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J M Enoch

Publications and source records attributed to J M Enoch.

At least 91 records · Page 5Linked to original sources
PubMed1981

Inferred positive phototropic activity in human photoreceptors.

The Stiles-Crawford (S.-C.) function, a measure of the directional sensitivity of the retina, was used to infer the alignment characteristics of the sampled retinal elements. One assumes that the peak of the photopic S.-C. function reflects the central alignment tendency of renal elements sampled, and that the shape of the function reflects, among other factors, distributive qualities. Here two tests were performed to determine whether the function sampled reflected positive phototropic activity. The natural eye pupil was dilated and artificial pupils were substituted having specified eccentricity from the centre of the natural pupil. This was achieved with a displaced iris contact lens. After a series of complex experiments, it was finally shown that the peaks of the S.-C. function shifted towards the displaced aperture of the contact lens. As a second test, individuals were occluded uniocularly with a black patch for periods of time up to 10 days. This caused remarkable flattening of the measured S.-C. function. That flattening occurred in determinations of both photopic and scotopic S.-C. functions. Comparable effects were not seen in the second eye or if a diffuser was substituted for the black patch. Change and recovery in both experiments occurred within 3-5 days. On the basis of these experiments it is inferred that there is an active mechanism behaving in a positive phototropic manner present in the human retina.

Humans↗
PubMed1981

Radiation therapy in and about the retina, optic nerve, and anterior visual pathway. Psychophysical assessment.

Visual changes may develop in patients receiving radiation therapy for malignant neoplasms in and about the optic nerve and anterior visual pathway. Cases have been studied using a series of psychophysical tests, including kinetic perimetry, increment threshold determinations, Flashing Repeat Static Test, and sustained- and transient-like functions. A characteristic time-dependent reduction in sensitivity has been identified in these patients. This finding, in addition to the presence of nerve fiber bundle defects, appears to place the pathologic changes in the axon of the ganglion cell posterior to the lamina cribrosa. Any change in the sustained- and transient-like functions, the organization of which appears to be in the neural retina, was seen only if a concomitant radiation retinopathy was identified.

Adenocarcinoma↗
PubMed1981

Photoreceptor orientation. A graded disturbance bordering a region of choroidal atrophy.

Retinal photoreceptor orientation was found to be disturbed in the region bordering an area of choroidal atrophy in the eye of a human observer. This disturbance was inferred from the locations of the peaks of psychophysical Stiles-Crawford functions. These peak locations progressively shifted from a normal location near the center of the pupil to well beyond the nasal pupillary margin as the retinal test location approached the visible lesion. We conclude that this disturbance of photoreceptor orientation reflects the operation of tractional forces that interfere with the reorientation of the receptors toward the pupil in a sizable area of the retina surrounding the traction-inducing lesion.

Adolescent↗
PubMed1980

Different functional changes recorded in open angle glaucoma and anterior ischemic optic neuropathy.

The retinal ganglion cell exhibits two types of functional change. The difference in response appears to depend on whether or not the retrobulbar portion of the optic nerve is actively involved. This may imply differences in the myelinated and non-myelinated portions of the optic nerve and associated structures. In open angle glaucoma, alterations in the sustained- and transient-like functions but not in the flashing repeat static test are found. That is, there are changes in spatial neural interactions, but there is no evidence of a visual fatigue or saturation-like effect. In optic nerve radiation damage without evidence of retinal vascular changes, in optic neuritis secondary to multiple sclerosis, chiasmal lesions, and ischemic optic neuropathy (considered here) varying degrees of visual fatigue or saturation-like effects are demonstrated with little or no change in the sustained- or transient-like functions.

Aged↗
PubMed1980

A simple psychophysical technique provides early diagnosis in optic neuritis.

Patients with optic neuritis describe image fading which is particularly evident at bright light levels. The effect is dependent on adaptation level, and high adaptation levels serve as a provocative test. Kinetic and static perimetry and interferometric acuity tests repeated in time reveal this loss in sensitivity. The latter test, using a large field and a high luminance level, is particularly sensitive to both the residua of pathology and very early phases of disease, often before subjective manifestations of anomalies are present. These effects are large in patients with demyelinating diseases. Here, we show that such changes may be revealed in optic neuritis due to other causes as well. Note, the same form of response may be detected in more central lesions, but usually in more circumscribed areas of field.

