Biomedical subjects

K M Daum

Publications and source records attributed to K M Daum.

At least 19 recordsLinked to original sources

PubMed1994

A statistical analysis of Modified Clinical Technique vision screening of preschoolers by optometry students.

Fourth year optometry students screened 745 preschoolers using a slightly altered Modified Clinical Technique (MCT) under the supervision of a faculty doctor. Children who failed the MCT were randomly selected and then matched by age, sex, and ethnic origin to children who had passed the screening battery. The 61 screening failures and 45 matched controls were later given full eye examinations with cycloplegia by University of Alabama at Birmingham faculty doctors who were unaware of the screening results. The positive predictive value (PPV) (0.52) and negative predictive value (NPV) (0.78) of the MCT were calculated directly from the 2 x 2 contingency table crossing screening results and a standard diagnosis. Sensitivity [0.50, k(1,0) = 0.29], specificity [0.79, k(0,0) = 0.30], efficiency [0.70, k(0.5,0) = 0.29] of the MCT, and the prevalence (0.30) of children failing the standard diagnosis were estimated using statistics appropriate to the prospective sampling design. The reproducibility of the diagnosis, estimated by analyzing multiple, independent diagnosis of each study child by seven doctors was moderate (kappa D 0.58). Statistics summarizing the agreement between the MCT and the diagnosis by the individual study doctor are similar to those obtained with comparison to the standard diagnosis. The characteristics of the MCT may be generalized only to similar populations that are screened by clinicians with similar experience, using the same tests.

Child↗

PubMed1992

Effects of residual astigmatism in contact lens wear on visual discomfort in VDT use.

The purpose of this study was to evaluate the effects of the residual astigmatism of contact lens wearers on the visual comfort of these individuals when using a video display terminal (VDT). We hypothesized that small amounts of uncorrected residual astigmatism of the type that is normally left uncorrected produce visual discomfort in the use of these devices even though visual acuity is relatively unaffected. Twelve subjects (ages 18 to 36 years) with corrected visual acuities of at least 20/25 (in each eye at distance with their contact lens correction) participated. All subjects were soft contact lens wearers who reported comfortable, well-adapted lens wear for a minimum of 1 year prior to the study. All subjects had between 0.50 and 1.00 D of residual astigmatism in each eye (mean = 0.68D). Our double-masked cross-over experiment included two 25-minute periods during which the subject read from a VDT. In a trial frame over their contact lens correction, the subjects were randomly assigned to wear either a test lens pair or a control lens pair (+0.12 DS) during the first period and the alternative pair during the second period. The test lens pair corrected all residual astigmatism (the over refraction). The control lens pair was considered a placebo. A questionnaire was used to obtain ratings of visual discomfort. Our analysis of the data indicated greater reported visual comfort for the test lens pair (Wilcoxon signed-rank test, p less than 0.01). These results suggest careful consideration be given to the correction of residual astigmatism of contact lens wearers who are VDT users.

Adolescent↗

PubMed1991

Visual discomfort and astigmatic refractive errors in VDT use.

The purpose of this study was to evaluate the effects of small amounts of uncorrected astigmatism on the visual comfort of video display terminal (VDT) users. We hypothesized that these small errors produce visual discomfort in the use of these devices even though visual acuity is relatively unaffected. Eight subjects (ages 23-35 years) with corrected visual acuities of 20/20 participated. Our double-masked cross-over experiment included two 25-minute periods during which the subject read from a VDT. The subjects were randomly assigned to wear either the test lens pair (+0.50 D x 090) or a control lens pair (+0.12 DS) over their best correction during the first period and the alternative pair during the second period. A questionnaire was used to obtain ratings of visual discomfort. Our analysis of the data indicated greater reported eyestrain for the test lens pair (Wilcoxon signed-rank test, p = 0.01). These results suggest careful consideration be given to the correction of small amounts of astigmatic errors for VDT users.

