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PubMed1978

The neuronal pathway subserving the pupillary light reflex.

The pupillary light reflex was investigated using electrical stimulation along the pathway and recording in the short ciliary nerves. The discharge of single units in the ciliary ganglion was compared during diffuse light stimuli and electrical stimuli. It was concluded that the early reflex discharge in the short ciliary nerves following electrical stimulation on the optic tract is due to excitation of fibres active during the pupillary light reflex. The light reflex is conveyed by slow (less than 10 m/sec) optic tract fibres which synapase in the medial part of the pretectal area. In turn, pretectal neurones with conduction velocities of about 6 m/sec pass to the Edinger-Westphal complex from which the preganglionic 'pupilloconstrictor' neurones originate. Latency measurements show that there are synapses in the pretectal region and the Edinger-Westphal nucleus. The amplitude of the 'pupilloconstrictor' responses in the short ciliary nerves can be used as a measure of the excitability in the pathway of the pupillary light reflex under various conditions, e.g. following conditioning stimuli of other interacting pathways. In addition to the 'pupilloconstrictor' response there is also another short-latency discharge in the short ciliary nerves following stimulation of the posterior commissure and the Edinger-Westphal nucleus. That discharge is presumably due to activation of fibres which cause accommodation of the lens.

Animals↗
PubMed1991

Isoflurane, but not mild hypothermia, depresses the human pupillary light reflex.

The pupillary light reflex is often evaluated in the perioperative period as a measure of cranial nerve and midbrain integrity. Although surgical concentrations of some anesthetic agents and severe hypothermia qualitatively alter the light reflex, confounding factors frequently present during postanesthetic recovery have not been specifically quantified. We therefore studied 12 volunteers to determine the effects of residual isoflurane concentrations and typical (mild) hypothermia on the human pupillary light reflex. Young, healthy volunteers were assigned to one of three treatments: 1) normothermic isoflurane-oxygen anesthesia; 2) isoflurane-oxygen anesthesia with 2.2 +/- 0.5 degree C central hypothermia; and 3) central hypothermia (1.6 +/- 0.3 degree C) without anesthesia, induced by internal jugular infusion of iced lactated Ringer's solution. In normothermic anesthetized volunteers, the amplitude of the light reflex was depressed 80-90% at end-tidal concentrations greater than 0.5% isoflurane: reflex (percent of control) = 14 - 67.log (percent isoflurane); r = -0.92. In the mildly hypothermic anesthetized volunteers, pupillary responses were not statistically different from those in anesthetized normothermic volunteers: reflex (percent of control) = 16 - 62.log (percent isoflurane); r = -0.97. Hypothermia alone did not alter the magnitude of the light reflex. Our data suggest that mild hypothermia does not depress the light reflex but that isoflurane reversibly depresses the light reflex in a dose-related manner.

Adult↗
PubMed1979

Neuroticism and the effect of stress on the pupillary light reflex.

The pupillary light reflex was recorded under control, stress and fatigue conditions for 30 subjects equally divided into groups low, moderate, and high in Neuroticism. The effects of stress were distinguished by a decrease in both latency and extent of pupillary constriction during the initial light stimulation trials, as well as by a greater magnitude of redilation. Latency to maximum constriction and extent of constriction and redilation progressively decreased during the fatigue condition. No differences between Neuroticism groups were observed although it was noted that Neuroticism was negatively correlated with magnitude of redilation during the post-stress condition.

Humans↗
PubMed1991

The cause of increased pupillary light reflex latencies in diabetic patients: the relationship between pupillary light reflex and visual evoked potential latencies.

In 42 diabetic patients the relationship between the latency of the pupillary light reflex and the pattern reversal visual evoked potential (P100) was examined. Fifty-five percent of diabetic patients had pupillary light reflex latencies above the normal range. In 19% the visual evoked potentials were prolonged when compared to the normal range. Latencies of pupillary light reflexes and VEPs showed no correlation. There was a minimal correlation between the presence of retinopathy and prolongation of both the pupillary light reflex and the visual evoked response latency (kappa coefficients respectively: 0.31, P less than 0.01 and 0.36, P less than 0.02). The presence of an increased pupillary light reflex latency was positively correlated with a reduced respiratory sinus arrhythmia (kappa coefficient: 0.58, P less than 0.0001). Increased VEP latencies showed no correlation with signs of cardiovascular autonomic neuropathy. We conclude that the afferent optic pathway can be affected in diabetic patients. However, prolongation of pupillary light reflex latency in diabetic patients is primarily due to an efferent pupillary defect and represents parasympathetic dysfunction.

Adult↗
PubMed1992

The pupillary light reflex. 2. Prevalence of pupillary autonomic neuropathy in diabetics using age-dependent and age-independent pupillary parameters.

