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J M Enoch

Publications and source records attributed to J M Enoch.

At least 19 recordsLinked to original sources
PubMed1992

Variation of the hyperacuity gap function with age.

Responses to hyperacuity stimuli are processed in quite a different manner by the central nervous system than many other stimuli such as resolution targets or increment threshold stimuli. With increased attention being paid to visual response in aging individuals, it is important to study how these response paradigms are affected by age. In this analysis, otherwise normal observers 20 to 85 years of age were studied. The hyperacuity gap test was used. As defined, this is a vernier test using a two-point test array. This particular format was chosen because the resultant data are less distorted by image blur, scatter, and astigmatism than other designs we have studied. The gap or feature separation between the two small targets (which were aligned vertically) was increased logarithmically using octave steps and the hyperacuity threshold (setting variance) was measured for each step. No systematic variation of vernier hyperacuity threshold was found with increasing age within the range of ages or gaps tested. This is important because it can serve as a valuable control and reference for other clinical studies of aging.

Adult↗
PubMed1992

Everett Kinsey Lecture. Hyperacuity, a technique for assessment of results of refractive surgery.

In recent years there have been rapid advancements in corneal refractive surgery. The results of keratorefractive procedures are generally not predictable and wound healing effects interfere with the stability. The problems with predictability and stability make the usual visual performance indices such as visual acuity and contrast sensitivity testing insufficiently refined for functional assessment of visual performance after keratorefractive surgery. We argue that there is a need for precise visual functional analysis that parallels and complements the advanced technologies employed in ophthalmic surgery. Results from hyperacuity test paradigms are put forth as one set of precise, reliable bench marks for characterizing the results of refractive surgery. Hyperacuity testing is well suited for analysis of visual performance after keratorefractive surgery because the procedure is resistant to optical image degradation and requires a higher-order analysis by the visual system. The uses of hyperacuity techniques are discussed.

Humans↗
PubMed1991

Anomalous kinetic visual fields found in family members of patients with a confirmed diagnosis of Gilles de la Tourette syndrome.

Three visual manifestations of Gilles de la Tourette syndrome (TS), a neuropsychiatric disorder, have been previously reported. In this paper we report anomalies in the measured kinetic paracentral visual field of TS patients and their family members. We found that 96% of TS patients exhibited paracentral kinetic visual field defects (nasal and temporal steps, enlargement, "ringing," and/or baring of the blind spot). Ninety-three percent of fathers of TS children and, surprisingly, about 80% of mothers exhibit these characteristic visual field anomalies. Sample data and examples of family studies are reported.

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↗
PubMed1979

Visual resolution in a patient exhibiting a visual fatigue or saturation-like effect: probable multiple sclerosis.

A rapid visual resolution test conducted on available equipment reveals the presence of rapid falloff in acuity in a case of probable multiple sclerosis. Intense large field illumination was used, and grating acuity was tested using laser red light. The effect is so large that minor anomalies (not subjectively appreciated) or the residuum of earlier minor attacks of retrobulbar optic neuritis can be readily detected. A related "visual fatigue or saturation-like syndrome" was described earlier. In bright environments these patients' vision fades. Briefly closing the eyes restores visual sensitivity. Providing filters or lowering the light level tends to maintain vision. This test must be studied intensively. It offers a noninvasive simple means of showing underlying anomalies in neural conduction of the visual signal. Such anomalies can be prognostic and previously have been revealed only with sophisticated electrophysiological techniques.

Adult↗
PubMed1979

Interferometric visual acuity testing in anterior segment disease.

Preoperative and posteroperative visual acuities for Landolt ring targets and for a grating target of comparable retinal illuminance produced by two-beam interference were assessed in patients with anterior segment disease. Good preoperative interferometric acuities (6/12 or better) were found in over half of the cases in which Landolt acuities were 6/90 or worse. In general, good preoperative interferometric acuities were predictive of good postoperative Landolt acuities. However, poor interferometric acuities in patients with opacified media did not preclude good Landolt acuities postoperatively. We conclude that interferometric acuity testing can provide valuable information about potential macular resolution capacity in some cases. Both the strengths and weaknesses of interferometric acuity testing must be appreciated for successful application.

