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At least 145 records · Page 8Linked to original sources
PubMed2002

Changes in Listing's plane after sustained vertical fusion.

PURPOSE: To determine whether prolonged fusion of an imposed vertical disparity leads to a change in the orientation of Listing's plane, even when measured during monocular viewing. METHODS: Four normal subjects (age range, 24-37 years) wore Fresnel prisms of increasing power for 72 hours to produce a final left-over-right disparity (range, 7-11 prism diopters [approximately 3.9 - 6.2 degrees]) that was still fusible. Eye movements were measured binocularly, using three-axis search coils, as subjects fixed on an array of light-emitting diodes (LEDs) arranged on a flat screen, 124 cm away. A regression was used to fit the data points to a plane (Listing's plane) during monocular and binocular viewing. From each planar fit, the horizontal and vertical components of primary position (the direction of gaze that is perpendicular to Listing's plane) were calculated. Baseline data were collected in the unadapted state, either just before or at least 4 days after wearing the prisms. RESULTS: After the period of viewing through the prisms, there was a change in vertical phoria (prism adaptation) ranging from 1.6 to 3.3. There was a significant (P < 0.01) shift of the relative orientation of the vertical component of primary position between the two eyes of 6.3 +/- 1.7 degrees (right eye value minus left eye, up being positive, each measured during monocular viewing). There was no consistent pattern of change in the horizontal component of primary position. CONCLUSIONS: Prolonged fusion of a vertical disparity is associated with a change in the orientation of Listing's plane that persists under monocular viewing. Possible mechanisms include phoria adaptation, the prolonged fusional effort itself, and the residual disparity that must be overcome by sensory mechanisms.

Adult↗
PubMed2002

[Visual function study in work with computer].

This investigation searched for the relationship between amount of nearwork, asthenopic symptoms and visual function, in a group of office workers engaged in telemarketing. Phoria, monocular accommodative facility with +/- 2 lens flippers and near point of convergence were measured in 100 office workers (mean age 21 +/- 2.6 years) whose uncorrected visual acuity was 20/30 or better. Daily hours of reading hard-copy and of computer use, and the level of asthenopic symptoms, were measured using a questionnaire. In this sample, telemarketers were involved 5.84 +/- 2.02 daily hours in computer use, and 2.87 +/- 2.13 daily hours in reading. The following asthenopic symptoms were present twice or more times in a week: headaches 16%, pain in the eyes 17%, red eyes 18%, blurred vision 10%, double vision 3%, burning eyes 19% and watery eyes 19%. An association was found between the amount of hours using computers and red eyes (chi 2 = 4.4, p = 0.0359) or blurred vision (chi 2 = 8.35, p = 0.0038). And also between deficit of convergence and headaches (chi 2 = 4.3313, p = 0.0374) or red eyes (chi 2 = 3.6416, p = 0.0564). No other associations could be found between the accommodative facility test results, the near point phoria, and the amount of nearwork or the asthenopic symptoms. In conclusion, computer use in telemarketing is associated with few asthenopic symptoms. Near point of convergence should be routinely measured, as it is associated with some asthenopic symptoms.

Accommodation, Ocular↗
PubMed2003

The effects of varying examiner position on alternating cover test results.

BACKGROUND: Although the alternate cover test is a widely accepted test of ocular alignment, clinical ambiguity exists with regard to the specific location of the examiner. This study was an attempt to replicate the findings of a previous study that compared two examiner positions and their effect on heterophoria measurement at 40 cm. METHODS: Fifty-seven adult subjects (mean age, 24.0 +/- 2.88 years) with normal binocular vision were measured for heterophoria posture using the alternate cover test while the examiner position was varied between midline and offset 30 degrees to the right of patient midline. RESULTS: A significant difference between midline and offset position of 1.3delta was found (p < 0.0001). The results show that a greater exophoric measurement was seen when the examiner performed the test in the 30 degrees offset position. DISCUSSION: A 1.3delta difference in measured phoria associated with examiner position is consistent with, though smaller than previously reported. Why the examiner position should influence the phoria is possibly related to proximal awareness or prismatic measurement error. Given the small magnitude of the effect found in this study, its relevance for patients with normal binocular vision is slight, though examiner position may contribute to variability in cover test measures between examiners or on test-retest.

Adult↗
PubMed2004

The intraexaminer and interexaminer repeatability of the alternate cover test using different prism neutralization endpoints.

