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PubMedDate not supplied

Stability of the postoperative alignment in adjustable-suture strabismus surgery.

We reviewed the postoperative alignment drift in 201 patients between the ages of 14 and 75 years who underwent rectus muscle surgery with adjustable sutures from 1984 to 1989. We analyzed results for 42 primary esotropia (ET) surgeries and 37 reoperations (groups IA and IB, respectively), 34 exotropia (XT) primary surgeries and 66 reoperations (groups IIA and IIB, respectively), and 22 hypertropia (HT) surgeries (group III). Forty percent of patients required postoperative muscle adjustment. All patients underwent a minimum of 8-weeks follow up; 66% underwent 6-months follow up or longer. The postoperative drifts in alignment for primary surgeries versus reoperations were not significantly different for either ET or XT patients. The mean postoperative drift in prism diopters from the alignment immediately after the adjustment, or after the surgery if no adjustment was needed, for each group as measured during the most recent follow up was 1.3 eso-shift for group IA, 1.2 exo-shift for group IB, 4.8 exo-shift for group IIA, 4.1 exo-shift for group IIB, and 1.5 hyper-shift for group III. Only for groups IIA and IIB were these drifts found to differ significantly from zero. Based on these drift patterns, we align ET patients to orthotropia, XT patients to 5 to 7 delta esotropic, and HT patients to 1 to 2 delta hypotropic positions.

Adolescent↗
PubMedDate not supplied

Augmented surgery for esotropia associated with high hypermetropia.

Historically, surgical formulas for the management of accommodative esotropia have been based on the residual deviation with full hypermetropic correction. This "standard surgery" has resulted in a high incidence of undercorrection. In response to the large number of undercorrections with standard surgery, the authors have devised a formula for augmenting the amount of rectus recession based on the average of the near deviation with and without correction. In this study, we compare augmented surgery to standard surgery in patients who underwent bilateral medial rectus recessions for residual esotropia after prescribing full hypermetropic spectacle correction. Seventy patients with acquired esotropia after 6 months of age, and hypermetropia of +3.00 or more, were retrospectively studied. Thirty of these patients had undergone standard surgery, while 40 had augmented surgery. The follow up on each group was at least 1 year. Of the 30 patients in the nonaugmented group, 22 (74%) had postoperative deviations of 10 prism diopters or less with 8 (26%) showing a significant undercorrection. Of the 40 patients who received augmented surgery, 35 (88%) had postoperative deviations of 10 delta or less and 5 (12%) were exotropic while wearing full hypermetropic correction. Of the 5 patients with a consecutive exodeviation while wearing full hypermetropic correction, 2 corrected to orthotropia by reducing the spectacle correction by +1.50 diopters and +1.25 D (93% success), 2 were converted to orthotropia by removing +3.00 spectacle correction (97% success), and 1 continued to have an intermittent exodeviation even after removing spectacle correction. This brought the overall success rate for augmented surgery to 98%.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗
PubMed1998

Vergence control across saccades in dyslexic adults.

Many aspects of vision have been investigated in developmental dyslexia. Some research suggests deficits in vergence control (e.g. Buzzelli, 1991, Optom. Vision Sci. 68, 842-846), although ability to control vergence across saccades has not yet been investigated. We have explored this question indirectly using Enright's (1996 Vision Res. 36, 307-312.) sequential stereopsis task. The task requires observers to set two adjacent targets (whose textures cannot be resolved simultaneously if either is fixated) to appear equi-distant. Enright has argued that sequential stereopsis stereoacuity thresholds offer an indication of vergence control across saccades. We report two experiments using a total of 17 dyslexic and 18 control adults. Performance was measured on a sequential stereopsis task and an ordinary 'simultaneous' stereopsis task. No significant differences between groups were found. However, whereas practice of the sequential task lowered control group thresholds on the simultaneous task, for the dyslexic group it significantly raised thresholds, suggesting that visual fatigue is especially important in investigations of visual functions in dyslexia. Although the small samples used limit conclusions at this stage, the main sequential stereopsis results suggest that, if Enright is correct, dyslexic adults can show normal vergence control across saccades.

Adult↗
PubMed2000

Coding of border ownership in monkey visual cortex.

