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PubMed1982

The afferent and efferent callosal connections of retinotopically defined areas in cat cortex.

We compared the callosal afferent and efferent connections of different retinotopic loci within a given visual cortical area as well as the connectivity patterns among similar retinotopic loci in different visual areas. Small injections (75 nl) of a mixture of horseradish peroxidase and [3H]leucine were made through a recording pipette at injection sites identified by retinotopic mapping. A small locus of cortex within a callosally connected region had precise reciprocal connections with the homotopic locus in the contralateral hemisphere. This small locus also was callosally connected with a variable number of heterotopic loci. Both reciprocal and nonreciprocal heterotopic callosal connections were found. Homotopic and heterotopic connections appeared to have a high degree of retinotopic fidelity. Precisely homotopic connections were present not only between locations on the vertical meridian representations at the left and right area 17/18 borders but also, for example, between mirror-symmetrical points on the peripheral horizontal meridian representation in the left and right posteromedial lateral suprasylvian areas. In several experiments, we found that both callosal neurons and terminals in the homotopic cortex were grouped into two to three distinct clusters ranging from 600 to 900 micrometers in width. Callosal neurons with homotopic connections were primarily pyramidal cells in lower layer III and upper layer IV. Outside of areas 17 and 18, there was a significant number of pyramidal and fusiform-shaped callosal neurons in layers V and VI. The majority of callosal terminals were located in layers II, III, and IV.

Afferent Pathways↗
PubMed1984

Experimental modification of the corneal curvature by means of scleral surgery.

Most surgical procedures for correcting astigmatism are done on the cornea. The present article shows the modification of the corneal curvature by scleral surgery. The experiments were conducted on rabbit eyes. The most spherical eyes were chosen according to the keratometric measurements. A geometrical analysis of the astigmatism shows that beginning with an ellipse (image of an astigmatic eye in the corneascope), by modifying the main radii of the ellipse, while the perimeter is maintained constant a perfect circle is thus obtained. This analysis enables us to calculate the amount of sclera surgery required to obtain a given correction for a given degree of astigmatism. Four scleral procedures were investigated: folds, resections, imbrications, and sclerotomies; the results show that the first three procedures steepen the meridian where the surgery is performed while flattening simultaneously the ortogonal meridian. The main advantages of scleral surgery vs corneal surgery for correction of astigmatism are: (a) the cornea remains untouched, (b) the surgical area will be protected by the conjunctiva, (c) the stitches are left permanently, and (d) larger astigmatic errors can so be corrected.

Animals↗
PubMed1984

Visuotopic organization of the prelunate gyrus in rhesus monkey.

We have examined topographic organization of the prelunate gyrus and adjacent cortex buried in the lunate and superior temporal sulci. We recorded from cortex of awake rhesus monkeys performing a fixation task. Multiunit receptive fields were mapped with small, stationary spots of light to determine borders and points of strongest driving or "activity centers" of the fields. We found evidence for several distinct subdivisions of this cortex. A representation of the vertical meridian runs across the gyrus, and two crude topographic representations of the central 30 degrees of the lower quadrant, the posteromedial and anterolateral areas (area PM and area AL), share this representation of the meridian. Area AL extends from the prelunate gyrus into the posterior bank of the superior temporal sulcus; it is separated from the MT area by a narrow strip of cortex. Area PM occupies part of the prelunate gyrus and extends into the anterior bank of the lunate sulcus. Receptive field size in both AL and PM is an increasing function of eccentricity and is similar for the two areas. Medial to areas PM and AL on the prelunate gyrus is another cortical region with qualitatively different topographic organization.

Animals↗
PubMed1983

A new eikonometer: the multimeridional apparent frontoparallel plane.

A new method for diagnosing and measuring aniseikonia is described. It is based on apparent frontoparallel plane (AFPP) settings when rod stimuli are presented in 45 and 135 degrees meridians as well as in the vertical meridian. The oblique presentation of the stimulus introduces a new approach to the study of aniseikonia. To explain the results obtained, new theoretical concepts have been presented. Clinically, the method is distinguished by its ease of application to nearly all patients with functional binocular vision.

