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At least 1,009 records · Page 56Linked to original sources
PubMed1979

Vision threshold profiles in sector retinitis pigmentosa.

Absolute vision thresholds were measured along the horizontal and vertical meridians in four patients from one pedigree and one patient from a second pedigree with dominantly inherited sector retinitis pigmentosa. From these studies we find that (1) visual function is decreased for all parts of the retina, including the fovea, (2) rod and cone systems are affected to the same degree, and (3) the disease progression is confined to the inferior portion of the retina.

Adolescent↗
PubMed1980

Computerized profile perimetry in glaucoma.

The new profile testing mode of the COMPETER automatic perimeter was clinically tested and compared with careful manual profile perimetry on the Tübinger perimeter. Each of 110 patients with glaucomatous field defects, patients with suspected glaucoma, and normal subjects had one meridian tested. All of the 55 patients who showed an abnormal result on the manual profile also had abnormal findings on the automatic test. Two (4%) of the profiles labeled as normal on initial manual perimetry were identified by the automatic perimeter to be abnormal, and these defects were confirmed on repeated manual profile perimetry. The automatic perimetry gave five (9%) false-positive results in the 53 normal manual profiles, thus giving a specificity of 91%. In two of these cases, the automatic profile indicated defects in areas where the manual profile appeared normal, but there was abnormality in the manual kinetic perimetry in the affected area. The automatic profiles of the COMPETER automatic perimeter are accurate, sensitive, time-saving, and clinically useful.

Adolescent↗
PubMed1981

A screening method for chiasmal visual-field defects.

A strategy that selectively explores the vertical fixational meridian of the visual field was as sensitive as conventional quantitative Goldmann perimetry in detecting chiasmal hemianopic field defects, although it required only one quarter of the usual testing time. A trained but "masked" perimetrist, applying this abbreviated method to the examination of 28 eyes with hemianopic defects, 17 eyes with nerve-fiber defects, and 14 normal eyes, detected 100% of the hemianopias when using the Goldmann perimeter, 92% when using the conventional tangent screen, and 87% when using the projection tangent screen. False-positive diagnoses of hemianopic defects were 16%, 11%, and 14% on the respective instruments. While this strategy did not define the field defects fully, it accurately identified the features of diagnostic importance. By its efficiency, this approach may encourage greater use of visual fields as a determinant in managing the conditions of patients with unexplained visual loss.

Hemianopsia↗
PubMed1981

Corneal topography. Corneascope.

We present an introduction to a clinical quantitative corneascope for measurement of corneal topography in detail. This instrument provides contour keratometry in all corneal meridians. We review the normal myopic and hyperopic eye contours, keratoconus, pellucid marginal degeneration, and wound gape and compression related to cataract surgery. We present a modified Placido disk for office use that incorporates the unique incident light image of the corneascope for rapid review of irregular corneal contours. Corneal topography irregularities frequently contribute to devastating refractive states of the eye and should be examined carefully when keratorefractive surgery is considered.

Cornea↗
PubMed1984

In vivo observation of tear dynamics using fluorophotometry.

Fluorophotometry was used to evaluate the effect of the blinking process on tear spreading. In normal individuals, when the intensity of fluorescence was monitored over the central 1 mm of the cornea, forceful blinking was found to substantially increase tear film thickness. Weak blinking was found to decrease tear film thickness. When tear film fluorescence was monitored along different regions of the corneal vertical meridian, the tear film thickened superiorly while thinning inferiorly. It is postulated that the vertical spreading of meibomian oils is accompanied by the movement of a portion of the aqueous tear phase that thickens the superior tear film at the expense of thinning inferiorly.

Blinking↗
PubMed1986

Scotopic sensitivity loss in glaucoma.

Photopic and scotopic increment thresholds were measured at selected visual field positions for 39 patients suspected of having glaucoma, 39 patients with diagnosed glaucoma, and 31 age-matched normal control subjects. Stimuli were presented at equal-eccentricity pairs of positions just above and below the nasal horizontal meridian. Both photopic and scotopic thresholds were elevated significantly for both the suspect and glaucoma groups. The average photopic and scotopic threshold elevations were the same for the suspect group, but scotopic threshold elevations were substantially greater than photopic threshold elevations for the glaucoma group. In a more detailed analysis of the glaucoma group data, local and diffuse components of the photopic and scotopic threshold elevations were operationally defined. The analysis revealed that localized photopic and scotopic scotomas were of equal depth, but diffuse scotopic defects exceeded diffuse photopic defects by a factor of 2:1 log units. These findings suggest that not all ganglion cell types are equally susceptible to glaucomatous damage and also point to scotopic perimetry as a potentially sensitive test for early glaucoma detection.

