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At least 919 records · Page 51Linked to original sources
PubMed1992

Regional variations in binocular summation across the visual field.

Binocular summation for a contrast detection task was measured as a function of eccentricity and target size along the horizontal and vertical meridians for ten young normal subjects. Binocular summation at the fovea was of the order of 1.4 for all target sizes, although there was some intersubject variation. Binocular summation was highest along the vertical meridian. With increasing eccentricity from the fovea, binocular summation for target size I (0.108 degrees projected diameter) decreased, remained relatively constant for target size III (0.431 degrees projected diameter) and increased with increasing eccentricity from the fovea for target size V (1.724 degrees projected diameter). For target sizes I and III, binocular summation was present only when interocular differences in sensitivity were under 5 dB, for target size V this relationship did not hold. Influences such as stimulation of corresponding retinal points and cortical representation are considered.

Adult↗
PubMed1992

Calculation and least-squares estimation of surface curvature and dioptric power from meridional measurements.

The calculation or estimation of dioptric power or surface curvature from meridional measurements is an important problem with applications in a number of areas. By phrasing the problem in terms of matrices and applying new results in the mathematics of matrices one is able to reformulate the problem into a standard form that is well known in mathematics and statistics. As a result the solution can be written down directly. The method copes with any number of measurements along any number of meridians, including repeated measurements along the same meridian, and is more general than methods previously proposed. It gives least-squares and best estimates of the true surface curvature or dioptric power. Being phrased in standard statistical terms the method lends itself readily to extension to related types of problems such as least-squares estimation under certain types of constraints. Matrix methods employed in this paper are likely to find wider application in optometry and the vision sciences.

Mathematics↗
PubMed1992

Early postkeratoplasty astigmatism following placement of anterior chamber lenses and transsclerally sutured posterior chamber lenses.

Intraocular pseudophakic correction during penetrating keratoplasty (PK) for aphakic or pseudophakic bullous keratopathy may be achieved either with anterior or posterior chamber lenses. Posterior chamber lenses can be fixed to the iris or sclera in eyes lacking adequate posterior capsular support. Post-PK astigmatism can delay early visual rehabilitation of the patient. We reviewed the last 15 patients at our institution who had undergone PK and anterior chamber lens placement for bullous keratopathy. These were compared to the last 15 patients who had undergone PK and transsclerally sutured posterior chamber lens placement. Patients who had placement of a flexible anterior chamber lens at time of PK had a mean astigmatism of 6.73 D at the last visit before any sutures were removed. There was no predominant axis of astigmatism or relationship of the axis of astigmatism to the meridian of lens placement. Patients with placement of a transsclerally sutured posterior chamber lens at time of PK had a mean astigmatism of 5.18 D at the last visit before any sutures were removed. Mean astigmatism was not significantly different (P greater than 0.05) from that seen with anterior chamber lens placement. In the majority of patients the axis of post-PK astigmatism was oriented perpendicular to the meridian of the transsclerally sutured posterior chamber lens.

Aged↗
PubMed2005

[Changes of the structure of neuronal connections in visual cortex of cats with experimentally induced bilateral strabismus].

The spatial distribution of neuronal connections in cortical area 17 in cats with bilateral convergent strabismus, surgically induced on postnatal days 10-14, was investigated. Single cortical columns of areas 17 and 18 were microiontophoretically injected with horseradish peroxidase and retrogradely labeled cells in both hemispheres were detected. The intrahemispheric connections in area 17 along the mediolateral direction (the projection of visual field horizontal meridian) were found to be either dilated or reduced. For most columns, the interhemispheric connections in this direction were increased, which may provide for more reliable unification of two visual hemifields. Moreover, the extension of intra- and interhemispheric connections in rostrocaudal direction (along the visual field vertical meridian projection) was detected in some cortical columns. Thus bilateral strabismus induced during the developmental critical period, modifies the structure of both of intra- and inter-hemispheric spatial neuronal connections of individual cortical columns in areas 17 and 18.

Animals↗
PubMedDate not supplied

[Asymmetry of the latent periods of saccades in human depending on visual space complicity].

Saccadic latencies of visually-guided saccades of 10 right-handed subjects with right-leading eyes were studied. Stimulation paradigm was spatially bidimentional, and stimuli were shown along horizontal and vertical meridians. Three traditional single step GAP - NO DELAY - OVERLAP temporal paradigms were used. In the first experiment, each paradigm was applied separately (simple visual space). In the second experiment, all the three paradigms were varied pseudo-random order and equiprobably, which complicated the time parameters of visual stimulation (complicated visual space). Asymmetry of visually-guided saccades along the vertical and horizontal meridians was revealed. The character of this asymmetry varied between subjects. MANOVA showed that the factor of visual space complicity (simple or complicated visual space) affected the latent period of saccades to a greater extent than the factor of stimulus lateralization (stimulus presentation in the left/right or upper/lower visual hemifields).

