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At least 757 records · Page 42Linked to original sources
PubMed2003

Computerised calculation scheme for ocular magnification with the Zeiss telecentric fundus camera.

Littmann (1982) described a method to determine the magnification of the eye in order to relate the size of a retinal feature to its measured image size on a telecentric fundus camera film. This required information only about ametropia and corneal curvature. Several other methods have been reported since then which consider other biometric data to enhance the accuracy of this classical method. The purpose of this study is to describe a numerical calculation scheme to determine the magnification q of the eye in two cardinal meridians using paraxial raytracing. Our calculation scheme is based on ametropia, keratometry, as well as biometric data such as axial length, anterior chamber depth and thickness of the crystalline lens. It is described step-by-step in order (1) to determine the refractive powers of both surfaces of the crystalline lens, which are not directly measurable in vivo, (2) to derive the retinal image conjugate to a circular object using paraxial raytracing, (3) to fit an ellipse to the retinal image, (4) to determine the secondary principal points (Gaussian length) separately for both cardinal meridians and (5) to calculate the ocular magnification q. The power of the crystalline lens is estimated to compensate for the spherocylindrical refraction at the spectacle plane and the corneal refraction with an astigmatic component thus creating a sharp image focused at the retinal plane. The capabilities of this computing scheme are demonstrated with five clinical examples and are related to the respective values of the classical Littmann formula as well as to enhanced methods described by Bennett (1988), Bennett et al. (1994) and Garway-Heath et al. (1998).

Anterior Chamber↗
PubMed2001

How traditional Chinese medicine acupuncturists would diagnose and treat chronic low back pain: results of a survey of licensed acupuncturists in Washington State.

OBJECTIVES: This survey was undertaken to learn how Traditional Chinese Medicine acupuncturists' diagnose and treat patients with chronic low back pain in order to develop a standardized treatment for a clinical trial of that condition. DESIGN: We surveyed a randomly selected group of 56 acupuncturists in Washington State, USA about styles of acupuncture they used for treating chronic low back pain, diagnoses made, and key features of treatment for this condition. RESULTS: While substantial variability existed among practitioners, there was agreement on several broad features of treatment including: the use of local and distal acupuncture points (86% of practitioners), the use of acupuncture points on the meridians traversing the back (especially the UB meridian, 90%) the use of acupoints determined by palpation (82%), the importance of eliciting de qi (60%), and of providing up to eight treatments for achieving therapeutic results (79%). CONCLUSION: The use of practitioner surveys can enhance the systematic development of acupuncture treatment protocols and should be part of this process in future clinical trials of common conditions.

Acupuncture Points↗
PubMed2001

Is there a place for auricular therapy in the realm of nursing?

Several theories, such as the 'homuncular reflex theory' 'delta reflex theory', and 'meridian theory' point to the fact that the ear is related to all parts of the human body and internal organs. Being one of the approaches in traditional Chinese medicine, auricular therapy is a therapeutic method by which specific points on the auricle are punctured or pressed. Auricular therapy can activate meridians and collaterals, regulate the Qi and blood, help to achieve the balance between Yin and Yang status of internal organs, and is therefore suitable for treating many disorders of the body. Successful examples of previous studies using this therapy including insomnia, weight reduction, hypertension, treatment of addiction, and pain reduction. However, inconsistency in the treatment protocol among studies, or the use of combined therapies, makes it impossible to draw a strong causal relationship between this therapy and the treatment effect. More appropriate clinical trials are therefore necessary to understand in depth the therapeutic effect of auricular therapy. Ideally, these trials can take place in the context of nursing practice so as to explore the application of this therapy in the realm of nursing, and to enable nurses to make a more effective contribution to primary health care.

Acupuncture Points↗
PubMed1997

[Limbus-parallel keratotomies with compression sutures in treatment of high astigmatism after perforating keratoplasty: a vector analysis and topographic study].

