Electrophysiologic evidence for normal optic nerve fiber projections in normally pigmented squinters.
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The Siamese cat, a type of albino, has a visual pathway anomaly in which too many optic nerve fibers cross at the optic chiasm, and also frequently has strabismus. The correlation of strabismus with this defect suggests that a similar pathway defect without pigmentation anomalies, may be the cause of much human strabismus. Creel, Witkop, and King have used evoked potential methods to show that such a pathway defect likely occurs in the human albino. While unpublished control experiments verified their results on human albinos, no such defect has been found in the normally-pigmented human squinter. It is concluded that the visual pathway anomaly is limited to albinism and is not a likely cause of most human strabismus. (+info)
Effect of ADCON-L on adjustable strabismus surgery in rabbits.
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BACKGROUND/AIMS: In search of a way to prevent postoperative adhesion after strabismus surgery, an animal study was performed to assess the effect of a gel consisting of a polyglycan ester in a gelatin matrix (ADCON-L). METHODS: Bilateral recessions of superior rectus muscle (SR) were performed on 16 rabbits. ADCON-L was applied beneath and over the SR in the right eyes of all rabbits, while the operative fields in the left eyes were irrigated with a balanced salt solution (BSS). The adjustment was performed on each SR at 4 and 7 days postoperatively on the same eye. The length and force of the adjustment and the degree of adhesion were recorded. At 3 weeks postoperatively, disinsertional force was measured in several of the eyes, and the other eyes were enucleated. RESULTS: The length of the adjustment was longer and the force of the adjustment was less in the ADCON-L group than in the BSS treated group at 4 and 7 days postoperatively (p=0.00). A significant reduction (p=0.00) in the degree of adhesion was noted in eyes treated with ADCON-L. There was no significant difference in disinsertional force between the two groups. Histopathological evaluation of the muscle revealed decreased fibrosis of perimuscular connective tissue in eyes treated with ADCON-L at 3 weeks postoperatively. CONCLUSION: This study suggests that ADCON-L helps to prevent postoperative adhesion in rabbits and enables adjustment twice within 7 days postoperatively without complications. (+info)
Indocyanine green angiography of the anterior segment in patients undergoing strabismus surgery.
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BACKGROUND: Anterior segment imaging using fluorescein angiography is only suitable in lightly pigmented irides as the brown pigmentation of the iris masks fluorescein transmission. Indocyanine green (ICG) angiography has excellent penetration of pigment epithelium and, therefore, has potential application in detecting perfusion changes of dark irides after strabismus surgery. METHODS: A prospective study was conducted on patients older than 15 years undergoing strabismus surgery. A fundus camera was focused on the arteriolar tufts of the pupillary margin and 50 mg of ICG (concentration of 12.5 mg/ml) was given intravenously. Images were then obtained at 1 minute intervals of 5 minutes' duration. RESULTS: 45 patients with a mean age of 54.6 years and a mean follow up period of 8.6 weeks were studied. There were 23 patients in the primary surgery group, 11 in the secondary surgery group, and 11 in the staged group. Iris ICG angiograms were successfully performed in all patients. No persistent filling defect was detected in the primary and secondary horizontal recti surgery groups or in the secondary or staged vertical and combined vertical rectus groups 6-8 weeks postoperatively. 57% of both primary vertical and combined vertical and horizontal groups showed defects in the early postoperative phase. Only three cases demonstrated late perfusion defects in this series. CONCLUSION: ICG can detect iris perfusion changes in dark irides after strabismus surgery. Iris reperfusion was achieved in the majority of the cases. (+info)
The functions of the proprioceptors of the eye muscles.