Adolescent↗
PubMed1991

Bioelectrical homeostasis as a component of acupuncture mechanism.

Low frequency electrical current and super-high frequency electromagnetic field were applied to acupuncture points of stomach meridian in dogs. The stimulation effect on Bioelectrical potentials of 5 acupuncture points of stomach, spleen, liver, kidney, small intestine meridians and non-acupuncture skin zones was studied in conditions of blocked autonomic ganglia or neuro-muscular junctions of the dog. The influence of ganglioblockading and myorelaxating drugs on Bioelectrical potentials of acupuncture points was also researched. The results are discussed from the neurohumoural and bioelectrical hypotheses points of view. The conclusion that both mechanisms of acupuncture supplement each other is drawn. The principle of bioelectrical homeostasis as a component of acupuncture mechanism is proposed. Bioelectrical homeostasis along with other kinds of homeostasis forms a system of first level homeostats which is united into second level homeostat by the autonomic nervous system.

Animals↗
PubMed1991

[Benign pathology of the facial bones].

Benign pathology of the facial bones is divided into three groups: congenital, infectious and neoplastic. The knowledge of segmentation of the face into meridians is important for understanding malformations. Panoramic X-rays remain their diagnostic value. CT is able to define the exact location and contents of the tumor. Nowadays, MRI, sometimes gives information concerning the exact contents of tumors. The face is divided into meridians numbered from 0 to 7 and from 8 to 14 counting from the middle part to the external auditory neatus. Infection from dental caries may spread to the maxilla and the mandible and sometimes into masticator spaces. It can be responsible for maxillary fungal sinusitis in tumor. The main problem is not exact diagnosis but the exact location and extent of the disease in order to allow large surgical removal.

Facial Bones↗
PubMed1991

[Effects of chronoacupuncture na ja fa on gastric acid secretion, plasma gastrin and prostaglandin E1 in patients with peptic ulcer].

Observations on gastric acid secretion, plasma gastrin and prostaglandin E1 in patients with peptic ulcer disease were made after giving acupuncture with Na Ja Fa. The relationship between the chosen points and their effects was also discussed so as to provide more evidence to evaluate and practice the traditional chronoacupuncture more accurately. The results of this experiment were: (1) The gastric acid output of patients with peptic ulcer disease was decreased, while the plasma gastrin and prostaglandin E1 were increased after puncturing with Na Ja Fa. This reveals that the decrease of acid output was not caused by the change of plasma gastrin, however the plasma prostaglandin E1 may be involved in this process. (2) By using points on Stomach and Spleen meridians, there was a better inhibiting effect in acid output than treating the points of other meridians. This showed that using chronoacupuncture should include choosing points according to differentiation and only by laying stress on the relative specialization of the actions of these points one could expect improvement in efficiency. (3) There were no obvious differences between the standard opening points and the group of points which changed to opening points by Dr Shan Yu Tang. This proves that these two groups of points do have some similar functions and are both effective for clinical use.

Acupuncture Therapy↗
PubMedDate not supplied

Relaxing incisions with compression sutures to reduce astigmatism after epikeratoplasty.

Relaxing incisions with compression sutures were performed in seven eyes with high astigmatism following epikeratoplasty for keratoconus and in one case of posttraumatic aphakia. Mean preoperative keratometric astigmatism was 7.64 +/- 2.51 diopters (range 5.50 D to 13.00 D) in the epikeratoplasties for keratoconus and about 10.00 D in the hyperopic epikeratoplasty. The surgical procedure consisted of a free-hand dissection perpendicular to the steeper meridian along the scar between the edge of the epikeratoplasty lenticule and the recipient cornea, with an additional incision into the recipient stroma to an approximate depth of 80%. Following the incisions, compression sutures were added 90 degrees away in the flatter meridian. After surgery, the net decrease in keratometric astigmatism was 6.50 D +/- 2.90 D (range 5.00 to 13.00 D) in the eyes with epikeratoplasty for keratoconus and 6.50 D in the eye with hyperopic epikeratoplasty. Uncorrected visual acuity improved in six eyes and remained unchanged in two eyes. Spectacle-corrected visual acuity improved in every eye and contact-lens-corrected visual acuity improved in seven eyes and was unchanged in one eye. This procedure, already employed for astigmatism correction after penetrating keratoplasty, was effective in decreasing astigmatism after epikeratoplasty.