Aniseikonia↗
PubMedDate not supplied

Inverse arcuate incision: a new approach to the correction of astigmatism.

Standard concentric arcuate transverse corneal relaxing incisions flatten the meridian incised and steepen the meridian 90 degrees away, a phenomenon designated "coupling". We have demonstrated a new method of reducing the steep corneal curvature without inducing coupling, by utilizing both transverse and radial components of an inverse arcuate incision. This technique has been found useful in cases of myopic astigmatism because it reduces the myopic spherical equivalent, which is left unchanged by standard arcuate incisions, without having to place radial incisions.

Aged↗
PubMed1995

[2 years corneal small-incision surgery. Results and indications].

Small-incision surgery has contributed considerably to accelerated wound healing and minimization of surgically induced astigmatism. A variation of this surgical technique is sutureless cornea small-incision surgery with preparation of a corneal tunnel of 4.5 mm or less. To date, 195 patients have been operated on with this technique. In 130 cases the incision was made in the upper temporal area, in 65 cases laterally. Visual outcome and development of induced astigmatism over a period of 2 years were compared with the results achieved with corneoscleral small-incision surgery. Four weeks postoperatively, the vision in all three groups was > 0.5 in 67% of the patients. Also in the further course no significant changes were found. Regarding the average astigmatism, more severe fluctuations during the whole follow-up period and approximately 0.4 D higher values were observed with clear corneal incision via an oblique meridian at the same initial value. After 2 years, the value found in this group was 1.5 +/- 0.7 D. The development of surgically induced astigmatism, determined according to Jaffe and Clayman, indicates the same relationship. Following clear corneal incision in the upper temporal area, the value decreased within 1 year postoperatively to an average of 0.85 +/- 0.55 D, followed by an increase after 2 years to 1.26 +/- 0.44 D, in contrast to a temporal or corneoscleral approach, where no severe fluctuations were found. Based on our experience, we only apply clear corneal incisions via the oblique or vertical meridian when try to correct preexisting astigmatism. Corneoscleral small-incision surgery remains our standard operation technique. If corneoscleral tunneling is not possible or is unfavorable, a clear corneal incision is placed laterally.

Aged↗
PubMed1994

[Observation on cunkou pulse picture, sphygomogram and forearm rheohemogram of acute stroke patients].

Observation of Cunkou pulse picture, main wave of sphymogram (MW) and foreman rheohemogram and blood pressure (BP) were made on 41 acute stroke patients divide into two groups according to Syndrome Differentiation of TCM; including those involved in viscera and in meridian. The difference between these two groups were significant. The MW, the forearm blood volume (FBV) and BP were all significantly higher in those involved in viscera than that of in meridian. In the different phases of disease course, the MW, FBV and BP changed gradually. During recovery, the MW, FBV and BP were lowered gradually, and finally it remained stable.

Adult↗
PubMed1994

Spatial distribution of the inhibition elicited by the offset of a visual cue on manual reaction time to a visual target.

Simple reaction time (RT) to a peripheral visual target (S2) is shortened when a non-informative cue (S1) is flashed at the S2 location 100-150 ms before target onset (early facilitation). Afterwards, RTs to targets appearing at the S1 location are lengthened (inhibition of return). In the present investigation we studied the spatial distribution of the inhibition elicited by the offset of S1. Twelve subjects were asked not to respond to S1 which appeared on a horizontal meridian located 5.5 degrees above the fixation point (FP), but to respond, by pressing a key, to a target (S2) occurring at 5.5 degrees to the left or to the right. S1 could appear at one of 9 locations along this meridian (5.5, 3.5, 1.5, and 0.5 degrees to the left, 0.0 and 0.5, 1.5, 3.5, and 5.5 degrees to the right) and S2 occurred only at the most eccentric positions. Each trial began with the presentation of FP. Five-hundred ms later, S1 appeared and remained on for 700 ms. One hundred or 800 ms after S1 offset, S2 appeared in the same or in the opposite hemifield. We found that the offset of S1 elicits an inhibition (OFF-inhibition) which has the following features: a) it is maximal at cue's position; b) it spreads to other positions in the cued hemifield, and c) it decreases when the time interval between S1 offset and S2 onset increases from 100 to 800 ms.

