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Corneal topography and photokeratoscopy.

A keratometer measures the radius of curvature of the two principal meridians that correspond to the steepest and flattest meridians, by projecting an illuminated circle onto the corneal surface from a fixed distance. A photokeratoscope allows a permanent record to be made and further evaluated. It takes a picture primarily of the intermediate zone of the cornea. By measuring the distance between reflected rings and comparing them to the actual distance between the rings on the instrument, the curvature of the cornea can be ascertained at any given point.

Cornea↗
PubMed1989

Changes in completed family size and reproductive span in Anabaptist populations.

The Anabaptist Amish, Hutterite and Mennonite peoples trace their origins to the Reformation. Although they share certain beliefs, such as adult baptism and the separation of church and state, each group is culturally unique. The Hutterite and Amish are highly fertile and their populations exhibit stable rates of growth. These demographic characteristics reflect communal living among the Hutterites and labor intensive farming practices among the Amish. The Mennonites are the most receptive Anabaptist group to outside socioeconomic influences and provide a demographic contrast to the more conservative Amish and Hutterites. Demographic data collected during a study of aging in Mennonite population samples from Goessel and Meridian, Kansas, 1980, and Henderson, Nebraska, 1981, formed the basis of a cohort analysis in order to assess fertility change over time. Completed family size has decreased significantly in all three communities since 1870. Since the early 1900's the mean age of the mother at first birth has fluctuated but the mean age of mother at the birth of the last child is decreasing significantly for the communities of Goessel and Henderson, thus effectively shortening the reproductive span. The pattern is somewhat different for Meridian, the most conservative of the three communities.

Adolescent↗
PubMed1989

[Experimental and histologic studies on fetal membrane tensility and membrane rupture].

The collagen microfibrils of the amniotic connective tissue are irregularly textured. In all a preference for a meridional orientation perpendicular to the placental-rim can be observed. There are randomly dispersed weak spots between dense bundles of collagen fibres. The chorion connective tissue consists also of fibril bundles in a meridional main orientation. Within the bundles or bands there is an unmistakable pattern of latticed arranged fibrils. The framework receives its stability from the bundles that run perpendicular or inclined to the previously mentioned bundles. There are randomly dispersed weak areas between the dense fibril aggregates. In general the amniotic and chorionic connective tissues are both of variable strength. The tensile strength of both membranes is regionally varying due to the irregular texture. At times it varies within the same fetal membrane or from fetal membrane to fetal membrane considerably, where by the variation in membrane thickness also is of influence. It is to be observed that in general the resistance perpendicular to the meridian direction is smaller than along the meridian direction. During the rupture of the membranes the latticed arranged fibres from the bundles of the chorionic connective tissue give way and tear in an arbitrary weak spot. In the amniotic tissue the tearing also begins in a weak spot and continues to tear in a non predictable direction between the irregular pattern of bundles.

Amnion↗
PubMed1989

Monocular geometry is selectively distorted in the central visual field of strabismic amblyopes.

Strabismic amblyopia is associated with a distorted perception of visual space. The aim of our study was to investigate the monocular space perception of strabismic observers at several locations in the central and peripheral visual field. We tested nine observers with strabismic and/or anisometropic amblyopia, two strabismic subjects with alternating fixation and two normal control subjects. The task was to align a light stimulus with two vertically arranged reference marks. Testing conditions included three separations of the references along the vertical meridian (10 degrees, 20 degrees and 40 degrees) as well as several presentation sites of the vertical references in the nasal and temporal peripheral visual field (5 degrees, 10 degrees and 20 degrees from fixation). Performance with the amblyopic eye was clearly impaired as compared to the nonamblyopic eye. For alignment along the vertical meridian, all amblyopic eyes showed increased uncertainty in their position judgements. Most of the squinting eyes of amblyopes also displayed a systematic lateral displacement of the test stimulus in relation to the reference marks, in the most extreme case up to almost 7 degrees. Usually, larger errors were found with wider separations of the reference marks. In the peripheral field, the differences between the amblyopic and the nonamblyopic eye diminished or disappeared. Thus, monocular geometry appears to be selectively impaired in the central visual field of the deviated eye of strabismic amblyopes. These spatial distortions might be related to the different states of binocular correspondence in the central vs. peripheral visual field, shown by some strabismic amblyopes.

Amblyopia↗
PubMed1989

[Central physiologic relative scotoma after dark adaptation].

