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At least 1,189 records · Page 66Linked to original sources
PubMed1984

Effect of a concurrent counting task on dynamic visual accommodation.

The visual accommodation of four male subjects was selectively recorded over a 3-day period using an objective, continuously recording, infrared optometer to determine the effects of a concurrent counting task on their ability to accommodate to a sinusoidally changing focus stimulus ranging from 0.0 to 3.0 D. There was an increase in their steady-state errors in the direction of negative accommodation of from 0.25 to 0.50 D, but the magnitude of the steady-state error induced by the concurrent task did not change over the three sine wave frequencies used (0.1, 0.2 and 0.4 Hz). The results are discussed in terms of an accommodative "lag" model of sympathetic-parasympathetic arousal induced by superimposing an extraneous mental task.

Accommodation, Ocular↗
PubMed1986

Suppression behavior analyzed as a function of monovision addition power.

Monovision, the use of a monocular addition for near viewing, is a clinical technique sometimes used to correct presbyopia. This technique attempts to maintain binocular function while requiring a degree of central suppression. We examined suppression behavior in spectacle monovision as a function of addition power. Suppression behavior was determined by measuring the length and frequency of periods of suppression for a range of monocular addition powers. Testing was conducted at viewing distances of 6 m and 40 cm. The most striking result is the existence of a near/distance differential: the monocular addition power required to stabilize suppression at near is greater than at distance. It was also found that suppression behavior may be stable even in the presence of a relatively high level of stereoscopic acuity. The relation between the contradictory needs for suppression and binocular functioning under monovision conditions is discussed.

Adult↗
PubMed1986

Low contrast charts effectively differentiate between types of blur.

Test charts with three different contrast levels were used to measure acuity of six subjects at distance and near. Reduction in measured acuity as a result of refractive defocus was shown to be independent of contrast level. Reduction in measured acuity with diffusive blur was greater on the medium and low contrast charts than on the high contrast chart. We advocate the use of charts with two different contrast levels to help differentiate between causes of visual degradation.

Distance Perception↗
PubMed1987

Relation between refraction, education, occupation, and age among 26- and 46-year-old Finns.

Refraction of four hundred sixty-six 26- and 46-year-old Finns revealed that the mean refraction of 26-year-olds was about 1 D more myopic than that of 46-year-olds. Myopic refraction was related to education and occupation. The means of refraction were +0.54 D for those whose education was elementary only and -0.70 D for those with secondary and higher education. Those in managerial positions had a mean refraction of -0.49 D, whereas the unskilled or semiskilled in manufacturing or the service trades had a mean refraction of +0.49 D, and farmers and agricultural workers had +0.33 D. The mean astigmatism of the myopes was +0.74 D and that of the nonmyopes +0.51 D. Both the myopic and hyperopic showed more astigmatism than the emmetropic. The estimated proportion of "late myopia" was 25 to 34% of the myopes at the age of 26 years. Present myopia was higher the earlier the first spectacles were received.

Adult↗
PubMed1988

Relation between distance heterophoria and tonic vergence.

The distance heterophoria was measured using both the von Graefe and Maddox rod clinic procedures under standard reduced illumination conditions and in total darkness. Tonic vergence was measured in total darkness. The phoria measures were more divergent than tonic vergence, with the von Graefe being the more divergent of the two measures. The difference between the phoria and tonic vergence position is believed to be due to accommodative divergence derived from the decrease of accommodation, relative to the tonic level, required to focus the distance phoria target. Equations were derived to predict tonic vergence from the phoria value.

Adult↗
PubMed1990

Proximal vergence and perceived distance.

Proximal vergence was measured haploscopically in response to a change in physical distance of a large screen of blurred horizontal lines. These responses were compared to proximal vergence measurements made using a clinical method. Perceived distance of the horizontal stripes was estimated according to the perceived size of a projected afterimage. For 18 normal observers the change in vergence measured haploscopically (in prism diopters per meter angle change in test distance) averaged 2.59 (SD = 1.44) binocularly and 2.11 (SD = 1.22) monocularly. Clinical measures averaged 2.88 (SD = 1.57) binocularly and 2.10 (SD = 1.27) monocularly. Haploscopic and clinical measures of proximal vergence correlated only when the clinical technique was modified by viewing through pinholes. Taking estimated perceived distance into consideration only partially reduced the differences between proximal vergence measured haploscopically and clinically as well as binocularly and monocularly. Both haploscopic and clinical measures of proximal vergence were sizeable, indicating that this vergence component can contribute significantly to the normal vergence response.

Accommodation, Ocular↗
PubMed1990

Effect of target proximity on the open-loop accommodative response.

Proximal stimuli to accommodation were assessed by comparing the open-loop accommodative responses (AR's) to stimuli placed at viewing distances of 5 m (0.2 D) and 0.33 m (3D) in 10 late-onset myopes (LOM's) and 10 emmetropes. The accommodation and vergence loops were opened by subjects viewing targets monocularly through 0.5-mm pinholes. Pre- and post-task levels of tonic accommodation (TA) were used to assess the accommodative adaptation induced by the task. For the 0.2 D condition there was no significant difference between pre-task TA, within-task AR, or post-task TA, indicating that accommodation was open-loop throughout this distal condition. When viewing the 3 D target both refractive groups exhibited significant increases in AR, emmetropes showing higher levels of proximally induced accommodation (PIA) when compared with LOM's. The data indicate that target proximity will influence AR even when both blur and vergence cues have been stabilized.