Adult↗
PubMed1990

[Surgical correction of corneal astigmatism].

Corneal astigmatism can be treated optically or surgically. First, we try to manage the astigmatism with glasses or contact-lenses. If it cannot be managed successfully with optical devices, a surgical approach may be indicated. Corneal wedge resections and relaxing incisions can be effective. The wedge resection is the more difficult procedure with reasonably predictable results. In recent years corneal relaxing incision has gained popularity because it is a simple technique with fairly rapid visual rehabilitation. However, the correction result is quite unpredictable. We try to evaluate the factor that created the astigmatism. The steep and flat corneal meridian are identified with keratoscopy, and the correction is performed at the end of the corneal meridian causing the astigmatism. The technique and results are discussed.

Astigmatism↗
PubMed1990

[Radionuclide study of acupuncture points].

During recent years, upon investigation of the meridian which is an important part of the traditional concept in Chinese medicine, we have obtained several significant findings using radionuclide: 1. By subcutaneous injection (SC) of Tc-99m pertechnetate at acupuncture points K-3 and B-60, it was found that certain acupuncture points may be closely related to the venous drainage. 2. A new technique of radionuclide venography, namely SC-RNV of the lower limbs, was established through the above study. The SC-RNV subsequently proved to be clinically available in diagnosis of DVT and calf varicose veins. By SC injection of Tc-99m pertechnetate at various acupuncture points (APP) and nonacupuncture points (non-APP) it seemed that not every APP is closely related to venous drainage, and so is not the non-APP. As for the mechanism of SC-RNV, through SC injection of T1-201 chloride and Ga-67 citrate at K-3 respectively, it was found that the Na-K pumping system may play a major role in the drainage of soft tissue fluid from the APP into th venous flow. We now continue to investigate the meridian with radionuclide and hope to understand more clearly the physiological function of the APP, especially its relationship with the veins.

Acupuncture Points↗
PubMed1990

The visuotopic component of the multisensory map in the deep laminae of the cat superior colliculus.

A well-defined map of visual space is located in the deep laminae of the cat superior colliculus. The horizontal meridian is oriented rostral-caudal, while the vertical meridian is oriented perpendicular to it in the rostral third of the structure. This map represents the entire contralateral visual field and extends approximately 40 degrees into ipsilateral visual space. Although the deep-laminae visuotopy is similar to that found in the superficial laminae of the same structure, the topographic register among these maps is most secure rostrally but becomes increasingly poorer at more caudal and lateral locations. The combination of 2 features distinguish the deep-layer visual representation from that found in the superficial laminae and in geniculocortical systems: (1) the constituent visual receptive fields are very large (mean diameter, 66.9 degrees), and (2) the majority (greater than 70%) of the neurons composing it receive nonvisual inputs. Because the visual receptive fields of visual-multisensory neurons are significantly larger than those of neighboring neurons that respond only to visual stimuli, far more visual-multisensory neurons are activated by any given visual stimulus. These data, when coupled with those from previous studies, suggest that, from a functional perspective, deep-laminae visual neurons form one component of an integrated multisensory map, and that their topographic organization is essential for the normal dynamics of multisensory integration.

Animals↗
PubMed1990

[The results of simulating congenital pathology of the extraocular muscles].

The paper describes results after calculating the distribution of tensions in the cornea in case of anomalies in the action and insertion of oculomotor muscles. The calculation was made on the basis of theories of thin coats considering the gradient of corneal thickness. By the results of the calculation, the lines of equal tensions (isochroms) were built, the forms of which is well correlated with clinical results. The calculation has shown that the rounding of one of the angles of interference rhombus and its displacement towards the centre of the picture speak about either a functional deficiency of a muscle inserted into the eye ball in this place or about displacement of the point of its insertion from the limbus along the meridian of its action; displacement of one the angles of interference rhombus from the meridian speaks about displacement of the point of efforts exertion of the corresponding muscle into the same direction. The calculation made confirms correctness of our knowledge about the nature and properties of interference pictures observed on the cornea in a polarised light.

Biophysical Phenomena↗
PubMed1990

Bilateral altitudinal visual fields.