Adaptation, Ocular↗
PubMed1988

Variable expressivity of autosomal dominant microcornea with cataract.

Autosomal dominant microcornea with a cataract, previously described in four families, was documented in a seven-generation family. Eighteen family members had microcornea and a cataract, and an additional six had sclerocornea or Peters' anomaly. Most individuals with microcornea had a corneal diameter of less than 11 mm in both meridians, with moderately steep corneal curvatures. The inherited cataract progressed to form a total cataract after visual maturity had been achieved. In the four affected children who had not undergone cataract extraction, the common abnormality was a posterior polar lens opacity. The variability of expressivity of the dominant gene would suggest that the embryological origins of microcornea and sclerocornea are similar.

Adolescent↗
PubMed1988

The influence of simulated light scattering on automated perimetric threshold measurements.

The effect of light scattering by ocular media opacities on OCTOPUS and Humphrey perimeter threshold measurements was simulated with randomly ordered sequences of six ground-glass diffusers in the right eyes of five subjects. Threshold measurements were performed at 0 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees, and 25 degrees nasally along the 180 degrees meridian with the F4 program on an OCTOPUS perimeter, and with twice-repeated profiles on a Humphrey perimeter. The reduction in differential light sensitivity correlated well with the 2.7-dB to 16.7-dB reduction in stimulus intensity caused by the 46% to 98% scattering of incident light by the diffusers. Contrast sensitivity in the presence of a glare source (Miller-Nadler glare test) was also affected by the diffusers, such that a 75% contrast target was not visible through the strongest diffuser whereas a 5% contrast target was visible without a diffuser. Conversely, the diffusers had very little effect on visual acuity measurements that were performed with projected high-contrast targets in a darkened room. Our data suggest that even minimal light scattering, such as might be caused by a cataract that has a relatively insignificant effect on visual acuity, may influence threshold measurements.

Adult↗
PubMed1989

Quantitating the superior visual field loss associated with ptosis.

The effect of blepharoptosis on the superior visual field was assessed using a series of specially designed contact lenses to simulate ptosis in normal subjects. We found a progressive decrease in the superior visual field at the 90 degree vertical meridian, which was proportional to the degree of simulated ptosis. Our results were in close agreement with both a theoretical model and previous clinical observations. These results are important in evaluating patients contemplating ptosis surgery, as well as in visual field testing for neuro-ophthalmic disorders.

Adult↗
PubMed1991

Quantitative descriptors of corneal topography. A clinical study.

Quantitative descriptors of corneal topography determined by computerized algorithm and designed to augment the information derived from topographic maps were evaluated in a clinical study. The surface regularity index, a measure of central corneal optical quality, was highly correlated with best spectacle-corrected visual acuity (rho = 0.80, P less than .001). The relatively low correlation between the surface asymmetry index, a measure of central corneal asymmetry, and best spectacle-corrected visual acuity (rho = 0.62, P less than .005) suggests that corneal symmetry is a lesser but still important determinant of the optical performance of the anterior corneal surface. There was also a high correlation between factors determined from computer-generated orthogonal simulated keratometer values and clinical keratometry values (mean corneal power, total corneal cylinder, and the location of the steepest corneal meridian). The information derived from these algorithms has both clinical and research applications and can be incorporated into computer-assisted topographic analysis systems.

Algorithms↗
PubMed1991

Photorefractive keratectomy to create toric ablations for correction of astigmatism.

Excimer laser photorefractive keratectomy, developed to perform radially symmetric ablations to correct myopic or hyperopic refractive errors, was used to create toric ablations designed to correct cylindrical errors. An expanding slit was created, with no refractive change intended parallel to the slit opening, and central flattening was induced in the meridian in which the slit was expanded. In polymethyl methacrylate blocks, the induced cylinder (as measured with a lensometer) agreed closely (r2 = .99) with intended change, and in plastic corneas, induction of the cylinder could be demonstrated with computer-assisted topographic analysis. Adult pigmented rabbits underwent induction of toric ablations in two-diopter increments; measured keratometric change correlated with desired change (r2 = .87 at 3 weeks; r2 = .89 at 12 weeks). Toric ablations with the excimer laser appear to represent a promising strategy for the correction of cylindrical errors that do not rely on creation of deep corneal incisions, excisions, or compression sutures.

Animals↗
PubMed1991

Photorefractive keratectomy for astigmatism. Initial clinical results.