Adult↗

PubMed1990

Ganzfeld blankout occurs in bowl perimetry and is eliminated by translucent occlusion.

An intermittent darkening of the visual field (ganzfeld "blankout") is perceived during bowl perimetry. Since this may be a form of rivalry, we hypothesized that occluding the nontested eye with a translucent occluder may eliminate the phenomenon. Ten normal subjects underwent visual field testing with both a translucent and an opaque occluder. Eight of the 10 reported darkening to occur with the opaque patch, while none reported it with the translucent occluder. The darkening occurred with a mean latency of 10.9 seconds, occupied 34.4% of the time, and on average occurred 3.25 times per minute. With the translucent occluder, retest threshold variability was 18.8% less and sensitivity was increased by 0.7 dB. The elimination of this darkening using translucent occluders in bowl perimetry will allow reduced variability and increased sensitivity and comfort.

Adult↗

PubMed1990

Measuring visual acuity in children using preferential looking and sine wave cards.

Preferential looking using square waves is commonly used to measure visual acuity of infants. Since sine-wave gratings have the advantage of presenting only a single spatial frequency, we completed a study to develop and validate a set of acuity cards using sine waves. The subjects were 83 children (mean age = 41.5 months, range = 3 to 69 months). The sine-wave cards were compared with Teller cards. Identical visual acuity was determined in 83% of the cases. Wilcoxon non-parametric analysis provided no evidence to reject the null hypothesis of equal visual acuities between the two methods. We conclude that sine-wave cards may be used to measure the preferential looking acuity of children.

Child↗

PubMed1990

Rigid contact lens base curve constancy between wet and dry lens storage conditions.

The purpose of this study was to investigate dry storage of rigid gas-permeable contact lenses as an alternative to wet storage. This study evaluated the constancy of lens base curve between the two storage methods for lens materials that spanned the spectrum of oxygen permeability values. The differences found in lens base curve between wet and dry storage for any lens material evaluated did not reach a level considered to be clinically significant, although differences in average base curve constancy did exist among the lens materials. Base curve change did not increase with increasing lens material oxygen permeability value (Dk).

Contact Lenses↗

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↗

PubMed1989

Clinical characteristics of anomalous correspondence.

The correspondence status of 68 constant, early-age onset strabismics was evaluated with three common clinical tests to determine the prevalence of anomalous retinal correspondence (ARC) and which clinical features of the strabismus were most highly associated with the ARC. Ninety-six per cent, 71%, and 51% of the patients manifested ARC with the striated lens test, the synoptophore, and the afterimage test, respectively. The clinical features of the strabismus that were correlated, although weakly, with the diagnosis of ARC were: (1) the magnitude of the deviation at near for the striated lens test; (2) the age of the patient at the time of testing and the laterality of the deviation on the synoptophore; and (3) the age of the patient at the time of testing, the change in the deviation from distance to near, and the spherical equivalent refractive error for the afterimage test. A low correlation also existed between the age of the patient and the depth of ARC (superficial or deep-rooted). We conclude that the clinical features of strabismus cannot be utilized effectively to predict the status of retinal correspondence.

Adolescent↗

PubMed1988

Horizontal and vertical vergence training and its effect on vergences and fixation disparity curves: I. Horizontal data.

The purpose of this study was to assess the effects of horizontal and vertical vergence training on fusional vergences and the fixation disparity (FD) curve. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. Before and after the 4 week training period, vergences and FD curves were measured by a single individual who was intentionally uninformed of each subject's group. We hypothesized that the subjects in the horizontal training group would have increased vergence amplitudes and flatter FD slopes. Our analysis revealed that the positive vergences increased significantly for those in the horizontal group. No evidence was found to suggest changes in any variables related to the FD curve. Because type II errors were likely to be unacceptably large, further work is necessary to determine the relation between fusional vergence training and variables derived from the FD curve.

Adult↗

PubMed1988

Horizontal and vertical vergence training and its effect on vergences, fixation disparity curves, and prism adaptation: II. Vertical data.