Accommodation, Ocular↗
PubMed1990

Homo quintadus, computers and ROOMS (repetitive ocular orthopedic motion stress).

Inherent conflict exists between computer systems and ocular physiology of Homo quintadus. Adverse ocular side effects of excessive saccades, excyclotorsion, supraduction, excessive field-of-fixation usage, capitas extension, astigmatic changes, otostatic reflex mismatching, and needless orthopedic malfunctions are imposed upon computer operators. Although the orthopedic dysfunctions are commonly grouped under the heading of Repetitive Strain Injuries (RSI), the inextricable linkage to poor ocular-neurological function argues for postulation of a broader schema entitled Repetitive Ocular Orthopedic Motion Stress (ROOMS). Concepts of good tool usage, total tactile familiarity, total proprioceptive familiarity, and visual cone-of-comfort clash with the installed-equipment base and indicate need for an integrated computer work station to facilitate near covisualization of screen/keyboard and to afford freedom-of-choice for optimal hand/eye synchronicity. The advocacy of computer operators' needs by user-welfare groups, universities, labor unions, and government agencies are portents for achieving genuine improvements.

Biological Evolution↗
PubMed1990

Dynamic eye accommodation evoked by apparent distances.

A three-dimensional optometer (TDO), which can measure simultaneously three major ocular functions in a working environment, was used to measure the visual responses of human subjects viewing: (1) actual artworks and (2) corrugation presented by moving random dots on a cathode ray tube (CRT). Measurements were performed in natural viewing conditions on two emmetropic females. Both subjects demonstrated distinct accommodative responses for the stimuli presented at a fixed distance. The results indicate that the accommodation generally shifts in accord with changes of perceived distance. The usefulness of the TDO was demonstrated in these experiments.

Accommodation, Ocular↗
PubMed1990

Distance heterophoria and tonic vergence.

It has previously been suggested that the difference between tonic vergence (TV) and distance heterophoria may relate either to proximally induced vergence or accommodative divergence. To identify which of these components was responsible for this difference, the present study compared TV and distance heterophoria in a population of 20 subjects. However, distance heterophoria was now assessed with open-loop accommodation. No significant difference was observed between these two measures. This suggests that the previously observed variations between TV and distance heterophoria (with accommodation closed-loop) were produced by accommodative divergence. However, in a subgroup of 7 subjects, measurements of TV were more convergent (greater than 2 delta) than the distance heterophoria. In these subjects, proximally induced vergence may have accounted for the difference in response.

Accommodation, Ocular↗
PubMed1991

Dynamic demonstration of proximal vergence and proximal accommodation.

The complex interactions between accommodation and vergence have been described by dual interactive models which include influences of convergence accommodation and accommodative vergence. Using an SRI Eyetracker, we investigated changes in vergence and accommodation stimulated while looking through prisms or lenses, and while looking at real targets located at different distances. Our results suggest that both proximal accommodation and proximal vergence are stimulated when looking from a distant to a near real target. We suggest that models of convergence and accommodation interactions include proximal accommodation and proximal vergence before the crosslinks.

Accommodation, Ocular↗
PubMed1991

Proximal vergence and age.

A number of previous investigations have suggested that the relative contribution of proximal vergence to the overall vergence response may increase with age. Accordingly the present study has examined the proximal convergence/test distance (PC/T) ratio in a clinical population of 106 subjects ranging from 6 to 47 years of age. PC/T was assessed by comparing accommodative convergence/accommodative stimulus (AC/As) ratios obtained using the gradient and heterophoria techniques. With the former method, the stimulus to accommodation was produced optically using spherical lenses whereas in the latter technique, the change in accommodative stimulus arose from variation in actual target distance. The difference between these two measurements of AC/As reflected the output of proximal vergence. No significant variation in PC/T was observed with increasing age. It is proposed that increased disparity-vergence, rather than proximal vergence, is more likely to compensate for any age-related decline in AC.

Accommodation, Ocular↗
PubMed1992

Variation of congenital nystagmus with viewing distance.

Involuntary oscillations of the eyes in persons with congenital nystagmus often dampen in intensity (amplitude x frequency) with near viewing. This study examined how changes in viewing distance affect the duration and position variability of foveation periods (intervals of low eye velocity when the target's image is at or near the fovea), as these parameters generally correlate better with acuity than nystagmus intensity. To do so, the horizontal positions of both eyes were recorded by infrared limbal tracking in 4 subjects with congenital nystagmus and 4 normals during monocular and binocular fixation at 200, 40, and 20 cm. At nearer distances, position variability (the standard deviation of horizontal eye position) increased in normal subjects, as well as during foveation periods in the subjects with nystagmus. Other parameters of the nystagmus varied idiosyncratically with viewing distance. In none of the subjects with nystagmus was visual acuity (measured psychometrically) better at 40 cm than at distance. The results show that characteristics of congenital nystagmus do not necessarily improve and, in some instances worsen, with near viewing.