Adult↗
PubMed1980

Vertebrate receptor optics and orientation.

Vertebrate photoreceptors act as optical waveguides. They exhibit directionality, non-uniform distribution of energy within and immediately about the receptor, etc. Photolabile pigment absorption favors light traveling axially down the receptor. Clearly these properties influence response of the transducer. Retinal receptors, rods and cones, are aligned normally with a point approximating the center of the exit pupil of the eye. Taken together, these findings suggest that a prime role of receptor optics is to favor acceptance of the pertinent visual stimulus passing through the pupillary aperture and to inhibit stray light noise contained in the integrating sphere-like eyes. Many intriguing problems remain to be resolved. It is necessary to relate the properties of the receptor as a waveguide to determinations of directional sensitivity of the retina (Stiles-Crawford effects), and in particular, to understand mechanisms leading to fine receptor alignment. There must also be a pathology of receptor orientation--a science still in its infancy.

Animals↗
PubMed1980

Functional analysis of vision in patients after retinal detachment repair.

A number of tests of vision were performed in patients after surgical repair of retinal detachment. The major tests performed were Snellen visual acuity, interferometric acuity, Stiles-Crawford function, and increment-threshold analysis. In two patients it was possible to evaluate all functions preoperatively. Althrough the sample it modest (ten eyes in nine patients), trends in visual recovery are identified and discussed.

Adaptation, Ocular↗
PubMed1980

An apparent failure of the photoreceptor alignment mechanism in a human observer.

Using the psychophysical Stiles-Crawford function, the orientation of the retinal photoreceptors was shown to be directed toward a region near the center of the eye rather than the pupil in one eye of a human observer. Since an observable pathologic condition was not present, this eye was concluded to represent the first demonstrated instance of a primary global disturbance of the normal receptor alignment mechanism. The examination of this unique observer permits the visual importance of normal receptor orientation to be assessed and allows potential photoreceptor alignment mechanisms to be evaluated.

Adult↗
PubMed1980

Evidence for alteration in photoreceptor orientation.

The effect of incident light, its point of origin, and its magnitude on receptor orientation was determined. A non-invasive test of vision, the Stiles-Crawford Effect (SCE), was used to investigate retinal directional sensitivity and alignment. The simple act of monocular black patching for a period of three to five days caused marked reduction in directional sensitivity and/or apparent dispersal of alignments. Recovery occurred in a comparable time period in normal adults 20 to 50 years of age. Special painted iris contact lenses with displaced pupillary apertures were worn to investigate the factors influencing alignment. Both light induced effects which caused alignment to shift toward a displaced aperture, and mechanical factors resulting in other alignment shifts were recorded. Thus, retinal receptors and/or associated anatomic components are apparently phototropic and subject to multiple forces influencing their directionality and/or alignment, and the milieu of the retinal receptor is active.

Adult↗
PubMed1980

Visual sensitivity, resolution, and Rayleigh matches following monocular occlusion for one week.

Following three to four days of monocular light exclusion, the directional sensitivity of the retina was reduced at all areas tested. Changes in the shape of the Stiles-Crawford (SC) function were evident at both photopic and scotopic adaptation levels. The flattening of the SC functions was primarily a result of increased sensitivity to light entering through the periphery of the eye pupil. Here, concentration is on concomitant changes in other visual functions including an overall increase in visual sensitivity and a decrease in resolution of low-intensity gratings. Anomaloscope settings revealed a modest increase in red required for a yellow match.

Adult↗
PubMed1980

Anomalous pigment epithelial photoreceptor relationships and receptor orientation.

In order to further investigate the factors influencing retinal receptor orientation, three patients with local disturbances of the receptor/pigment epithelium (PE) interface have been evaluated. Psychophysical and clinical tests have been used to characterize the observed abnormalities. The following conclusions are made. Receptor orientation is lost following a serous detachment of the neurosensory retina and can recover following reattachment of the retina. Orientation may be retained despite the presence of serous detachment of the PE, loss of the light/dark component of the electro-oculogram, and vitelliform-like lesions between the receptors and the PE.