Adult↗
PubMed1994

The changes of ocular axial length and corneal curvatures after scleral buckling for retinal detachment.

As myopia plays an important role in the pathogenesis of retinal detachment, alterations of refractive components after scleral buckling procedures for retinal detachment may be an important factor for retinal redetachment. To find out the refractive change following retinal detachment surgery, we prospectively followed up the alterations of corneal curvature, and axial components (axial length, anterior chamber depth, lens thickness, and vitreous length) of 44 eyes of rhegmatogenous retinal detachment before and after operations. The procedures consisted of encircling scleral buckling (12 eyes) and segmental scleral buckling (32 eyes). All patients were followed for 6 months postoperatively. The corneal curvatures were measured with a keratometer, the axial length and axial components were measured with an A-scan ultrasonography. The methods and materials used in operation were recorded in detail to correlate with the refractive changes. The corneal curvature showed a trend to flatten early after operation (the 1st week), and gradually reversed to steepening. But, the difference was statistically significant only at the K2 (vertical meridian) in the 1st postoperative week and the K1 (horizontal meridian) in the 4th postoperative week. Lengthening of eyeballs were noted in the encircling group (12 eyes), but only the elongation in the 1st postoperative week was statistically significant. While in segmental buckling group, the axial length of the eyeballs was transiently shortened. The shortening was significant in the 2nd, 4th, and 6th week after operation. The reduction of eyeball's axial length was related to the shortening of vitreous length and shallowing of anterior chamber.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMedDate not supplied

Shape and radius of posterior corneal surface.

BACKGROUND: The posterior corneal surface is often ignored in predictive models concerned with refractive surgery. In previous studies, the radius of this surface has been measured in a variety of ways, primarily over a large chord diameter of the surface, with the common assumption that the surface is spherical. The asphericity of this surface has not been adequately addressed in the past. METHODS: An algorithm is derived for the calculation of posterior corneal surface apical radius and using characteristics of the anterior corneal surface and topographic corneal thickness variation. Anterior corneal asphericity was measured using a commercially available photoelectric keratoscope. Using a marked soft contact lens, a simple method of locating noncentral corneal sites is described as an aid to ultrasonic pachometry. RESULTS: In a group of 20 normal subjects ranging in age from 19 to 23 years, the average posterior corneal surface apical radius and asphericity (p) was 5.80 mm (SD = +/- 0.42) and 0.64 (SD = 0.37) for the vertical meridian, and 5.82 mm (SD = +/- 0.40) and 0.52 (SD = 0.30) for the horizontal meridian. Average central corneal thickness was 533 mu (SD = +/- 19). CONCLUSIONS: The average asphericity values are below 1, hence the posterior corneal surface is described as a flattening ellipse. The rate of flattening of this surface is greater than the rate of flattening along the averaged anterior corneal surface.

Adult↗
PubMed1995

Visual field damage proximal to fixation in normal- and high-tension glaucoma eyes.

