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Guntram Kommerell

Publications and source records attributed to Guntram Kommerell.

11 recordsLinked to original sources
PubMed2006

Ocular prevalence and stereoacuity.

BACKGROUND: Most people attribute a higher weight to the input from one eye than to that from the other eye when they have to align stereodisparate objects in the same visual direction. This preference for visual directions has been termed 'ocular prevalence', according to the Latin praevalentia = superior power. QUESTIONS: (1) Is ocular prevalence of one eye (or its correlate, partial suppression of the other eye in the prevalence task) restricted to large stereodisparities, close to Panum's limit, or does it occur also at small stereodisparities, near the stereoscopic threshold? (2) Is ocular prevalence a handicap for stereoacuity? METHODS: Six non-strabismic observers with equal visual acuity of their two eyes were examined. To determine their ocular prevalence, they were presented with vertical vernier lines at stereodisparities ranging between 30 and 430 arcsec. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. Their stereoscopic threshold was measured with an adaptive staircase procedure, using the Freiburg Stereoacuity Test. RESULTS: All six observers exhibited some ocular prevalence. It changed considerably on repeated measurements. In three observers, it even switched from one eye to the other. Ocular prevalence occurred not only at large stereodisparities, close to Panum's limit, but also at small stereodisparities. The stereoscopic threshold of the six observers ranged between 1.7 and 12.3 arcsec. CONCLUSION: Ocular prevalence is common, intra-individually variable and occurs even at small stereodisparities close to the stereoscopic threshold. It is compatible with 'optimal' stereoacuity. Hence, ocular prevalence appears to be a harmless feature of normal binocular vision.

Adult↗
PubMed2005

The reversed fixation test: a diagnostic test for dissociated horizontal deviation.

BACKGROUND: Dissociated horizontal deviation is one of several conditions that manifest unequal horizontal deviations depending on which of the 2 eyes is fixating. PURPOSE: To describe the reversed fixation test as an essential tool to establish the diagnosis of dissociated horizontal deviation. METHODS: Analysis of 4 case scenarios depicting the utility of the reversed fixation test. RESULTS: The reversed fixation test distinguishes dissociated horizontal deviation from an unequal exodeviation of the 2 eyes resulting from postoperative slippage or weakness of a horizontal rectus muscle. CONCLUSION: The reversed fixation test is necessary to establish the diagnosis of dissociated horizontal deviation.

Diagnostic Techniques, Ophthalmological↗
PubMed2004

Vernier acuity for stereodisparate objects and ocular prevalence.

QUESTION: How precisely can objects, located in different depth planes, be aligned to the same visual direction? METHODS: Twenty normal observers were presented with vertical Vernier lines at various stereodisparities. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. RESULTS: Over a stereodisparity range from zero to 62'', the threshold for detecting a lateral offset between the Vernier lines remained at the "hyperacuity" level of about 7''. With larger stereodisparities, the threshold increased about fourfold, probably due to a mutual, partial suppression of the position signals from the right and left eyes. The reference point from which the observers judged the relative visual directions between stereodisparate objects was not located midway between the eyes; rather, it was often decentred towards the right or the left eye, meaning that the observers had an "ocular prevalence". Their ocular prevalence was, however, not strong enough to have an effect on the Vernier acuity for stereodisparate objects. (Under pathological conditions like strabismic amblyopia, one should expect a 100% prevalence of the good eye, implying that the Vernier acuity reaches the monocular level, irrespective of any depth difference between objects.) CONCLUSION: Vernier acuity decreases with increasing stereodisparity. Ocular prevalence, occurring frequently among persons with normal eyes, has no effect on Vernier acuity for stereodisparate objects. For a typical everyday viewing condition, the reduced Vernier acuity beyond a stereodisparity of 62'' means that, from a viewing distance of 40 cm, precision mechanics have to guide their instrument as close as 0.4mm to a workpiece, until they can utilise their best position acuity.

Adult↗
PubMed2003

Retrobulbar irradiation for thyroid-associated orbitopathy: double-blind comparison between 2.4 and 16 Gy.