BACKGROUND: Visual acuity following penetrating keratoplasty is frequently limited by excessive astigmatism which cannot be compensated for with spectacles or contact lenses. The purpose of the study was to determine the effects of arcuate keratotomies and compression sutures on the amount and regularity of corneal astigmatism and on the visual acuity. PATIENTS AND METHODS: Between June 1989 and August 1995, 56 eyes from 56 patients (30 women, 26 men, average age 53 +/- 16 years) with excessive post-penetrating keratoplasty astigmatism were treated with paired arcuate cuts and compression sutures 4.8 +/- 3.5 years after suture removal (45% keratoconus, 30% scars, 20% dystrophies). The incisions were made along the meridian of maximum dioptric power in a sector extending for 60 +/- 15 degrees (6 mm diameter). Incision depth was standardized at 450 microns. Compression sutures were placed 90 degrees away in the flat meridian. Eight patients required more than one procedure to obtain the desired effect. Best corrected visual acuity (VA), keratometric readings and topographic power maps were analyzed pre- and postoperatively. We categorized the topographic maps into six groups: from group 1 (regular) to group 6 (irregular). For description of the astigmatic change after surgery, the formulas by Naylor and Jaffe (vector-corrected astigmatism) were applied. RESULTS: The mean preoperative astigmatism was 10.8 +/- 3.1 (4.2 to 19.2) diopters (D). After a mean follow-up of 1.1 years, the mean net astigmatism was 5.8 +/- 3.2 (0 to 16) D. The mean preoperative visual acuity (VA) was 0.38 +/- 0.31 (from 0.03 to 1.0). At the end of follow-up, the mean VA was 0.43 +/- 0.25. Non-refractive reasons for poor visual acuity included amblyopia (n = 5), macular degeneration (n = 4), glaucoma (n = 4), cataract (n = 2), and others (n = 5). Twenty-seven percent of the preoperative topographic maps were categorized into groups 1 and 2 and only 10% into groups 5 and 6. At the end of the follow-up, none of the 53 available topographic maps was categorized into group 1, 7.5% into group 2 and 30% into groups 5 and 6. The mean astigmatic change (vector-corrected astigmatism) was 12.3 +/- 5.2 (1.0 to 29.8) D with a turn of the axes ranging from -39 to 44 degrees. CONCLUSIONS: Arcuate incisions with compression sutures are easily performed and hold a low complication rate in comparison with other refractive operations. Definition of successful surgery is even broader when a significant reduction of astigmatism that usually allows the use of spectacles or contact lenses is considered. A disadvantage is that each particular case is unpredictable because of the tendency of the topography to irregularity and possible regression of the effect.

Adult↗
PubMed1992

[Correction of astigmatism after penetrating keratoplasty].

Nine patients had a surgical correction of high astigmatism following perforating keratoplasty. In seven of them the reason for the perforating keratoplasty was keratoconus, in two of them Fuchs' endothelial dystrophy. The correction was performed in the seven 31-69 yrs old keratoconus patients 4-19 years (median 10 yrs) after the transplant, in the patients with Fuchs' dystrophy 13 month and 1 year following corneal transplant. In eight cases two circular shaped relaxing incisions of 60 degrees were performed in the steeper meridian, seven times combined with sutures in the opposite meridian. Once a wedge resection was performed. The astigmatism before correcting surgery was 8-19 dpt (median 13 dpt), 3-24 month (median 11 month) 1.75-13 dpt (median 8 dpt). The reduction of astigmatism was 3-10 dpt (median 8 dpt). In 5 of 9 patients the astigmatism could be corrected by spectacles, in two more patients no spectacles were prescribed because of cataract. After this series of astigmatic correction we think that incisions without sutures are superior. This method could replace rekeratoplsty in the future.

Adult↗
PubMed1982

[Topography of early glaucomatous visual field defects in computerized perimetry].