To compare in more detail the central visual field damage in normal-tension glaucoma (NTG) and high-tension glaucoma (HTG) eyes, a pointwise inner-group comparison of the data obtained with the Humphrey 10-2 was carried out in 68 NTG cases with maximum intraocular pressure (IOP) of < or = 21 mmHg and 62 HTG cases with maximum IOP of > or = 25 mmHg. All eyes had the usual field defects, with a mean deviation of > or = -15 dB (MD, STATPAC). Age, refraction and MD were matched between the two groups. Total deviation (TD, STATPAC), the difference between the measured threshold and the age-corrected normal reference at each test point of the 10-2 program, was used for pointwise inter-group comparisons. The data were analyzed with Wilcoxon rank-sum test and logistic discriminant analysis. The latter method was also applied to the data of the 30-2 program to confirm the results obtained with the 10-2 program. The comparisons using the different methods and programs gave consistent results. For a given amount of overall visual field damage in the two types of glaucoma, a superior arcuate area extending down to the horizontal meridian just nasal to the fixation point was significantly more depressed and an area inferior to the horizontal meridian and inferior temporal to the fixation point significantly less depressed in NTG eyes. HTG eyes were significantly more diffusely damaged in the central 10-degree visual field. NTG and HTG may have unique patterns of central visual field damage. These differences may implications in following NTG patients and studying the pathogenesis of this glaucoma.

Fixation, Ocular↗
PubMed1996

Changes in corneal radius and thickness in response to extended wear of rigid gas permeable contact lenses.

PURPOSE: In this study we assessed patients' clinical tolerance to extended wear of Hoya Hard EX contact lenses, which have a Dk of 125, and determined resulting changes in corneal radius and thickness. METHODS: Hoya Hard EX rigid gas permeable contact lenses (Dk = 125) were fitted to 57 eyes of 29 patients; all eyes were free of pathology. The average duration of contact lens wear was 5.28 +/- 1.43 days. Changes in the radius and thickness of the cornea were measured after 1,3, and 6 months of lens wear. RESULTS: At 1 month, keratometer readings indicated significant flattening in both the horizontal (P < 0.01) and vertical meridians (P < 0.001). At 3 and 6 months, the flattening of both meridians had become more significant (P < 0.001). Although there were no statistically significant changes in corneal thickness at 1 month, significant decreases in thickness were observed at 3 and 6 months (P < 0.001). During the study, patients' vision was stable and lens wear caused no serious complications. At the end of the study, all 29 patients continued extended wear of their contact lenses. CONCLUSIONS: High-Dk RGP contact lenses are an alternative to soft lenses for extended wear.

Adolescent↗
PubMed1996

[Corneal distortion induced by speculum--studies with computer-assisted corneal topography].

The corneal distortion induced by the presence of an eyelid speculum was analysed by the Videokeratoscope-Eyesys Corneal Analysis System (EYESYS), with a Barraquer type speculum (B group) in 22 normal eyes and with a Kratz-Barraquer type speculum in 38 normal eyes (KB group). The following differences were evaluated in the 2 groups: intraocular pressure (IOP), refractive power, change in astigmatism of the Cravy method, and corneal refractive power before and after the specula were put in the interpalpebral fissure. Significant differences were found in the IOP in the KB group, in spherical equivalent in the B and KB groups, and in corneal refractive power in the B groups. Then the 38 eyes of the KB group were divided into two groups by the average level of proptosis and the average difference of IOP, and the corneal refractive power of the two groups was compared by statistical analysis. Significant difference was found in the direction of 0 degree/ 180 degrees in the group with higher than average proptosis and in the direction of 90 degrees/ 270 degrees in the group with higher than average difference in IOP. Multiple regression analysis suggested that higher grades of proptosis were related with steeper vertical meridians and that wider palpebral fissures were associated with steeper horizontal meridians. Multiple regression also showed that the speculum did not cause corneal distortion with the proper relation between level of proptosis and width of the palpebral fissure.

Adult↗
PubMedDate not supplied

The effect of trephination on corneal topography.

