Biomedical subjects

B Wick

Publications and source records attributed to B Wick.

At least 37 records · Page 2Linked to original sources

PubMed1991

Stability of retinal correspondence in normal binocular vision.

Although many studies have suggested absolute stability of retinal correspondence, perhaps more have concluded that the correspondence of adult subjects with normal binocular vision is capable of small variation, particularly with strong sustained demands upon vergence, in order for binocular vision to be maintained. In this comprehensive review of the literature, the reasons for these differences are critically discussed and areas still to be resolved are pointed out.

Depth Perception↗

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

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

Convergence accommodation: laboratory and clinical evaluation.

The accommodation stimulated by convergence, CA/C, was measured under laboratory and clinical conditions. There was a small nonlinearity to the CA/C ratios measured under laboratory conditions for three of six subjects. We found that convergence accommodation decreases with decreasing accommodative amplitude but not as rapidly as has been reported in the literature. Our results suggest that convergence accommodation can contribute substantially to the near accommodative response for many patients.

Accommodation, Ocular↗

PubMed1990

Stability of retinal correspondence during divergence: evaluation with afterimages and Haidinger brushes.

Retinal correspondence has been described as invariant during normal binocular vision. However, there is substantial evidence that casts doubt on this interpretation and implies that retinal correspondence varies under certain conditions. This article reports the results of two experiments that appraise the stability of correspondence during fusional vergence in persons with normal binocular vision. In the first experiment, afterimages stimulated vertically corresponding retinal meridians prior to divergence. Three of six subjects gave data that indicated a change in the afterimage alignment significantly different from chance. The second experiment determined corresponding retinal areas with Haidinger's brushes. When divergence was maximally maintained, all six subjects who could appreciate the low-contrast Haidinger's brushes on the randomdot background saw two brushes while stereopsis and fusion remained present. Increases in plus lens power increased estimated brush separation.

Afterimage↗

PubMed1989

Magnitude and velocity of proximal vergence.

Until recently proximal vergence was considered to play only a minor role in the eye alignment changes that occur when looking between distant and near targets. We measured the magnitude and velocity of proximal vergence using infrared limbal sensing to record vergence responses between two untextured luminous horizontal rods which lacked disparity and accommodative cues. The magnitude of proximal vergence responses averaged 3.9 degrees for convergence and 3.8 degrees for divergence, about 70% of the total vergence "demand." Peak velocities for proximal convergence and divergence averaged 69 and 53 deg/sec, substantially faster than the velocities of comparably sized disparity or accommodative vergence responses. Its rapid velocity makes proximal vergence well suited to initiate the eye alignment changes between distant and near targets.

Accommodation, Ocular↗

PubMed1988

Binocular vision complications after radial keratotomy.

Radial keratotomy (RK), a popular procedure for reducing myopia, does not always have a successful outcome. Of the adverse effects reported in the literature, there have been few reports of undesirable disturbances of binocular vision. Four representative cases are reviewed which presented clinically with varying binocular problems induced by RK. The treatment considerations and final solutions for each are discussed. In the presence of RK-induced anisometropia, aniseikonia can be a particularly debilitating binocular vision problem for some patients.

Adult↗

PubMed1988

Lens-induced fixation disparity curves.

Change in fixation disparity was measured as lens sphere power was changed at distance and near on a young adult population. The results were graphed to yield a lens-induced fixation disparity curve. The lens curves found were grouped into four basic types (A through D). Two types (A and B) had increasing eso fixation disparity with increasing minus lens power. Type C had little change in fixation disparity with any change in lens power, whereas type D had an initial increase and then no further change with increasing minus power. In addition, approximately 74% of the 38-subject sample had different curve types at distance and near. Possible clinical uses of the lens-induced fixation disparity curve include the prescribing of near additions for pre-presbyopes based on measures of the binocular vergence response to various lens sphere combinations.

Accommodation, Ocular↗

PubMed1988

The Hirschberg test: a double-masked clinical evaluation.

Though the Hirschberg test has been used for over a 100 years, several different formulas are still being recommended and used clinically to determine the amount of a given ocular deviation. The purpose of this study was to obtain a double-masked clinical evaluation of the Hirschberg test. Several strabismic patients were evaluated by one investigator using the alternate cover test and by another investigator using a photographic Hirschberg procedure in a double-masked procedure. It was determined that the Hirschberg test can be used for strabismic patients of all ages and that the most appropriate formula to use is 1 mm = 22 delta.

Clinical Trials as Topic↗

PubMed1987

Analysis of binocular visual function using tests made under binocular conditions.

