Loss Of Binocular Vision Research Articles

Task-Dependent Constraints in Motor Control: Pinhole Goggles Make the Head Move Like an Eye

In the 19th century, Donders observed that only one three-dimensional eye orientation is used for each gaze direction. Listing's law further specifies that the full set of eye orientation vectors forms a plane, whereas the equivalent Donders' law for the head, the Fick strategy, specifies a twisted two-dimensional range. Surprisingly, despite considerable research and speculation, the biological reasons for choosing one such range over another remain obscure. In the current study, human subjects performed head-free gaze shifts between visual targets while wearing pinhole goggles. During fixations, the head orientation range still obeyed Donders' law, but in most subjects, it immediately changed from the twisted Fick-like range to a flattened Listing-like range. Further controls showed that this was not attributable to loss of binocular vision or increased range of head motion, nor was it attributable to blocked peripheral vision; when subjects pointed a helmet-mounted laser toward targets (a task with goggle-like motor demands but normal vision), the head followed Listing's law even more closely. Donders' law of the head only broke down (in favor of a "minimum-rotation strategy") when head motion was dissociated from gaze. These behaviors could not be modeled using current "Donders' operators" but were readily simulated nonholonomically, i.e., by modulating head velocity commands as a function of position and task. We conclude that the gaze control system uses such velocity rules to shape Donders' law on a moment-to-moment basis, not primarily to satisfy perceptual or anatomic demands, but rather for motor optimization; the Fick strategy optimizes the role of the head as a platform for eye movement, whereas Listing's law optimizes rapid control of the eye (or head) as a gaze pointer.

Binocular interactions and visual acuity loss in esotropic cats.

Visual acuity was measured behaviorally in various groups of cats by using a two-choice discrimination procedure. Cats in group 1 were rendered strabismic soon after birth by sectioning the tendon of the lateral rectus muscle (unilateral esotropia); at adulthood, their visual acuity (VA) was evaluated, after which the optic chiasm was sectioned and VA reassessed. Cats in group 2 were not only tenotomized but also chiasmatomized neonatally, while cats in group 3 underwent a neonatal section of the optic chiasm only. VA was measured at adulthood in the two latter groups. Group 4 consisted of adult cats whose VA was evaluated before and after an optic chiasm section. Stimuli consisted of square-wave gratings of various spatial frequencies. Results showed that in normal cats, the average threshold values under monocular viewing were identical for each eye (4.76 cycles/degree); however, following optic chiasm section, monocular VA was reduced to 1.23 cycles/degree. VA in early optic chiasm section cats was lower than that of the normal cats but higher than that of late-lesioned animals (2.33 cycles/degree). In strabismic cats, mean VA was 1.25 cycles/degree for the deviated eye and 2.8 cycles/degree for the normal eye. Following the optic chiasm section at adulthood, VA was lower not only for the deviated eye (< 0.17 cycles/degree) but also for the normal eye (1.14 cycles/degree). Similar results were found when both the deviation and chiasmatomy were performed neonatally. The elimination of interocular interactions through chiasm transection failed to improve VA in the strabismic eye.

Video-assisted thoracoscopic surgery--indications, results, complications, and contraindications.

In recent times minimally invasive surgery has secured a firm place among the therapeutic options in thoracic surgery. The experience and results gained from video-assisted surgery on 109 patients between January 1, 1992 and July 31, 1993 are critically discussed. The procedure could be completed thoracoscopically on 94 of them. A change of method was necessary nine times for technical reasons and six times for oncological reasons (two times due to metastasis, four times due to bronchial carcinoma). A total of 154 individual operations were conducted. Sixty-three patients with recurrent spontaneous pneumothorax were successfully treated. The relapse rate was 1.5%. With the exception of three rethoracotomies (one due to postoperative hemorrhaging and two to persistent fistula) no significant complications occurred. Further indications included capsulated pleural empyema (n = 1), persistent hematothorax (n = 2), pleurectomy for malignant pleural effusion (n = 2), pleural tumors (n = 3), pulmonary parenchyma (n = 2), interstitial lung diseases (n = 3), bullous emphysema (n = 2), peripheral lung nodules (n = 18), mediastinal tumors (n = 8), and sympathectomy (n = 2). The advantages of video-assisted thoracoscopic surgery for patients include cosmetic considerations, low pain, earlier postoperative mobilization, and for some indications, a shorter operation period. The significant disadvantages for the surgeon are the loss of binocular vision as well as the impossibility of intraoperative palpation.

Distance Visual Acuity and Monovision

We have investigated aspects of visual acuity with monovision correction. Binocular distance visual acuity with monovision was approximately equal to monocular visual acuity for addition powers (monocular defocus) of +1.00 to +2.50 D, using both high and low contrast logMAR visual acuity charts. Neither the eye chosen to be defocused (dominant or nondominant) or pupil size (3.5, 5 and 7 mm) affected the binocular visual acuity loss with monovision for high contrast charts. We also investigated the effect of induced residual astigmatism (+0.50, +1.00, and -1.00 D) on binocular distance visual acuity in monovision correction. Residual astigmatism caused a significantly greater reduction of binocular visual acuity in the monovision condition than it did in normal binocular conditions. This effect appears to be related to a process of meridional interocular suppression. It may therefore be of clinical importance to correct low amounts of residual astigmatism in monovision corrections to provide optimum binocular visual acuity.