PURPOSE: Retrobulbar irradiation is used as a standard therapy for thyroid-associated orbitopathy. The evidence of its effectiveness is, however, scarce. Doses from 2.5 to 20 Gy have been recommended. METHODS: Forty-three patients with active thyroid-associated orbitopathy were irradiated with 2.4 Gy and 43 with 16 Gy. Five measures of outcome were used: (1) appearance of the eye region, documented with photographs; (2) Hertel exophthalmometry; (3) range of vertical eye movements; (4) eye muscle thickness (sum of three MRI sections across the eight rectus eye muscles); and (5) complaints, indicated on a visual analog scale. RESULTS: At 3 and 6 months after irradiation, no difference between 2.4 and 16 Gy was found in any of the five outcome measures (p between 0.099 and 0.993; Kruskal-Wallis test, Holm correction). Most outcome measures were slightly, but not significantly, improved in both the 2.4 and the 16 Gy groups. Patient complaints had improved significantly in both groups and the eye muscle thickness was significantly reduced in the 2.4 Gy group after 6 months. CONCLUSION: The lack of a difference between 2.4 and 16 Gy is compatible with four different interpretations: (1) the irradiation could be ineffective; (2) the maximal effect could be already reached at 2.4 Gy; (3) the maximal effect could lie between 2.4 and 16 Gy; and (4) the effect could increase beyond a threshold of >or=16 Gy. From general experience with inflammatory disease, the last two possibilities are unlikely; only the first two interpretations carry some probability. Although the design of the study did not allow a distinction between these two possibilities, we conclude that retrobulbar irradiation for thyroid-associated orbitopathy should not exceed 2.4 Gy.

Adult↗
PubMed2003

Ocular prevalence versus ocular dominance.

UNLABELLED: Ocular dominance manifests itself in tests that contain stereo-objects with a disparity beyond Panum's area, e.g. in pointing a finger. These tests force subjects to decide in favour of one or the other eye. In contrast, ocular prevalence is determined using stereo-targets imaged within Panum's areas. These tests allow a graded quantification of the balance between the eyes. Here we present the computer-based Freiburg Ocular Prevalence Test in which stereo-disparate targets have to be aligned, and compare it with the Haase Stereo-balance Test that requires an estimation of the horizontal distance between stationary stereo-disparate objects. In addition, we compare ocular prevalence with ocular dominance. METHODS: (1) We measured the influence of a neutral-grey filter in front of one eye to assess the suitability of the Freiburg and the Haase Tests in revealing graded amounts of ocular prevalence. (2) About 20 subjects with equal vision of their two eyes underwent the Freiburg and the Haase Tests for ocular prevalence, and Parson's Monoptoscope Test for ocular dominance. RESULTS: (1) In both the Freiburg and the Haase Tests, the neutral-grey filter shifted ocular prevalence by about 50%. (2) An ocular prevalence of more than 10% occurred in 13 of the 20 subjects using the Freiburg, and in 14 using the Haase Test. On average, the ocular prevalence was 24.1+/-3.8% in the Freiburg and 32.0+/-8.2% in the Haase Test. The dominant eye coincided with the prevalent eye in 15 of the 20 subjects. DISCUSSION: The effect of the neutral-grey filter indicated that both the Freiburg and the Haase Tests can be used to measure fractions of ocular prevalence, although the Freiburg Test carries a higher reproducibility. Spontaneous ocular prevalence occurs frequently in persons with equal vision of their two eyes. This suggests that ocular prevalence does not represent a condition that requires treatment. Rather, partial suppression of one eye, the correlate of ocular prevalence, may play a physiological role in that it helps to disregard double images at stereo-disparities close to the limits of Panum's area.

Adult↗
PubMed2003

Stereoacuity versus fixation disparity as indicators for vergence accuracy under prismatic stress.

BACKGROUND: Fixation disparity has been widely used as an indicator for vergence accuracy under prismatic stress. However, the targets used for measuring fixation disparity contain artificial features in that the fusional contours are thinned out. We considered that stereoacuity might be a preferable indicator of vergence accuracy, as stereo targets represent natural viewing conditions. METHODS: We measured fixation disparity with a computer adaptation of Ogle's test and stereoacuity with the automatic Freiburg Stereoacuity Test. Eight subjects were examined under increasing base-in and base-out prisms. RESULTS: The response of fixation disparity to prismatic stress revealed the curve types described by Ogle and Crone. All eight subjects reached a stereoscopic threshold below 10 arcsec. In seven subjects the stereoscopic threshold increased before double vision occurred. CONCLUSION: Our data suggest that stereoacuity is suitable to assess the range of binocular vision under prismatic stress. As stereoacuity bears the advantage over fixation disparity in that it can be measured without introducing artificial viewing conditions, we suggest exploring whether stereoacuity under prismatic stress would be more meaningful in the work-up of asthenopic patients than is fixation disparity.

Adult↗
PubMed2002

Interindividual variability of learning in stereoacuity.

