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PubMed1989

Evaluation of a new criterion of binocularity.

The purpose of this study was to assess a new criterion for binocular comfort analogous to the classical Sheard's criterion. Instead of equating the fusional demand with the monocular phoria as is done when Sheard's criterion is applied, the new criterion uses a calculated binocular fusional demand. The binocular demand was derived using a clinical measurement of the convergence accommodation per convergence (CA/C) ratio. Sheard's criterion was also evaluated. Other commonly used indicators of binocularity (heterophoria, vergences, accommodative amplitude, facility and response, fixation disparity, and the associated phoria) were measured. One hundred subjects (52 males, 48 females; mean age 26 years) were classified as either symptomatic or asymptomatic by an interviewing clinician. The examining clinician was intentionally masked as to the classification of the subjects. We hypothesized that the new criterion would best discriminate between the two groups of patients inasmuch as it is based on currently accepted dual-interaction models of accommodation and vergence. Our analysis confirmed that the CA/C ratio corresponded closely to those published previously (mean = 0.06 D/delta). Significant differences (p less than 0.05) were determined between the symptomatic and asymptomatic groups for gender, near phoria through a +2.00 D add, accommodative amplitude, positive vergences at near, and both the classical Sheard's and the new criterion. The new criterion was the best discriminator between the groups, identifying 72% correctly, an improvement of 6% over the classical Sheard's. However, various stepwise discriminant analysis procedures consistently failed to demonstrate that the calculated binocular fusional demand or the new criterion was superior to the near phoria or the classical Sheard's value. These results suggest potential clinical utility for new procedures based on recently described models of accommodation and vergence, but further development appears necessary.

Accommodation, Ocular↗
PubMed1991

Nongaussian distribution curve of heterophorias among children.

The purpose of this study was to measure the distribution curve of horizontal and vertical phorias among children. Kolmogorov-Smirnov goodness of fit tests showed that these distribution curves were not Gaussian among (N = 2048) 6- to 13-year-old children. The distribution curve of horizontal phoria at far and of vertical phorias at far and at near were leptokurtic; the distribution curve of horizontal phoria at near was platykurtic. No variation of the distribution curve of heterophorias with age was observed. Comparisons of any individual findings with the general distribution curve should take the nonGaussian distribution curve of heterophorias into account.

Adolescent↗
PubMed1999

Oculomotor function after virtual reality use differentiates symptomatic from asymptomatic individuals.

UNLABELLED: Some individuals who use virtual reality (VR) head-mounted displays (HMD) have adverse visual symptoms. PURPOSE: We measured oculomotor functions of symptomatic (n = 10) and asymptomatic (n = 10) individuals to determine if there were fundamental oculomotor performance differences. METHOD: Before and after 20 min of biocular VR-HMD use, we measured: phorias, fixation disparity, gradient accommodative convergence to accommodation ratio (AC/A), stereopsis, and nearpoint of convergence. RESULTS: We observed an exophoric shift in the nearpoint phoria of almost all subjects, whereas the farpoint phoria showed no trend. Interestingly, we observed that the phoric shift at far and near was highly correlated for the asymptomatic subjects but not for the symptomatic subjects. In addition, the (stimulus) AC/A ratio of symptomatic subjects was reduced after a period of VR-HMD use, whereas asymptomatic subjects' AC/A ratio was not reduced. CONCLUSION: The oculomotor changes among the symptomatic subjects (increased exophoria at near and reduced AC/A) appears consistent with a reduced accommodative response. In contrast, the asymptomatic subjects show changes (correlated change in phorias) which seem most consistent with adaptation in the tonic component of vergence and/or accommodation.

Accommodation, Ocular↗
PubMedDate not supplied

Near esophoria is associated with high myopia.

BACKGROUND: A retrospective study was undertaken to examine the hypothesis that esophoria is associated with higher amounts of myopia. METHODS: One hundred and forty-four subjects were selected from the files of optometry clinics at the Department of Optometry, National University of Malaysia, from the years 1995 to 1998 inclusive. These subjects were matched in terms of age group, sex, race and near phoria group. Near phorias were determined by Maddox wing technique and were classified into three groups: more than six prism dioptres exophoria, zero to six prism dioptres exophoria and any esophorias. RESULTS: One way analysis of variance revealed that there were significant differences in mean myopias between the three phoria groups (ANOVA, F(2,141) = 5.34, p < 0.01). Further analysis with the Student-Newman-Keuls test showed that the amount of myopia is significantly higher in the esophoric group than in the other two groups. CONCLUSIONS: The results support the hypothesis that near esophoria is associated with high myopia. This study suggests that near phoria might be an important factor in myopia development.

Journal Article↗
PubMed1994

Effect of fixation disparity on distance binocular visual acuity.