A total of 301 visual fields of 215 glaucoma patients exhibiting early glaucomatous field loss up to Stage II according to Aulhorn were investigated to determine the frequency distribution of absolute and relative defects at the 73 test points of Program 31 of the Octopus computer perimeter. The following results were obtained: (1) The frequency of absolute and relative defects was higher in the upper half of the visual field; (2) The frequency of both absolute and relative defects increased from 6 to 30 degrees eccentricity in the upper visual field, predominantly in the upper nasal quadrant, whereas in the temporal lower quadrant there were less absolute defects but equally frequent relative defects; (3) Defects in the nasal quadrant and above the horizontal meridian are most frequent (between 18 and 30 degrees absolute, between 12 and 30 degrees relative), while temporally of the blind spot and below the horizontal meridian they are quite rare; (4) In the upper half of the field, defects are closer to the fixation point and blind spot; the area between blind spot and macula largely free of defects. --In 71 eyes of 69 patients a similar frequency distribution was found with the Competer computer perimeter (test field 15-20 degrees eccentricity) giving good correlation with the Octopus results. --In 301 eyes of 215 patients with early glaucomatous defects the four test points in the region of the blind spot were evaluated and compared with the results of 121 eyes of 71 patients with ocular hypertension and no field changes. It appears highly probable that an increase in the size of the blind spot is associated with the incidence of field defects. --The distribution of early glaucomatous field defects in 214 eyes revealed a combination of paracentral scotomata with peripheral defects in 75.2%, exclusively peripheral scotomata in 19.6% and exclusively paracentral scotomata in 5.1%. The significance of the results with regard to the pathophysiology of glaucomatous visual field loss is discussed.

Computers↗
PubMed1982

The role of the vertical dimension in stereoscopic vision.

It is shown how the full three-dimensional structure of a scene may in principle be computed from a correlated pair of retinal images, when all that is known about the orientations of the two eyes is that the planes of their horizontal meridians accurately coincide. The vertical dimension plays a crucial role in the theory; visible points which lie on the horizontal meridian supply no information about the angle of convergence or the direction of gaze. (i) If the scene contains three or more nonmeridional points, not all lying in a vertical plane, then their positions in space are fully determined by the horizontal and vertical coordinates of their images on the two retinas. (ii) If just two nonmeridional points are visible, or more than two, lying in a vertical plane, then their retinal images admit, in general, just two distinct three-dimensional interpretations. One of these is usually unrealistic; but a choice between them may be perceptually difficult if the vertical plane containing the points is nearly perpendicular to the interocular axis. These results suggest that vertical disparities may play an important role in the binocular perception of absolute depth. Elsewhere (Mayhew, this issue) this suggestion is found to provide a quantitative explanation of Ogle's 'induced effect'.

Depth Perception↗
PubMed1983

Factors influencing the apparent rotation of a line on radially transformed backgrounds.

The expansion and contraction of a display consisting of a stationary grating with a superimposed inclined line leads to the apparent rotation of the line. This phenomenon has been investigated in six experiments with the use of a television system with a motorized zoom lens to effect such transformations. The maximum apparent line rotation occurs with the line at 45 degrees to the grating. In experiment 1 a greater magnitude of apparent rotation was found with a vertical grating and an oblique line than vice versa. Zoom-out (contraction) also produced greater rotation than zoom-in (expansion). The orientation anisotropy was not dependent upon the orientation of the display to the retinal meridian (experiment 2): the extent of apparent line rotation was approximately the same with a vertical grating when the head was upright or tilted so that the retinal meridian was at 45 degrees. At a constant rate of zooming, a zoom duration of 2 s produced a larger apparent line rotation than one of 1 s, but it was not influenced by the initial angular subtense of the superimposed line (experiment 3). Neither the spatial frequency of the grating nor the width of the line affected the apparent rotation (experiments 4, 5, and 6). Experiment 5 compared the apparent rotation when the display was zoomed (i) with a fixed surround and (ii) with a surround that also expanded during zooming. The magnitude of rotation in the latter condition was reduced to about 25% of that with a fixed surround. The results are discussed in terms of the discrepancy between the perceived transformations of the background grating and the superimposed line.

Discrimination Learning↗
PubMed1995

Visual processing of the motion of an object in three dimensions for a stationary or a moving observer.