BACKGROUND: In the evaluation of therapies aiming at binocular vision, for instance by the use of prisms or orthoptic training in the case of heterophoria, stereoacuity is often the primary outcome measure. To assess therapeutic effects it is necessary to separate them from perceptual learning with repeated testing. Learning stereoacuity has been investigated only in a few studies with up to six subjects. METHODS: To ascertain the interindividual variability of learning in stereoacuity we examined 24 subjects, 12 with and 12 without experience in psychophysical experiments. In a two-alternative forced-choice paradigm, subjects reported whether a vertical bar appeared in front of or behind a reference frame. Estimates of stereo threshold were obtained using an adaptive staircase procedure ("best PEST"). RESULTS: We found a highly significant learning effect ( P<0.0001) with a marked interindividual variability. In some subjects the stereoacuity improved by a factor of >30 and in others it did not improve at all. The median of the learning factor was 1.7. There was no significant difference between novices and experienced subjects. CONCLUSION: The great interindividual variability of learning in stereoacuity has important implications for therapeutic tests that use stereoacuity as an outcome measure: To distinguish therapeutic effects from improvements due to repeated testing, each subject's individual learning behaviour has to be taken into account, for example by starting out with an adequate training phase. The number of test repetitions required to reach a fairly constant level appears to be similar among individuals: in our paradigm most of the learning occurred within the first six blocks with 100 target presentations each.

Adult↗
PubMed2002

[Do prisms according to Hans-Joachim Haase improve stereoacuity?].

BACKGROUND: The "Measuring and Correcting Methodology" after H.-J. Haase (MKH) aims at converting "fixation disparity" into bicentral fixation, using prismatic spectacles. In the context of the MKH, fixation disparity is diagnosed by a series of subjective tests. According to H.-J. Haase, a long-standing fixation disparity can lead to "disparate correspondence" between the central areas of both retinae, which consolidates the fixation disparity and gradually converts a "young" into an "old fixation disparity". In "old fixation disparity" it is thought that bicentral fixation does not occur anymore, so that stereoacuity is impaired. However, prismatic spectacles can, according to H.-J. Haase, restitute bicentral fixation and consequently improve stereoacuity, even in some cases of "old fixation disparity". METHODS: Ten non-strabismic subjects with a visual acuity of >/= 1.0 in both eyes were examined. It turned out that all ten had, according to MKH, a "disparate correspondence", 5 subjects with a "young" and 5 with an "old fixation disparity". According to the MKH, a correcting prism was determined. All 10 subjects underwent the automatic Freiburg Stereoacuity Test, without and with the MKH-prism. RESULTS: Without the MKH-prism, the stereoscopic threshold ranged between 1.5 and 14.5 arcsec. With the MKH-prism, the values were not significantly different. CONCLUSION: Stereoacuity ranged between good and excellent in the 5 subjects with "young" as well as in the 5 subjects with "old fixation disparity". The MKH-prism did not improve the stereoacuity in any of the subjects. These results cast doubt on Haase's assertion that an "old fixation disparity" implies a reduced stereoacuity. Hence, the premise for a benefit of the MKH-prism with respect of stereoacuity is not substantiated. In the 5 subjects with a "young fixation disparity", the good stereoacuity is consistent with Haase's theory, so that a benefit of the MKH-prism for stereoacuity was not expected. In previous studies, stereoacuity was found to be better with the MKH-prism than without it. These studies are questionable since learning with repeated testing was not taken into account. We conclude that there is no sound evidence for the assumption that the MKH-prism can improve stereoacuity.

Adult↗
PubMed2002

[Do prisms according to Hans-Joachim Haase influence ocular prevalence?].

BACKGROUND: Ocular prevalence is defined as an unequal weighting of the eyes in the directional perception of stereo objects. Opinions differ as to the cause and relevance of ocular prevalence. Hans-Joachim Haase suggested that ocular prevalence is due to fixation disparity, brought about by incomplete compensation of heterophoria. He further suggested that prismatic spectacles determined by his "measuring and correcting methodology" (MKH) could restore bicentral fixation and thus establish a perceptual balance between both eyes. METHODS: We examined 10 non-strabismic subjects with a visual acuity of > or = 1.0 in both eyes. It turned out that all 10 had a "fixation disparity type II", characterised according to Haase by a "disparate retinal correspondence". All subjects underwent the automatic Freiburg Ocular Prevalence Test, without and with MKH prisms. In addition we examined ocular prevalence under forced vergence and compared ocular prevalence with stereoacuity. RESULTS: Spontaneous ocular prevalence ranged between 1 and 69 %. Averaged over all 10 subjects, ocular prevalence without and with the MKH prisms were not significantly different. Statistical evaluation of single subjects revealed only in one of the 10 a significant difference (Bonferroni-corrected p = 0.001). In the subgroup of 5 subjects who underwent forced vergence, ocular prevalence remained unaltered between 0 and 18 Delta base out. The stereoscopic threshold of all 10 subjects ranged between 1.5 and 14.5 arcsec. There was no correlation between ocular prevalence and stereoscopic threshold (r = - 0.2, p = 0.5). CONCLUSION: Our results indicate that ocular prevalence is largely independent of phoria correction and vergence stress. The excellent stereoacuity of all subjects suggests that ocular prevalence is abandoned for the sake of optimal resolution when very small differences in depth have to be judged.

Adult↗