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PubMed1986

Should a central fusion stimulus be used on the disparometer?

Clinical measurements of fixation disparity made with the disparometer have used a 1.5 degree diameter peripheral fusion stimulus. The addition of a central fusion stimulus decreases the variability of test measurements and more closely simulates everyday visual tasks. However, this also changes the fixation disparity measurement, associated phoria, slope of the curve, and possibly the curve type. Normative data and correlation data to other clinical tests are not available for the central fusional measurements as they are for the peripheral fusional measurements. More importantly, the peripheral fusional measurements have been shown to correlate with patient symptoms, whereas such studies have yet to be performed with the central stimulus. Until normative and discriminative information data are available for the central fusional stimulus, the peripheral stimulus is more useful clinically.

Fixation, Ocular↗
PubMed1989

Adaptation ability of subjects with different refractive errors.

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 the adaptation ability of subjects with different refractive errors to horizontal prisms. The results showed that emmetropes, late-onset myopes (LOM's), and early-onset myopes (EOM's) can adapt to prism-induced phorias at distance and at near. The early-onset myopes demonstrated the greatest amount of adaptation after 3.5 min of binocular viewing in all cases. However, the differences found between the refractive groups in the amount of adaptation after 3.5 min of binocular viewing are not statistically significant.

Adaptation, Ocular↗
PubMed1989

Influence of extraocular muscle imbalance on binocular performance.

In assessing binocular performance, it is possible that extraocular coordination is more significantly involved than presently recognized. Dynamic phorometry or phorometric testing in the nine cardinal directions of gaze is advised for evaluating the extraocular muscular system. These case reports used interrelation of phorias to evaluate binocular problems. The interpretation of these data helps determine the amount of horizontal prism necessary to reduce compensating vergences. Although a control group was not used, the elimination of associated vertical fixation disparity in these cases seemed to ameliorate binocular stress.

Aniseikonia↗
PubMed1990

Relations between accommodation and vergence in darkness.

Prior studies reported that the resting postures of accommodation and vergence are uncoupled in darkness, calling into question whether accommodation-vergence synkinesis persists when both systems are deprived of stimulation. We tracked the postures of accommodation and vergence of 20 normal subjects for 15 min in darkness, using a Vernier optometer and dichoptic nonius lines. Consistent with previous reports, the mean resting postures of accommodation and vergence correlated weakly (r = 0.19); spontaneous fluctuations of accommodation and vergence in darkness also exhibited little correlation (median r = 0.15). However, resting vergence postures could be predicted (r = 0.65) from the clinically measured distance phoria and the resting posture of accommodation, when subjects' AC/A ratios were taken into account. We conclude that the relaxation of accommodation and vergence to separate resting postures in darkness is compatible with the persistence of synkinesis; independent noise in the two systems may reduce apparent coupling under open-loop conditions.

Accommodation, Ocular↗
PubMed1990

Prism adaptation without binocular vision.

The assumption that vergence adaptation to a prism could only take place during single binocular vision was investigated by having subjects wear a prism while fusion was dissociated. Adaptation was evaluated by its effect on lateral heterophoria. Dissociation and measurement of heterophoria were by means of an automated version of Duane's screen and parallax test. A preliminary investigation with 37 subjects fixating at 6 m while wearing 4 delta base-out and with 33 other subjects fixating at 50 cm while wearing 3 delta base-in showed that at least 25% adapted to the prism. Results of an investigation with 2 subjects fixating at 6 m (4 delta base-out and base-in) and with 3 subjects fixating at 50 cm (3 delta base-in) are presented as evidence that prism adaptation can take place. It was also found that the power of the added prism could just as well be provided by the phoria test's variable prism. In other words, there is a possibility that adaptation will occur when heterophoria is measured with a variable prism.

Adaptation, Ocular↗
PubMed1991

Clinical accommodation and heterophoria findings preceding juvenile onset of myopia.

This study was performed to test the hypothesis that accommodation and convergence differences precede the onset of myopia in children. Records of children who were emmetropic and became myopic (became myopic group) and children who remained emmetropic (remained emmetropic group) were collected from seven private optometry practices. The practices were located in Illinois, Iowa, Oklahoma, and Oregon. Near-point phorias and positive relative accommodation (PRA) findings were significantly different in the two groups by t-test. Negative relative accommodation (NRA) did not show a statistically significant difference in the two groups. Binocular cross-cylinder findings were shown by analysis of variance (ANOVA) to be significantly affected by group (became myopic vs. remained emmetropic) and by practice location. These results support the hypothesis that differences in accommodation and convergence function may be precursors of juvenile onset myopia.