Distance Perception↗
PubMed1993

Relation between the dark focus of accommodation and refractive error--a cycloplegic study.

We measured distance refractive error (Dist R), dark refractive error (Dark R), and cycloplegic refractive error (Cyclo R) in 196 subjects whose ages ranged from 4 to 17 years, using the Canon Autoref R-1. We defined the values of (Dark R--Dist R) as DFcus (Dist R) and those of (Dark R--Cyclo R) as DFcus (Cyclo R) in this study. Although DFcus (Dist R) was larger in less myopic and more hyperopic eyes similar to DFcus (Cyclo R), it was zero or plus in high hyperopic eyes, unlike DFcus (Cyclo R). We found Dist R was more strongly influenced by Cyclo R than was Dark R. It is not adequate to use Dist R as the far point for precise evaluation of the dark focus. We should use the difference between Dark R vs. Cyclo R as the true value of the dark focus of accommodation.

Accommodation, Ocular↗
PubMed1993

Distance visual acuity and monovision.

We have investigated aspects of visual acuity with monovision correction. Binocular distance visual acuity with monovision was approximately equal to monocular visual acuity for addition powers (monocular defocus) of +1.00 to +2.50 D, using both high and low contrast logMAR visual acuity charts. Neither the eye chosen to be defocused (dominant or nondominant) or pupil size (3.5, 5 and 7 mm) affected the binocular visual acuity loss with monovision for high contrast charts. We also investigated the effect of induced residual astigmatism (+0.50, +1.00, and -1.00 D) on binocular distance visual acuity in monovision correction. Residual astigmatism caused a significantly greater reduction of binocular visual acuity in the monovision condition than it did in normal binocular conditions. This effect appears to be related to a process of meridional interocular suppression. It may therefore be of clinical importance to correct low amounts of residual astigmatism in monovision corrections to provide optimum binocular visual acuity.

Adult↗
PubMed1995

Vergence adaptation and the order of clinical vergence range testing.

When measuring horizontal relative vergence ranges, the conventional clinical procedure is to assess the base-in (or divergence) range before the base-out (or convergence) determination. The rationale for this order of testing is that the convergence responses stimulated during the base-out measurements may produce vergence adaptation (i.e., a fusional aftereffect), which may temporarily bias the subsequent base-in values in the base-out direction. However, the effect of reversing this order of testing (i.e, base-out before base-in) has not been directly evaluated. Accordingly, the present study compared distance base-in vergence ranges measured both before and after base-out testing at separate test sessions. Additionally, tonic vergence (TV) was assessed before and after each vergence range measurement. The results indicated that base-out vergence range testing stimulated vergence adaptation, and furthermore produced a statistically significant reduction in the subsequently measured base-in recovery value. However, the magnitude of this shift was less than the estimated degree of repeatability of the vergence range measurement. Therefore, a more appropriate order of testing would be to assess the heterophoria compensating range first in order to obtain accurate results during this more critical measurement.

Adaptation, Ocular↗
PubMed1999

Distance, lighting, and parental beliefs: understanding near work in epidemiologic studies of myopia.

PURPOSE: To develop measures and indices of factors (distance of eye from object, posture, and lighting) that may modify a possible effect of near work activity on myopia. METHODS: The duration of near work, the distance of an object from eye, lighting conditions, and other sociodemographic characteristics were asked in an interview. Both distance and lighting information from the questionnaire were compared with more precise measurements. RESULTS: Diopter hours were quantified as the duration of near work multiplied by the reciprocal of the distance which the activity was performed. The intraclass correlation coefficient of the reliability of distance information for each type of near work activity ranged from 0.43 to 0.91. Home light meter readings were significantly higher for children who were reading under both room and reading light, and the distances from the questionnaire were comparable to the measured distances. CONCLUSIONS: Measures of posture, distance, and lighting factors have been developed to study the possible effect modifiers of the effects of near work on myopia.

Accommodation, Ocular↗
PubMed2002

The proximity-fixation-disparity curve and the preferred viewing distance at a visual display as an indicator of near vision fatigue.

PURPOSE: This laboratory study investigates the relation between measures of fixation disparity (FD) (and other optometric measures) and near vision fatigue at a computer workstation. METHODS: Young adult subjects with normal binocular vision performed three blocks of a visual task of 30 min each. In Block A, the viewing distance was 100 cm, as a reference without near vision. In Block B, the viewing distance of 50 cm induced a defined near vision load. In Block C, subjects were free to choose a comfortable viewing distance. This preferred viewing distance was used as an indicator of near vision fatigue because subjects adopting longer viewing distances in Block C had more near vision fatigue at 50 cm in Block B. RESULTS: Subjects with preferred viewing distances longer than average (63 cm) had steeper slopes of FD as a function of viewing distance (100-30 cm), as shown by discriminant analyses. CONCLUSIONS: Thus, this steep proximity-FD curve indicates a weak disparity vergence system that may cause near vision fatigue. This may explain why some young adults prefer longer viewing distances at the computer workstation.

Computer Terminals↗