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This article sets out to present a fairly comprehensive review of our knowledge about the functions of the receptors that have been found in the extraocular muscles--the six muscles that move each eye of vertebrates in its orbit--of all the animals in which they have been sought, including Man. Since their discovery at the beginning of the 20th century these receptors have, at various times, been credited with important roles in the control of eye movement and the construction of extrapersonal space and have also been denied any function whatsoever. Experiments intended to study the actions of eye muscle receptors and, even more so, opinions (and indeed polemic) derived from these observations have been influenced by the changing fashions and beliefs about the more general question of how limb position and movement is detected by the brain and which signals contribute to those aspects of this that are perceived (kinaesthesis). But the conclusions drawn from studies on the eye have also influenced beliefs about the mechanisms of kinaesthesis and, arguably, this influence has been even larger than that in the converse direction. Experimental evidence accumulated over rather more than a century is set out and discussed. It supports the view that, at the beginning of the 21st century, there are excellent grounds for believing that the receptors in the extraocular muscles are indeed proprioceptors, that is to say that the signals that they send into the brain are used to provide information about the position and movement of the eye in the orbit. It seems that this information is important in the control of eye movements of at least some types, and in the determination by the brain of the direction of gaze and the relationship of the organism to its environment. In addition, signals from these receptors in the eye muscles are seen to be necessary for the development of normal mechanisms of visual analysis in the mammalian visual cortex and for both the development and maintenance of normal visuomotor behaviour. Man is among those vertebrates to whose brains eye muscle proprioceptive signals provide information apparently used in normal sensorimotor functions; these include various aspects of perception, and of the control of eye movement. It is possible that abnormalities of the eye muscle proprioceptors and their signals may play a part in the genesis of some types of human squint (strabismus); conversely studies of patients with squint in the course of their surgical or pharmacological treatment have yielded much interesting evidence about the central actions of the proprioceptive signals from the extraocular muscles. The results of experiments on the eye have played a large part in the historical controversy, now in at least its third century, about the origin of signals that inform the brain about movement of parts of the body. Some of these results, and more of the interpretations of them, now need to be critically re-examined. The re-examination in the light of recent experiments that is presented here does not support many of the conclusions confidently drawn in the past and leads to both new insights and fresh questions about the roles of information from motor signals flowing out of the brain and that from signals from the peripheral receptors flowing into it. There remain many lacunae in our knowledge and filling some of these will, it is contended, be essential to advance our understanding further. It is argued that such understanding of eye muscle proprioception is a necessary part of the understanding of the physiology and pathophysiology of eye movement control and that it is also essential to an account of how organisms, including Man, build and maintain knowledge of their relationship to the external visual world. The eye would seem to provide a uniquely favourable system in which to study the way in which information derived within the brain about motor actions may interact with signals flowing in from peripheral receptors. The review is constructed in relatively independent sections that deal with particular topics. It ends with a fairly brief piece in which the author sets out some personal views about what has been achieved recently and what most immediately needs to be done. It also suggests some lines of study that appear to the author to be important for the future. (+info)
Results of cataract surgery in young children in east Africa.
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BACKGROUND: Cataract is the leading cause of blindness in children in east Africa. The results of surgery are poor, partly because of inadequate correction of aphakia. METHODS: A retrospective survey of 118 eyes in 71 children with bilateral cataract. All eyes had implantation of an IOL at the time of cataract surgery. The average age at surgery was 3.5 years. 28 patients(39%) were less than 2 years old at the time of surgery on their first eye. RESULTS: Preoperatively, 75.4% of eyes and 76.1% of patients were blind. A follow up of at least 3 months was available in 91 (77.1%) eyes. In these eyes, 44% had a latest corrected vision of 6/18 or better and 91.2% had a latest corrected vision of 6/60 or better. Eyes with zonular cataract, and eyes operated after the age of 2 years were more likely to obtain a vision of 6/18 or better. 3.3% of eyes and 1.8% of patients had an acuity of less than 3/60. Nystagmus was present in 42.3% of patients before surgery. In those patients followed up for a minimum of 6 months, 10.2% still had nystagmus. The most frequent complication was severe fibrinous uveitis, which occurred in 36 (30.5%) eyes. 62 (52.5%) eyes had a posterior capsulotomy at the time of cataract extraction. Of the remaining 56 eyes, 20 (35.7%) had so far required a posterior capsulotomy. The leading cause of poor visual outcome was amblyopia. Two patients developed severe complications related to the intraocular lens. CONCLUSIONS: Insertion of a lens implant at the time of cataract extraction appears to be well tolerated in the short term, and may offer significant advantages in an African setting. (+info)
Ocular significance of intraventricular haemorrhage in premature infants.