Subjects with appreciable values (2 delta and greater) of associated 'phoria, as measured by a Mallett unit, had their distance monocular and binocular visual acuities measured. In the latter case measurements were taken both with the associated 'phoria corrected by prisms and without such a correction. The improvement in binocular acuity compared to monocular acuity was less than would occur in normal subjects with minimal associated 'phorias although the improvement differed accordingly as to whether the readings were eso- or exo-in mature. When the associated 'phorias were corrected with prisms the improvement in binocular over monocular visual acuity was similar to that found in normal subjects.

Adult↗
PubMed1989

Depth perception after prolonged usage of night vision goggles.

The present study was initiated following a report that a few helicopter pilots had failed a test of stereoscopic depth perception after a prolonged training flight employing night vision goggles (NVGs). In order to determine the cause of the loss, 12 helicopter pilots/copilots were assessed for depth perception, lateral and vertical phoria, and contrast sensitivity before and after training flights requiring the pilots to wear night vision goggles for the duration of the flight. Pilots flew one to three missions while wearing either PVS-5A or AN/AVS-6 goggles. Mission duration ranged from 1 to 4 h. The results indicate that contrast sensitivity and depth perception when monocular cues are present did not degrade over the course of the mission. Lateral phoria, however, did demonstrate an average exophoric shift of 1.5 prism diopters for 12 out of the 24 missions. The results indicate that the original report of a loss of depth perception based on a test of depth requiring stereopsis might have been caused by a shift in lateral phoria. It would be expected that as additional fusional effort is required, the minimum resolvable disparity degrades due to the increase in accommodation brought about through vergence accommodation. Possible causes for the phoria shift and future testing are discussed.

Accommodation, Ocular↗
PubMed1981

Comparison of nearpoint techniques.

Thirteen subjects, 11 males and 2 females, from 24 to 35 years of age, were tested at the nearpoint. Three testing procedures, the Mallett near unit, the traditional examination technique, and the Borish nearpoint card, were performed. Results were analyzed to see whether a significant difference exists between the 3 types of nearpoint testing techniques. The Borish card differed significantly from the traditional technique (p less than .05) on tests of visual acuity, unfused crossed cylinder and fused cross cylinder. Donder's amplitude of accommodation on the Mallett unit and on the Borish card differed significantly (p less than .05). No significant difference was noted with the traditional technique versus the Borish card on tests of lateral phoria, vertical phoria, and vergences, or between the Mellett and Borish test on lateral associated phorias, vertical associated phorias, fine suppression, balance of sphere at near and cylinder power at near. Gross suppression was found in 2 of 26 measurements on the Mallett tests. No subjects indicated gross suppression on the Borish card.

Adult↗
PubMed1975

Binocular convergence in man during total sleep deprivation.

It was proposed that binocular convergence (lateral phoria) for near and far vision would reflect the states of visual functioning and that there would be a progressive reduction in phoria during sleep deprivation. Six young male subjects underwent two conditions of sleep deprivation on separate occasions. One condition incorporated a high visual load and the other a low load. Exercise and sound were balanced. Lateral phoria for near and far vision was carefully measured, regularly, before, during and after sleep deprivation. It was found that a reduction in convergence (exophoria) for both near and far vision became increasingly apparent with progressive sleep deprivation, especially with near vision and under high visual load. The near vision measure, which included accommodation convergence, appeared to be more sensitive to sleep deprivation generally, whereas far vision tended to produce a greater differentiation between the conditions. The implications of these findings for REM sleep and oculomotor innervation are discussed.

Accommodation, Ocular↗
PubMed2002

Changes in cyclotorsion and vertical eye alignment during prolonged monocular occlusion.

When binocular vision is prevented with monocular occlusion, the two eyes assume a position of rest related to the combination of underlying tonic innervation of the oculomotor system, cross-coupled accommodative-vergence input and vergence responses to perceptual cues for spatial location relative to the head. When the latter two are controlled, the covered eye has been shown in the majority of subjects to turn outward (exophoria) and upward (hyperphoria) after prolonged monocular occlusion. The present study investigates the change in torsional eye alignment and its relation to vertical eye alignment after eight hours of monocular occlusion. The results revealed an excyclophoria during occlusion in four out of five subjects. The patched eye also became elevated in two subjects and depressed in two others. Thus, during prolonged monocular occlusion, the relative directions of cyclophoria and vertical phoria appear to be independent. In addition, there were non-concomitant changes in vertical phoria with horizontal gaze, toward a state where the adducted eye was elevated relative to the abducted eye. Simulations with Orbit(TM) suggest that these non-concomitant changes in vertical phoria with a concomitant excyclophoria may be based upon orbital mechanics. Excyclophoria appears to be the baseline state of binocular alignment.

Humans↗
PubMed1983

Induced esophoric shifts in eye convergence and illusory distance in reduced and structured viewing conditions.

