Giant neural systems in the inner retina and optic nerve of small whales

Giant neural cell systems (dendrites, cell bodies, and axons) are present among more usual structures in the retina and optic nerve of the small whale (dolphin) Tursiops truncatus retina. Giant cell body dimensions range up to 75 microns in diameter. Nuclei of the cells are frequently larger (greater than 20 microns) than nearby ganglion, bipolar, and receptor cell bodies. The presence of the giant cell system and giant elements in the nerve fiber layer agree with the unusually broad fiber spectrum of the dolphin optic nerve where more than 6% of the axons are greater than 15 microns in diameter. Smaller axons in the size distribution are typical of dimensions found in terrestrial mammals. The axon estimate totaled 157,000 per optic nerve. The giant cell-axon systems of the whale retina may be a unique expression of the large ganglion cell-axon (transient or "Y" functional unit) systems recently identified in terrestrial mammals.

Pattern evoked retinal response (PERR) in human: effects of spatial frequency, temporal frequency, luminance and defocus

Spatial and temporal tuning were examined for both retinal and cortical signals using low contrast sinusoidol gratings. Maximum PERR and VECP responses occurred at the 4 Hz alternation rate and at 0.68 and 2.2 cpd, respectively. A 25% low spatial frequency attenuation (LSFA) was observed for the PERR. To test the possibility that prior inability to detect LSFA of the PERR was due to the masking of a pattern contrast response by a large amplitude local luminance response, mean luminance and optical power were varied in separate experiments. Greater relative LSFA was observed with a lower mean luminance and defocus differentially affected responses elicited by high and low spatial frequency gratings. In addition greater relative LSFA was observed when power at the second harmonic rather than amplitude was the dependent measure. We conclude that LSFA may be observed. The absence of spatial tuning in previous reports is explained by the masking of pattern contrast by local lumnance responses. Detection of LSFA in the present experiments is attributed to use of stimulus conditions which minimize local luminance responses and the use of an objective response measure with a high signal-to-noise ratio, i.e., power at the second harmonic of the stimulation frequency.

LASCER Bode plots for normal, amblyopic, and stereoanomalous observers

Indices of laterality, interocular response latency difference, and binocular summation derived from Bode plots (amplitude-versus-temporal frequency and phase lag-versus-temporal frequency) of cortical responses evoked by laser speckle (LASCER) are correlated with common tests used in clinical refraction. We evaluated eight normal observers and eleven observers with histories of amblyopia and/or stereoanomalies. We find that: (1) LASCER amplitude is reduced in the amblyopic eyes relative to the unaffected fellow eyes, (2) LASCER response latency is increased in the amblyopic eyes relative to the unaffected fellow eyes, and (3) binocular LASCER summation is reduced in stereoanomalous observers. The phenomenal appearance of laser speckle is different for amblyopic eyes than unaffected fellow eyes. Neural disturbances in pattern perception may account for these results.

The EOG and choroidal malignant melanomas

Fifty-four patients with a unilateral pigmented choroidal lesion were studied with electrooculography (EOG). Eighteen of 21 patients with histologically proven (13) or presumed (8) malignant tumors of the choroid had light peak-dark trough ratios (L/D) less than or equal to 150. Seventeen of 21 patients in the malignant group had an interocular L/D difference (L/Dd) greater than or equal to 23%, whereas only one of 33 patients with nevi or a condition simulating a nevus had a percent difference of such magnitude. Combining the L/D and L/Dd criteria resulted in a 98% accurate double-blind prediction of the final clinical/pathological results. The EOG is an objective, noninvasive test useful in the diagnosis of choroidal malignant melanomas.

The visual sensitivity of women during the menstrual cycle

Five women were examined with dark adaptometry and a signal detection procedure for seven consecutive days in the middle of their menstrual cycles. Their discriminability indices show significant (p < 0.05) increases in visual sensitivity on the basal body temperature rise day, while five control observers show no changes across four consecutive days.

Anomalous pigment epithelial photoreceptor relationships and receptor orientation

In order to further investigate the factors influencing retinal receptor orientation, three patients with local disturbances of the receptor/pigment epithelium (PE) interface have been evaluated. Psychophysical and clinical tests have been used to characterize the observed abnormalities. The following conclusions are made. Receptor orientation is lost following a serous detachment of the neurosensory retina and can recover following reattachment of the retina. Orientation may be retained despite the presence of serous detachment of the PE, loss of the light/dark component of the electro-oculogram, and vitelliform-like lesions between the receptors and the PE.

A BASIC program for calculation of intraocular lens power

A program in BASIC for calculation of intraocular lens power, derived from previously published formulas, is presented for use on small computer systems.

Static and kinetic properties of the dolphin pupil

In dim illumination, adult human pupil area becomes asymptotic at about 51 mm2 whereas the dolphin pupil achieves an area of about 70 mm2 under equivalent conditions. At moderate illumination levels (greater than 100 lx), the dolphin pupil becomes a horizontally oriented ellipse and develops a pronounced central constriction with additional light. The relative relationship between pupil area and illumination copmares closely with published human data. Rates of pupil response to step increments in illumination are very similar for the two species. Although the pupil has been proposed as a mechanism for correction of the dolphins' high aerial myopia, correlation of the laboratory findings on static and kinetic pupil properties with visually controlled aerial behaviors disclosed no special interdependence.