PURPOSE: The alternate cover test (ACT) measures the magnitude of a deviation, but different prism endpoints may be used. This study investigated the intraexaminer and interexaminer repeatability of the ACT using two different prism neutralization endpoints. METHODS: To determine repeatability of two prism neutralization endpoints (first neutral and midpoint of reversal), two experienced examiners measured near point phoria on 72 subjects. Measurements were repeated with examiners masked to each other and the first results. Paired t-tests were used to assess interexaminer and intraexaminer repeatability and the agreement between different prism endpoints for each examiner within each session. Signed and absolute differences in phoria magnitude were calculated. RESULTS: For two different test sessions with the same examiner using the same prism neutralization endpoint (intraexaminer repeatability), none were significant except examiner 1 using first neutral (p = 0.038). Average signed differences (ASD's) between two test sessions for each comparison were <0.5 prism diopter (pd) with SD's of </=2.56 pd. Absolute differences ranged from 1.30 to 1.89 pd. When two different examiners used the same prism endpoint within the same session (interexaminer repeatability), there were no significant differences between examiners. ASD's between the two examiners for each comparison were </=0.53 pd with SD's </=2.03 pd. The absolute differences ranged from 1.19 to 1.67 pd. Comparisons of the two different prism endpoints by the same examiner at a single test session were all significantly different (p < 0.005), but the differences (<1 pd between the two endpoints) were not clinically significant. ASD's were <1 pd with SD <2 pd. Absolute differences ranged from 1 to 1.58 pd. CONCLUSIONS: With experienced examiners, either prism endpoint provides high interexaminer and intraexaminer repeatability (</=0.5 pd). Although the two prism endpoints differ statistically, the differences are not clinically significant.

Adult↗
PubMed2006

[The roles of AC/A ratio and other ocular motor parameters in the induction of late-onset myopia].

OBJECTIVE: This study was to explore ocular motor parameters (accommodation and convergence) in late myopia onset and development. METHODS: Eleven Emm (emmetrope), 14 S.M. (stable late-onset myopia), and 9 P.M. (progressing late-onset myopia) were include in this study. Phoria at distance and near, positive and negative relative accommodation (NRA/PRA), accommodative convergence and accommodation response were measured. RESULTS: Response AC/A ratio of P.M. was higher than that of Emm or S.M. (P < 0.05); But statistically AC/A ratio was not significant difference (P > 0.05). Accommodation response (3.00 D) of Emm was higher than P.M and S.M (P < 0.05). There was significant difference in phoria in near between LOM and Emm, but none in that of distance. There was no significant difference in NRA. However, PRA of LOM was lower than that of the Emm (P < 0.05). CONCLUSIONS: Ocular motor parameters are important in LOM onset and development. Response AC/A ratio (not calculated AC/A ratio) is one of key parameters among them, Response AC/A ratio is the highest in P.M, which indicates out of focus of retinal image in the developing LOM.

Accommodation, Ocular↗
PubMed1990

The validity of Titmus Vision testing results.

A comparison was made between results obtained through the Titmus Vision Tester and those obtained through more common open field optometric procedures. Specific tests performed with the Titmus Vision Tester included near and distance visual acuities, distance lateral and vertical phorias, color discrimination, and stereo acuity. Results were also obtained using Snellen near and distance charts for visual acuities, Maddox rod for vertical and lateral phorias at distance (neutralized with prism), Ishihara plates for color discrimination, and Stereofly Wirt Dot for stereo acuity. The purpose was to determine whether results obtained by the Titmus Vision Tester are significantly different from those obtained by performing the above specific tests on the patient population.

Adult↗
PubMed1988

Trochlear nerve palsy following minor head trauma. A sign of structural disorder.

Trauma-induced superior oblique palsy usually results from contusion or avulsion of the trochlear nerve or from decompensation of a congenital trochlear nerve palsy. Severe craniocerebral trauma is often associated with the former mechanism, whereas more minor closed-head injuries can decompensate a congenital phoria. We report a patient who developed an isolated trochlear nerve palsy following minor head trauma. Investigation revealed an unsuspected tentorial vascular malformation that was compressing the trochlear nerve in its subarachnoid course. In the absence of other features (e.g., documentation of old head tilt, large vertical fusion amplitudes) that support decompensation of a congenital phoria, compressive lesions should be sought in cases of fourth cranial nerve palsies that follow minor head trauma.

Cranial Nerve Diseases↗
PubMed1987

Near vision stress: vergence adaptation and accommodative fatigue.