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AIM: To document ocular outcome in premature infants with intraventricular haemorrhages (IVH). METHODS: 68 preterm infants with IVH were examined. RESULTS: Mean gestational age was 28.1 weeks (range 24-35). Mean birth weight was 1045.9 g (630-2240). Mean follow up was 54.6 months (6-150). IVH is graded from 1 to 4 based on the severity of haemorrhages. The incidence of ocular abnormalities was compared between low grade IVH (grade 1 and 2) and high grade IVH (grade 3 and 4). Of the 68 infants with IVH, ROP occurred in 33 infants (48.5%); 13 (43.3%) had low grade IVH; 20 (52.6%) had high grade IVH. Strabismus developed in 30 infants (44.1%); 14 (46.6%) had low grade IVH; 16 (42.1%) had high grade IVH. Infants with high grade IVH were at significant greater risk than infants with low grade IVH for the development of optic atrophy (31.5% v 16.6%), hydrocephalus (57.8% v 10%). CONCLUSION: This study highlights the serious significance of all grades of IVH with the higher incidence of optic atrophy and hydrocephalus with high grade IVH. (+info)
Short-latency disparity vergence in humans.
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Eye movement recordings from humans indicated that brief exposures (200 ms) to horizontal disparity steps applied to large random-dot patterns elicit horizontal vergence at short latencies (80.9 +/- 3.9 ms, mean +/- SD; n = 7). Disparity tuning curves, describing the dependence of the initial vergence responses (measured over the period 90-157 ms after the step) on the magnitude of the steps, resembled the derivative of a Gaussian, with nonzero asymptotes and a roughly linear servo region that extended only a degree or two on either side of zero disparity. Responses showed transient postsaccadic enhancement: disparity steps applied in the immediate wake of saccadic eye movements yielded higher vergence accelerations than did the same steps applied some time later (mean time constant of the decay, 200 ms). This enhancement seemed to be dependent, at least in part, on the visual reafference associated with the prior saccade because similar enhancement was observed when the disparity steps were applied in the wake of saccadelike shifts of the textured pattern. Vertical vergence responses to vertical disparity steps were qualitatively similar: latencies were longer (on average, by 3 ms), disparity tuning curves had the same general form but were narrower (by approximately 20%), and their peak-to-peak amplitudes were smaller (by approximately 70%). Initial vergence responses usually had directional errors (orthogonal components) with a very systematic dependence on step size that often approximated an exponential decay to a nonzero asymptote (mean space constant +/- SD, 1.18 +/- 0.66 degrees ). Based on the asymptotes of these orthogonal responses, horizontal errors (with vertical steps) were on average more than three times greater than vertical errors (with horizontal steps). Disparity steps >7 degrees generated "default" responses that were independent of the direction of the step, idiosyncratic, and generally had both horizontal and vertical components. We suggest that the responses depend on detectors that sense local disparity matches, and that orthogonal and "default" responses result from globally "false" matches. Recordings from three monkeys, using identical disparity stimuli, confirmed that monkeys also show short-latency disparity vergence responses (latency approximately 25 ms shorter than that of humans), and further indicated that these responses show all of the major features seen in humans, the differences between the two species being solely quantitative. Based on these data and those of others implying that foveal images normally take precedence, we suggest that the mechanisms under study here ordinarily serve to correct small vergence errors, automatically, especially after saccades. (+info)
Spontaneous reversal of nystagmus in the dark.
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AIM: To report five children with horizontal jerk nystagmus in whom eye movement recordings in the dark revealed a spontaneous reversal in the direction of the nystagmus beat. Three patients were blind in one eye and were diagnosed as having a manifest latent nystagmus (MLN), and two patients had strabismus and congenital nystagmus (CN). METHODS: Eye movements were recorded using DC electro-oculography with simultaneous video recording, including infrared recording in total darkness. RESULTS: Four patients had decelerating velocity slow phase jerk nystagmus when recorded under natural lighting conditions; the fifth case had accelerating velocity and linear slow phase jerk nystagmus. Under absolute darkness, nystagmus reversed in direction of beat with a mixture of linear and decelerating velocity slow phase waveforms. One child with unilateral anophthalmos could wilfully reverse the beat direction of his nystagmus by trying to look with his blind eye in the light and dark. CONCLUSIONS: These observations support the theory that LN/MLN beat direction is determined by the "presumed" viewing eye and may be consciously controlled. The spontaneous reversal of beat direction in the dark suggests eye dominance is predetermined. Eye movement recordings identified mixed nystagmus waveforms indicating that CN (accelerating velocity slow phases) and LN/MLN (linear/decelerating velocity slow phases) coexist in these subjects. (+info)