The human heart rate response profiles to five vagal maneuvers.
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Healthy teens and adults performed four vagotonic maneuvers. A large series of strabismus surgery patients had deliberately quantified tension on extraocular rectus muscles during general anesthesia. The mean bradycardia was greatest for diving response (apneic facial exposure to cold) and Valsalva maneuver and least for pressure on the globe and carotid sinus massage. Bradycardia occurred for every subject for the non-surgical maneuvers, however, extraocular muscle tension frequently caused no change in heart rate or even tachycardia. The inter-subject variance in percent heart rate change was greatest for surgical oculocardiac reflex. Of the rectus muscles, the inferior caused the most bradycardia while the lateral caused the least. The percent oculocardiac reflex was not age dependent. Occasional patients demonstrated profound bradycardia with strabismus surgery. Of these maneuvers, diving response has theoretical advantage in treating paroxysmal atrial tachycardia. The human cardiac vagal efferent was stimulated by several carefully controlled maneuvers resulting in wide inter-maneuver differences in bradycardia magnitude. The greatest intra-maneuver variability occurred with surgical oculocardiac reflex. (+info)
Detecting disorder in spatial vision.
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In normal foveal vision, visual space is accurately mapped from retina to cortex. However, the normal periphery, and the central field of strabismic amblyopes have elevated position discrimination thresholds, which have often been ascribed to increased 'intrinsic' spatial disorder. In the present study we evaluated the sensitivity of the human visual system (both normal and amblyopic) to spatial disorder, and asked whether there is increased 'intrinsic' topographical disorder in the amblyopic visual system. Specifically, we measured thresholds for detecting disorder (two-dimensional Gaussian position perturbations) either in a horizontal string of N equally spaced samples (Gabor patches), or in a ring of equally spaced samples over a wide range of feature separations. We also estimated both the 'equivalent intrinsic spatial disorder' and sampling efficiency using an equivalent noise approach. Our results suggest that both thresholds for detecting disorder, and equivalent intrinsic disorder depend strongly on separation, and are modestly increased in strabismic amblyopes. Strabismic amblyopes also show markedly reduced sampling efficiency. However, neither amblyopic nor peripheral vision performs like ideal or human observers with added separation-independent positional noise. Rather, the strong separation dependence suggests that the 'equivalent intrinsic disorder' may not reflect topographic disorder at all, but rather may reflect an abnormality in the amblyopes' Weber relationship. (+info)
New ideas about binocular coordination of eye movements: is there a chameleon in the primate family tree?
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Many animals with laterally placed eyes, such as chameleons, move their eyes independently of one another. In contrast, primates with frontally placed eyes and binocular vision must move them together so that both eyes are aimed at the same point in visual space. Is binocular coordination an innate feature of how our brains are wired, or have we simply learned to move our eyes together? This question sparked a controversy in the 19(th) century between two eminent German scientists, Ewald Hering and Hermann von Helmholtz. Hering took the position that binocular coordination was innate and vigorously challenged von Helmholtz's view that it was learned. Hering won the argument and his hypothesis, known as Hering's Law of Equal Innervation, became generally accepted. New evidence suggests, however, that similar to chameleons, primates may program movements of each eye independently. Binocular coordination is achieved by a neural network at the motor periphery comprised of motoneurons and specialized interneurons located near or in the cranial nerve nuclei that innervate the extraocular muscles. It is assumed that this network must be trained and calibrated during infancy and probably throughout life in order to maintain the precise binocular coordination characteristic of primate eye movements despite growth, aging effects, and injuries to the eye movement neuromuscular system. Malfunction of this network or its ability to adaptively learn may be a contributing cause of strabismus. (+info)
Long term follow up of premature infants: detection of strabismus, amblyopia, and refractive errors.
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AIM: To establish recommendations for long term ophthalmological follow up of prematurely born infants. METHODS: 130 infants with a gestational age (GA) <37 weeks and born between 1 November 1989 and 31 October 1990 were enrolled in a prospective study about the development of strabismus, amblyopia, and refractive errors. Infants were subdivided in three groups according to GA: A <28 weeks (n=32), B >/=28-32-<37 weeks (n=34). Ophthalmological assessment took place at the postconceptional age of 32 weeks, at term and at 3, 6, 12, and 30 months post term. At the age of 5 years parents received a questionnaire and a majority of the children was examined again (n=99). RESULTS: At the age of 5 years 46 infants were known to have strabismus (n=29) and/or amblyopia (n=22) and/or refractive errors (n=22). Statistical analysis showed that gestational age, duration of supplementary oxygen, and duration of hospitalisation were important predictive variables for the development of strabismus, amblyopia, or refractive errors (SAR) at the age of 5 years (p<0.05). Infants with a GA 32 weeks, who developed an incidence comparable with the normal population. Strabismus developed mainly in the first year of life and at the age of 5 years. Most infants with amblyopia were detected at the age of 2-3 years. Refractive errors were found in the first year of life and at the age of 2.5 and 5 years. CONCLUSION: Infants with a GA <32 weeks should be selected for long term ophthalmological follow up. These infants should be screened at the age of 1 year, in the third year of life (preferably at 30 months), and just before school age (including testing of visual acuity with optotypes). (+info)
Korean hand acupressure reduces postoperative vomiting in children after strabismus surgery.