Areas V1 and V2 of the visual cortex have traditionally been conceived as stages of local feature representations. We investigated whether neural responses carry information about how local features belong to objects. Single-cell activity was recorded in areas V1, V2, and V4 of awake behaving monkeys. Displays were used in which the same local feature (contrast edge or line) could be presented as part of different figures. For example, the same light-dark edge could be the left side of a dark square or the right side of a light square. Each display was also presented with reversed contrast. We found significant modulation of responses as a function of the side of the figure in >50% of neurons of V2 and V4 and in 18% of neurons of the top layers of V1. Thus, besides the local contrast border information, neurons were found to encode the side to which the border belongs ("border ownership coding"). A majority of these neurons coded border ownership and the local polarity of luminance-chromaticity contrast. The others were insensitive to contrast polarity. Another 20% of the neurons of V2 and V4, and 48% of top layer V1, coded local contrast polarity, but not border ownership. The border ownership-related response differences emerged soon (<25 msec) after the response onset. In V2 and V4, the differences were found to be nearly independent of figure size up to the limit set by the size of our display (21 degrees ). Displays that differed only far outside the conventional receptive field could produce markedly different responses. When tested with more complex displays in which figure-ground cues were varied, some neurons produced invariant border ownership signals, others failed to signal border ownership for some of the displays, but neurons that reversed signals were rare. The influence of visual stimulation far from the receptive field center indicates mechanisms of global context integration. The short latencies and incomplete cue invariance suggest that the border-ownership effect is generated within the visual cortex rather than projected down from higher levels.

Animals↗
PubMed2002

[Eyestrain induced by stereogram on 3-D display--differences between types of correction].

PURPOSE: We investigated eyestrain in normal subjects induced by gazing at a random-dot stereogram on a parallax barrier system 3-D display. METHODS: The 41 subjects were divided into 4 groups according to the type of correction. Near point of accommodation, accommodative relaxation, and contraction times were measured with an accommodo-polyrecorder before and after a stereoscopic visual load, and 15 min and 30 min after a rest. The subjective symptoms were assessed by a 7-point rating questionnaire at the same time as the measurements. RESULTS: After 15 min of sustained visual load, the near point of accommodation was prolonged significantly in the groups without correction and with soft contact lenses(SCL), and accommodative contraction and relaxation times were significant delayed in the groups without correction, with hard contact lenses(HCL), and with SCL but not in the group with spectacles. These changed values of accommodation returned to their previous value following the rest. Significant increase in the rating questionnaire was found in the subjective symptoms of "eyestrain", "eye heaviness", "clouding", "eye dryness" and "irritation of eyes" after loading in the groups without correction, with HCL, and with SCL. In the spectacle group, there was no significant change in the subjective symptoms of "clouding" and "eye dryness". CONCLUSION: From these results, it is concluded that gazing at stereoscopic images on the parallax barrier system 3-D display causes severer eyestrain in cases of correction with contact lenses and in uncorrected cases than in cases with spectacles.

Accommodation, Ocular↗
PubMed2003

Motion parallax is computed in the updating of human spatial memory.

As we move through space, stationary objects around us show motion parallax: their directions relative to us change at different rates, depending on their distance. Does the brain incorporate parallax when it updates its stored representations of space? We had subjects fixate a distant target and then we flashed lights, at different distances, onto the retinal periphery. Subjects translated sideways while keeping their gaze on the distant target, and then they looked to the remembered location of the flash. Their responses corrected almost perfectly for parallax: they turned their eyes farther for nearer targets, in the predicted nonlinear patterns. Computer simulations suggest a neural mechanism in which feedback about self-motion updates remembered locations of objects within an internal map of three-dimensional visual space.

Adult↗
PubMedDate not supplied

Effect of aniseikonia on fusion.

Physiological aniseikonia is the basis of stereopsis but beyond certain limits it becomes an obstacle to fusion. It is not well established as to how much aniseikonia can be tolerated by the fusional mechanism. Different tests under different testing conditions have given a wide range of variation. On the synoptophore we had observed tolerance upto 35% aniseikonia in some cases. Under more physiological conditions on a polaroid dissociation stereoprojector we observed lesser baseline fusional vergences but tolerance in about 70% of the cases upto 30% aniseikonia while 25% could tolerate even 35% aniseikonia. However we realise that these indicate the maximal potential and not the symptom free tolerable limits.

Aniseikonia↗
PubMed1990

Fixational drift and nasal-temporal pursuit asymmetries in strabismic amblyopes.

This study evaluated to what extent inaccurate and asymmetric smooth pursuit in strabismic amblyopic eyes is attributable to abnormally high-velocity eye drifts that these eyes exhibit during monocular fixation. Smooth pursuit gains (peak eye velocity/peak target velocity) were determined in the amblyopic and nonamblyopic eyes of 11 strabismics for nasalward and temporalward motion; the target oscillated across 6 degrees of the horizontal meridian at frequencies ranging from 0.0625 to 1 Hz. In general, pursuit gains were higher for nasalward than temporalward motion, for both amblyopic and nonamblyopic eyes. Correction for each eye's mean velocity of fixational drift eliminated this nasal-temporal pursuit asymmetry for most of the nonamblyopic eyes, but not for the amblyopic eyes. Compared to the nonamblyopic eyes, corrected pursuit gains of the amblyopic eyes averaged about 0.2 lower nasalward and about 0.4 lower temporalward, but substantial variation occurred among individuals. We suggest that the overall reduction of pursuit gain in strabismic amblyopic eyes (after correction is made for fixational drift bias) stems from the use of a nonfoveal (eccentric fixation) locus for tracking; the further reduction of temporalward gain may result from a nasal-temporal asymmetry in processing motion signals.