The paper describes data on conditions for appearance of a physiologic central retinal scotoma of dark adaptation. Examinations of 80 eyes with normal visual functions have shown that central scotoma of dark adaptation is revealed in conditions of scotopic illumination 20-25 minutes after dark adaptation. The optimal duration of dark adaptation is 40-45 minutes. More frequently scotoma is displaced upwards from the point of fixation, its sizes varying from 4 degrees to 10 degrees by the horizontal meridian and from 3 degrees to 8 degrees by the vertical meridian. The presence of this scotoma should be considered when examining the state of the visual analyser in conditions of scotopic illumination. This can play a certain role in differential diagnostics of clinical ophthalmopathology.

Adolescent↗
PubMed1989

The visually guided control of simulated altitude.

Simulated "flights" over three different ground textures were used to examine people's ability to extract optical information useful for active regulation of altitude. The textures were regularly spaced lines as follows: 1) orthogonal to the direction of flight (latitude texture); 2) parallel to the direction of flight (meridian texture); and 3) both parallel and orthogonal (square texture). Visual constant velocity forward flight simulations were displayed on a CRT screen, and subjects asked to maintain one of three initial altitudes using a rate control stick. This task was made difficult by the presence of lateral (irrelevant) and vertical (relevant) "wind gusts." The attitude never varied as winds, forward speed, and vertical rate control resulted in only translational movements. Adjusted root mean square errors (ARMSE) showed altitude regulation was more difficult at higher altitudes and when flying over meridian textures. Refined analysis of a single subject's data showed that this was due both to poorer regulation of the vertical wind disturbance and to a tendency to confuse the lateral wind disturbance for a vertical disturbance.

Adolescent↗
PubMed1988

[A study on the effects of different keratectomies for astigmatism in rabbits' eyes].

Three kinds of wedge resections with sutures at limbus were carried out in grown rabbits. Keratometry was performed for 8 weeks. Corneal curvature and corneal astigmatism were not significantly changed by 90 degrees of the circumference. But in the group of 180 degrees resection, the radius perpendicular to the wound increased and 3. 5 D corneal against-the-rule astigmatism was brought about in a week after surgery. Therefore, when operated at the limbus by same extension, one longer wedge resection changed more the radius than 2 symmetric resections did. It was thought this against-the-rule astigmatism was due to the decrease of total surface, another side of the wound being sclera, and other factors. They are properties of suture material, the provoked tissue reaction, and so on. Pulling on domed tissue should be looked at again. Loss of effect was remarkable. So, to get permanent effect, we should study more about the time of suture removal, acting over the sclera and the sutures penetrating cornea. Secondly, two kinds of keratectomies perpendicular to vertical meridian were situated midway between limbus and corneal apex. The changes of total refractive power were followed up by skiascopy for 3 months. As a result, 1.0 D-1.5 D against-the-rule astigmatism was surgically induced in both keratectomies. This was almost due to myopic change of the opposite meridian, which was parallel to the resections. Loss of effect of rectangle-shaped keratectomy was less than that of crescent-shaped. It suggested cutting Ligamentum Circulatum situated near limbus was necessary to prevent the reduction of induced astigmatism with time. In addition, limbus of wedge resection was histologically observed. Markedly wavy appearance of lamellas was seen in the stroma. Like this, reactions to 8-0 virgin silk proved to be intensive. So, suture associated with less inflammatory reaction like 10-0 monofilament is recommended.

Animals↗
PubMed1987

A new donor cornea marker and punch for penetrating keratoplasty.

We describe a new device to mark and punch donor corneas for penetrating keratoplasty. The device contains eight marking-suction holes that make circular marks in the periphery of the donor cornea and fix the tissue in position during trephination. The eight peripheral marks correspond in location to meridians of an eight-blade radial keratotomy marker. When used in conjunction with this marker for the host bed, the donor cornea marker facilitates alignment of meridians on donor and host tissues, radial placement of sutures, and quantitative placement of sutures equi-distant from the wound margin.

Corneal Transplantation↗
PubMed1988

Central visual fields for short wavelength sensitive pathways in glaucoma and ocular hypertension.

