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PubMed1984

Optokinetic sensations evoked by local stimulation of the peripheral retina.

Optokinetic sensations of movement have been investigated by means of a moving pattern of stripes presented in the periphery of the visual field. Linear sensations of movement occur. The more peripheral in the visual field the pattern is presented, the more sensitive the retina becomes. Stimuli perpendicular to the horizontal meridian evoke stronger reactions than stimuli presented perpendicular to the vertical meridian. Vertically directed stimuli in the temporal field of vision give rise to more intense sensations than the same stimuli applied to the nasal field. An upward movement of stimulus pattern causes a more pronounced sensation of 'lift' than a downward movement. As for horizontal stimulation, sensations are more pronounced when stripes move from temporal to nasal than in the opposite direction. Only stimulation perpendicular to the meridian, either horizontal or vertical, induces sensations of movement. Stimulation in the same direction as these meridians, whether upward or downward for the vertical axis or to the left or the right for the horizontal axis, do not induce linear or circular vection. The results may be of importance in working with monitor screens. The differences between the method routinely used in optokinetic examination and the present stimulus method, are discussed.

Evoked Potentials, Visual↗
PubMed1981

Representation of the visual field in the optic tract and optic chiasma of the cat.

The fibre arrangement in the optic chiasma (OC) and tract (OT) was investigated with anatomical and physiological methods. In silver impregnated material, principal fibre streams can be demonstrated. In the OC, fibre bundles from each eye cross in a regular basket weave pattern, but deviations of single fibres from the predominant stream are often seen. In the OT, fibres run essentially parallel, and crossings of individual fibres are mainly restricted to the periphery of the tract, or around capillaries. Fibres in the upper segment of the OT are of thin, in the lower segments of thick diameter. Individual fibres labelled by HRP injected in the lateral geniculate body (LGB) run essentially parallel over long distances. Ventromedially to the LGB, bifurcations are found with one branch entering the LGB, the other continuing. 57% of OT-fibres had a receptive field (RF) in the contralateral, 43% in the homolateral eye; 60% in the lower, 40% in the upper visual field; and 6% had a RF in the homolateral visual field, mostly near the vertical meridian. Fibres from the central area were underrepresented in our sample. Fibres from the two eyes were mixed. The RFs of consecutively recorded fibres showed a systematic progression only exceptionally. After plotting RFs of a single penetration on a transformed isodensity ganglion cell map of the visual field, the RF's were distributed along elongated paths on this map. In the OT, such paths ran parallel or slightly inclined relative to the horizontal meridian. They were restricted to either the upper or the lower quadrant or to a path along the horizontal meridian. In the OC, the RF-paths mostly crossed the horizontal meridian at an obtuse angle (average 70 degrees). Thus, the visual field representation rotates by nearly 90 degrees from the OC to the OT. In the OC, the central area is located anteriorly, in the OT dorsally, with the upper visual quadrant laterally and the lower medially. Fibres from the two eyes were mixed and, within the range of the scatter, RFs from the homo- and contralateral eye were in register. It is concluded, that the distribution of fibres in the OC and the OT show a basic retinotopic organization superimposed by scatter.

Animals↗
PubMed1982

Visuotopic organization of the superior colliculus of the opossum.

The representation of the visual field in the upper layers of the opossum's superior colliculus was studied by recording the response of multi-units to visual stimulation. Overall, the visual topography is similar to that of other non-primate mammals. Along the horizontal meridian and magnification factor decreases assymetrically about the vertical meridian, falling more abruptly in the region of the representation of the ipsilateral hemifield. The colliculus may be divided into three parts on the basis of the projections from the retina: a rostral region that does not receive any ipsilateral retinal afferents, a region that receives binocular retinal projections and a monocular region that receives only contralateral retinal input. Electrophysiological recording revealed that the rostral region contains a representation of 40 degrees of the ipsilateral field. The representation of the vertical meridian forms the border between the rostral region and the binocular region and the representation of the 40-45 degrees longitude meridian forms the border between the binocular and monocular regions.