A rate of change of relatively disparity is a sufficient binocular stimulus for the perception of motion in depth. For motion within the meridian that contains the eyes, disparity change associated with approaching motion is processed through four channels, each tuned to a different direction of motion in depth. Directional discrimination is most acute but detection sensitivity falls to a minimum for a trajectory passing approximately midway between the eyes. This can be explained if discrimination depends on the relatively of the four channels. Two binocular retinal-image correlates of the direction of the motion of an object in depth are the ratio between the velocities of the retinal images of the object in the left and right eyes [(d phi/dt)R/(d phi/dt)L], and the ratio between the translational velocity of the binocularly fused images and the rates of change of disparity [(d phi/dt)/(d gamma/dt)]. Directional discrimination is possible by using the second cue alone. An isotropic rate of expansion of the retinal image is a sufficient monocular stimulus for the perception of motion in depth. There is no evidence that expansion is processed through channels tuned to the direction of motion in depth. Two monocular correlates of the direction of the motion of an object in depth are the ratio between the translational velocity and the rate of expansion of the retinal image of the object [(d phi/dt)/(d theta/dt)], and the ratio between the velocities of opposite edges of the retinal image [(d alpha 1/dt)/(d alpha 2/dt)]. Subjects are able monocularly to discriminate the direction of motion in depth with high acuity (better than 0.1 deg threshold) in the vertical, horizontal, or oblique meridians, even when the direction and the speed of translational motion are removed as cues. Visual discrimination of time to contact with an approaching object can be disconfounded from discrimination of its rate of expansion and vice versa with a threshold separation ratio of as much as 100:1.

Cues↗
PubMed1995

Visual factors affecting the rod-and-frame illusion: role of gap size and frame components.

In two studies the effect of the distance between the tip of the rod and the frame sides (gap) in the rod-and-frame (RF) illusion was examined and the effect of a full-square condition was compared with that of two different frame amputations. In both studies, there were more rod-setting errors in the direction of the tilt of the inducing figure with a small gap than with a large one. These findings are consistent with the idea that in the case of small gap size local interactions contribute to determining the RF illusion. The actual length of the rod was varied in order to keep the gap constant across different frame tilts; therefore these findings cannot be due to the co-variation between gap size and frame tilt which is typical of standard apparatuses. The effect of frame amputations was compared to the full-square condition. According to Wenderoth and Beh, amputations that maintain the two orthogonal contours of the square produce the typical angular function of the RF illusion. This prediction was confirmed in both studies. However, results indicate that the full square has a stronger illusory effect in the case of a small degree of tilt of the inducing stimulus, irrespective of gap size. It is suggested that this 'square superiority' effect is related to global, not local, mechanisms. To pursue Wenderoth and Beh's observations, amputations close to the vertical meridian were used in one experiment and those close to the horizontal meridian in the second experiment. Contrary to predictions, these conditions produced overlapping results.

Adult↗
PubMed2002

Optical imaging reveals retinotopic organization of dorsal V3 in New World owl monkeys.

Optical imaging of intrinsic responses to visual stimuli in extrastriate cortex of owl monkeys provided evidence for the dorsal half of the third visual area, V3. Visual stimuli were used to selectively activate locations in dorsolateral V2 and the rostrally adjoining presumptive V3. Consistent with the proposed retinotopies of dorsal V2 and dorsal V3, small bars of drifting gratings along the horizontal meridian of the contralateral hemifield activated cortex along the V2V3 border, whereas such stimuli along the vertical meridian activated cortex along the rostral border of V3. Stimuli in limited locations in the lower visual quadrant revealed mirror reversals of retinotopy in dorsal V2 and V3, whereas stimuli in the upper visual quadrant failed to activate either region. Brain sections processed for cytochrome oxidase from the same cases provided architectonic borders of V2 that matched those indicated by the optical imaging. The results support the concept that a narrow dorsal V3 exists in monkeys. V3d borders dorsal V2 and contains a smaller, mirror-image representation of the lower visual quadrant.