Control of interocular suppression as a function of differential image blur

This experiment studied normal adults, normal children, and corrected strabismics with alternating fixation, evaluating their ability to detect information presented to one eye under viewing conditions which might affect their eye preference. An apparatus was used which allowed unconstrained, binocular viewing of a video monitor, but in which the image seen by one eye was blurred while that seen by the other eye was in sharp focus. Under these viewing conditions, subjects were asked to identify a sharply focused letter which was shown briefly to the eye which was seeing the blurred background image or to the one which was watching the well-focused image. The question was whether there would be general suppression of the eye that was shown a degraded background, causing a reduction in its ability to process other information being presented. The results indicate no performance penalty for children, a mild decrement in recognition accuracy for normal adults, and a severe deficit in the ability of corrected strabismics to attend to the eye which views a blurred image. These results suggest that the loss of binocular vision that accompanies childhood strabismus is not a result of an inherent sensitivity to blurring, insofar as such vulnerability is reflected by these acute testing conditions.

Binocular vs. monocular task performance.

Functional advantages of binocularity were investigated by having 13 subjects perform a group of occupational-type tasks under monocular and binocular conditions. Significant binocular advantages ranging from 29.5% (pointers in straws) to 3.7% (reading speed) were measured. Tasks with many disparity cues showed the greatest binocular advantage. This shows that patients with normal binocular vision use binocular cues, most likely stereopsis, to enhance performance. In a second experiment, three subjects with normal binocular vision underwent monocular occlusion for 5 days to investigate whether monocular skills improved to compensate for the loss of binocular vision. During that period binocular performance was consistently better than monocular performance, and both monocular and binocular performance improved, even though the subjects were only gaining monocular experience. Although the 5 day occlusion period does not simulate the long-term denial of normal binocularity that strabismics or monocular patients experience, it shows that binocular superiority remains after short-term loss of binocularity.

Reconstruction of the floor of the orbit following subtotal maxillectomy by transposition of the septal wall as a local flap

The use of the septal wall for restoring defects of the orbital floor following subtotal maxillectomy is described. In our experience this method provides: (i) A viable, easily adaptable, mainly bony wall (perpendicular plate and vomer) that allows the surgeon to adjust the displaced eyeball. (ii) The possibility of re-adjustment of a secondarily sunken eyeball, with loss of binocular vision, by means of a Silastic implant, the transposed septal wall offering sufficient resistance. (iii) A substantial contribution to the hygiene of the resection cavity by introducing an actively secreting mucous membrane as part of the lining. In addition a modification of the Fergusson-Weber incision is described.

Nasotemporal overlap in retinal projections in man

In humans, the nasal retina projects to the contralateral hemisphere, whereas the temporal retina projects ipsilaterally. The nasotemporal line that divides the retina into crossed and uncrossed parts coincides with the vertical meridian through the fovea. This normal projection of the retina is severely altered in albinism, in which the nasotemporal line shifted into the temporal retina with temporal retinal fibers cross the midline at the optic chiasm. This study proposes the loss of binocular vision as direct cause for misrouting of temporal retinal fibers and shifting of the nasotemporal line temporally in albinism. It is supported by many observations that clearly indicate that loss of binocular vision causes uncrossed retinal fibers to cross the midline.This hypothesis may alert scientists and clinicians to find ways to prevent or minimize the loss of binocular vision that may occur in some diseases such as albinism and early squint. Hopefully, this will minimize the misrouting of temporal fibers and improve vision in such diseases.

Effects of the Kestenbaum operation on nystagmus-induced compulsive head posture

A report on 39 patients who underwent Kestenbaum-Anderson Surgery for a compulsive head posture caused by nystagmus. The problems of this compulsive posture of the head and the deterioration in visual acuity, as well as the diagnosis, timing and conditions leading to the operation are discussed. The dose usually has to be higher than originally stated by Kestenbaum. No negative results were observed after these operations. Even an occasional hypereffect is of value for a general improvement on posture. Loss of binocular vision does not occur. Kestenbaum's operation can also be performed on patients with squint because of the dosage, choice of muscle, choice of eye on which surgery is to be performed, or a second operation.

Physiological basis of amblyopia

Amblyopia is a defect of visual acuity. In this article Hisako Ikeda describes the physiological basis of normal visual acuity, and then continues, to describe retinal defects that might cause amblyopia. She emphasizes that the development of amblyopia is not by the same processes that bring about loss of binocular vision, and hence treatment of the two disorders should be considered separately.

Protection of employees with defective vision.

An employer has a special duty towards a one-eyed man (Paris v. Stepney Borough Council, 1951) but does not have a special duty to a man with normal sight because employment could normally continue with good monocular vision. Clearly, a man with very defective vision in one eye needs the same consideration as a one-eyed man so we examined the level of visual acuity which should alert the employer to giving a man special consideration. Two consultant oculists examined a chemist with Leber9s syndrome and found 6/24 vision in each eye. One consultant advised taking greater care of the man9s eyes because if one eye was lost, or became further damaged, he would have difficulty in continuing laboratory work. His colleague advised that the loss to the man would be of binocular vision and a no greater proportional loss than to the man with normal sight. Loss of binocular vision is considered greater in a man with poor eyesight because his visual acuity might, as in the present case, go from 6/18 using both eyes to 6/24 using one. We consider that wherever an employee9s (corrected) sight is 6/18 or less in either eye then his case should be given special consideration which may then indicate the need for the provision of extra eye protection.