The purpose of this study was to assess the effects of horizontal and vertical vergence training on vertical fusional amplitudes, the vertical fixation disparity (VFD) curve, and prism adaptation. Thirty-four subjects were divided into three groups. One-third served as controls and the other two-thirds underwent 5 h of supervised horizontal and vertical vergence training, respectively. We hypothesized that subjects in the vertical group would manifest increased vertical vergence amplitude and coefficients of adaptation in concert with flatter VFD slopes. Before and after the 4-week training period, vertical vergences, fixation disparity (FD) curves, and coefficients of vertical prism adaptation were measured by a single individual who was intentionally uninformed of each subject's group. Analysis of the data suggests that changes in the vertical fusional amplitudes increased slightly. Although changes in the VFD slope and coefficient of prism adaptation were not statistically significant, the changes were much greater in the vertical group and in the hypothesized direction. We suggest that the results offer preliminary support for our hypothesis.

Adaptation, Ocular↗

PubMed1988

Characteristics of convergence insufficiency.

Convergence insufficiency (CI) is a well-known syndrome of binocular visual dysfunction. In a review of 58 papers, considerable variation was noted in the criteria used to define the condition. Symptoms and decreased positive fusional vergences (both at the nearpoint) were the only criteria named in more than one-half of the studies. An extended nearpoint of convergence (NPC) and increased exophoria at near were criteria in about one-third of the papers. Examination of data in the reviewed papers shows that although considerable variability was noted, the distance exodeviation, distance negative vergences, visual acuity, refraction, and stereopsis were about the same as population norms. Positive vergences, negative vergence at near, and NPC were somewhat less than population norms. Vergences relative to Sheard's criterion, the near exophoria, accommodative amplitude, and the AC/A ratio were consistently below those derived from population norms. This considerable variation may largely be a result of different criteria used for diagnosis, subpopulations within the data, and other confounding factors.

Accommodation, Ocular↗

PubMed1988

Symptoms in video display terminal operators and the presence of small refractive errors.

Although the effects of using video display terminals (VDTs) have been examined from a number of perspectives, there has been relatively little study of the effect of small uncorrected refractive errors in the production of visual discomfort. The purpose of this study was to examine the level of six commonly assessed symptoms in a sample of 32 VDT operators via a questionnaire and to determine whether these were related to their habitual small refractive errors. The subjects reported substantial prevalence (55-81%) of each of the symptoms except double vision (16%). After a complete vision examination, the VDT operators were classified as relative myopes, hyperopes, astigmats or emmetropes. The criterion was a minimum of 0.50 D in the most ameotropic eye. Using this criterion, analysis showed that small refractive errors were significantly related to the reported level of symptoms of VDT operators. These results suggest the utility of proper refractive correction for the comfortable use of a VDT and the value of further research into this putative causal relationship.

Adolescent↗

PubMed1988

Accommodative spasm: a study of 17 cases.

Accommodative spasm (AS) is rarely reported in the literature. We studied 17 patients with accommodative spasm. Most patients were clinically emmetropic. Ten patients also manifested a spasm of the near reflex (SNR). The probable etiology of the accommodative disorder for most patients was psychogenic as revealed by case histories and visual field analysis. Treatment consisted primarily of plus reading lenses and, in some instances, orthoptic training. Some patients also underwent psychological counseling. Follow-up ranged from 2 months to 30 months. Although visual symptoms improved for most patients, only four patients had complete resolution of the spasm.

Accommodation, Ocular↗

PubMed1987

Efficacy of computerized vergence therapy.

The purpose of this study was to determine the efficacy of computerized fusional vergence therapy and the effect of two different vergence training velocities. Six subjects received positive vergence training using a slow vergence training rate (0.75 delta/s) and six subjects received positive vergence training using a fast vergence training rate (5.00 delta/s). Six subjects served as controls and did not receive therapy. The duration of therapy was 80 min over a period of 4 weeks. All training activities were monitored. All vergence evaluations were double masked. Subjects using a slow training rate showed significant increases in positive vergence ranges as measured with the major amblyoscope, whereas subjects training with fast rates did not. We conclude that vergence therapy using a computerized video display is an effective technique for increasing the amplitudes of positive fusional vergence and that slower rates are more productive than faster rates.