While conventional clinical visual acuity and kinetic visual fields may be essentially normal in ocular hypertension and early stages of glaucoma, other foveal aspects of vision (eg color, spatial and temporal contrast sensitivity) may be quite abnormal. Specifically, a selective vulnerability of the short wavelength sensitive (SWS) visual pathways in these conditions has previously been noted. Here we studied the central visual fields of 33 primary open angle glaucoma (POAG) patients, 32 ocular hypertensives (OHT), and 24 age-matched normal controls using blue and yellow test flashes on bright yellow backgrounds. SWS cone and MWS and/or LWS cone pathway sensitivities were measured at the fovea and at 2.5 degrees, 5 degrees, 10 degrees and 15 degrees eccentricities, in either the inferior temporal (for OHT) or horizontal nasal retina (for POAG). As expected, all groups had normal sensitivity to yellow flashes--detected by LWS and/or MWS cones--in these meridians. By comparison, for the blue flashes--detected by the SWS cones--the POAG and OHT groups had sensitivity deficits, uniformly across the central visual field, of about 6X and 1.8X, respectively, compared to normals. While six of 31 (19%) OHT subjects had localized glaucomatous field defects (greater than 0.4 log units) in the non-foveal inferior temporal retina, none of the 12 OHT subjects who were also tested in the horizontal nasal retina showed loss in this meridian. Finally, while no POAG subjects had localized sensitivity loss for yellow flashes in the horizontal nasal retina, four did show local field defects with blue test flashes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1988

Functional anatomy of macaque striate cortex. II. Retinotopic organization.

Macaque monkeys were shown retinotopically-specific visual stimuli during 14C-2-deoxy-d-glucose (DG) infusion in a study of the retinotopic organization of primary visual cortex (V1). In the central half of V1, the cortical magnification was found to be greater along the vertical than along the horizontal meridian, and overall magnification factors appeared to be scaled proportionate to brain size across different species. The cortical magnification factor (CMF) was found to reach a maximum of about 15 mm/deg at the representation of the fovea, at a point of acute curvature in the V1-V2 border. We find neither a duplication nor an overrepresentation of the vertical meridian. The magnification factor did not appear to be doubled in a direction perpendicular to the ocular dominance strips; it may not be increased at all. The DG borders in parvorecipient layer 4Cb were found to be as sharp as 140 micron (half-amplitude, half width), corresponding to a visual angle of less than 2' of arc at the eccentricity measured. In other layers (including magnorecipient layer 4Ca), the retinotopic borders are broader. The retinotopic spread of activity is greater when produced by a low-spatial-frequency grating than when produced by a high-spatial-frequency grating. Orientation-specific stimuli produced a pattern of activation that spread further than 1 mm across cortex in some layers. Some DG evidence suggests that the spread of functional activity is greater near the foveal representation than near 5 degrees eccentricity.

Animals↗
PubMed1988

The distribution and kinetics of visual pigments in the cat retina.

An imaging fundus reflectometer has been used to study the distribution and regeneration of visual pigments in the retina of the adult living cat. Measurements were made over an area of tapetal retina extending 25 degrees nasal and 40 degrees temporal to the area centralis on the horizontal meridian and 5 degrees inferior to 40 degrees superior on the vertical meridian. The measured density differences show large variations with retinal location, with values in the central retina up to 60% higher than those in the superior region. The area of high density differences forms a horizontal streak. There are two peaks of density difference values, one centered on the area centralis and the second in the nasal section of the streak. Spectral measurements indicate that the contribution of cone pigments is negligible everywhere except at the area centralis, where it is about 5%. The distribution of density differences is shown to correlate well with anatomical data if the effects of fundal stray light are taken into account and if it is assumed that the cross section of light capture by the rods is determined by the dimensions of the inner segments. The time required for essentially complete regeneration of rhodopsin depends on retinal location, varying from about 80 min in the superior retina to more than 90 min in the regions of peak densities.

Animals↗
PubMed1987

The use of spherical power effect bitoric rigid contact lenses in hospital practice.

In this retrospective study of astigmatic contact lens dispensing in the hospital setting, 680 patients were noted to have been dispensed new contact lens prescriptions over a specific 20-month period. Seventy-five patients (11%) received at least one astigmatic rigid or hydrogel contact lens. Forty-nine patients received at least one rigid astigmatic lens; 43 patients (63 eyes)--or about 87% of all rigid lens fittings--were dispensed spherical power effect (SPE) design rigid contact lenses. We find that we usually prescribe bitoric rigid lenses with the flatter (longer) meridian of the lens base curve about 0.50 diopters steeper than the flattest (longest) corneal meridian. Mean diameter was 9.3 mm, and about 80% of lenses were made from rigid gas permeable materials. The majority of patients were successful from a clinical perspective, with most attaining visual acuity equal to or better than with maximum spectacle correction, and with good comfort and physiological results.