Adult↗
PubMedDate not supplied

[Possible usage of parallax phenomenon in dental radiography].

The authors describe a method of X-ray recording which uses the phenomenon of parallax in determination of exact localisation and inter-relationship of some elements within the upper and lower jaws. By describing the method in detail, the authors also point out its advantages in everyday estimation of the position of impacted teeth and their relationship to the surrounding anatomical points.

Humans↗
PubMed1989

[Additive hypotheses of the effect of head and eye movement on dark convergence].

Dark vergence depends on the vertical direction of gaze; it decreases with raised gaze and increases with lowered gaze. The vertical direction of gaze can be varied by means or raising or lowering the eyes or by way of tilting the head forward or backward. The effects of both manipulations on dark vergence are different. According to Heuer (1988) the effects of head tilt and eye inclination on dark vergence are almost, but not exactly, additive. In Exp. 1 the hypothesis of additive effects of gaze direction and eye inclination was tested and could not be rejected. The two additive hypotheses (head tilt and eye inclination vs. gaze inclination and eye inclination) result in different predictions for dark vergence with "compensatory" head and eye inclinations, which leave the direction of gaze in space invariant. In Exp. 2 it was shown that predictions from both hypotheses deviated from the observed values of dark vergence. Thus none of the two additive hypotheses provides exact predictions of dark vergence for all possible combinations of head tilt and eye inclination. For practical purposes the approximation might be sufficient. In particular, although mean dark vergence cannot be predicted exactly, individual differences can be predicted quite accurately.

Adolescent↗
PubMed1989

[Universal treatment of ophthalmic migraine].

It's about a therapeutic method, particular to the author, which gets its universality from an optic prescription with a prismatic aspect. The ophthalmic headache's crisis is caused, in fact, by a spasm of convergence on an unknown exophory of which the amplitude of fusion is satisfying, and the presence of which can only be seen with test under screen.

Convergence, Ocular↗
PubMed1989

Bagolini lenses vs. PFL filters in the diagnosis of correspondence.

This study introduces a new product, the PFL-7501 filter (prism linear filter), as a test for correspondence. Thirty consecutive strabismic subjects were asked to verbally describe, then draw, the images seen from a small light source through the Bagolini #4 striated lenses and the PFL-7501 filters. A 97% concordance was found between the two materials. The bright, multicolored streaks seen through the PFL filters were easier for all subjects to see and describe than the images seen through the Bagolini striated lenses.

Adolescent↗
PubMed1989

[Difficulty in the implantation of intraocular lenses by "hidden" parallax].

Although this is not the intent of the surgeon, many posterior chamber lenses are nevertheless placed asymmetrically--one loop in the sulcus and the other in the capsular bag. Difficulties can arise during implantation of even the first loop, which is mostly done in the 6 o'clock position. In this situation, a deficit or loss in steroscopic vision is observed. According to the law of Garten, depth perception is increasingly disturbed as the angle between the connection line of the two observer eyes and two smooth, stretched contours being steroscopical objects diminishes to zero. The reason is not a loss of parallaxis, but the fact that there are no structures that can be matched for stereopsis in a horizontal direction. Thus, stereoscopic vision can be improved dramatically by: (1) twisting the axis of the IOL loops into the five to four o'clock direction; (2) enlarging the magnification of the operating microscope until the grain of the structures is visible. It will then be possible to implant the IOL into the capsular bag (or the ciliary sulcus), which is what was intended.

Depth Perception↗
PubMed1988

Pseudo-pseudo-Foster Kennedy syndrome.

An 80-year-old woman presented with a classic story and findings of an anterior ischemic optic neuropathy in her left eye. Her right eye had slow and progressive decreased vision, ostensibly secondary to a cataract. However, the right eye showed slight temporal pallor of the optic disc and a superior temporal field defect was found. Her radiologic exam showed a tuberculum sella meningioma extending into the right optic canal compressing the right optic nerve. Two diseases, ischemic optic neuropathy and meningioma, in one patient may be termed a pseudo-pseudo-Foster Kennedy syndrome.

Aged↗