Seventy-seven diabetics with a duration of the disease ranging from 2 to 55 years (average 18.5 years) were studied with infrared videopupillometry. The prevalence of diabetic autonomic neuropathy at the pupillary control system (pANP) was studied comparatively using several pupillary tests. The average prevalence using age-dependent parameters was 30.2% [maximal pupillary area: 22.1%, maximal contraction velocity: 24.7%, contraction velocity at 1 s (CV1): 28.6%, and dilation velocity at 6 s (DV6): 45.5%]. Comparing these percentages to prevalences of other diabetic late complications, e.g. retinopathy (49.4%), DV6 seems to be good for the diagnosis of pANP. If CV1 and DV6 are expressed in percent of the maximal pupillary area (CV1% and DV6%), they become age-independent. The average CV1% and DV6% of diabetics differ highly significantly from those of normals (CV1%: 58.6 +/- 14.5 vs. 64.1 +/- 6.4%, 2 p less than 0.005, and DV6%: 6.0 +/- 2.9 vs. 7.3 +/- 1.1%, 2 p less than 0.001). The average prevalence of pANP using these age-independent parameters was 25.4%. These data suggest that the prevalence of pANP, especially disorders of pupillary dilation (DV6), is high in long-standing diabetes. Furthermore, CV1% and DV6% have proved to be valid parameters in finding differences in the light reflex in non-age-matched study groups.

Adolescent↗
PubMed1994

The anatomical substrates subserving the pupillary light reflex in rats: origin of the consensual pupillary response.

While the olivary pretectal nucleus has been shown to be central to the pupillary constriction response in rats, it is not at all clear at which level the consensual response is generated. To examine this we have investigated the efferent projections of this nucleus, as well as the effect of unilateral lesions of the olivary pretectal nucleus, on the direct and consensual pupillary light reflexes. The results demonstrate that the olivary pretectal nucleus projects bilaterally to the Edinger-Westphal nucleus, as well as to the nucleus of the posterior commissure, which itself projects bilaterally to the Edinger-Westphal nucleus. The olivary pretectal nucleus also projects to the ipsilateral ventral lateral geniculate nucleus. Unilateral lesions of the olivary pretectal nucleus decrease, but do not abolish, the direct and consensual pupillary light reflexes by as much as 66%. Since some degree of consensual response remains, this is likely to be due to the bilateral projection from the olivary pretectal nucleus, either directly or indirectly through the nucleus of the posterior commissure, to the Edinger-Westphal nucleus. These results show that while the bilateral projection from the olivary pretectal nucleus to the Edinger-Westphal nucleus contributes to the consensual pupillary light reflex, the bilateral retinal projection to the olivary pretectal nucleus is the more determinant component of the pathway. In addition to providing insights into the anatomical substrates of the pupillary response, this work also provides a background to ongoing studies of the retinal graft-mediated pupillary light reflex, as well as serving as a model of a relatively simple reflex system.

Animals↗
PubMed1984

Pupillary light reflex in amblyopia.

The pupillary light reflex of 15 strabismic and anisometropic amblyopes, and eight subjects who had recovered from functional amblyopia was studied by using an infrared electropupillogram. Ten of the fifteen amblyopes had significantly longer latencies of contraction when the amblyopic eyes were stimulated than when the normal eyes were stimulated. However, there was no relationship between the delay in pupillary light reflexes and reduced visual acuity of amblyopic eyes. The amplitudes and maximum velocities of the contraction were not altered significantly in amblyopic and normal eyes. All of the subjects who had recovered showed no significant difference of the latencies of the pupillary responses to stimulation between normal and amblyopic eyes. These findings indicate that a retinal mechanism in amblyopic eyes may be responsible for the abnormally long pupillary light reflex latency.

Adolescent↗
PubMed1993

Evaluation and significance of the pupillary light reflex in trauma patients.

The pupillary light reflex is an important component of the neurologic examination of the trauma victim. Although the normal reflex can be predictably altered by specific head injuries, a variety of other factors common to trauma patients such as alcohol, illicit drugs, narcotics, paralyzing agents, hypothermia, and orbital or ophthalmic injury can confound the evaluation of the pupillary light reflex. This report reviews the anatomy and neurophysiology of the pupillary light reflex and discusses the impact these confounding variables may have on this key component of the initial trauma evaluation.

Humans↗
PubMed2000

Characteristics of the pupillary light reflex in the macaque monkey: metrics.