Cataract↗
PubMed1979

Measurement of visual resolution at high luminance levels in patients with possible demyelinating disease.

An interferometric acuity device (Takata) has been used to study visual resolution in individuals with possible demyelinating disease. The instrument employed provides a large field with a continuous range of grid or fringe frequencies and a relatively intense (10(5) mean photopic trolands) stimulus. After a brief period of time with eyes closed, resolution thresholds of patient are repeatedly determined during a five minute period. In all individuals suspected of having a demyelinating disease tested to date, a fall off in resolution capability has been found in time when using this intense stimulus display. This occurs whether eye signs have been present, are present or have not yet been observed. Normal observers do not exhibit comparable decrements. The fall off in resolution capability may or may not occur at lower stimulus levels, and is often not revealed when testing routine Snellen acuity. Outer and inner retinal pathology (division based on vascular support) do not cause a comparable fall off in resolution in time. The interferometric acuity test is a non-invasive, easily applied test.

Adult↗
PubMed1979

Physiology of monocular aphakia.

The refraction of the unilateral aphakic patient has been aided by recent improvements in the ophthalmometer. New techniques simplify retinoscopic assessment of the patient. Choice of the type of correction, ie, spectacle, contact lens, contact lens-spectacle combination, or intraocular lens, depends on several factors. One factor is image size difference in aphakic and phakic eyes, particularly if removal of a second cataract is not imminent and vision is good in both eyes. Simple approaches that allow approximate size correction and effective restoration of binocularity are described. The current status of correction of vision in unilateral aphakic infants and young children is also discussed.

Adult↗
PubMed1979

Specification of the directionality of the Stiles-Crawford function.

An index to specify the directionality (spread) of Stiles-Crawford function and related retinal photoreceptor directional sensitivity data is proposed. This index, termed the half-sensitivity half-width (or angle) is the displacement in the pupil (or the change of angle of incidence at the retina) which results in a reduction of sensitivity to one-half that at the function maximum (0.3 log unit decrease). The half-sensitivity half-width or angle, unlike other currently used indices of retinal directionality, can be assessed empirically and is not intrinsically dependent upon curve-fitting assumptions or procedures.

Humans↗
PubMed1979

A study of the Stiles-Crawford (S-C) function at 35 degrees in the temporal field and the stability of the foveal S-C function peak over time.

Directional sensitivity of the retina (the Stiles-Crawford function of the first kind) was measured at a point 35 degrees from fixation and at the point of fixation. Three normal observers were used. The peripheral test point intercepted the retina between the optic nerve head and the ora serrata. At both test points, photopic and scotopic (one subject) Stiles-Crawford function peaks were contained within the pupillary bound and approximated the center of the pupil. Directionality at the two points was rather similar. These findings add strength to the argument that retinal receptors align approximately with the center of the exit pupil of the eye. Evidence for stability in Stiles-Crawford peak location in time is also presented.

Adolescent↗
PubMed1979

Effect of uniocular occlusion on selected visual functions.

Uniocular occlusion (dark patching) of adults for a period of days produces marked reduction in the directional sensitivity of the eye (Stiles-Crawford effect). The effect reaches a maximum 3 to 5 days after the onset of patching. Recovery occurs in a comparable period. The second eye is not affected, and a simple light diffuser fails to produce the same effect. Coupled with alteration in directional sensitivity are an overall increase in sensitivity and modest resolution and perceived colour changes. These findings, with other research, suggest that directional sensitivity is at least partially mediated by light and that orientation of photoreceptors is an active process.

Adult↗
PubMed1978

Retinal receptive field-like properties and Stiles-Crawford effect in a patient with a traumatic choroidal rupture.

Simple psychophysical techniques were used in order to assess layer-by-layer retinal functions in a patient with sub-retinal fluid due to a choroidal rupture following ocular trauma. A substained-like and a transient-like function believed to reflect retinal receptive-field-like properties, and an indicator of retinal receptor orientation (the Stiles-Crawford effect) have been followed in time. Central visual acuity was also measured. Initially all measured functions provided anomalous responses in affected retinal areas. Of interest here is the nature and order of recovery of the measured response functions. Most notable was the rapid rate of recovery of receptor orientation and the slower rate of recovery of the transient-like function.

Adolescent↗