Action Potentials↗
PubMed2001

Reduction of astigmatism after infancy in children who did and did not wear glasses and have strabismus.

The purpose of this study was to record and explain the changes in astigmatism as normal and strabismic infants grew. Two-hundred-and-eighty-nine hypermetropic infants were randomly allocated to wear glasses from the age of six months. Changes in astigmatism and in hypermetropia of the horizontal and vertical meridia were compared in those who did and did not wear glasses and have strabismus. Mean astigmatism decreased significantly (p < 0.001) in both eyes of normal and strabismic children, but the 'last' astigmatism was significantly (p < 0.001) larger in both eyes of those who had strabismus. There was a similar progressive decrease of hypermetropia in both meridia of both eyes within each diagnostic group, but with the exception of the vertical meridian of the non-fixating eyes (in which the difference approached statistical significance), this was significantly (p < 0.01) larger in the normal children. The consistent wear of glasses was not associated with change in both meridia of both eyes in the normal children (p < 0.005), but had no significant effect on the changes in astigmatism. Since the changes in the two meridia were proportional to the starting level, hypermetropia decreased more in the meridian which was, initially, the more hypermetropic one, and the difference between them, i.e. astigmatism, tended to disappear whether or not the child eventually had strabismus.

Astigmatism↗
PubMed2001

The dynamics of filamentous structures in the apical band, oral crescent, fission line and the postoral meridional filament in Tetrahymena thermophila revealed by monoclonal antibody 12G9.

The ciliate Tetrahymena thermophila possesses a multitude of cytoskeletal structures whose differentiation is related to the basal bodies - the main mediators of the cortical pattern. This investigation deals with immunolocalization using light and electron microscopy of filaments labeled by the monoclonal antibody 12G9, which in other ciliates identifies filaments involved in transmission of cellular polarities and marks cell meridians with the highest morphogenetic potential. In Tetrahymena interphase cells, mAb 12G9 localizes to the sites of basal bodies and to the striated ciliary rootlets, to the apical band of filaments and to the fine fibrillar oral crescent. We followed the sequence of development of these structures during divisional morphogenesis. The labeling of the maternal oral crescent disappears in pre-metaphase cells and reappears during anaphase, concomitantly with differentiation of the new structure in the posterior daughter cell. In the posterior daughter cell, the new apical band originates as small clusters of filaments located at the base of the anterior basal bodies of the apical basal body couplets during early anaphase. The differentiation of the band is completed in the final stages of cytokinesis and in the young post-dividing cell. The maternal band is reorganized earlier, simultaneously with the oral structure. The mAb 12G9 identifies two transient structures present only in dividing cells. One is a medial structure demarcating the two daughter cells during metaphase and anaphase, and defining the new anterior border of the posterior daughter cell. The other is a post-oral meridional filament marking the stomatogenic meridian in postmetaphase cells. Comparative analysis of immunolocalization of transient filaments labeled with mAb12G9 in Tetrahymena and other ciliates indicates that this antibody identifies a protein bound to filamentous structures, which might play a role in relying polarities of cortical domains and could be a part of a mechanism which governs the positioning of cortical organelles in ciliates.

Actin Cytoskeleton↗
PubMed1980

The effects of retinal eccentricity and orientation on perceived length.

An experiment was performed to examine the effects of line orientation and retinal locus on the perceived length of a single line. Thirty-five male and female undergraduate volunteers each monocularly judged the length of five test lines presented in two orientations (horizontal and vertical) at five different retinal loci. Displacement of horizontal lines from the fovea on either the horizontal or vertical meridian produced decreases in perceived size. The perceived length of vertical lines, however, decreased only with displacements on the vertical meridian.

Humans↗
PubMed1984

Information processing in near peripheral vision.