Improved electrode for electroretinography

Corneal electrodes useful for clinical electroretinography require topical anesthesia, interfere with vision, can abrade, and are not well accepted by most children and many adults. A low mass conductive thread, corneal (DTL) electrode is described and comparatively tested against the Burian-Allen electrode. The DTL electrode was found to have few of the limitations of the hard contact lens electrode. Furthermore, the DTL electrode signal quality was comparable to that of the Burian-Allen electrode and provided less between-patient variability.

Cortical responses evoked by laser speckle

Human cortical evoked responses elicited by patterns are very size and focus dependent, but those produced by moving laser speckle patterns (LASCERs) remain similar in amplitude and subjective sharpness over a wide (+/- 20 D) variation in added lens power. Moreover, cortical signal amplitudes evoked by speckle displays with high average spatial frequencies are significantly larger than those reported for check stimuli equivalent in spatial frequency.

The transscleral VER: prediction of postoperative acuity

In 33 patients with corneal or lens opacities, the VER was recorded in response to a series of retinal stimuli delivered by the transscleral route (TVER). Based on the preoperative TVER characteristics, predictions of the postoperative acuities were made on a 1 to 5 scale. The predicted acuities were compared with those measured 6 months after surgery and showed that the TVER is a good predictor of postoperative acuity (r = 0.8). The criteria used for acuity estimates are presented.

The transscleral VER: normal responses

Normative data taken on a sample of 10 eyes indicate that transscleral visual evoked response (TVER) stimulation of the cortical evoked response with a range of lights and at lower adaptation levels produces replicable, low-variance responses which may be of sufficient quality for the clinical evaluation of retinal and visual pathway condition. Response amplitudes were related to the radiant peak-power of white stimuli but were greater for red stimuli. Attenuation of the subjective brightness of the stimulus delivered through the inferior lid and sclera was about 0.4 log units compared to corneal delivery. Typical signal:noise ratios were 5:1.

An in vitro and in vivo analysis of anodized tantalum capacitive electrodes: corrosion response, physiology, and histology

Oxidation-reduction reactions which can destroy high current-density metal-stimulating electrodes are avoided when using capacitive electrodes. The results of in vitro and in vivo testing of anodized, high surface area, sintered tantalum electrodes are presented. The corrosion response of the electrodes is excellent; there is no evidence of dissolution of the electrode. A deposit forms on the surface of the electrodes, but has little effect on the voltage response to constant current stimulation. The physiological and histopathological results indicate the capacitive tantalum electrode to be the safest yet tested.

Marijuana and vision--after ten years' use in Costa Rica

Several tests of visual function were applied to an abstaining user (10 years or more) group and a nonuser group carefully preselected to be free of clinical signs of eye disease. The groups were matched on several criteria. The results show that all findings from both groups are within established limits of normalcy. Small differences and trends were found between the groups. These would have been undetected without large samples. Relative to the nonuser group, tests showed these user trends: increased basal lacrimation, increased intraocular pressure, increased photosensitivity, decreased dark adaptation, decreased color-match limits, and decreased Snellen acuity. These differences were associated with statistical probabilities, p=0.07 to p=0.001. There were no significant differences or clear trends between the user and nonuser groups in incidence of pathological fundus signs, conjunctival hyperemia, pterygia, or color-match midpoints.

The electrical stimulation of the retina by indwelling electrodes

Chronically implanted intraocular electrodes were used to stimulate visual cortical responses to current passage through the retina. Electrical current threshold for the light-adapted cat retina lies in the region of 30 to 100 X 10(-6) amps. for the conditions used. Dark adaptation caused a large threshold increase. Retinal excitability also decreased when electrical stimuli were delivered more often than one per 5 seconds. Effective charge-density threshold was moderately greater than reported for frogs and humans.

Retina viability in the Necturus

Electroretinograms (ERG's) were recorded from the eyes of paralyzed normal and decapitated mudpuppies (Necturus maculosus). Fully dark-adapted responses to a range of stimulus intensities were compiled hourly under both conditions. Statistical analyses indicate no significant change in responsiveness in paralyzed normal animals during periods up to 6 hours. After decapitation, there was a significant decline of sensitivity to light during the first 3 hours. An oxygen-sensitive component similar to the c-wave was observed with DC recording but only in normal eyes. Anoxic mudpuppy eyes show an ERG decline with an average time constant of 1.5 hours.

The visual cortex during chronic stimulation

The lateral and suprasylvian gyris of cats have been stimulated anodically by surface electrodes for a total of 40 h by biphasic square waves. Peak currents were +/-6.0 mA, O to peak. Control electrodes were never stimulated. Electrode materials were low-temperature isotropic carbon and metals (Rh, Pt, Au). Reductions in tissue impedance quickly followed the onset of stimulation. The impedance change was related to stimulus current and to the incidence of motor seizures but not clearly to the electrode material. Utilizing concentric electrodes, the impedance change was not localized to the stimulating electrode - tissue interface. No protection from stimulation-associated impedance modifications was provided by the systemic administration of a material of high osmolarity (Mannitol) but the usual impedance decrease was not seen after systemic administration of a glucocorticoid.

Cortical histopathology following stimulation with metallic and carbon electrodes

Stimulation of the cat striate cortex with polished 1 mm2 gold, platinum, rhodium or carbon electrodes for 40h, at 50 Hz, and 0.5 msec duration, results in tissue damage at current densities of 0.6 A/cm2. At 0.1 A/cm2 rhodium and carbon were toxic to brain. In vitro gold and platinum corroded after 1,500-2,300 h of testing in simulated cerebrospinal fluid. The materials utilized are not suitable for long-term chronic electrodes for neural prosthetics.