Accommodation, Ocular↗
PubMed1991

Diagnostic occlusion and clinical management of latent hyperphoria.

Occasionally in patients who have symptoms suggestive of a vertical heterophoria no deviation is found, even on careful examination. Six days of occlusion have been recommended for uncovering such "latent" vertical deviations. We investigated prolonged monocular occlusion (Part I) and found that vertical deviations of varying amounts manifested on symptomatic and asymptomatic subjects. Thus, results of prolonged occlusion can be difficult to interpret. Nonadaptive vertical vergence systems have been implicated in development of symptoms. Therefore, it may be that diagnostic monocular occlusion is not appropriate unless patients have symptoms of vertical imbalance. We used (24 h) occlusion and associated phoria measurements (Part II) to determine vertical prism prescriptions which eliminated symptoms of seven symptomatic patients who did not show significant vertical heterophoria on routine clinical testing. We present data and case reports which elucidate the efficacy of this procedure.

Adolescent↗
PubMed1991

Retinal eccentricity of fusion detail affects vergence adaptation.

Adaptation of tonic vergence ("vergence adaptation" or "prism adaptation") may be produced by sustained accommodative, disparity, or proximal vergence innervation. Phoria measures were used in the present study as indices of tonic vergence adaptation to convergence and divergence stimuli in five subjects. Amblyoscope targets stimulated fusion either over the central or peripheral retina while holding accommodative and proximal stimuli constant. The magnitude and rate of tonic vergence adaptation were greater under the central fusion condition than under the peripheral fusion condition, even though the vergence stimuli were matched between central and peripheral fusion conditions. These results show that tonic vergence adaptation is influenced by the retinal eccentricity of target fusional patterns. However, additional work is required to identify the mechanism(s) underlying this eccentricity effect.

Adaptation, Ocular↗
PubMed1991

Influence of ocular gaze and head position on 4 m heterophoria and fixation disparity.

Four-meter heterophoria and fixation disparity measurements were taken from a sample of 40 young adults in primary gaze, 33 degrees left and right lateral gaze, and in 2 head/gaze positions related to golf putting. Comparisons using analysis of variance were made between the mean values in each gaze position and between the test-retest range of values in each gaze position. Mean heterophoria was more eso (p less than 0.05) in the two head/gaze positions related to golf putting than in other gaze positions, whereas mean fixation disparity was more eso (p less than 0.05) in rightward than in primary gaze. Phoria test-retest range was less (p less than 0.05) in all nonprimary gaze positions than in primary gaze. One of the putting-related gaze positions showed smaller (p less than 0.05) fixation disparity ranges than the primary or leftward position of gaze. All measures were highly variable among subjects. Trends present in the data suggested greater esophoria and eso fixation disparity mean values, and lesser heterophoria and fixation disparity test-retest range values in all nonprimary positions relative to primary gaze. The behavior of exophoric and esophoric subjects differed only in regard to changes in heterophoria associated with left and right lateral gaze. These data indicate differences in oculomotor postural tendencies relative to position of gaze. Relevance of the results to athletes is discussed.

Adult↗
PubMed1993

Comparison of fixation disparity measurements obtained with the Wesson Fixation Disparity Card and the Sheedy Disparometer.

We compared the fixation disparity measurements obtained with the Disparometer to those of the Wesson Card. Previous studies suggest that the measurements obtained by these two instruments gave different results. The results of previous studies were based on the analysis of pooled data, which may have led to spurious results. Analysis of our data done in this manner (pooled data) revealed the same findings. However, after analysis of the data based on the separation of subjects according to phoria (exophoria/esophoria), no statistically significant difference was found between the measurements obtained with the Wesson Card and those with the Disparometer.

Adult↗
PubMed1994

Effect of prescribed prism on monocular interpupillary distances and fitting heights for progressive add lenses.