Animals↗
PubMed1982

Effect of beam directional alterations on left ventricular shortening fraction.

In this study, the dependence on beam direction of the echocardiographically derived fractional shortening of the left ventricular minor axis was evaluated. A directionally oriented, steerable cursor was used to select M-mode lines from a 2-dimensional image at the chordal level. Seven M-mode traces were derived from each image, 1 along the true ventricular meridian and 3 at known deviations on either side of the meridian. M-mode traces, thus derived, all appeared acceptable for measuring wall or cavity dimensions. Results indicate a progressive increase in shortening fraction (p less than 0.05) for deviations more than 25% of the distance between the meridian and the lateral or medial papillary muscle heads. Decreases in left ventricular dimensions in diastole and systole with progressive deviation from the meridian accounted for the decrease in shortening fraction. Spatial orientation is required for reproducible shortening fraction measurements.

Adolescent↗
PubMed1984

Changes in corneal curvature induced by sutures and incisions.

To clarify the mechanisms by which incisions and sutures produce corneal astigmatism, we made incisions and wedge resections closed by sutures in the corneoscleral limbus of human eye bank eyes, studying the changes in corneal curvature by shadowgraph photography of the corneal contour, by central keratometry, and by measurement of corneal diameter. The compression of tissue within the sutures or the closure of an excision of a wedge of tissue by sutures induced astigmatism in the meridian of surgery regardless of changes in the sagittal depth of the anterior chamber. Sutures and wedge resections closed by sutures in the anterior part of the cornea compressed or removed more tissue from the anterior part than the posterior part, producing a depression of the limbal cornea toward the anterior chamber and steepening the central cornea in the meridian of surgery. The corneal diameter decreased in that meridian. In the opposite meridian, the cornea flattened, the corneal diameter increased, and the sagittal depth decreased.

Astigmatism↗
PubMed1987

Distribution in the visual field of the costs of voluntarily allocated attention and of the inhibitory after-effects of covert orienting.

By using a simple reaction time (RT) paradigm we have investigated the spatial distribution of the benefits and costs of voluntarily directed attention and of the inhibitory after-effects of covert orienting. In the first experiment subjects deliberately allocated attention to each one of five stimulus positions disposed along the horizontal meridian, while at the same time fixing their eyes on the central position. The separation in visual angle between the central position and the two nearest positions, one on the left and the other on the right, was 10 degrees; that between the central position and the two most eccentric positions was 30 degrees. By comparing RT to brief flashes of light presented at each position during directed attention with RT to identical flashes at the same position during diffuse attention (i.e. in a condition in which subjects paid equal attention to all five positions), it was possible to determine that benefits, that is RT decreases relative to the diffuse-attention condition, were strictly limited to the attended position. Costs, i.e. RT increases relative to the diffuse-attention condition, showed a more diffuse and complex spatial pattern. When attention was directed to one of the noncentral positions, costs were apparent at the two contralateral positions and at the central position, but not at the ipsilateral position. When attention was directed to the central position, costs occurred at all other positions. This suggests a special role for the vertical meridian in delimiting the area of costs when one covertly orients towards the opposite right or left visual half field. Work of others and our preliminary evidence indicate that the area of costs is similarly limited by the horizontal meridian when one orients toward the opposite upper or lower visual field. In the second experiment we studied the inhibitory after-effect of covert orienting. Orienting to a light stimulus without moving the eyes to it may induce a short-lived facilitation of the speed of response to a second stimulus presented at the same position, but this facilitation is followed by a profound and prolonged RT retardation. By using a two-flashes paradigm we observed this RT retardation not only when the two stimuli appeared at the same position, but also when they occurred at different locations in the same altitudinal or lateral visual hemifield. There were no inhibitory after-effects when the two stimuli appeared on opposite sides of the vertical or horizontal meridian.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

Visual field asymmetries in pattern discrimination: a sign of asymmetry in cortical visual field representation?

