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At least 199 records · Page 11Linked to original sources
PubMed1999

Luminance of the surround and visual fatigue of VDT operators.

Luminance distribution in the visual field is considered as one of causal factors with a significant influence on visual fatigue, especially for intensive and extended Video Display Terminal (VDT) work. The aim of the study was to define visual fatigue of VDT operators for different values of surrounding luminance. Experiments were carried out in laboratory conditions under 3 lighting conditions. Only 1 lighting parameter--the luminance of the wall behind the display (surrounding luminance)--changed. Visual fatigue was measured both by a subjective evaluation of different visual complaints (asthenopic symptoms) and by objective measurements of changes in the following visual functions: accommodation, convergence, habitual horizontal phoria, critical fusional frequency (CFF), and visual acuity. The same experiments were done for CRT (Cathode Ray Tube) and LCD TFT (Liquid Crystal Display with Thin Film Transistor) screens. The results of the study have shown that there was no significant influence of the value of surrounding luminance on the asthenopic symptoms for either type of screen. A general tendency towards bigger visual complaints for LCD TFT than for CRT participants was found. An objective evaluation of visual fatigue demonstrated a tendency towards bigger changes in visual functions with an increase of surrounding luminance for both screens. Statistical analysis of the results has shown that surrounding luminance influences significantly the reduction of the accommodation amplitude (significance level <.05).

Adolescent↗
PubMed1992

Neurology of latent nystagmus.

We report eye movement findings in 30 patients with latent nystagmus and who were found to have a variety of associated oculomotor disorders. Latent nystagmus is defined clinically as nystagmus which appears on covering one eye and beats towards the uncovered eye. Recordings showed that the latent nystagmus in 28 patients had slow phases with linear or exponentially decreasing velocity. This nystagmus is termed 'LN'. In 13 of these patients certain manoeuvres (e.g. pursuit) provoked nystagmus with exponentially increasing slow phase velocities characteristic of the congenital form of nystagmus termed 'CN' and we propose that this is a forme fruste of CN. In two patients the nystagmus provoked by cover was latent CN. Twenty-nine patients had a history of strabismus and one had a marked phoria. Some patients had amblyopia whilst others had normal vision in each eye. Although binocular vision was usually absent, six patients had varying degrees of stereopsis. A temporonasal predominance of monocularly elicited optokinetic response previously associated with LN, was present only in a minority of patients. Some responses were bidirectionally absent or of low velocity, possibly the result of a cortical impairment of visual motion detection. The most deranged responses had slow phases which were in the opposite direction to the stimulus as described in CN. The presence of 'forme fruste' CN in many of these patients suggests that some of the derangements of optokinetic responses are due to CN. The findings indicate a greater overlap between the incidences of LN and CN than previously estimated. Thirty percent of patients had large saccadic 'square wave' intrusions. These were not present when there was marked amblyopia. They are attributed to a competitive incongruence of visual fields and eye positions. Dissociations found between the presence and severity of strabismus, stereopsis, amblyopia and optokinetic abnormalities point to these features being relatively independent although associated in typical clusterings. This is evidence against the theory that strabismus and LN are directly caused by nasotemporal optokinetic imbalance which persists because of failure to develop binocular vision. The variability of findings favours the view that LN and CN arise from a genetic or acquired embryological disorder with various degrees and directions of expression.

Adolescent↗
PubMed1996

Combined paresis and restriction of the extraocular muscles after orbital fracture: a study of 16 patients.

Sixteen patients with combined paresis and restriction of extraocular muscle(s) orbital fracture repair were studied before and after in order to determine the clinical features and management of such patients. All 16 patients showed limited ductions of the involved eye in the field of action of the entrapped, paretic muscle and of the antagonist muscle after orbital fracture. Single extraocular muscles (13 patients) and two extraocular muscles (three patients) were demonstrated adjacent to the fracture site on orbital computed tomography (CT). In three patients prior to orbital surgery, a deviation in primary position was present. After fracture repair with release of the entrapped muscle in all patients, evidence of paresis of the muscle was demonstrated by underaction in its field of action and overaction in the field of its antagonist. There was a resultant manifest tropia or phoria in the primary position. In seven patients, the paresis gradually improved with no tropia and little diplopia in the functional fields of gaze. Three patients had minimal deviations and required no further treatment. Six patients with significant deviations required prisms (three patients) or strabismus surgery (three patients). The latter three patients had two muscles involved. Results of this study demonstrate that the ophthalmologist must appropriately diagnose patients with paresis and restriction of an extraocular muscle and counsel them that "new" diplopia may occur after orbital fracture repair and that this diplopia may require additional therapy.

Adolescent↗
PubMed1978

Association of symptoms with measures of oculomotor deficiencies.