Adolescent↗
PubMed1987

Functional properties of parietal visual neurons: mechanisms of directionality along a single axis.

The directional properties of parietal visual neurons (PVNs) were examined using the method of single-neuron analysis in waking monkeys. PVN properties were determined with passive visual stimuli as the animal executed a simple detection task. Parietal area PG was studied in 10 hemispheres of 6 male Macaca mulatta. Each class of parietal neurons was identified in PG: the fixation, projection, visual, and oculomotor neurons; 613 PVNs were identified, 323 were studied quantitatively, and 188 were studied with one or more of the protocols described. The receptive fields of PVNs are commonly large and bilateral, and at the limit some may fill the visual field; for many, the central zone of the visual field is spared when the fields are determined by stimuli that enter from the periphery and transit meridians. The receptive fields vary with the behavioral state, the angle of gaze, and the parameters of the stimuli used to determine them. PVNs are sensitive to stimulus movement but relatively insensitive to stimulus speed; many respond over a speed range of 5 degrees-500 degrees/sec. Stimulus-response relations may be incremental or decremental with increasing speed or show maxima or minima in the midrange of speed, but the response variation over the full range is rarely greater than 2:1. The directional preferences of PVNs with bilateral receptive fields are opponently organized; the preferred directions point either inward toward or outward away from the central line of gaze along the 4 meridians tested, which were equally spaced in the circular dimension of the visual field. The mechanism of the axis directionality of PVNs was studied using conditioning-test paradigms. They revealed a feed-forward inhibition preceding a stimulus, an effect that extends from the leading edge of the stimulus for 10 degrees-20 degrees in front of the moving stimulus and lasts for several hundred milliseconds. A double-Gaussian model of superimposed but unequal excitatory and inhibitory effects suffices to explain the present observations. It places demand upon the projection of functional properties from the contralateral hemisphere or from the ipsilateral prestriate areas that project upon PG over multistaged pathways and minimal demands upon intracortical processing mechanisms.

Action Potentials↗
PubMed1985

[Reaction of the biologically active points of the skin to immunization with typhus vaccine].

Electroacupuncture diagnosis was used to demonstrate the reaction of biologically active points of the skin (BAPS) to immunization with typhus vaccine. In 7 persons immunized with chemical and live (strain E) typhus vaccines, the reaction differed significantly from the initial parameters and other measurement data obtained in a group of unvaccinated subjects. The reaction of the BAPS was noticeable starting from the first day after vaccination and was far ahead of seroimmune shifts detectable in the host. The best correlation was established between the seroimmune response and the activity of the acupuncture points on meridians X and I (a positive correlation) and on meridians III, VIII and XI (a negative correlation).

Acupuncture Therapy↗
PubMed1986

Retinal constraints on orientation specificity in cat visual cortex.

Most retinal ganglion cells (Levick and Thibos, 1982) and cortical cells (Leventhal, 1983; Leventhal et al., 1984) subserving peripheral vision respond best to stimuli that are oriented radially, i.e., like the spokes of a wheel with the area centralis at the hub. We have extended this work by comparing directly the distributions of orientations represented in topographically corresponding regions of retina and visual cortex. Both central and peripheral regions were studied. The relations between the orientations of neighboring ganglion cells and the manner in which the overrepresentation of radial orientations is accommodated in the functional architecture of visual cortex were also studied. Our results are based on an analysis of the orientations of the dendritic fields of 1296 ganglion cells throughout the retina and the preferred orientations of 1389 cells located in retinotopically corresponding regions of cortical areas 17, 18, and 19 in the cat. We find that horizontal and vertical orientations are overrepresented in regions of both retina and visual cortex subserving the central 5 degrees of vision. The distributions of the orientations of retinal ganglion cells and cortical cells subserving the horizontal, vertical, and diagonal meridians outside the area centralis differ significantly. The distribution of the preferred orientations of the S (simple) cells in areas 17, 18 and 19 subserving a given part of the retina corresponds to the distribution of the dendritic field orientations of the ganglion cells in that part of retina. The distribution of the preferred orientations of C (complex) cells with narrow receptive fields in area 17 but not C cells with wide receptive fields in areas 17, 18, or 19 subserving a given part of the retina matches the distribution of the orientations of the ganglion cells in that part of retina. The orientations of all of the alpha-cells in 5-9 mm2 patches of retina along the horizontal, vertical, and oblique meridians were determined. A comparison of the orientations of neighboring cells indicates that other than a mutual tendency to be oriented radially, ganglion cells with similar orientations are not clustered in the retina. Reconstructions of electrode penetrations into regions of visual cortex representing peripheral retina indicate that columns subserving radial orientations are wider than those subserving nonradial orientations. Our results provide evidence that the distribution of the preferred orientations of simple cells in visual cortex subserving any region of the visual field matches the distribution of the orientations of the ganglion cells subserving the same region of the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