Accommodation and vergence have a complex relation which occasionally breaks down, resulting in a loss of visual efficiency along with symptoms of discomfort associated with use of the eyes. Studies of accommodation/vergence interactions and tonic vergence disorders indicate that, using classical analysis techniques, separate methods are frequently necessary to determine whether existing binocular deficiencies are causing reported symptoms. The problem with current systems of binocular visual function analysis is that the vergence error which exists under binocular conditions is often not the same as that which is measured under monocular conditions. A rationale for, and technique of, analyzing binocular function using results of tests made under binocular conditions is described. This analysis incorporates the concepts of CA/C, proximal vergence (PV), and fixation disparity along with several accommodative measures (facility, lag, sustaining ability, and accuracy). By identifying relevant binocular components and the interrelations, the clinician should be better able to assess the contribution of each and examine which may be modified most easily by vision therapy, lenses, and/or prism intervention.

Accommodation, Ocular↗

PubMed1987

Management of anomalous correspondence: efficacy of therapy.

The last paper to review thoroughly the success of treatment for esotropia with anomalous correspondence was published by Flom in 1963. In reviewing the literature of that era, which included surgical intervention, Flom found documented cures in only 11 of 262 esotropic patients with anomalous correspondence--a cure rate of less than 5%. We evaluated recent reported success rates for treatment and present an estimate of the prognosis for successful binocular re-education of patients with esotropia and anomalous correspondence. Based on current therapy techniques reported in the literature, with careful aggressive therapy, 50% of esotropic patients with anomalous correspondence should be expected to achieve binocular vision provided sufficient time (up to 12 months) can be devoted to binocular re-education.

Biofeedback, Psychology↗

PubMed1987

Relation among accommodative facility, lag, and amplitude in elementary school children.

Normative data for accommodative lag, facility, and amplitude of children have been presented in the literature for each of the parameters separately. This paper delineates the relation among accommodative amplitude, lag, and flexibility for grade school children. Approximately 200 children were screened. Those who wore corrective lenses, had uncorrected acuity worse than 6/9 (20/30) in either eye, had strabismus, had a refractive error outside the range from 0.00 to +0.75 D; or astigmatism greater than 0.50 D were excluded from the study. Of the 123 who remained, 53% had a deficit in accommodative facility, 26% had a deficit in lag, and 25% had a deficit in amplitude from that which would be expected from their age. Sixteen percent had deficits in both facility and lag. Eighteen percent had deficits in both amplitude and lag. Twenty-four percent had deficits in both facility and amplitude. Only 4% had deficits in all three of the accommodative functions considered--amplitude, lag, and facility. Clinically, these results indicate that when a patient's accommodative dysfunction is examined all facets of accommodation--lag, facility, and amplitude--need to be evaluated.

Accommodation, Ocular↗

PubMed1987

Accommodative esotropia: efficacy of therapy.

Retrospective examination was performed on the records of 54 patients who had undergone treatment of accommodative esotropia. The patients were classified based on the Duane classification as having either convergence excess (n = 11) or equal esodeviations (n = 43). Over 90% of the patients achieved total restoration of normal binocular function with treatment. The results and implications of this study are discussed.

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

Forced vergence fixation disparity curves in presbyopia.

Forced vergence fixation disparity curves were measured at distance and near on an asymptomatic presbyopic adult population (average age 62.7 +/- 7.0 years, range 51 to 79). Approximately 42% of the 62-subject sample had the same curve types at distance and near (type I-38.4%; type II-3.5%). Different curve types were found in 58.1% of the sample. Detailed breakdown of the curve types is provided. The results are compared with findings published previously on an asymptomatic prepresbyopic sample of the same size. The necessity to establish normative data for fixation disparity curves at distance and near for different vergence states, age groups, and symptomatic subjects is stressed.

Aged↗

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

Forced vergence fixation disparity curves at distance and near in an asymptomatic young adult population.

Forced vergence fixation disparity curves were measured at distance and near on an asymptomatic young adult population (average age 24.7 +/- 5.2 years, range 14 to 35). Approximately 60% of the 62 subject sample had the same curve types at distance and near (type I, 50%, type II, 9.7%). Unlike curves were found in 40.3% of the sample. Detailed breakdown of the unlike curve types is provided, along with a discussion of the results. Clinical implications of the necessity to establish normative data for fixation disparity curves at distance and near for different vergence states, age groups, and symptomatic patients are stressed.

Adolescent↗

PubMed1984

A comparison of the Snellen chart and the S-chart for visual acuity assessment in amblyopia.

A standard Snellen chart and a chart that controls contour interaction effects and gives equal numbers of acuity trials for all letter sizes (the S-chart) were used to compare visual acuities for 30 amblyopic patients (17 with central fixation, 13 with eccentric fixation). No statistically significant difference appeared between S-chart and Snellen acuity in the acuity range 20/30 to 20/80. When amblyopic acuity was below 20/100, S-chart and Snellen acuities differed significantly.

Amblyopia↗