Biomedical subjects
Publications and source records attributed to E Peli.
A patient with uncorrected antimetropia was found to attain motor fusion through blinking. Although this patient was also able to attain motor fusion through saccadic vergence and slow fusional vergence, he usually relied on blink vergence. In this patient, blink vergence was an efficient alternative to slow fusional vergence.
We investigated a number of image processing techniques for enhancing the retinal nerve fiber layer (NFL) in fundus photographs taken with red-free light. Wedge-type defects within the NFL were enhanced best by contrast enhancement algorithms such as histogram modification and extremum sharpening. Narrow, slitlike NFL defects can be enhanced by directional enhancement techniques. Normal NFL features were enhanced best by high-pass filtering techniques such as homomorphic filtering and adaptive enhancement. The enhanced normal NFL may be useful in the analysis of diffuse NFL loss. All of these successful enhancements of normal and defective features indicate that enhancing fundus photographs with digital image processing techniques should facilitate early detection of optic nerve damage from glaucoma and other diseases.
Circular polarizing filters have recently been introduced in several ophthalmic applications. These applications include clinical instruments for ophthalmoscopy, slit-lamp specular microscopy, and fundus photography, as well as consumer products such as 3-D movie projection and viewing systems and glare-control screens for computer visual display terminals. The nature of circularly polarized light and mode of operation of the circular polarizing filters in various applications are discussed. In view of the advantages of circular polarizers in vectographic applications, the current linearly polarized vectographic systems used for binocular testing and visual training should be replaced with circular polarizing systems.
To investigate how patients with macular scotomas use residual functional retinal areas to inspect visual detail, a scanning laser ophthalmoscope (SLO) was used to map the retinal locations of scotomas and areas used to fixate. Three patients with dense macular scotomas of at least 20 months duration and with no explicit low vision training were tested. SLO stimuli were produced by computer modulation of the scanned laser beam, and could be placed on known retinal loci by direct observation of the retina on a television monitor. Videotaped SLO images were analyzed to produce retinal maps that are corrected for shifts of stimulus position due to fixational eye movement, thus showing the true retinal locations of scotomas and fixation loci. Major findings were as follows: 1) each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma to fixate, and did not attempt to use the nonfunctional foveola, 2) fixation stability with the eccentric fixation locus was as good as, or better than, that of ocularly normal subjects trying to fixate at comparable eccentricities, 3) fixation stability was not systematically related to clinical visual acuity, and 4) there is good agreement as to the shape and overall size of SLO and standard clinical tangent screen scotoma maps for these three patients.
A simple and inexpensive technique for enhancing the visibility of corneal endothelial cells in specular reflection biomicroscopy involves the insertion of a circular polarizer in front of the patient's eye, intersecting both the incident and reflected light beams. This filter significantly reduces the glare from the epithelium and enables more comfortable and clearer viewing of the endothelial cells.
A visual evoked potential (VEP) component that appears in the power spectrum only during binocular fusion has recently been discovered. When both eyes are stimulated with the same checkerboard but at different pattern reversal rates, this fusional component appears at a frequency intermediate between the two stimulus frequencies. We have proposed a model to explain the appearance of this intermediate component and have tested the model's predictions that the fusional component will remain constant independent of binocular or monocular changes in stimulus contrast. As predicted by the model, changes in contrast over the range of 10 to 90% produced no significant change in the power of the fusional component.
Explore the source record for details and available documents.
A signal derived from continuous measurement of eye position is displayed on a visual frame of reference, thereby closing a secondary visual feedback (2VFB) loop. The distance between a target and the displayed gaze point provides the subject with an extra, artificial position error. Experiments show that subjects can use the 2VFB to generate smooth eye movements, even in the absence of any smoothly moving independent targets. Under these conditions, both direction and velocity can be brought under voluntary control by the subjects. As a control signal for the smooth-eye-movement mode, the 2VFB is robust and easily manipulated and provides an attractive means for the investigation of the smooth-movement control system in a variety of tasks and under different conditions.
