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At least 1,045 records · Page 58Linked to original sources
PubMed1998

Neural encoding of subject-object distance in a visual recognition system.

Domestic chicks follow a familiar (imprinted) object when it recedes. In behaving, imprinted chicks with no experience of objects at different distances, neuronal activity was recorded from the intermediate and medial part of the hyperstriatum ventrale (IMHV), a brain region crucial for the recognition memory underlying imprinting. We found that (i) some neurones responded equivalently, irrespective of the subject-object distance d (d-invariant); (ii) other neurones responded differently at different values of d (d-sensitive); (iii) these response types were found in monocular chicks and in chicks with both eyes exposed; (iv) the action potential shape of d-invariant neurones was different from that of other neurones and (v) the spontaneous firing rate of some neurones was correlated with locomotor activity. Taken together with previous findings, the results raise the possibility that IMHV has a major role to play in the sensory and motor-control aspects of imprinting in addition to its mnemonic functions.

Action Potentials↗
PubMed1999

The effect of target proximity on the aniso-accommodative response.

Aniso-accommodation (unequal binocular accommodation) to lens-induced anisometropia has been demonstrated by subjective and objective measurement techniques (Marran and Schor, Vision Res. 38(22), 3601-3619). The gain of the response was significantly reduced for some subjects when aniso-accommodation was stimulated by a target at 1 m compared to a target at 20 cm, even when the targets viewed were matched in retinal image size, convergence levels and aniso-accommodative stimuli. The two conditions did differ in both the accommodative level and proximity of the target. Thus the higher gain of the response in the 20 cm condition could have arisen from either high proximity, high accommodative level or a combination of both. In this investigation, target proximity and accommodative level were manipulated independently while extra-retinal cues such as absolute disparity and image size were held constant. The results show that high target proximity alone rather than accommodative level or a combination of the two was responsible for the distance dependent effect demonstrated by subjects. Furthermore, accommodative level did not affect the response when target proximity was held constant. Subjects who demonstrated invariant aniso-accommodation with changes in viewing distance also demonstrated invariant aniso-accommodation with experimental manipulation of target proximity at the target distances tested, as would be expected. These results suggest that high level processing, rather than a reflex blur response, is involved in aniso-accommodation. This conclusion is strengthened by the previous finding of long reaction and response times, 11 and 15 s respectively, to step aniso-accommodative stimuli (Marran and Schor, Vision Res. 38(22), 3601-3619). Since the experimental target provided subjects with visual feedback of the relative blur of the dichoptically viewed letters, subjects had access to perceptual blur information cues. Some subjects seemed to have required both aniso-blur and proximity to exercise this volitional response. Those subjects who showed a distance invariant aniso-accommodative response may have been able to use perceived aniso-blur alone and their ability to disregard proximal cues may have resulted from greater experience with the aniso-accommodative stimuli. Alternatively, these subjects may have had a lower threshold to proximal stimuli and experienced target proximity at the more distant (1 m) viewing condition.

Accommodation, Ocular↗
PubMed2001

Reliability of mean power recorded during indoor and outdoor self-paced 40 km cycling time-trials.

The purpose of this study was to assess reliability of both indoor and outdoor 40 km time-trial cycling performance. Eight trained cyclists completed three indoor 40 km time-trials on an air-braked ergometer (Kingcycle) and three outdoor 40 km time-trials on a local course. Power output was measured for all trials using the SRM powermeter. Mean performance time across three indoor trials was 54.21 +/- 2.59 (min:sec) and was significantly different (P<0.05) to mean time across three outdoor trials (57.29 +/- 3.22 min:sec). However, there was no significant difference (P = 0.34) for mean power across three indoor trials (303+/-35W) when compared to outdoor performances (312 +/- 23 W). Within-subject variation for mean power output expressed as a coefficient of variation (CV) improved in both indoors and outdoors for trials 2 and 3 (CV = 1.9%, 95% CI 1.0 - 3.4 and CV = 2.1 %, 95 % CI 1.1 - 3.8) when compared to trials 1 and 2 (CV=2.1%, 95% CI 1.2-3.8 and CV=2.4%, 95% CI 1.3-4.3). These findings indicate that power output measured using the SRM powermeter is highly reproducible for both laboratory-based and actual 40 km time-trial cycling performance.