The present study required that Ss name briefly exposed single lower-case letters that were presented at a total of 24 locations (8 meridians X 3 retinal eccentricities, 0.5 degrees, 2.75 degrees, and 5.0 degrees from a central fixation point, 0 degrees). One group of 12 Ss received a set size (load) of 2 letters, and another group of 12 Ss received a set size (load) of 24 letters. Ss given the larger load were significantly less accurate and significantly slower (longer vocal latencies) in naming the letters. In addition, significant main effects of retinal eccentricity and meridian were found. Ss performed more poorly as the stimuli were presented more eccentrically. Also, performance tended to be somewhat poorer above and below the fixation point than it did left or right of fixation. There was also some tendency toward a right visual field superiority. Unlike an earlier study, there was little evidence in favor of a "tunnel vision" interpretation, which would have required an interaction of load X retinal eccentricity. Possible reasons for the different results from the two studies are discussed in terms of a levels-of-processing interpretation.

Cognition↗
PubMed1999

Further studies on fecal parasites in antiquity.

This is a continuation study of the survival of antigenic material over the centuries using mummified human remains from the Andean area of South America. The fluorescent antibody kit from Meridian Diagnostics (Cincinnati, OH) was used to identify some Cryptosporidium species and Giardia species found in feces from the intestines of mummies 500 to 3,000 years old. The specimens that were positive by direct visualization using fluorescent antibody were then tested with an enzyme-linked immunosorbent assay reaction using a Meridian kit just released on the market. Since all of the feces used were formed, it would seem that the organisms found were from carriers rather than active cases of disease. Similar fecal specimens were shown to harbor antigens from Helicobacter pylori almost 3,000 years old.

Animals↗
PubMedDate not supplied

Organization of the second visual area in the megachiropteran bat Pteropus.

The organization of peristriate cortex was studied in nine flying foxes (genus Pteropus). Based on receptive field mapping and architectonic data, we report on the organization of the second visual area (V2). V2 forms a continuous belt 2-4 mm wide bordering V1 anteriorly. In each hemisphere, V2 contains a precisely organized representation of the entire contralateral visual field. The vertical meridian of the visual field (VM), and a short strip of the ipsilateral hemifield are represented at the posterior border of V2, with V1. The area centralis is represented approximately at the center of the posterior border of V2. At each mediolateral level, progressively more peripheral portions of the visual field are represented as V2 is crossed from posterior to anterior. The representation of the upper quadrant is continuous, and confined to the lateral half of V2. In contrast, the representation of the lower quadrant is split along a line running from the temporal edge of the field of vision to the optic disk. As a result of this arrangement, the portions of the lower quadrant close to the VM are represented medially, and those away from the VM laterally in V2. The entire representation of the horizontal meridian is located in lateral V2, and is not split between medial and lateral V2 as in primates. The linear cortical magnification factor (CMF) decays by a factor of 3-5 from the central to the peripheral representation. The CMF is anisotropic, and equal distances in the visual field are magnified twice as much parallel to the V1/V2 border than perpendicular to this border. Moreover, points in the lower quadrant are magnified relative to symmetrical points in the upper quadrant. V2 is histologically distinct from all surrounding areas in both cytochrome oxidase- and Nissl-stained sections. These results suggest that V2 is an homologous area common to all archontans, and imply that much of the variability reported among mammals may be due to technical factors, rather than true species differences.

Animals↗
PubMedDate not supplied

Retinotopic organization of human visual cortex: departures from the classical model.

Retinotopic mapping strategies similar to those used for invasive electrophysiological studies to identify multiple visual areas in monkeys have been adapted for noninvasive studies in humans, using magnetic recordings of brain activity in conjunction with anatomical magnetic resonance imaging. The retinotopic organization of the primary visual area (V1) in the left hemisphere of human subjects was examined by presenting a small patterned stimuli near the vertical and horizontal meridians in the lower right visual field. In contrast with the classical model of V1 retinotopy, our results suggest that the representation of the horizontal meridian does not necessarily correspond in a one-to-one manner with the base of the calcarine fissure and that some lower field stimuli can activate regions in the lower bank of the fissure. The results also indicate significant individual variability in the details of how V1 maps around the calcarine fissure.

Brain Mapping↗