Phoria, vergence, and fixation-disparity were measured at near working distances for a nonclinical sample of 3rd-yr optometry students. A questionnaire divided the sample into 33 symptomatic and 44 asymptomatic subjects. Discriminant analysis was used to determine which clinical measures best predicted the group to which each subject belonged. Sheard's criterion was a good discriminator for exo deviations, and a variant of Percival's criterion was good for eso deviations. Fixation-disparity variables proved to be valuable diagnostically. The best fixation-disparity measures were the curve slope, curve type, and amount of fixation disparity.

Asthenopia↗
PubMed1978

Population study of fixation disparity, heterophoria, and vergence.

Data on phorias, vergences, and fixation disparities were gathered for distant and near viewing conditions from a nonclinical, young adult population. Normative values were computed from the data for analysis and comparison. Our study revealed slightly less exophoria at far and near than Morgan's study, together with large base-out vergence readings. We found proportionately more esophores with exo fixation disparity who require base-in prism to neutralize the fixation disparity than Ogle's studies found.

Adult↗
PubMed1979

A visual profile of the alcoholic driver.

Some visual characteristics of the chronic alcoholic were investigated in a sample of 100 male alcoholic patients and 100 matched controls. The purpose of the retrospective study was to determine whether these characteristics may contribute to an increased motor vehicle accident rate among alcoholics. Significant differences between the two groups, which might affect driving abilities, were found for color vision deficiencies and the breakage and loss rate of spectacles. No significant differences were found for stereopsis deficiencies, limitation of visual field, distance phorias, ductions, or the need to wear spectacles for driving. An analysis of the refractive data suggests that alcoholic patients may be slightly more hyperopic and less astigmatic than others; however, these differences are not sufficient to influence driving ability.

Alcoholism↗
PubMed1980

Monocular vergence movements produced by external visual feedback.

An external visual feedback procedure was used by three subjects with normal binocular vision to produce monocular lateral vergence (duction) movements. Feedback was provided by monitoring eye position with an alternating magnetic field system and by displaying the position of the monitored eye to the subject on an oscilloscope screen. Each subject was able to produce both unilateral abduction and adduction. For one subject, phorias were measured prior to several of the abduction feedback sessions, and an increase in exophoria and a decrease in the accommodative covergence/accommodation ratio was observed over the preexperimental measurement.

Accommodation, Ocular↗
PubMed1980

The vision of submariners and National Guardsmen: A longitudinal study.

This study was designed to differentiate among possible causes of an increased incidence of myopia and related symptoms among submariners by making a longitudinal comparison of the visual functions of two groups of subjects, submariners and National Guardsmen. Refractive error, visual acuity, phorias, accommodation, and depth perception were measured. Submariners showed statistically significantly greater losses in visual acuity, accommodation, and depth perception over a 3.5-year period than did the guardsmen, but the differences were very small. Comparison with data in the literature gives evidence of large shifts in refractive error for young men, both submariners and guardsmen, born in recent years. it is suggested that whatever factors are responsible for the increase in myopia in the general population are operating even more effectively among submariners.

Accommodation, Ocular↗
PubMed1980

Fixation disparity analysis of oculomotor imbalance.

A device and method for measuring forced vergence fixation disparity curves in clinical situations are described. Phoria, vergence, and fixation disparity are measures of different functions of the oculomotor system. In decreasing order of diagnostic effectiveness, four features of the fixation disparity curve are curve type, slope, Y-intercept, and X-intercept. Patients with exophoria and non-Type I curves are likely to have ocular discomfort. The steeper the curve, the more likely the patient is to have symptoms. However, Type IV curves are usually flat, and many of these patients do have symptoms. Patients with Type I curves respond well to visual training, but those with Type II curves generally need lenses or prisms to obtain relief. The Y-intercept gives information that is particularly useful in exophoric patients. A complete analysis of the oculomotor system requires measurement of both phoria/vergence and fixation disparity.

Eyeglasses↗
PubMed1981

Effects of base-out training on proximal convergence.

Proximal convergence/nearness ratios were determined before and after a program of base-out training. Ratios using base-out vergence, phoria, and base-in vergence data were found to fall after training while the base-out limit increased dramatically. Since the ACA's did not change, it was concluded that it is not the awareness of nearness that is enhanced in such training, but the amplitude of fusional convergence.

Accommodation, Ocular↗
PubMed1982

The course and effect of visual training on the vergence system.

The effect of a variety of vergence training procedures on the visual system of 35 asymptomatic young adults with normal binocularity was evaluated. The visual training took place on the weekdays of three consecutive weeks. Vergence ranges were measured before the study began and at the end of the 3-week period. Subpopulations were evaluated at one week and at 6 months to document further the course of the effects. Positive fusional vergence training significantly increased the vergence ranges after 1 week of training; a greater effect was measured after 3 weeks. The vergence capability was found to have decreased 6 months later, but the effects of the training were still apparent. Negative fusional vergence training was less effective; however, significant increases were demonstrable after 3 weeks of training. The phorias the accommodative amplitude were not affected by the orthoptics. We conclude that relatively short periods of training can provide long-lasting increases in the vergence ability of a group of binocular normals. The implications of such findings relative to possible neural control mechanisms and clinical visual training situations are discussed.