Excimer laser photorefractive keratectomy, developed to perform radially symmetric ablations to correct myopic or hyperopic refractive errors, was used to perform toric ablations designed to correct cylindrical errors. An expanding slit was used to flatten the cornea in the steep meridian. Four contact lens-intolerant patients underwent this procedure for correction of astigmatism (two patients after penetrating keratoplasty, one patient after corneal ulcer, and one patient with naturally occurring high astigmatism). In each patient, surgery reduced the regular component of the astigmatism; residual irregular astigmatism limited spectacle-corrected acuity in one patient. All patients experienced a shift in spherical equivalent toward hyperopia. Toric ablations with the excimer laser appear to represent a promising strategy for the correction of compound myopic astigmatism that does not rely on creation of deep corneal incisions, excisions, or compression sutures.

Astigmatism↗
PubMed1992

Glaucoma Hemifield Test. Automated visual field evaluation.

We have developed an algorithm, the Glaucoma Hemifield Test (GHT), for automated evaluation of single static threshold visual field test results in glaucoma. The GHT uses empirically determined limits of normality for up-down differences in the Statpac probability maps of the Humphrey Field Analyzer to detect localized visual field loss. It is also constructed to detect field loss that is symmetric around the horizontal meridian. Analysis is done in five corresponding pairs of sectors that are based on the normal anatomy of the retinal nerve fiber layer. Deviations from the age-corrected normal threshold in the most sensitive portions of the visual field are used to detect general reductions of sensitivity or abnormally high sensitivities. The GHT provides brief visual field evaluations printed on the field chart as plain text. The aim of this article is to describe the fundamentals of the analysis program and to provide clinical examples.

Adult↗
PubMed1996

Reduced trabecular meshwork height in juvenile primary open-angle glaucoma.

OBJECTIVE: To compare trabecular meshwork height in a series of patients with juvenile primary open-angle glaucoma (JPOAG) with that in normal control patients. METHODS: Ultrasound biomicroscopy and A-scan biometry were performed on 16 eyes with JPOAG and 24 normal eyes. A radial, perpendicular image in the horizontal temporal meridian detailing the line of Schwalbe, scleral spur, and angle anatomy was obtained for each eye by a single examiner. Trabecular meshwork height was defined as the distance from the scleral spur to the Schwalbe line. RESULTS: Mean patient age (P = .85, t test), refractive error (P = .68), sex distribution (P = .26, Fisher exact test) and axial length (P = .39) were similar between the groups. Mean +/- SE trabecular meshwork heights were 0.36 +/- 0.03 mm (range, 0.19-0.53 mm) for JPOAG and 0.58 +/- 0.02 mm (range, 0.40-0.80 mm) for controls (P < .001). Eyes with greater axial length tended to have larger trabecular meshworks in both groups (P = .012, multivariate regression). A trabecular meshwork height-axial length ratio of 0.021 or less was associated with a significantly increased risk for JPOAG being present (odds ratio, 57; 95% confidence interval, 6.0-541). CONCLUSIONS: The trabecular meshwork is smaller in eyes with JPOAG compared with that in normal eyes. This finding suggests a structural abnormality that may underlie the reduced outflow.

Adolescent↗
PubMed1992

Chin position in profile analysis. Comparison of techniques and introduction of the lower facial triangle.

Many patients undergoing rhinoplasty can benefit from chin augmentation, yielding a more balanced appearance. Preoperative facial analysis identifies patients with retrusive chins and suggests optimal chin position. Current profile analysis methods depend on subnasale position (Legan's angle) or require estimation of bony landmarks from soft-tissue photographs (Goode's alar crease perpendicular, Gonzalez-Ulloa's zero meridian, and Merrifield's Z-angle). We describe a technique for determining ideal chin position using soft-tissue landmarks. We compare this technique with Legan's, Goode's, Gonzalez-Ulloa's, and Merrifield's techniques in 35 women and conclude that this method provides accurate and rapid determination of ideal chin position.

Adult↗
PubMed1996

Visuotopic organisation of striate cortex in the marmoset monkey (Callithrix jacchus).