Success in fitting progressive addition lenses is dependent upon the accurate placement of the progressive zone. Both eyes must track simultaneously within the boundary of the progressive corridor. Vertical prism will displace the wearer's lines of sight and consequently eye position. Because fitting heights are measured using an empty frame, subjects with vertical phorias usually will fuse, and not show the vertical differences in pupil heights during the measuring process. Therefore, when prescriptions contain vertical prism one must consider the changes in measured fitting heights that will occur once the lenses are placed in the frame. Fitting heights must be altered approximately 0.3 mm for each vertical prism diopter prescribed. The fitting height adjustment is opposite from the base direction of the prescribed prism. An explanation of the effect of prescribed horizontal prism on monocular interpupillary distance (PD) measurements is also included.

Eye↗
PubMed1998

Frequency of convergence insufficiency in optometry clinic settings. Convergence Insufficiency and Reading Study (CIRS) Group.

PURPOSE: To estimate the frequency of convergence insufficiency (Cl) and its related characteristics among 8- to 12-year-old children randomly selected from 2 optometry clinic populations. METHODS: Clinic records of 620 children were randomly selected and reviewed according to a standard protocol, using a systematic sampling method based on the total number of 8- to 12-year-old children seen over a 1-year period at 2 optometry clinics. Records were reviewed for demographic and clinical data. Data on Cl-related symptoms were obtained at one of the sites. Records that met the eligibility criteria of: good visual acuity (20/30 or better in both eyes); minimal refractive error (-0.50 to +1.00 D and < or = 1.00 D of astigmatism in either eye, and < or = 1.00 D of anisometropia); and no strabismus were evaluated for Cl-related characteristics. Eligible children were classified according to the direction of their near heterophoria and the number of the following clinical signs present: (1) exophoria at near > or = 4 delta than at far; (2) insufficient fusional convergence [i.e., failing Sheard's criterion or minimum normative positive fusional vergence (PFV) of 12 delta base-out (BO) blur/15 delta BO break]; and (3) receded nearpoint of convergence (NPC) of > or = 7.5 cm break or > or = 10.5 cm recovery. Children were then classified as: no Cl (nonexophoric at near or < 4 delta difference between far and near); low suspect (exophoric at near and 1 sign); high suspect (exophoric at near and 2 signs); or definite Cl (exophoric at near and 3 signs). RESULTS: Sixty-seven percent (415/620) of the records met the eligibility criteria and had complete data on phoria, NPC, and PFV. The age (mean +/- SD) of the study population was 10.2 +/- 1.2 years. Ethnicity data were available for 85% of those eligible; the ethnic distribution was 36% African American, 29% Caucasian, 19% Hispanic, and 1% Asian. About one-half of the 415 children were classified as either low suspect (33%); high suspect (12%); or definite Cl (6%). Clinically significant Cl (high suspect and definite categories) was identified in 17.6% of the children. The percentage of children rated as symptomatic increased with the number of Cl-related clinical signs present. CONCLUSIONS: These findings suggest a high frequency of Cl in optometry clinic populations and a potential correlation between patient symptoms and the number of Cl signs present.

Child↗
PubMed1998

Vergence facility and target type.

PURPOSE: Target suppression-cues are considered important for valid binocular accommodative facility response. However, there are no comparable recommendations concerning the effect of target type on vergence facility response. METHODS: Ten subjects ages 16 to 19 years of either sex and any race were pooled, based on the lack of any asthenopic symptoms determined by a verbal interview with the investigator. Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, and near-normal phorias. Vergence facility response was tested over a 1-min period using 8 delta base-in (BI) and 20 delta base-out (BO) loose prisms at near (0.4 M) for 3 different vertically oriented targets: 6/9 (20/30) Snellen letters, back-illuminated anaglyphic shapes, and modified Wirt circles. RESULTS: For the group, the mean facility response was similar among the target types [Snellen letters: 9.5 cycles per minute (cpm) +/- 5.6; anaglyphic shapes: 9.0 cpm +/- 6.3; and Wirt circles: 9.4 cpm +/- 4.5]. Group response-differences were not significantly different by one-way ANOVA polynomial regression testing at the 0.05 level (F-value = 0.03, p = 0.97, df = 2). CONCLUSIONS: Whereas a binocular accommodative facility target must have additional vectographic or anaglyphic suppression-cues, vergence facility testing may incorporate a simple and available vertical row of 6/9 (20/30) Snellen letters, which provide inherent fusional suppression-cues, for a valid binocular response.