Adult↗
PubMed2001

[Near vision after implantation of monofocal versus multifocal intraocular lenses].

AIM: Object of this study was to compare the near visual acuity between eyes with monofocal intraocular lens (MONO) and myopic target refraction in comparison with eyes after refractive multifocal intraocular lens (MIOL) implantation and emmetropic to slight hyperopic target refraction. PATIENTS AND METHOD: 89 eyes of 83 patients underwent cataract surgery, in 49 eyes a MONO (SI-40NB, Allergan) was implanted, in 40 eyes a refractive MIOL (SA-40N, Allergan). At day 2 after surgery and after 5 months the uncorrected near visual acuity, the near visual aculty with distance correction and with an addition of +3 diopters (D) were determined. The refractive outcome targeted in case of MIOL implantation was emmetropia to slight hyperopia and myopia for the MONO subjects. The eyes with MONO were classified in 4 categories depending on their postoperative refractive error (spherical equivalent, SE): category 1 with SE +1 to > 0 D, category 2 with SE 0 to > -1 D, category 3 with SE -1 to > -2 D and category 4 with a SE -2 to > -3 D. RESULTS: We found a statistically significant better uncorrected near visual acuity in eyes with MIOL than in MONO subjects for category 1-3. In category 4 there was no statistically significant difference between MONO and MIOL. With best distance correction near visual acuity in MIOL was statistically significant better than in all 4 MONO categories. After adding 3 D, there was no statistically significant difference between the groups. CONCLUSION: Even in case of a myopic target refraction near visual acuity in eyes of the MONO group was statistically significant worse than in the eyes of the MIOL group. Only in case of postoperative SE of < or = -2 D eyes of the MONO group had a near visual acuity similar to the eyes of the MIOL group. This advantage is accomplished with a decrease in the uncorrected distance visual acuity.

Aged↗
PubMed2005

[Diagnosis of horner syndrome by pupil dilation lag].

BACKGROUND: In the first seconds after switching off the lights, Horner pupils often show a dilation lag. This dilation lag is diagnostic for Horner syndrome. We investigated whether the visibility of the dilation lag can be improved by increasing the amplitude of pupil dilation. PATIENTS AND METHODS: In four patients with pharmacologically confirmed Horner syndrome pupil sizes were registered bilaterally simultaneously with an infrared camera. Dilation lag was induced by switching off the light while the patient was fixating at distance or by turning off the light and changing fixation from near to far at the same time. An increase of anisocoria of 0.5 mm or more within the first 4 seconds was interpreted as dilation lag. RESULTS: Dilation lags were seen in one patient with both methods, in two patients only with the second method, and in one patient with neither method. CONCLUSIONS: Dilation lag visibility can be improved by asking the patient to change fixation from near to far at the moment when the lights are switched off.

Adult↗
PubMed1998

[Effects of presbyopia on clinical phoria].

BACKGROUND: Due to accommodation-vergence cross-link we can expect that presbyopia will affect vergence as well. From investigations of cross-link as function of age one may assess strain of visual system due to presbyopia. Furthermore, this observation will give hints on innervation of ciliary muscle. MATERIAL AND METHOD: Vergence is assessed as function of stimulus of accommodation in 27 subjects (24-65 years). RESULTS: Presbyops tend to be exophoric for near vision. Vergence is linked to accommodation by means of a quadratic polynome rather than by a linear function. CONCLUSIONS: We may expect, that missing vergence strains visual system of presbyops. Results support Hess-Gullstrand theory of presbyopia and indicate a loss of innervation of ciliary muscle with increasing age.

Accommodation, Ocular↗
PubMed1997

[Determination of far vision with DIN 58220 (criterion 6/10): computer vision test with high resolution monitor in comparison with vision charts].