Adult↗

PubMed1987

Exotropia associated with defective accommodation.

Despite the close association of convergence and accommodation, accommodative dysfunction is not often associated etiologically with exotropia. We studied 13 adolescent and young adults having intermittent exotropia and severely reduced accommodative function. Most patients had a prolonged history of visual symptoms that had not responded to therapy in the past. Clinical testing indicated that the patients had severely reduced amplitudes of accommodation and difficulty sustaining accommodation. Exotropia was manifest when the accommodative response was inadequate; relative orthophoria existed when the accommodative response was adequate. Treatment of the accommodative defect as well as the strabismus was successful for some patients. We recommend careful evaluation of accommodation for adolescent and young adults with exotropia to rule out an accommodative defect as a contributing cause.

Accommodation, Ocular↗

PubMed1986

Negative vergence training in humans.

Two healthy subjects (male and female, ages 22 and 25 years) spent 50 h over a period of 7 consecutive weeks training the negative vergence system. The training was performed in two 45-min daily sessions, usually immediately before and after the workday. The training was exclusively negative vergence training using devices such as variable vectograms, the aperture rule, the synoptophore, and loose or bar prisms. An extensive examination of the visual systems before, after, and periodically during the training demonstrated that the negative vergences increased at distance by 5.0 delta and at near by 9.1 delta (using hand-held prisms, bar prisms, and the synoptophore). The phorias of both subjects became more exophoric or less esophoric at both distance and near by 3.6 delta (using average of changes on the cover test, von Graefe subjective phoria technique, and the synoptophore). A haploscope equipped with a coincidence optometer showed only small increases in vergence amplitude but confirmed that the lag of accommodation became more stable after the training than it was before. Other testing suggested that the negative relative accommodation, the angle of deviation at both distance and near, positive vergences, the associated phoria, and the slope of the fixation disparity curve changed significantly over the period of training. I conclude that negative vergence training can increase the negative vergence capabilities and also affect the phoria position of the eyes via feed-back into the slow vergence system.

Accommodation, Ocular↗

PubMed1986

Characteristics of exodeviations: I. A comparison of three classes.

A retrospective study of 179 patients (69 males and 110 females) with binocular visual dysfunction and an exodeviation at distance or near or at both distances has been completed. The mean age of 19.7 years was significantly younger than the population from which they were referred. The patients were classed as convergence insufficiency, equal exodeviation, or divergence excess, based on the relation of the distance and near angles of deviation. Based on these criteria, interaction was found to be present between the diagnostic class and the frequency of the deviation, the symptoms reported, and a variety of clinical parameters such as the angles of deviation at distance and near, the AC/A ratio, positive and negative vergence values, the amplitude of accommodation, and the threshold of stereopsis. A number of statistical relations were noted between the frequency of the deviation vs. the symptoms reported and a variety of the clinical parameters. The implications of these results are discussed.

Accommodation, Ocular↗

PubMed1986

Characteristics of exodeviations: II. Changes with treatment with orthoptics.

This study examined retrospectively the records of 179 patients who had binocular visual dysfunction as a result of an exodeviation (either at distance or near or both). The patients were classified as having convergence insufficiency (N = 110), equal exodeviations (N = 49), or divergence excess (N = 18). The diagnostic groups and the different frequencies of deviation reacted differently to treatment with a standard orthoptic regimen. Nearly all the patients (97%) achieved some improvement in either objective or subjective areas or both. However, fewer were able to satisfy the criteria set for total success. Factors correlated with the success of the treatment were the initial angle of deviation at distance and the initial level of stereopsis. The results and implications of this study are discussed.

Adolescent↗