A visual field asymmetry is described relative to the discrimination of mirror symmetric bars with ramp-like luminance profiles. Along the vertical meridian the discrimination is better performed for patterns oriented parallel to the meridian than for patterns oriented orthogonally at all eccentricities tested (2-8 deg). Along the horizontal meridian, the preference for radially oriented stimuli is present at 2 deg from the fovea, but vanishes at larger eccentricities. The meridional asymmetry thus revealed psychophysically may reflect asymmetries in the representation of the vertical and horizontal meridians in the human visual cortex.

Discrimination, Psychological↗
PubMed2006

Nitric oxide modulation of norepinephrine production in acupuncture points.

The purpose of this study was to examine the levels of norepinephrine (NE) turnover in skin tissues and to determine the effect of nitric oxide (NO) on NE production in acupuncture points (acupoints) and meridians. The rats were pretreated with alpha-methyl-tyrosine methyl ester and intravenously infused with L-(2,3,5,6-(3)H)-tyrosine. Blood was withdrawn and skin tissues were excised from the low skin resistance points, non-acupoint, and non-meridian areas located on leg, arm, or trunk. The results showed that the skin NE concentration and (3)H-NE release in acupoints were significantly higher than those in non-acupoints and non-meridian controls. (3)H-NE releases in the acupoints were increased by intravenous infusion of 2-N,N-diethylamino-diazenolate-2-oxide, an NO donor, but lowered by N(G)-Propyl-L-arginine, an inhibitor of neuronal NO synthesis. NE turnover rates in the acupoints were lower in the NO donor treated group while the inhibitor of NO synthesis reversed the trend. In contrast, NE turnover rates were not altered by NO donor and inhibitor of NO synthesis in non-acupoint and non-meridian control tissues. This is the first evidence that NE turnover was consistently decreased in acupoints and enhanced NE synthesis/release in acupoints were facilitated by presence of an NO donor and inhibited by an inhibitor of NO synthesis. The data suggest that skin NE synthesis/release in acupoints/meridians is increased in skin acupoints, which is modulated by L-arginine-derived NO synthesis in sympathetic nervous system.

Acupuncture Points↗
PubMed2004

Diurnal patterns of cortisol and thyroid hormones in the Harbor seal (Phoca vitulina) during summer and winter seasons.

A leading hypothesis for the dramatic population decline of the Alaskan harbor seal over the last 2-3 decades have related environmental changes to a decrease in the quality or quantity of available prey. If harbor seals are experiencing some sort of nutritional stress, it is important to understand the physiological and endocrine mechanisms controlling metabolic homeostasis in this species. The purpose of this research project was to determine whether circadian patterns of cortisol and total and free thyroxine (T(4)) and triiodothyronine (T(3)) are present in the harbor seal during the summer and winter seasons, and identify how they might alter metabolic rate and maintenance of body reserves. This study was carried out at the Alaska SeaLife Center in Seward, Alaska in June 2000 and January 2001. Blood samples were obtained every 2-3 h over a 24-h period through in-dwelling catheters inserted the day before sampling. The presence of a diurnal rhythm was determined by comparing levels between ante meridian (12 am to noon) and post meridian (noon to 12 midnight) time periods. Mean daily cortisol concentrations were not significantly different between seasons, but cortisol displayed a circadian rhythm only during the summer. Mean concentrations of cortisol (51.5 ng/ml+/-20.3) in the summer hours of ante meridian differed significantly from levels in the hours of post meridian (28.5 ng/ml+/-17.4). Neither total and free T(4), nor T(3), displayed a diurnal rhythm in either season. However, tT(4), tT(3), and fT(3) levels were significantly higher in the winter than in the summer. There was no seasonal effect on fT(4) levels. The absence of a circadian rhythm of cortisol during the winter may have been a result of the limited amount of daylight as well as the continual need to produce metabolic heat as a by-product of gluconeogenesis. Higher levels of thyroid hormones in the winter indicate an adaptive mechanism to cope with the low temperatures of winter.

Aging↗
PubMed1995

Topographic determination of corneal asphericity and its lack of effect on the refractive outcome of radial keratotomy.