Changes in the visual system following prolonged near work were investigated. Fifteen young, normal subjects undertook a severe, two hour long, binocular near visual task at 20 cm without any breaks. Fusional stress was assessed by near 'phoria change. Refractive change was measured with an autorefractometer to investigate whether transient myopia occurred and its subsequent recovery. The near task caused vergence adaptation which was primarily due to the fusional stress of the task (accounting for 67% of its variance). The 'phoria change was to a lesser extent (40%) dependent on the accommodative "stress" of the task. Fatigue of the accommodative system resulted in increased accommodative innervation to maintain the same accurate response. Increased innervation can continue after the task on subsequent distance viewing, resulting in transient myopia (mean 0.29 DS). This transient myopia was found to be due to a transient regression of the far point towards the subject's tonic accommodation level. This can be accounted for by a shift of the tonic level as well as an increased bias towards the pre-task tonic level.

Accommodation, Ocular↗
PubMed1987

Vertical fixation disparity correction: effect on the horizontal forced-vergence fixation disparity curve.

Following a suggestion made by Percival in regard to dissociated phorias, we corrected vertical associated phoria in several patients who had disparities in both vertical and horizontal fixation. The principal objective result of this correction was a flattening of the slope of the type I horizontal forced-vergence curve. This result may be significant particularly because the slope has been identified as being a good prognosticator of patients likely to be symptomatic. Attention to a concurrent vertical component may offer a convenient way to normalize a steep slope on horizontal fixation disparity curves.

Adult↗
PubMed1986

Lateral short-term prism adaptation in clinical evaluation.

Data were obtained from a normal clinical population regarding heterophoria, associated phoria and short-term prism adaptation in an attempt to differentiate between those subjects with symptoms and those without. Correlation between heterophoria, associated phoria, prism adaptation and symptoms was low. A short prism-adaptation test was found to be of little value in diagnosing decompensated heterophoria in the general population. Subjects diagnosed as having decompensated heterophoria did not have an abnormal short-term prism-adaptation system. The clinical implications of these findings are discussed in relation to the diagnosis of decompensated heterophoria and the prescribing of prismatic corrections.

Adaptation, Ocular↗
PubMed1979

Amblyopia and the monofixation syndrome.

Children with a Monofixation syndrome often show a small angle constant esotropia with an overlying esophoria of variable and often large angle. Commonly the phoria is well controlled unless the child is very tired, or the eyes are dissociated. Treatment of a concomitant amblyopia by patching may result in an inability to control the phoria, with breakdown of the strabismic angle to a large esotropia. Illustrative cases are presented.

Amblyopia↗
PubMed1982

Oculomotor adaptation to induced heterophoria and anisometropia.

In the first part of the paper we demonstrate that the oculomotor system adapts to prism-induced heterophoria over limited motor fields. In the second part we demonstrate that it can also adapt to an induced anisometropia. When normal subjects are made 3 diopters anisometropic, they initially exhibit a phoria whose magnitude is dependent on eye position. After 21/2 hr of binocular visual experience, this incomitant phoria has largely disappeared.

Adaptation, Physiological↗
PubMed1994

Effect of spectacle correction on the progression of myopia in children--a literature review.

BACKGROUND: Methods used to attempt to control childhood myopia progression have included various types of spectacle correction. The most commonly studied technique has been the use of bifocal lenses. METHODS: The literature on the effects of bifocals, undercorrection, and part-time wear of spectacles on the rate of myopia progression in children was reviewed. RESULTS: The data available on undercorrection and part-time wear of spectacles is limited. There have been several studies on the effects of bifocals. Some studies reported no effect with bifocals, some studies reported reduced rates with bifocals, and some noted lower rates with bifocals may be associated with particular ocular or visual findings. CONCLUSIONS: Critical analysis of the literature suggests that when the nearpoint phoria is eso, greater rates of progression occur, and that some degree of myopia control may be established by shifting the phoria into the normal range by spectacle corrections such as bifocals.

Child↗
PubMed1995

A quantitative analysis of eye movements during the cover test--a preliminary report.

The aim of this study was to carry out quantitative analyses of eye movements during the cover test on a group (n = 57) of asymptomatic emmetropes. Eye movements were recorded during an automated cover test while subjects fixated a distance (3.4 m) and near (0.4 m) target. There was a significant difference between the amplitude of phoria measured after 2 s of occlusion compared to 10 s (P < 0.01). The mean phoria after 10 s of occlusion was 0.1 degree (eso) for distance fixation and 1.6 degrees (exo) for near fixation. The distribution was approximately normal for both distance and near fixation but the standard deviation was greater for near (2.0 degrees) than distance fixation (1.4 degrees). The pattern of eye movements during the recovery phase was more complex than is often assumed, in many cases consisting of a variety of saccadic and vergence movements involving both the covered and 'fixing' eye. The latency of the first recovery movement was significantly shorter for exophoric than esophoric deviations (P < 0.01) and the latency of some recovery movements were very short (< 150 ms).