The topography of ganglion cell production in the cat's retina.

The ganglion cells of the cat's retina form several classes distinguishable in terms of soma size, axon diameter, dendritic morphology, physiological properties, and central connections. Labeling with [3H]thymidine shows that the ganglion cells which survive in the adult are produced as several temporally shifted, overlapping waves: medium-sized cells are produced before large cells, whereas the smallest ganglion cells are produced throughout the period of ganglion cell generation (Walsh, C., E. H. Polley, T. L. Hickey, and R. W. Guillery (1983) Nature 302: 611-614). Large cells and medium-sized cells show the same distinctive pattern of production, forming rough spirals around the area centralis. The oldest cells tend to lie superior and nasal to the area centralis, whereas cells in the inferior nasal retina and inferior temporal retina are, in general, progressively younger. Within each retinal quadrant, cells nearer the area centralis tend to be older than cells in the periphery, but there is substantial overlap. The retinal raphe divides the superior temporal quadrant into two zones with different patterns of cell addition. Superior temporal retina near the vertical meridian adds cells only slightly later than superior nasal retina, whereas superior temporal retina near the horizontal meridian adds cells very late, contemporaneously with inferior temporal retina. The broader wave of production of smaller ganglion cells seems to follow this same spiral pattern at its beginning and end. The presence of the area centralis as a nodal point about which ganglion cell production in the retinal quadrants pivots suggests that the area centralis is already an important retinal landmark even at the earliest stages of retinal development. This sequence of ganglion cell production differs markedly from that seen in the retinae of nonmammalian vertebrates, where new ganglion cells are added as concentric rings to the retinal periphery, and also bears no simple relationship to the cat's retinal decussation line. However, it can be related in a straightforward manner to the organization of axons in the cat's optic tract, suggesting that the fiber order in the tract represents a grouping of fibers by age.

Animals↗
PubMed1985

Corneal curvature modification by scleral surgery: preliminary results.

The preliminary results of a scleral technique designed to correct mixed and myopic compound astigmatism are given, and the mathematical basis of this technique is explained. The amount of scleral resection per diopter of astigmatism is indicated. This procedure steepens the flattest meridian and flattens the meridian localized at 90 degrees from the first one.

Astigmatism↗
PubMed1981

The visual claustrum of the cat. II. The visual field map.

Physiological and anatomical methods were used to study the representation of the visual field in the cat's dorsocaudal claustrum. In one set of experiments, the visual receptive fields of claustral neurons were plotted in multiple electrode penetrations. In another set of experiments, the termination of the corticoclaustral pathway was examined autoradiographically after the injection of [3H]proline at retinotopically defined sites in the visual cortex. Results obtained by the two methods were in close agreement. The claustrum was found to contain a single, orderly map of the contralateral hemifield and a small part of the ipsilateral field. High elevations are represented caudally and ventrally, low elevations rostrally and dorsally. The surface of the claustrum represents the periphery of the visual field, while the vertical meridian lies more ventrally, where the visual claustrum abuts the non-visual part of the nucleus. Visual field lines (isoazimuths or isoelevations) are represented as planes in the claustrum. The map is unusual in that isoazimuth planes are strongly curved and nested within each other, with peripheral ones enclosing those closer to the vertical meridian. This arrangement permits an expanded representation of the periphery compared with what is seen in visual cortex. The inputs from areas 17, 18, 19, 21a, and PMLS (posteromedial lateral suprasylvian area) are convergent, each projection retinotopically to the entirety of the claustral map.

Animals↗