PURPOSE: The normal human cornea flattens peripherally. The amount of flattening, or asphericity, has traditionally been calculated from multiple keratometric measurements. We devised a mathematical technique for determining asphericity from computed corneal topography. We then determined whether asphericity affects the refractive outcome of radial keratotomy. METHODS: One eye each of 41 patients who underwent four- or eight-incision radial keratotomy and preoperative computed corneal topography was identified retrospectively and analyzed. The asphericity, P, of each cornea was calculated by fitting Baker's equation (y2 = 2r0x-Px2) to each meridian of the topographic map. For each patient, we calculated the difference between the refractive outcome in diopters for radial keratotomy and the prediction of a quadratic least-squares best-fit model involving optical zone size and age. RESULTS: Aspericity could be calculated from the topographic maps in all 41 patients and ranged from 0.33 to 1.28, with mean +/- S.D. of 0.82 +/- 0.21. Aphericity varied among the meridians of a cornea, with an average standard deviation among meridians of 0.17. No statistical correlation was found between calculated asphericity and refractive outcome. CONCLUSIONS: Corneal asphericity can be calculated from corneal topographic maps. Asphericity is not constant in the different meridians of a normal cornea. Corneal asphericity is not useful in predicting the refractive outcome of radial keratotomy.

Adult↗
PubMed1999

Stereopsis, cyclovergence and the backwards tilt of the vertical horopter.

It is generally recognized that the vertical horopter has a backwards tilt such that it passes through the fixation point and a point near the feet of the observer. The basis of the tilt has been attributed to either a shear in binocular retinal correspondence along the vertical meridian or the presence of cyclovergence eye movements. In an attempt to determine empirically the mechanisms underlying the tilt of the vertical horopter, retinal correspondence along the vertical meridian was investigated as a function of viewing distance. In addition, binocular measurements of torsional eye position were made in the same observers under similar viewing conditions. The vertical horopter was determined using two criteria. In the first instance, increment depth discrimination thresholds for both crossed and uncrossed disparities were measured as a function of retinal eccentricity along the vertical meridian, up to 5 degrees superiorly and inferiorly, and the horopter was defined by the region in space which had the lowest stereo-threshold. Secondly, subjective alignment of dichoptically presented nonius lines defined the horopter by identical visual directions. Both criteria were used to determine the horopter at 2 m while only the criterion of identical visual direction was used at the nearer distance of 50 cm. The vertical horopter showed a backwards tilt that decreased from an average of about 12 degrees at 2 m to 3 degrees at 50 cm, with some variability between observers. Torsional eye position did not change significantly between fixation distances. These results confirmed the geometric relation between the backwards tilt in the vertical horopter and fixation distance and support Helmholtz's original contention that the tilt is a consequence of a shear in retinal correspondence in the vertical meridian.

Convergence, Ocular↗
PubMed1997

Optic disc shape, corneal astigmatism, and amblyopia.

OBJECTIVE: The cornea and the optic disc form the anteroposterior opening of the sclera. This study evaluated whether an abnormal shape of the optic disc is associated with an abnormal configuration of the cornea measured as corneal astigmatism. DESIGN: The study design was a cross-sectional one. PARTICIPANTS: The study included 882 subjects (430 women, 452 men) with a mean age of 45.9 +/- 13.6 years (mean +/- standard deviation; range, 8-87 years) and a mean refractive error of -1.09 +/- 2.76 diopters (range, -21.0 diopters to +7.0 diopters). INTERVENTION: Corneal astigmatism was determined by keratometry, and the optic disc was analyzed morphometrically by planimetric evaluation of optic disc photographs. MAIN OUTCOME MEASURES: Corneal astigmatism, ratio of minimal-to-maximal disc diameter, and optic disc form factor were measured. RESULTS: The amount of corneal astigmatism was significantly (P < 0.001) correlated with an increasingly elongated optic disc shape. Corneal astigmatism was significantly (P < 0.01) higher in eyes with tilted discs. It was significantly (P = 0.006) smaller in eyes with an almost circular disc shape. Amblyopia was significantly (P < 0.05) associated with an elongated optic disc shape and high corneal astigmatism. The axis of corneal astigmatism was correlated with the orientation of the longest disc diameter. The optic disc was significantly (P < 0.05; chi-square test) more often horizontally oval in eyes with a steeper horizontal corneal meridian than in eyes with a steeper vertical corneal meridian. Correspondingly, the disc was significantly (P < 0.05) more often vertically oval in eyes with a steeper vertical corneal meridian than in eyes with a steeper horizontal corneal meridian. CONCLUSIONS: An abnormal optic disc shape is significantly correlated with corneal astigmatism. Especially in young children, if an abnormal optic disc shape is found on routine ophthalmoscopy, refractometry should be performed to rule out corneal astigmatism and to prevent amblyopia. The direction of the longest optic disc diameter can indicate the axis of corneal astigmatism.