Adolescent↗
PubMed1995

Distance cues for vertical vergence adaptation.

Vertical vergence can be trained to respond to vertical and/or horizontal conjugate eye position, horizontal vergence, and vertical head tilt. This cross-coupling is manifest as a vertical phoria aftereffect (monocular vertical vergence response) that varies with direction and distance of gaze. The function of the spatially dependent adaptation is to maintain the calibration between vertical eye alignment and intended placement of the two retinal images. Oculomotor adaptation stabilizes our sense of spatial localization and calibrates a body-referenced coordinate representation of visual space that is necessary for visually guided motor responses. We have tested the possible association of vertical phoria adaptation with perceptual cues to distance in the absence of any other associated motor activity. During adaptive training, vertical disparity vergence was associated with variations of perceptual distance cues (including loom, overlap, relative size, and relative motion), oculomotor distance cues (horizontal vergence), or a combination of both classes of cues. We observed that in a 2-h period the open-loop (monocular) vertical vergence response could not be trained to occur as an aftereffect in association with the perceptual cues to distance, whereas it could be trained in association with oculomotor cues. We conclude that the spatial specificity of vertical vergence aftereffects caused by short-term adaptation results from an associated cross-coupling with supranuclear sources of oculomotor activity.

Adaptation, Ocular↗
PubMed1997

The effect of edrophonium chloride on muscle balance in normal subjects and those with nonmyasthenic strabismus.

Because the Lancaster red-green test and the Hess screen are not widely used by most ophthalmologists, we used the alternate prism-cover test to study the effect of intravenous edrophonium chloride (Tensilon) on the ocular alignment of 30 normal subjects and 14 individuals with nonmyasthenic strabismus. After measurement of their baseline phorias and tropias, patients received an intravenous injection of Tensilon via the incremental dose technique until autonomic effects of the drug were noted or until 10 mg was administered. Another set of measurements of muscle balance was taken immediately postinjection and 2 and 5 min later. Apart from a small increase (mean, 2 prism dipoters; p = 0.004) in their exophoria at near, normal subjects exhibited no significant change in their phorias after Tensilon injection. One third to one half of the nonmyasthenic strabismics, however, showed a change in their vertical deviation after Tensilon (46% at distance and 38% at near), with the majority of them increasing their angle of squint. These changes were small (mean, 1.7 prism diopters; maximum, 5 prism diopters). In only one case did reversal of the direction of deviation occur. Tensilon produces a statistically significant increase in near exophorias of normal subjects and in vertical distance deviations of nonmyasthenic strabismics. These changes, however, are clinically insignificant and should not be considered to constitute a positive Tensilon test.

Adolescent↗
PubMed1997

[Eye damage and lighting among workers in the beer industry].

A cross-sectional study was realized to determine the occurrence of visual pathology in 143 male workers of the bottling area of a beer industry, in Zulia state, Venezuela; and it was compared with a control group of 143 male workers of the administrative area, similar in age, weight and height, with different periods of occupational exposure. A medical history, visual acuity, astigmatism, stereopsis, phoria, occupational visual capacity and tonometry tests, were realized. The risks in the occupational environment were identified through an industrial hygiene survey and inspection of the work sites. Lighting was measured according to the established COVENIN 2249-85 norm. The workers of the bottling area presented a greater frequency of pathological antecedents (conjunctivitis and foreign bodies); occupational and non-occupational antecedents; smaller frequency of pterygium and near sightedness; smaller values for the visual acuity in workers older than 40 years (p < 0.05); greater frequency of astigmatism, steropsis, phoria, below average visual capacity; and abnormal intraocular pressure. The point prevalence of the clinical findings was greater in the bottling area workers and the disparity reason corresponded to a non-significant causative association. The mean lighting measures were greater in the bottling area (p < 0.05); however, with the exception of the bottle washing area, they were below recommended levels. This study suggests the influence of occupational risks factors in the visual system and the need to implement prevention and control measures.

Adolescent↗
PubMed1986

Vergence adaptation: a review.

The present review aims to discuss the current researches on the ability of the vergence system to adjust to new information. A concomitant or non-concomitant binocular retinal disparity caused by a prism or an anisometropic prescription can be adapted to such that the induced phoria of fixation disparity reduces back to the original value. The features and mechanisms of this normal adaptation and also the response in subjects with abnormal binocular vision are discussed. The less extensive work on the adaptive ability of the accommodative vergence system is also reviewed.

Accommodation, Ocular↗