Adolescent↗
PubMed1998

Vergence facility: establishing clinical utility.

PURPOSE: Vergence facility testing attempts to assess the ability of the fusional vergence system to respond rapidly and accurately to changing vergence demands over time [defined as the number of cycles per minute (cpm) that a stimulus can be fused through, alternating base-in (BI) and base-out (BO) prisms]. Decisions to use vergence facility as a clinical test are hampered by a lack of systematically gathered normative data. METHODS: Twenty symptomatic and 20 control subjects with ages between 18 to 35 years of either sex and any race were pooled, based on vision-symptom level determined by a self-report questionnaire. Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye and normal phorias. Vergence facility response was tested over a 1-min period, using 16 combinations of BI/BO flip prisms at 4.0 and 0.4 m, based on Morgan's norms and pilot data. RESULTS: Horizontal vergence facility responses were not the same among those with and without symptoms, and not all magnitudes of BI/BO flip prisms produced the same response difference. A single flip prism, 3 delta BI/12 delta BO, was found to differentiate optimally between groups at distance and near. Repeatability of test results (with the 3 delta BI/12 delta BO prism) was poor at distance and good at near. CONCLUSIONS: In addition to providing valuable normative data, this study indicates that the vergence system nearly resets its "zero point" at any distance and sheds further light on the results of dynamic convergence and divergence stimulation on the accommodative-vergence system. From a clinical standpoint, the results improve the diagnosis of binocular vision abnormalities. The recommended near vergence facility test is easily implemented, using a commonly available flip prism (3 delta BI/12 delta BO) and having a clinical failure criterion that is easily recalled (15 cpm, sum of the BI and BO magnitudes).

Adolescent↗
PubMed2002

Is esophoria a factor in slowing of myopia by progressive lenses?

PURPOSE: Our previous findings suggest that myopia can be slowed by wearing progressive lenses, and one possible mechanism for this is through the oculomotor system. We reanalyzed our findings to investigate the relationship between baseline oculomotor parameters and change in refraction, and between the change in these values and change in refraction. METHODS: Children who wore progressive lenses (N = 38; 26 with +1.50 D addition, and 16 with +2.00 D addition) or single-vision lenses (N = 32) had refraction, distance heterophoria, near heterophoria, and stimulus AC/A ratio measured prospectively over a 2-year period. RESULTS: There were no statistically significant correlations between baseline heterophoria or AC/A values and change in refractive error. Distance and near heterophoria did not change significantly over the 2 years of the experiment; AC/A ratio decreased significantly, but in an equivalent manner for both groups. In the combined progressive lens group, change toward more exophoria at near was associated with less myopia progression. However three-way analysis of variance (visit x lens type x esophoria/nonesophoria) showed significant main effects in refraction over all five visits. There was a significant interaction between lens type and visits; there was no significant interaction between lens type and esophoria/ nonesophoria grouping. Three-way analysis of variance showed a statistically significant decrease of AC/A ratio over all five visits; there was no interaction of visit by lens or visit by phoria grouping. CONCLUSIONS: Although there were no statistically significant differences between esophoric and nonesophoric subjects, there was only 46% as much myopia progression in the progressive lenses-esophoric group as in the progressive lenses-nonesophoric group. In addition, there were no differences in AC/A ratio between esophoric and nonesophoric subjects. However these findings are not definitive. This experiment was not designed to discriminate between refraction and oculomotor changes in esophoric and nonesophoric subjects and lacked the necessary statistical power to do so.

Analysis of Variance↗
PubMed2002

Monocular estimate method retinoscopy: central tendency measures and relationship to refractive status and heterophoria.

BACKGROUND: Monocular estimate (estimation) method (MEM) is a widely used clinical test of accommodative response. Normative data for MEM are available based on the central tendency measures from a population of schoolchildren but not a clinical population. Also, the relationship of accommodative response to refractive status and heterophoria has been researched, but not with MEM as the determinant of the manifestation of accommodative response. METHODS: A group of 211 pre-presbyopic clinical subjects were tested with MEM for purposes of comparing the central tendency measures of a clinical population to established normative data and determining whether MEM varied with refractive status or near phoria. RESULTS: A lag of about one-third diopter was the mean MEM result for this clinical population. The median was +0.25 D. Myopia and near esophoria have a statistically significant relationship to MEM. CONCLUSIONS: The central tendency measures derived from MEM administered to this population replicate the central tendency measures found in a previous normative study. This study provides preliminary evidence that the difference between accommodative response and accommodative stimulus, as measured by MEM, may be influenced by myopia and esophoria.