Adolescent↗
PubMed1997

Treatment of hyperopic astigmatism.

PURPOSE: To analyze the results after laser-assisted in situ keratomileusis (LASIK) treatment for positive cylinder at the flattest meridian. SETTING: Instituto de la Visión, Buenos Aires, Argentina. METHODS: A prospective, nonrandomized study was conducted. Patients were divided into three groups: (1) simple hyperopic astigmatism (SHA); 15 eyes with a mean preoperative cylinder of +3.37 diopters (D) +/- 1.62 (SD); compound hyperopic astigmatism (CHA); 75 eyes with a mean preoperative cylinder of +3.34 +/- 1.39 D; (3) mixed astigmatism (MA); 73 eyes with a mean preoperative cylinder of +3.45 +/- 2.15 D. In all eyes, treatment of the cylinder was performed at the flattest meridian by LASIK using the Chiron-Technolas Keracor 116/117 laser. The following parameters were analyzed over time: uncorrected visual acuity; best corrected visual acuity; correction of the spherical equivalent and the cylinder; lines of visual acuity gained and lost. RESULTS: Six months after the procedure, refractive cylinder was reduced to +0.58 +/- 1.22 D in the SHA group, +0.12 +/- 1.23 D in the CHA group, and -0.11 +/- 1.28 D in the MA group. Uncorrected visual acuities were 20/20 or 20/25 in 66.7, 60.4, and 76.5% of the groups, respectively. CONCLUSIONS: Use of the LASIK technique with the Keracor laser to treat positive cylinder at the flattest meridian corrected simple and compound hyperopic astigmatism and mixed astigmatism with good predictability and safety. This treatment has not produced a hyperopic refractive change at the opposite meridian.

Adult↗
PubMed1997

Effect of incision location on preoperative oblique astigmatism after scleral tunnel incision.

PURPOSE: To evaluate the effect of incision location or clinically relevant preoperative oblique astigmatism. SETTING: Department of Ophthalmology, Virchow Medical Center, Humboldt-University, Berlin, Germany. METHODS: This prospective study included 68 patients who had phacoemulsification and posterior chamber lens implantation using a standardized 7.0 mm self-sealing trapezoidal scleral tunnel incision. Each patient was randomly assigned to one of three incision locations: Group A, conventional superior incision; Group B, temporal incision; Group C, oblique incision centered on the steeper meridian (modified BENT incision). Astigmatism analysis was performed by manual keratometry and corneal topography. RESULTS: A significant mean reduction in astigmatism of 0.58 diopter (D) (P < .01) was achieved in only the modified BENT incision group. Postoperatively, significant flattening of 0.27 D (P < .01) in the steeper meridian as well as steepening of 0.29 D (P < .01) in the flatter meridian occurred. No decrease in astigmatism was noted in the superior or temporal incision groups. Five months postoperatively, vector analysis showed that surgically induced astigmatism was significantly higher in the superior incision group (1.16 D +/- 0.44 [SD]) than in the temporal incision group (0.66 +/- 0.32 D) or modified BENT incision group (0.82 +/- 0.50 D). Corneal topographic analysis confirmed these results within +/- 0.3 D. CONCLUSIONS: Only the oblique incision centered on the steeper meridian (modified BENT incision) effectively and predictably reduced preoperative oblique astigmatism. In eyes with clinically relevant oblique astigmatism, we recommend using a modified BENT incision.