BACKGROUND: The results of nearly automated computerized determination of visual acuity by PC are compared to those of card measurements. The introduction of a new measuring technique should not change the dimension--visual acuity--itself, therefore there should be no difference between the results of the conventional technique and those of the PC. METHODS: Both methods were tested in a group of subjects (N = 100) with vision between 0.1-2.5. The nearly automated technique was developed and established by our department. Like the conventional method it keeps strictly to the DIN rates. For DIN-criterion we chose for the benefit of high reproducibility 6/10. RESULTS: In spite of some deficiencies in the presentation of the Landoltrings on the monitor, our analysis presents a surprisingly good correspondence between the results of the two methods. In the analysis, we are not comparing arithmetic mean values. Instead, we examine the individual difference between the two methods in acuity steps and its these distribution within the group of subjects. No statistically provable difference can be detected. This is valid for both single visual acuity and for visual line acuity, which can also be tested with the computer aided method. CONCLUSION: We conclude that the PC proves to be an equivalent method to the measurement with cards. Thus, it is suitable for the use in daily routine of vision examination with the advantage, that the investigator has less influence on the outcome of the test.

Adult↗
PubMed1994

[Examination procedure in automated determination of far and near vision].

BACKGROUND: Although the measurement of visual acuity at distance is more important in ophthalmological practice, the visual acuity at near should be tested additionally. In a recently published paper we showed that with today's computer technology visual acuity at distance can be measured in standardized procedures according to DIN 58220. We describe here an additional, integrated setup, which allows the measurement of visual acuity also at near. METHODS: For testing visual acuity at near, the whole set of optotypes is presented on a transparent overlay mask in front of a computer monitor which is used as a program-controlled light source. A certain optotype is chosen by illuminating its background. The patient's responses are read via a small console by the computer. The test procedure follows the DIN requirements. RESULTS AND CONCLUSIONS: First reliability tests showed that the test arrangement is qualified for rapid and standardized determination of visual acuity at near and at distance under nearly natural viewing conditions.

Adult↗
PubMed1993

[Visual compromise of automobile drivers by frontal photo-flash in mesoptic conditions].

The time for recovery of recognition of an optotype presented at a distance of 40 m subsequent to exposure to a flash gun (Eso company, Tettnang; flash energy 200 Ws, duration 1/1000 s; distance 10 m) was studied on 97 subjects aged 20 to 83 years. A Landolt-ring (contrast 1:5, diameter 29 cm), mounted on a disk (diameter 58 cm) which could be rotated in steps of 45 degrees served as a test target. The flash gun could be dimmed down by a red filter (Schott RG 665). The tests were performed at night without additional illumination except the low beam of the car. The flash gun was foveally fixated. After a white flash, a period of 93.1 s +/- 48.6 s (MEAN +/- SD) passed before the optotype could be recognized correctly again. By adding the red filter in front of the flash gun the recovery time could be shortened significantly (p < 0.0001; Wilcoxon signed-rank test) to 4.9 s +/- 1.7 s. "Time for re-adaptation" after dazzling by red flash is comparatively short and therefore strongly influenced by many variables (e.g. time for recognition and for verbalization). Because of that a final evaluation of dazzling by red flash seems to be impossible with this method. Subjects of advanced age and opacities of the ocular media showed an increase in the "time for re-adaptation" for the white as well as the red flash. In conclusion, a speed control using white flash guns at night can be considered as critical.

Adult↗
PubMed1993

[Asymmetric multizone lenses--a new concept in multifocal intraocular lenses].

BACKGROUND: Asymmetrical multifocal lenses (MIOLs) represent a new concept for binocular implantation of MIOLs: one asymmetrical IOL--destined for implantation in the dominant eye--is favouring distance vision by assuring that 60-70% of the light rays coming from an object will pass through the distance part of the optic. The other IOL--destined for implantation in the second eye--is favouring near vision, enabling that 60-70% of the light energy will be focused by the near zone(s) of the IOL. METHODS: Modulation transfer function (MTF), Strehl-Ratio (SR) and resolution efficiency (RE) were determined in both foci by in vitro measurement. Defocus curves were performed after clinical implantation as well as after "optical implantation" by means of an optical device developed by Reiner. RESULTS: In vitro measurements showed superior results of SR and RE in the favoured focus of the MIOL. Defocus curves after clinical and "optical" implantation yielded higher peaks for visual acuity and contrast in the favoured focus. CONCLUSION: First theoretical and clinical results do confirm the new concept of asymmetrical multifocal IOLs.