Accommodation, Ocular↗
PubMed2004

Prevalence of myopia in a group of Hong Kong microscopists.

PURPOSE: To study the prevalence and magnitude of myopia in a group of Hong Kong Chinese microscopists and compare it with that observed in microscopists working in the United Kingdom. METHODS: Forty-seven microscopists (36 women and 11 men) with a median age of 31 years and working in hospital laboratories throughout Hong Kong were recruited to the study. Information about past refractive corrections, microscopy work, and visual symptoms associated with microscope use were collected. All subjects had a comprehensive eye examination at The Hong Kong Polytechnic University Optometry Clinic, including measures of refractive error (both noncycloplegic and cycloplegic), binocular vision functions, and axial length. RESULTS: The prevalence of myopia in this group of microscopists was 87%, the mean (+/- SD) refractive error was -4.45 +/- 3.03 D and mean axial length was 25.13 +/- 1.52 mm. No correlation was found between refractive error and years spent working as a microscopist or number of hours per day spent performing microscopy. Subjects reporting myopia progression (N = 22) did not differ from the refractively stable group (N = 19) in terms of their microscopy working history, working hours, tonic accommodation level, or near phoria. However, the AC/A ratio of the progressing group was significantly greater than that of the stable group (4.59 delta/D cf. 3.34 delta/D). CONCLUSION: The myopia prevalence of Hong Kong Chinese microscopists was higher than that of microscopists in the United Kingdom (87% cf. 71%), as well as the Hong Kong general population (87% cf. 70%). The average amount of myopia was also higher in the Hong Kong Chinese microscopists than the Hong Kong general population (-4.45 D cf. -3.00 D). We have confirmed that the microscopy task may slightly exacerbate myopia development in Chinese people.

Adult↗
PubMed2004

Accommodative and vergence difficulties interfering with image clarity through a binocular indirect ophthalmoscope.

PURPOSE: This study sought to identify accommodative and vergence deficiencies that could explain why some students have difficulty seeing clearly when using a binocular indirect ophthalmoscope (BIO) containing its standard +2.00 D lenses. METHODS: A survey was distributed to Illinois College of Optometry 3rd- and 4th-year students. Based on the information supplied by the survey, students were divided into two groups: those who are unable ("BIO plano") and those who are able ("BIO plus") to obtain a clear image with the +2.00 D lenses in their BIO's. Forty-seven subjects participated: 22 in the BIO plano group and 25 in BIO plus group. Two of the authors, masked to subject group, measured all subjects' accommodative amplitudes and facilities, monocular estimation method (MEM) retinoscopy, negative relative accommodation and positive relative accommodation (NRA/PRA), distance and near vergence ranges, distance and near phorias, Worth 4-dot test, and near point of convergence (five times). RESULTS: The Mann-Whitney U analysis of numerical data for the two groups showed a statistically significant difference for accommodative facility in the right eye (p = 0.004). The difference between the two groups approached significance for accommodative facility with both eyes (p = 0.02), facility in the left eye (p = 0.03), distance base-out blur (p = 0.02), near base-out break (p = 0.02), and near base-out recovery (p = 0.04). For all findings in which the difference between the two groups was significant or approached significance, the BIO plus group had higher median values. When subjects were classified by difficulty with the plus side of the flippers during accommodative facility testing, there was a statistically significant difference with both eyes (Fisher exact test, p = 0.003) and with the right eye (p = 0.008) between the BIO plus and BIO plano groups. When subjects were classified by the presence or absence of an accommodative or binocular vision syndrome, categorical data analysis showed the difference between the two groups approached significance, with more BIO plano subjects having syndromes (p = 0.03). CONCLUSION: No one test absolutely defined who would have difficulty with the +2.00 D lenses in the BIO. There are several skills required; less developed plus acceptance and convergence may cause difficulties.

Accommodation, Ocular↗