Adult↗
PubMed1980

Transient-like function and associated retinal capillary anomalies. Analysis of a patient with early retinopathy secondary to juvenile-onset diabetes mellitus.

A juvenile diabetes patient exhibiting limited early microvascular changes in the retina has been studied intensively. Like some others showing early signs of diabetic retinopathy, he manifests anomalies in a retinally based transient-like function. At all points tested in this case the sustained-like function was found to be normal. Because his functional and anatomic anomalies are stable and cover a reasonably extensive area of visual field and retina, it is possible to attempt correlative studies with other visual response functions. The transient-like function proves to be a more sensitive indicator of anomaly in this patient than static perimetry or critical flicker frequency.

Adolescent↗
PubMed1979

Monocular light exclusion for a period of days reduces directional sensitivity of the human retina.

Single eyes of young adult observers were occluded for as long as 10 days. Directional sensitivity of the retina (the Stiles-Crawford effect of the first kind) under photopic conditions was dramatically reduced at every retinal location tested in all subjects. The maximum effect was observed within 3 to 5 days, and recovery took place at approximately the same rate after termination of patching.

Humans↗
PubMed1979

Contrast (modulation) sensitivity functions measured in patients with high refractive error with emphasis on aphakia: I. Theoretical considerations.

Recently, alterations in contrast (modulation) sensitivity functions of patients with high refractive errors have been noted. For example, this seems to be a common finding in aphakia. In some measure the observed alterations are due to the effect of the corrective lens and the optics of the eyes. These optical effects (in addition to blur) must be factored out in order to determine whether residual effects on the visual system remain. The argument is applicable to photographs of sine wave fringes as well as devices designed to produce interference patterns directly on the retina. A simple means for largely correcting these lens effects is discussed.

Aphakia↗
PubMed1979

Contrast (modulation) sensitivity functions measured in patients with high refractive error with emphasis on aphakia: II. Determinations of patients.

Measurements of Constrast Sensitivity Functions (CSF) were made on normal observers made artificially highly ametropic with spectacle lenses (with high back vertex) distance in order to determine the effect of retinal image size alterations upon CSF measures. While not an exact model for high ametropia per se, this experiment served to familiarize the experimenters with problems associated with the task. Image size alterations occur normally in aphakic patients and highly myopic patients. As a clinical trial, a series of aphakic observers were tested using an interferometric acuity device. CSF measures were made with the patient's spectacle corrections in place and again with correcting contact lenses substituted. The contact lenses reduce induced image size alterations in these cases. The use of contact lenses in such measures allows differentiation between artifactual low frequency fall off in aphakia due to lens effects and possible low frequency fall-off due to other causes.

Adult↗
PubMed1979

Comparison of visual function studies in two cases of senile macular degeneration.

In this paper two relatively early cases of senile macular degeneration are compared by making use of a number of tests of visual function, some relatively new, coupled with observation of the fundus and analysis by fluorescein angiography. The functional tests include visual acuity, the sustainedlike and transientlike functions which are believed to test inner retinal receptive field properties and to have origin in the inner and outer plexiform layers, the Stiles-Crawford function which reflects the directional sensitivity and orientation of photoreceptors, and increment threshold curves. In one case there was evidence of inner retinal involvement at the time the tests were conducted, but, because the Stiles-Crawford function remained essentially normal, it is assumed that the receptors were not disturbed relative to their orientation. In this case (as in many others), the zone or area exhibiting functional change does not necessarily match the area exhibiting anatomical change as observed by examination of the fundus, fundus photography, and fluorescein angiography. In the second patient there is evidence of both anomalous inner retinal function and disturbance in receptor alignment. The later suggests disorientation of the receptor bed. These findings correlated with the fundus observation and fluorescein angiographic evidence of a leak, resulting in the presence of serous fluid beneath the neurosensory retina. With resolution of this fluid there was a return of the functional tests toward normal. At this time, it is not possible to determine whether, in two cases, the functional changes are proceeding on a parallel course, but are at different stages, or whether they are the expression of somewhat different anomalies.

Aged↗