The effect of stimulus contrast changes on the binocular visual evoked response (VER) was investigated using pattern reversal VER, dichoptic stimulation, and Fast Fourier Transform. When the stimulus contrast was changed binocularly, the monocular components increased as the contrast increased. The binocular component first appeared at the level of 10% contrast; its magnitude was stable under all recording conditions. When the stimulus contrast was changed monocularly, the eye that received the higher contrast stimulation showed more power in the power spectrum. The binocular component appeared even when the difference in contrast between the two eyes was large. The magnitude of the binocular component was stable under all recording conditions. We concluded that the binocular and the monocular components differ in the magnitude of their responses to a contrast change and speculate that the pathways responsible for the two components are not identical.
The dynamics of unilateral cover test eye movements, never before systematically investigated with an objective recording system, are shown to be more complex than textbook accounts of them. We administered the cover test to nine heterophoric subjects by means of electromechanical occluders. Eye movements were recorded using the infrared photoelectric technique. Saccadic and vergence movements of the fixating eye were observed in almost all records when the occluded eye was uncovered. These movements were found in esophores and exophores and in both large and small phoria cases. Such movements were previously described in other asymmetric vergence tasks and appear to obey Hering's law of equal innervation. Uncovering the dominant eye, in cases of clear dominancy, resulted in shorter latency and larger amplitude saccades than did uncovering the nondominant eye. These large saccades were frequently of unequal amplitude in each eye. Trained subjects appear to use dynamic overshoots to increase this saccadic inequality and thereby attain vergence during saccades. Movements after the application of a cover to one eye, while grossly similar to textbook descriptions of them, are found to contain small vergence drifts and refixation (correcting) saccades in the nonoccluded eye.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Reflected glare often interferes with vision. Since such glare is usually polarized it can be controlled with polarizers. The use of polarized filters to eliminate vertically polarized glare from blackboards and glossy printed material is presented. Practical means for the construction of such filters are discussed.
Secondary visual feedback (2VFB) is a visual signal derived from continuous measurement of eye position and provides an extra artificial indication of the point of gaze. 2VFB may be eccentrically displaced and subjects are able to visually superimpose 2VFB onto a visual target signal and thus achieve and maintain eccentric fixation. Initial transient patterns of movement depend upon training but even naive subjects can achieve eccentric fixation within the first 40 s of such a task. Individual strategies and idiosyncratic patterns are exaggerations of normal control and fixational eye movements. The variance of maintained fixation increases with eccentricity and appears to be related to visual acuity as well as to precision of ocular motor control.
Displaying the point of gaze to the observer in addition to a point target provides a secondary visual feedback (2VFB). Eccentric fixation is achieved using a biased 2VFB to yield an experimentally imposed "eccentric fovea." The target is suddenly moved to a new position and the task is to regain it, in the "eccentric fovea". It is found that the pattern of eye-movement response consistently starts with saccadric foveal exploration of the target, but its latency has twice the duration of a regular voluntary saccade. Practice, however, makes for the shortened latency tending asymptotically to the regular saccadic duration.
Fundus imaging and photography are cornerstones of modern ophthalmic practice. The recent developments in electro-optic and computer imaging technology resulted in many improvements in the acquisition and analysis of fundus images, which already are being used in commercial fundus imaging systems. This paper reviews the basic aspects of the electro-optic methods for fundus imaging, with emphasis on the differences between these new techniques and conventional, film-based, fundus photography. Potential benefits of these systems in image acquisition, archival, communication, processing, and quantitative analysis, as as well as their current advantages and shortcomings are discussed.
Horizontal, smooth pursuit eye movements were recorded from adults and children with infantile and late-onset esotropia using a remote, video-based, eye-movement recording system. Each subject monocularly tracked a 0.5-degree target moving back and forth on a video monitor at a constant velocity of 10 degrees, over a range of 12 degrees. Each subject's nasal and temporal gain (eye velocity/target velocity) was measured. Confirming the results of previous studies, we found that infantile esotropes had asymmetrical pursuit eye movements (nasal gain greater than temporal gain) while late-onset esotropes had symmetrical gains. However, unlike previous investigators, we found that half of the late-onset esotropes had impaired pursuit gain. The magnitude of the pursuit abnormality and the amount of refractive error were correlated--patients with the highest refractive error had the lowest pursuit gain.