Two experiments measured distance judgments in reduced and structured viewing conditions before and after induced phoria. Experiment 1 induced phoria shifts with three 5-min. intervals of close handwork (i.e., needle threading) that had naturalistic characteristics of observers (a) choosing their own viewing distance, (b) moving their heads freely, and (c) viewing in a well-illuminated, structured environment. The handwork induced a 1.20-diopter esophoric shift and a 1.22-cm overestimation of distance under reduced test conditions. The handwork induced no measurable illusion under structured viewing conditions. Experiment 2 induced phoria shifts with 10 min. of fixation on a target 11 cm away. This procedure induced a 4.65-diopter esophoric shift, a 6.34-cm overestimation of distance in reduced conditions, and a 2.31-cm overestimation of distance in structured conditions. We argue that visual and motor information interact to determine perceptions and that induced esophoric shifts in everyday situations may shape the nature of that interaction.

Adaptation, Ocular↗
PubMed2005

Accommodation, accommodative convergence, and response AC/A ratios before and at the onset of myopia in children.

PURPOSE: The purpose of this study was to investigate accommodation, accommodative convergence, and AC/A ratios before and at the onset of myopia in children. METHODS: Refractive error, accommodation, and phorias were measured annually over a period of 3 years in 80 6- to 18-year-old children (mean age at first visit = 11.1 years), including 26 who acquired myopia of at least -0.50 D and 54 who remained emmetropic (-0.25 to + 0.75 D). Refraction was measured by noncycloplegic distance retinoscopy. Concomitant measures of accommodation and phorias were taken for letter targets at 4.0 m and 0.33 m using the Canon R-1 open field-of-view autorefractor with an attached motorized Risley prism and Maddox rod. The accommodation and phoria measurements were used to calculate response AC/A ratios. RESULTS: Compared with children who remained emmetropic, those who became myopic had elevated response AC/A ratios at 1 and 2 years before the onset of myopia, in addition to at onset and 1 year later (t's = -2.97 to -4.04, p < 0.01 at all times). The significantly higher AC/A ratios in the children who became myopic are a result of significantly reduced accommodation. Accommodative convergence was significantly greater in myopes only at onset. CONCLUSIONS: These findings suggest that the abnormal oculomotor factors found before the onset of myopia may contribute to myopigenesis by producing hyperopic retinal defocus when a child is engaged in near-viewing tasks.

Accommodation, Ocular↗
PubMed1997

Quantitative analysis of the accommodative convergence to accommodation ratio: linear and nonlinear static models.

Ogle and his colleagues proposed two measures of oculomotor linkage called the accommodative convergence to accommodation (AC/A) ratio. This ratio provided a clinically useful assessment of the drive of accommodation, or focusing system, on vergence, or binocular fixation system. The phoria method measured the relatively large deviation in eye alignment under the monocular condition, whereas the fixation disparity method measured the relatively small misalignment of the eyes under the binocular condition to obtain the AC/A ratio. Ogle et al. indicated that these two measures should be equal. However, experimental results showed a substantial difference between the AC/A ratios obtained by the two methods. To quantitatively assess the difference between the two methods, a linear static model was first evaluated. This model was based on an earlier successful model of the accommodation and vergence system. The linear-model solution showed that these two methods were equivalent and thus could not account for the differences found. Then, a nonlinear static model, containing the deadspace operators depth of field and Panum's fusional area (PFA), was evaluated. Since two solutions were possible for each deadspace operator, there were four basic solutions. However, there were two binocular-viewing paradigms. This resulted in four prism-viewing and four lens-viewing solutions. Finally, a difference was taken between the prism- and lens-viewing measures, giving a total combination of 16 solutions. Only four of these solutions were equal to that using the phoria method. Some of the other solution lines were widely separated, thus providing a range of possible data values across different solution lines. Calculations showed that the variation in AC/A ratio values for data across difference solution lines was comparable to that found experimentally. Thus, the deadspace operators in the nonlinear model were able to account for the discrepancy between the AC/A ratio determined by the phoria and fixation disparity methods.

Accommodation, Ocular↗
PubMed2005

Increasing the proportion of binocular vision makes horizontal prism adaptation complete.

In previous phoria adaptation experiments on normal subjects adaptation tends to reach only approximately 2/3 of the prism-induced phoria while clinical experience indicates that prism adaptation is usually complete. The present data show that increasing the proportion of binocular experience through the phoria-inducing prism allows adaptation to become complete. Longer periods of binocular vision give a better indication of vergence adaptation function. This is particularly important in experiments where normal and abnormal adaptive abilities are being compared.

Adaptation, Ocular↗
PubMed2004

[A study on difference of ocular motor parameters in myopia].

