities. Similarly, the ratio of cortical magnifications (mm-2/steradian) at any two eccentricites is a power function, with an exponent of 1.35, of the corresponding ratio of LGN magnifications.