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A double-blind, randomized, placebo-controlled study was conducted to investigate the effectiveness of Korean hand acupuncture in preventing postoperative vomiting in children scheduled for strabismus surgery. In one group, acupressure was performed 30 min before induction of anaesthesia by applying an acupressure disc onto the Korean hand acupuncture point K-K9; the disc remained in situ for at least 24 h. The second group functioned as placebo group. The treatment groups did not differ with regard to patient characteristics, surgical procedure and anaesthetic administered. In the acupressure group, the incidence of vomiting was significantly lower (20%) than in the placebo group (68%). We conclude that Korean hand acupressure of the acupuncture point K-K9 is an effective method for reducing postoperative vomiting in children after strabismus repair. (+info)
Histologic effect of mitomycin C on strabismus surgery in the rabbit.
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PURPOSE: To evaluate the efficiency of mitomycin C (MMC) in limiting the postoperative inflammatory response and scarring after strabismus surgery. METHODS: A prospective, two-stage, masked, controlled trial was conducted. In the first stage, the inflammatory response at the extraocular muscle reattachment site was increased after inferior rectus recession in eight rabbits. In the second stage, MMC (0.4 mg/ml) was applied during surgery to the eyes of 22 rabbits with inferior rectus recession. As a control, contralateral eyes were treated with saline solution. Seven weeks later, exenteration was performed, and the sites of muscle reattachment were processed for histologic examinations. The sums of the areas of the granulomas in the extraocular muscle reattachment sites of control and treated eyes were compared. RESULTS: There was no significant inhibitory effect of MMC on the inflammatory response of treated eyes compared with that of control eyes. CONCLUSIONS: The intraoperative use of MMC (0.4 mg/ml) was not effective in controlling the postoperative inflammatory response in rabbit eyes after extraocular muscle surgery. These data do not support the hypothesis that MMC reduces postoperative adhesions after strabismus surgery. (+info)
Amblyopic deficits in detecting a dotted line in noise.
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We compared detectability of a dotted line masked by random-dot noise for the amblyopic versus non-amblyopic eye of two strabismic amblyopes. Small but consistent deficits in the amblyopic eye of these observers were found, and shown to be limited to dotted-line targets composed of greater than seven dots (with performance being normal for targets of less than seven dots). These deficits were unrelated to impaired visual acuity, impaired sensitivity to dot density, and differential positional uncertainty between the eyes of our observers. The deficits were also unlikely to be due to CSF losses due to abnormal low-spatial-frequency filters involved in detecting long chains of collinear dots. Instead, the results of simulations indicate that the inefficiency in utilising large numbers of dots is due to deficits of global, integrative processes in strabismic amblyopes. These simulations also show that while neither undersampling nor positional uncertainty of inputs into integrative processes can themselves account for the amblyopic deficits, if such abnormal inputs lead to the development of stunted integrative processes then impaired sensitivity to long chains of collinear dots is indeed predicted. (+info)
Corneal dellen in the limbal approach to rectus muscle surgery.
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A retrospective study of 170 cases of horizontal rectus muscle surgery performed during the years 1969 and 1970 at the University of Illinois Eye and Ear Infirmary revealed a 6-5 per cent incidence of dellen with the limbal approach to the muscle and a 2-2 per cent of incidence of dellen with the nonlimbal or direct approach to the muscle. This was significant to the 5 per cent level of confidence by the chi2 test. We feel that this finding of an increased incidence of dellen with the limbal approach complements the current theory of desiccation as the cause of corneal dellen. We do not recommend abandonment of the limbal approach to rectus muscle surgery because of this finding, but suggest that surgeons scrutinize more carefully their postoperative patients for dellen. If dellen do not occur careful trimming of the conjunctiva to avoid bunching and thickening may perhaps eliminate them. (+info)