OBJECTIVE: This study sought to assess the difference of these ocular motor parameters in myopia onset and development were explored. METHODS: 31 emmetropia and 46 myopia adult subjects were included in this study. The myopia subjects were divided into three groups as mild myopia, moderate myopia and high myopia. Phoria at distance and near, positive and negative relative accommodation (NRA/PRA) were measured. Accommodative convergence and accommodation stimulus ratio (AC/A) was determined through phoria values' calculation. RESULTS: Calculated AC/A of myopia was higher than that of emmetropia, and there were trends of elevated AC/A with myopia power increasing. There was significant difference in phoria in near between the myopia group and emmetropia group, but none in that of distance. There was no significant difference in NRA. However, PRA of myopia was lower than that of the emmetropia (P <0.05). CONCLUSIONS: Ocular motor parameters are different in myopia eyes. AC/A is one of key parameters among them, and AC/A is increased in myopia, which indicates out of focus of retinal image in the developing myopia.

Accommodation, Ocular↗
PubMed1990

Horizontal fusional amplitudes after adaptation to prism.

Horizontal fusional limits and lateral phorias were measured subjectively on five normal subjects after adaptation to increments of base-in and base-out prism. Both the phoria and the fusional limits were found to change by approximately the amount of the adapting prism. The fusional amplitudes (the difference between the phoria and the fusional limits) were relatively unaffected by vergence adaptation except at the largest values of adapting prism. These results are in agreement with current models of disparity vergence eye movement control which suggest that there are independent fast and slow fusional vergence mechanisms, each with its own saturation limit.

Adaptation, Ocular↗
PubMed1990

Effects of atropine/2-PAM chloride, heat, and chemical protective clothing on visual performance.

Visual acuity, phoria, stereopsis, and contrast sensitivity were assessed over 6 h of continued exposure to combinations of atropine (2 mg) and 2-PAM chloride (600 mg), severe heat/humidity (95 degrees F (35 degrees C); 60% RH), and wearing either the U.S. Army battle dress uniform (BDU) or the BDU and the impermeable chemical protective clothing (MOPP-IV). Subjects were able to complete all 6 h of testing under severe heat when wearing BDU's, but only lasted 2 h under the same severe heat when wearing MOPP-IV. Acuity and phoria were significantly impaired by the drug in the BDU conditions. Acuity, phoria and stereopsis were all significantly impaired by heat, drug and continued exposure under MOPP-IV. Acuity was significantly impaired by drug even during the first 2 h of heat exposure in MOPP-IV. Contrast sensitivity was impaired mainly by continued heat exposure in MOPP-IV.

Adolescent↗
PubMed1982

The Kerala Decentration Meter. A new method and devise for fitting the optical of spectacle lenses in the visual axis.

Centring of spectacle lenses is much neglected field of ophthalmology. The prismatic effect caused by wrong centring results in a phoria on the eye muscles which in turn causes persistent eyestrain. The theory of visual axis, optical axis and angle alpha is discussed. Using new methods the visual axis and optical axis of 35 subjects were measured. The results were computed for facial asymmetry, parallax error, angle alpha and also decentration for near vision. The results show that decentration is required on account of each of these factors. Considerable correction is needed in the vertical direction, a fact much neglected nowadays; and vertical decentration results in vertical phoria which is more symptomatic than horizontal phorias. Angle Alpha was computed for each of these patients. A new devise called 'The Kerala Decentration Meter' using the pinhole method for measuring the degree of decentration from the datum centre of the frame, and capable of correcting all the factors described above, is shown with diagrams.

Asthenopia↗
PubMed1995

Comparison of fixation disparity curve variables measured with the Sheedy Disparometer and the Wesson Fixation Disparity Card.

BACKGROUND: Previous studies suggest differences in the fixation disparity curves obtained with the Sheedy Disparometer and the Wesson Fixation Disparity Card, the two most commonly used methods for measuring fixation disparity. In one study the investigators proposed that the differences do not exist for subgroups divided by phoria. The purpose of this paper is to try to clarify this issue by use of two large sets of data. METHODS: Dissociated phorias were measured by the von Graefe method. Fixation disparity curves were plotted using the Disparometer and the Wesson card. RESULTS: Type I fixation disparity curves were most common with the Wesson card. Type II curves were found more often with the Disparometer than with the Wesson card. The x-intercepts were shifted in the base-in (BI) direction with the Wesson card compared to the Disparometer. The y-intercepts were shifted in the exo direction with the Wesson card compared to the Disparometer. The differences were statistically significant regardless of whether the dissociated phoria was exo or eso. The slope of the fixation disparity curve was steeper with the Wesson card than with the Disparometer. The difference was statistically significant for exophores but not for esophores. The differences between results obtained with the two instruments are not consistent from one subject to another as shown by high standard deviations of the differences. CONCLUSIONS: The fixation disparity curves measured with these two instruments are different. Fixation disparity parameters obtained from one of these instruments cannot be used with normative findings from the other.

Evaluation Studies as Topic↗