The visuotopic organisation of the primary visual cortex (V1) was studied by extracellular recordings in adult male marmosets (Callithrix jacchus) that were anaesthetised with sufentanil/nitrous oxide and paralysed with pancuronium bromide. Extensive sampling of the occipital region in four individuals and partial coverage of V1 in five others allowed not only the establishment of the normal visuotopy but also the study of interindividual variability. As in other primates, there was a single, continuous map of the contralateral hemifield in V1, with the upper visual quadrant represented ventrally and the lower quadrant represented dorsally. The surface area of V1, which was measured in two-dimensional reconstructions of the cortical surface, varied from 192 to 217 mm2. There was a marked emphasis on the representation of the foveal and parafoveal visual fields: the representation of the central 5 degrees of the visual field occupied 36-39% of the surface area of V1, whereas the central 10 degrees occupied 57-59%. No asymmetry between the representations of the upper and lower quadrants was apparent. The visual topography of V1 was highly consistent between individuals, relative to both sulcal landmarks and stereotaxic coordinates. The entire contralateral hemifield was represented in V1; in addition, neurones with receptive fields whose borders invaded the ipsilateral hemifield were observed within V1, less than 800 microns from the V1/V2 boundary. The total invasion of the ipsilateral hemifield was less than 0.5 degree at the centre of the fovea but reached 8 degrees at the periphery of the vertical meridian. Our results demonstrate that the organisation of V1 is similar in diurnal New and Old World simians, despite major variations in size, ecological niche, and timing of postnatal development across species.

Animals↗
PubMed1999

Topographic organisation of extrastriate areas in the flying fox: implications for the evolution of mammalian visual cortex.

The organisation of extrastriate cortex was studied in anaesthetised flying foxes (Pteropus poliocephalus) by using multiunit recording techniques. Based on the visuotopic organisation and response characteristics, the cortex immediately rostral to the second visual area (V2) was subdivided into two fields: visual area 3 (V3) laterally and the occipitoparietal area (OP) medially. Area V3 is a 1.0-1.5 mm wide strip of cortex that represents the entire contralateral hemifield as a mirror image of the representation found in V2. The representation of the vertical meridian and the area centralis form the rostral border of V3. In area OP, receptive fields are much larger than those of V3 and form a separate visuotopic map, with the upper quadrant represented rostral to the lower quadrant. Multiunit clusters in the cortex rostral to area OP (posterior parietal area) respond to both visual and somatosensory stimuli. Farther laterally, in the cortex rostral to V3, the occipitotemporal area (OT) was found to form yet another map of the visual field. Similar to the middle temporal area in primates, area OT in the flying fox forms a first-order representation of the visual field, with the lower quadrant represented medially, the upper quadrant represented laterally, the area centralis represented caudally, and the visual field periphery represented rostrally. The cortex surrounding area OT rostrally and ventrally is also visually responsive but could not be subdivided due to the large receptive fields. Finally, visual responses were elicited from an area adjacent to the peripheral representation in the first visual area (V1) in the splenial sulcus. These results demonstrate that nearly half of the flying fox cortex is related to vision, which contrasts with that of microchiropteran bats, in which auditory areas predominate. A comparison of the flying fox with other mammals suggests that several areas, including homologues of V1, V2, V3, OT, and the splenial area, may have originated early in mammalian evolution and have been inherited by most present-day eutherians. However, studies in other species will be needed to distinguish patterns of common ancestry from parallel evolution.

Animals↗
PubMed1998

Intersubject variability of functional areas in the human visual cortex.

Intersubject variability of striate and extrastriate areas was mapped by conjoined use of positron emission tomography (PET) and magnetic resonance imaging (MRI). We used two dynamic bowtie-shaped random-dot patterns centered symmetrically around the vertical- and horizontal-meridian, respectively, presented during sequential PET scans in 11 subjects. Control condition was simple fixation on a central dot in absence of a surrounding random dot pattern. V1, V2, VP, V3, V3a, V4, V5, and "wordform" areas were identified. After spatial normalization to Talairach atlas space, mean locations and standard deviations about these mean locations for x-, y-, and z-axes were calculated for each area in both hemispheres and compared for differences. The mean standard deviation for all axes across all areas tested was found to be small (4.9 mm). No significant differences were found in the mean standard deviations for the x-, y-, and z-axes in the left hemisphere vs. their counterparts in the right hemisphere. However, when mean standard deviations in both hemispheres were polled together by axis, the mean standard deviation for the y-axis (5.3 mm) was found to be significantly different from the mean standard deviation for the x-axis (4.3 mm). Furthermore, in the left hemisphere, the mean standard deviation for the z-axis (5.7 mm) was significantly greater than the mean standard deviation for the x-axis (3.9 mm). The values reported in this study for mean location and standard deviation of visual areas can be used to establish confidence intervals for distinguishing normal variations from pathology and consequent brain reorganization.

Adolescent↗