BACKGROUND AND OBJECTIVE: A prospective study was performed to assess the effect of trephination on corneal curvature. MATERIALS AND METHODS: Thirty-seven fresh porcine globes with intact corneal epithelium were used. Radius of curvature, central dioptric power, and powers and axes of the steepest and flattest meridians were obtained using a vertically mounted computerized videokeratography unit. Following 8-mm vacuum trephination of the central donor corneas, the said parameters were reassessed on the resultant buttons. No globes with epithelial defects were included in the study. RESULTS: The mean corneal radius of curvature (mm) increased from 8.68 +/- 0.79 to 10.46 +/- 3.24 (P = .005), the central dioptric power (D) decreased from 39.36 +/- 3.84 to 36.31 +/- 10.15 (P = .08), and the total corneal asphericity (D) increased from 5.03 +/- 2.99 to 7.47 +/- 3.42 (P = .0001). No significant changes in the axes of the steepest and the flattest meridians were noted following trephination. CONCLUSION: Trephination leads to significant corneal flattening and increased asphericity. Corneal topography can be used successfully as a research tool for whole globes and trephined buttons.

Animals↗
PubMed1996

Thickness extrema at the edge of astigmatic lenses including those with straight, circular and elliptical edges.

The problem of locating the points of maximum and minimum thickness at the edge of a lens, and of calculating the thickness at those points, is examined for lens powers and for edge shapes in general. The edge extremal problem, as the problem is called, is solved explicitly for general powers along straight cut edges. The extremal problem is also analysed for lenses with circular and elliptical edges but explicit solutions are obtained only for centrally cut lenses, that is, lenses with coincident optical and geometrical centres. For edges that are neither straight nor centrally cut ellipses (including circles), it appears that explicit solutions cannot be obtained for the edge extrema: one has to resort to numerical solution of implicit equations or to the calculation of thickness at sufficiently many points around the edge. For the centrally cut ellipse the edge extremal problem turns out to be the eigenvalue problem of linear algebra. In general the thickness extrema at the edge do not lie on the principal meridians of the lens, nor do they lie on meridians that are mutually perpendicular. With minor modification the results apply equally well to the edge extrema for sagitta of a surface.

Astigmatism↗
PubMed1996

The influence of center of gravity and lens mass on rigid lens dynamics.

PURPOSE: Center of gravity and lens mass have both been shown to influence rigid lens centration and stability. The purpose of this study was to investigate the relative contributions of these two factors to rigid lens dynamics. METHODS: Eight subjects (four with high-riding lenses and four with low-riding lenses) participated in the study. Each subject was fit with 12 lenses-six designs in each of two materials. Center of gravity and lens mass were recorded in every case. For each lens, four lens dynamics variables were assessed over a five-blink cycle for both the vertical and the horizontal meridians: 1) initial lens position; 2) settled lens position; 3) amount of lens movement; and 4) rate of lens movement. RESULTS: Multiple regression and correlation analysis showed that center of gravity influences initial and settled lens position, in both the horizontal and the vertical meridians. Mass alone was found not to be a significant predictor of rigid lens dynamics. The effect of center of gravity on settled vertical lens position was only apparent when high rider and low rider subgroups were analyzed separately, with a posterior movement of the center of gravity being associated with a lowering of the settled lens position for high rider subjects, and a raising of the settled lens position for low rider subjects. The results suggest that a rigid lens will become more stable as the center of gravity is shifted further behind the lens vertex, but this effect is reduced as lens mass is increased. CONCLUSIONS: The location of the center of gravity of a rigid lens influences its on-eye centration and stability more so than does lens mass.

Contact Lenses↗
PubMed1996

[Normal values of retinal response densities in multifocal electroretinogram].

Multifocal electroretinograms (ERG) were recorded from 21 normal eyes to investigate the spatial distribution and inter-individual variation of local cone responses. To compensate for the effect of refractive lenses, test distances were adjusted to obtain a constant magnification on the retina. Significant nasal-temporal asymmetry was observed near the fovea with higher response densities in the temporal retina along the horizontal meridian. No significant supero-inferior asymmetry was observed along the vertical meridian. The average coefficient variation (standard deviation/average) of retinal response density for all areas was 0.35. In the clinical application of the multifocal ERG these results must be taken into consideration.

Adult↗