We describe two patients with absolute, complete, binocular inferior altitudinal hemianopias. These altitudinal visual-field defects (AVFDs) involved both nasal and adjacent temporal quadrants and respected the horizontal meridian. The reported conditions and locations in the visual system that cause "conventional" AVFDs and their bilateral occurrence are reviewed. Division of the visual system into altitudinal halves results from the topographic arrangement of nerve fibers and their blood supply in the retina, optic nerves, and visual cortex. Lesions at these locations resulting in AVFDs are usually due to vascular occlusion or may result from a penetrating missile injury to the superior occipital lobes. It is important to emphasize that the nerve fiber layer of the retina respects the horizontal meridian only in the nasal field, not in the temporal field; therefore incomplete AVFD is more common. Because of the anastomotic blood supply of the occipital pole, only AVFDs due to occipital infarcts spare fixation. Diagnosis of retinal branch artery occlusion or anterior ischemic optic neuropathy is aided by the presence of a unilateral AVFD along with ipsilateral funduscopic abnormalities and, in most bilateral examples, by its sequential temporal development. Bilateral occipital infarcts, as in our two cases, are characterized by sudden, simultaneous onset of AVFDs, an absence of retinal, retinovascular, or optic nerve abnormality and confirmation by computed tomographic scanning.

Aged↗
PubMed1990

A standard international acupuncture nomenclature: memorandum from a WHO meeting.

The WHO Scientific Group to Adopt a Standard International Acupuncture Nomenclature met in Geneva from 30 October to 3 November 1989. The main features of the recommended nomenclature are the use of the English translation of the name of each meridian and an alphanumeric code derived from the English names, and the use of the Chinese phonetic alphabet (Pinyin) names and the Han character names of the meridians and acupuncture points. This standard nomenclature will facilitate the teaching, research and clinical practice of acupuncture, as well as exchange of information globally.

Acupuncture Therapy↗
PubMedDate not supplied

A comparison of surgical keratometers.

Surgical keratometers were conceived as an aid that would help anterior segment surgeons minimize postoperative astigmatism, a major obstacle along the road to rapid visual rehabilitation. Two classes of surgical keratometers are commercially available at present. The first class of devices produces a keratoscopic image from which the surgeon must make a qualitative assessment of both the amount and location of astigmatism based upon distortion present in the keratoscopic image. The second class of devices quantitates corneal power at a chosen meridian and providing the surgeon with either an analogue or digital readout. Usually it is up to the surgeon to identify the meridian of greatest corneal power based on qualitative alterations of the keratoscopic image. These keratoscopes are based either on the optical principles of the von Helmholtz keratometer, or on nonparallel electronic image digitization. In this article we critically review commercially available surgical keratometers emphasizing their attributes and limitations.

Astigmatism↗
PubMed1989

A brief account of Far East medicine.

The analysis of the historical aspects of the development of the meridian system the curative points of which had been discovered in the course of centuries evidently shows the meridians to have been set up more as a methodological and didactic aid rather than as a result of exact research. Classical acupuncture then represents a therapeutic method in terms of Chinese philosophy it is based on, formulated and dependent on the integral idealistic thought of that time in which philosophy, medicine and other natural sciences constitute a closed system.

Acupuncture Points↗
PubMed1989

[Bipolar temperature controlled diathermy of the sclera for controlled refractive change of the cornea].

A bipolar scleral diathermy unit measuring tissue temperature beneath the electrodes was used in 27 autopsy eyes to induce corneal curvature changes in order to modify corneal refraction. The optimal coagulation temperature was found to be between 65 degrees and 70 degrees C. The refractive effect was influenced by the distance of the electrodes (1 mm, 2 mm, 3 mm), their location ("limbal distance") and their position in reference to the limbus ("radial", "parallel"). The highest corneal curvature changes were observed with diathermy applied directly at the limbus or 1 mm distance from the limbus. The corneal meridian corresponding to the treated sclera regularly became significantly steeper and the untreated 90 degrees meridian flatter. Limbus parallel diathermy administered directly at the limbus showed a 0.91 mm increase in the corneal curvature with a 2 mm distance or a 0.34 mm increase with a 3 mm distance of both electrodes. Placing the electrodes radially or parallel of the limbus revealed greatest changes in corneal refraction using diathermy directly at the limbus or 1 mm distant from the limbus. The refractive effect decreased as the distance from the limbus increased. Corneal astigmatism could be decreased and increased in a quasi-controlled manner. Over-lapping diathermy offered the potential of gradually changing the corneal power. Histological sections showed that scleral collagen had only a superficial coagulation effect. Scleral diathermy offers great advantages in comparison to corneal incisions for the therapy of corneal astigmatism. Further investigations are in progress.

Astigmatism↗