Accommodation, Ocular↗
PubMed1982

Control theory approach to accommodation and vergence.

A control theory model that treats the accommodative system and the vergence system each as negative feedback systems is investigated. The effects of accommodative vergence and vergence accommodation are included. The controllers in this model are assumed to be linear time-invariant operators. Only time-independent stimuli are considered. If vergence accommodation is neglected, the model is consistent with classical graphical analysis. By including vergence accommodation, several important changes occur. Disparity vergence is not, in general, equal to the dissociated phoria. The shape of the zone of single, clear, binocular vision is changed. Instabilities in the system arise.

Accommodation, Ocular↗
PubMed1983

Orthoptic treatment of subjects showing slow accommodative responses.

Five subjects showing slow accommodative responses were given orthoptic treatment. Speed of accommodative response improved after 3 to 6 weeks. No regressions were evident 18 weeks after the cessation of training. Slow accommodative responses were found in subjects with normal phorias and fusion limits. The technique of dynamic photorefraction is introduced for the clinical measurement of accommodative time characteristics.

Accommodation, Ocular↗
PubMed1983

Dynamics of cover test eye movements.

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.

Adult↗
PubMed1985

Clinical factors in proximal vergence.

Using forced vergence fixation disparity curves, proximal vergence was analyzed in two asymptomatic patient samples; 20 young adults (average age 25.2 +/- 4.71 years) and 20 presbyopes (average age 61.6 +/- 7.8 years). Total proximal vergence was significantly larger when measured under binocular (closed loop) conditions than monocular (open loop) conditions for pre-presbyopes (binocular 10.51 delta +/- 4.7 vs. 6.4 delta +/- 3.84 monocular) and presbyopes (binocular 11.59 delta +/- 3.13 vs. 4.71 delta +/- 2.15 monocular). Associated proximal vergence was shown to predict associated phoria magnitude in presbyopes and in pre-presbyopes when vergence adaptation and convergence accommodation (CA/C) interactions with accommodative convergence (AC/A) are included. A vergence/accommodation model is presented which includes influences of proximal vergence. Clinical implications of the findings relating to diagnosis and therapy are discussed.

Accommodation, Ocular↗
PubMed1985

Adaptation to lens-induced heterophorias.

In previous studies we have shown that subjects with normal binocular vision adapt to prism-induced heterophorias. In this study we have continued the work by investigating whether the oculomotor system can also adapt to lens-induced heterophorias. It was found that subjects gradually adapted to the esophoria induced when viewing a distance chart through negative lenses. Adaptation also occurred to lens-induced esophoria and exophoria at near, while at distance, where the visual feedback was unaltered, the phoria remained virtually constant. These findings demonstrate the flexibility of the oculomotor system.

Adaptation, Ocular↗
PubMed1986

Effect of bifocal lenses on the rate of childhood myopia progression.

Longitudinal records obtained from three optometry practices in the central United States were used to assess the effect of bifocal lenses on the rate of childhood myopia progression. Rates in D/year were derived by linear regression for age spans between 6 and 15 years of age. Records were available for 52 persons who wore single vision lenses (SV group) during this entire age span, and 60 persons who wore bifocal lenses (BF group) during the complete period of observation. The mean rates of myopia progression were -0.44 D/year for the SV group, and -0.37 D/year for the BF group (difference not statistically significant). When rates were determined as a function of nearpoint phoria and near binocular cross cylinder net, the BF group had rates of myopia increase which were lower in magnitude than the SV group in children with nearpoint esophoria and of higher cross cylinder net.

Adolescent↗
PubMed1986

Wide-field fusional stimulation in strabismus.

The effectiveness of wide-field fusional stimulation was evaluated on 57 strabismics and 29 patients with convergence insufficiency. The strabismics had fusion, normal retinal correspondence (even if it coexisted with anomalous retinal correspondence), a deviation not exceeding 30 delta, and visual acuity of 6/7.5 or better. The strabismics included intermittent exotropes, surgically overcorrected intermittent exotropes, and accomodative esotropes. Of these strabismic patients, 42 responded to therapy in which tropias were converted to phorias or the frequency of the manifest deviation was significantly reduced, fusional amplitudes were significantly enlarged, and in many cases, stereoacuity improved as well. In 16 cases, surgery that was recommended before treatment is no longer being considered. Of the patients with convergence insufficiency, 23 responded to therapy which resulted in the enlargement of fusional amplitudes and the alleviation of symptoms. Follow-up visits (for up to 5 years) confirm that the improvement persists, which indicates the utility and effectiveness of this technique.

Accommodation, Ocular↗