Contrast Sensitivity↗
PubMed1989

[Automated measurement of distance vision based on the DIN strategy].

A method for automated measurement of far vision is described which meets the test requirements laid down in the new DIN standards. The subject sits 5 m from a high-resolution monitor on which either Landolt rings or Snellen's types are generated by a computer. By moving a joystick the subject indicates to the computer whether he can see the critical detail (e.g., the direction of opening of the Landolt ring). Depending on the subject's input and the course of the test so far, the computer generates the next test symbol until the threshold criterion is reached. The sequence of presentation of the symbols and the threshold criterion are also in accordance with the DIN standard. Initial measurements of far vision using this automated system produced similar results to those obtained by conventional methods.

Distance Perception↗
PubMed1986

[Attention shifting and dissociated vertical squint].

Some patients with dissociated vertical deviation show an increasing upward drift of their squinting eye when reading small numbers at a distance of 5 m, making a special effort to shift attention to the non-squinting eye. This finding is at variance with the view that the manifestation of dissociated vertical deviation may be induced by visual inattention. The phenomenon could be explained by analogy to the occlusion test, by a binocular imbalance in visual information processing. The phenomenon may be found frequently in patients who require surgery for an especially disfiguring intermittent vertical squint. Looking for the phenomenon may be useful when deciding whether to operate for a dissociated vertical deviation: If increasing vertical deviation is observed during binocular acuity testing, surgical treatment should be considered.

Adolescent↗
PubMed1985

[Magnifying vision aids and their use by vision-handicapped patients].

Patients with visual acuities of below 0.4 at both long and short range cannot be sure of seeing well enough to read or watch TV. Low-vision aids improve vision to a such a degree that these activities can be performed once again. However, aside from this positive effect, low-vision aids have some disadvantages which sometimes prevent patients from actually using them. An investigation conducted among 150 patients revealed that 84% of them used their low-vision aids for about an hour or so a day.

Adolescent↗
PubMed1976

The contribution of relational factors to line-length matches.

Both Kunnapas and Rock and Ebenholtz investigated the effects of surrounding-frame size upon line-length judgments. Whereas Kunnapas obtained errors of the order of 10-15%, typical of those which occur in other geometrical illusion figures, Rock and Ebenholtz reported errors closer to 100%. Rock and Ebenholtz claimed that perceived size is largely relationally determined and that this fact was obscured in Kubnapas experiment by allowing observers to compare the test lines directly with each other and within a common framework provided by the wall of the room. On the contrary, the experiments reported here suggested that errors in the Rock and Ebenholtz study may have been inflated by their use of nondirective instructions and by the confounded effects of other variables. When the Rock and Ebenholtz experiments were repeated with adequat controls over these variables, the effect of surrounding frames on line-length matches were of the order of 15-19%, similar to those of Kunnapas but much smaller than those reported by Rock and Ebenholtz. The complexity of the stimuli in the Rock and Ebenholtz type of experiment is such, however, that the effects of a number of variables and possible cue conflicts remain to be investigated.

Distance Perception↗
PubMed1977

Brightness as an indicator to distance: relative brightness per se or contrast with the background?

A black and a white target are displayed, in five different conditions, on five grey backgrounds having different degrees of brightness (from very bright to very dark). The results show that the target having the higher contrast with its background is perceived as the nearer. With the off-white background, e.g., the black target appears as the nearer to the observer. This contradicts the well-known concept according to which the brighter target should in any case be perceived as the nearer ("relative brightness" cue). The conclusion is that the frame of reference must be taken into consideration: study of the indicators to distance in an empty space and per se is not sufficient.

Adult↗