To investigate whether the simian light reflex is a reasonable model for the human light reflex, we elicited pupillary responses in three behaving rhesus macaques. We measured the change in pupillary area in response to brief (100 ms), intermediate (1 s), and long (3-5 s) light flashes delivered by light-emitting diodes while the monkey fixated a stationary target. Individual responses in the same monkey to either 100-ms or 1-s stimuli of the same light intensity were quite variable. Nevertheless, in response to the 100-ms stimulus, average pupillary constriction and peak constriction velocity increased and latency decreased linearly with the log of stimulus luminance. The minimum average constriction latency across monkeys for the brightest flash was 136 ms. A linear decrease of constriction latency with stimulus luminance also occurs in humans, but their latencies are approximately 70 ms longer. In addition, peak constriction velocity was highly correlated with the decrease in pupillary area. Dilation metrics were not as well related to stimulus luminance as were constriction metrics. The latency from flash offset to the onset of dilation was relatively constant, averaging approximately 480 ms. Peak dilation velocity was also correlated, but less well, with the increase in pupillary area. Constriction generally was greater and of longer duration for 1-s light pulses than for 100-ms pulses of equal luminance. The initial time courses of the responses to the two stimuli of different durations were identical until approximately 150 ms after response onset. Human pupillary responses for long and short flashes also have identical initial time courses. For very long (3-5 s) and very bright constant-luminance stimuli, the simian pupil underwent oscillations at frequencies of 0.9-1.6 Hz. Similar oscillations, called hippus, occur in the human pupillary light reflex. Like humans, the monkeys also exhibited consensual and binocular pupillary responses. Except for response latency, the pupillary responses in the two primate species are otherwise quite similar. Therefore any knowledge we gain about the neuronal substrate of the simian light reflex can be expected to have considerable relevance when extrapolated to humans.

Animals↗
PubMed1993

The pupillary light reflex. Effects of anesthetics and hyperthermia.

BACKGROUND: The pupillary light reflex often is evaluated in the perianesthetic period to assess drug effects and brainstem function. Mild hypothermia alone or combined with isoflurane does not impair pupillary responses. Although perioperative hyperthermia is less common than hypothermia, abnormal increases in core temperature remain an important thermal disturbance. Accordingly, the pupillary effects of hyperthermia alone and hyperthermia combined with isoflurane and enflurane were evaluated. Additionally, the effects of nitrous oxide on pupillary responses were determined. METHODS: The pupillary light reflex was evaluated in 31 non-surgical volunteers participating in concurrent thermoregulatory studies. Pupillary reflexes were quantified using a portable infrared pupillometer during (1) hyperthermia alone (n = 9), (2) hyperthermia with 0.8% and 1.2% end-tidal isoflurane (n = 8), (3) hyperthermia with 1.7% end-tidal enflurane (n = 5), and (4) inhalation of 60% N2O (n = 9). RESULTS: Mild hyperthermia alone (core temperature 38.5 +/- 0.3 degrees C) produced no clinically significant change in the pupillary light reflex. Pupillary responses were decreased markedly with 0.8% isoflurane, 1.2% isoflurane, and 1.7% enflurane when the volunteers were normothermic. Mild hyperthermia combined with isoflurane or enflurane dilated the pupil and increased the amplitude of the light reflex. Sixty-percent nitrous oxide decreased the pupillary reflex only 26 +/- 4%. CONCLUSIONS: Anesthetic-induced inhibition of the pupillary response to light is reversed partially by core hyperthermia. In contrast to enflurane and isoflurane, 60% N2O has little effect on the pupil.

Adult↗
PubMed1977

The cerebellar control of the pupillary light reflex in the cat.

The effect of cerebellar lesions upon the pupillary light reflex was examined in anesthetized cats. The pupillary response elicited by a step and sinusoidally modulated light stimulus was used. In acute cerebellectomized cats, the high frequency cutoff of the frequency response of the pupillary reflex was moved to a lower level after cerebellar lesions. Selective lesions were made in the deep cerebellar nuclei and the frequency responses of the pupillary reflex were compared. The fastigial lesions produced the most prominent change in the frequency responses. Electrical stimulation of the deep cerebellar nuclei, especially the fastigial nuclei, induced pupillary dilatation. Thus the cerebellum appears to participate in the control of the pupillary light reflex by improving the frequency responses of the pupil so that it can follow changing light stimuli better, and this control is exerted via the bilateral fastigial nuclei.

Animals↗
PubMed1985

Luminance and darkness detectors in the olivary and posterior pretectal nuclei and their relationship to the pupillary light reflex in the rat. I. Studies with steady luminance levels.

In order to identify the pretectal nucleus which contains pupillomotor cells in the rat, cells were sought which were sensitive to changes in luminance level at the eye. Two types were found: Luminance detectors which showed a graded increase in firing with increase in luminance, and darkness detectors which showed a graded increase in firing rate with graded dimming of luminance intensity. All luminance detectors were located in the olivary pretectal nucleus, whereas darkness detectors were located in the posterior pretectal nucleus. Consensual pupil responses were recorded in conscious normal and sympathectomised rats using an infra-red sensitive T.V. pupillometer. Pupil diameter varied 2mm in an approximately linear fashion over six log units range in luminance intensity. Sympathectomy produced a general constriction of the pupil, but the overall response to light was unaffected. The changes in pupil size occurred over the same range of luminance that the firing rates of both luminance and darkness detectors changed. The olivary pretectal nucleus may therefore be involved in pupilloconstruction in the light, and the posterior pretectal nucleus, with pupillodilation in the dark.

Animals↗