Aged↗
PubMed1997

Discrimination of the direction and speed of motion in depth of a monocularly visible target from binocular information alone.

Thresholds for discriminating a monocularly visible object's direction of motion in depth and speed of motion in depth were measured using only binocular cues. Observers could discriminate the direction of motion in depth while totally ignoring speed and discriminate the speed of motion in depth while totally ignoring direction. Direction discrimination thresholds were the same for motion in depth within the vertical and horizontal meridians, even though a cue to trajectory was available for motion within the horizontal meridian that is not available for motion within the vertical meridian. Speed discrimination thresholds also were the same for motion in depth within the vertical and horizontal meridians. For the 3 observers the lowest direction discrimination thresholds were 0.14 degree, 0.18 degree, and 0.22 degree (means of horizontal and vertical thresholds).

Depth Perception↗
PubMed2001

Emerging paradigms in mind-body medicine.

The emerging paradigms in medicine can be seen through mind-body interactions. Observations in many meditative traditions suggest a series of objective indicators of health beyond absence of disease. Several of the physical signs have been confirmed by research or are consistent with modern science. Further correlation with long term health outcome is needed. Integration of meditation with conventional therapy has enriched psychotherapy with parallels drawn between the Nine Step Qigong and Freudian developmental psychology. A unified theory of the chakra system and the meridian system widely used in traditional mind-body interventions and acupuncture is presented in terms of modern science based on the morphogenetic singularity theory. Acupuncture points originate from the organizing centers in morphogenesis. Meridians and chakras are related to the underdifferentiated, interconnected cellular network that regulates growth and physiology. This theory explains the distribution and nonspecific activation of organizing centers and acupuncture points; the high electric conductance of the meridian system; the polarity effect of electroacupuncture; the side-effect profile of acupuncture; and the ontogeny, phylogeny, and physiologic function of the meridian system and chakra system. It also successfully predicted several findings in conventional biomedical science. These advances have implications in many disciplines of medicine.

Breathing Exercises↗
PubMed1991

Quadrantic visual field defects. A hallmark of lesions in extrastriate (V2/V3) cortex.

We report 2 patients with homonymous quadrantic visual field defects. The first patient experienced scintillations in the left lower quadrant, leading to the discovery of an astrocytoma in the cuneus of the right occipital lobe. Postoperatively she had a left lower quadrantanopia that precisely respected the horizontal meridian. The second patient presented with a left lower quadrantanopia, sparing the central 10 degrees of vision that also respected the horizontal meridian. An astrocytoma was resected from the right upper peristriate cortex. We must explain how a lesion in extrastriate cortex produced a homonymous field defect with a sharp horizontal edge in these 2 patients. Areas V2 and V3 are each divided along the horizontal meridian into separate halves flanking striate cortex. Consequently, the upper and lower quadrants in extrastriate cortex are physically isolated on opposite sides of striate cortex. We propose that a lesion involving V2/V3 may be sufficient to create a visual field defect. Although the lesion may have irregular margins, if it crosses the representation of the horizontal meridian in extrastriate cortex, it will produce a quadrantic visual field defect with a sharp horizontal border because of the split layout of the upper and lower quadrants in V2/V3.

Adult↗
PubMed1981

On the conformity of soft lenses to the shape of the cornea.

The assumption that a properly fitted soft contact lens conforms to the shape of the cornea in the central region was tested by measuring the apparent radius of curvature of the back surface of various soft contact lenses on the eye, with a high illumination keratometer. Real radius of curvature was calculated by means of an appropriate formula. It was found that soft lenses conform closely to the corneal shape. The mean difference between the radius of the back surface of the lens and corneal radius of curvature was +0.015 mm in the horizontal meridian, and +0.023 mm in the vertical meridian. The lenses were slightly flatter than the cornea in each meridian. The difference in conformity between the horizontal and vertical meridians was not significant. Slight differences were found in the degree of conformity of the three soft contact lens designs studied. The thicker, lower water content lenses showed slightly less conformity.

Contact Lenses, Hydrophilic↗