Iris Mechanics II. Influence of Pupil Size on Details of Iris Structure

Newsome, David A.; Loewenfeld, Irene E.

doi:10.1016/0002-9394(71)90133-4

Cited by 31 publications

(11 citation statements)

References 12 publications

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“…The results in the diabetic subjects show that the reflex reduction exceeds that to be expected from the small pupil alone. The restriction on reflex amplitude occurred with pupil diameters below 6 mm in the healthy subjects, in agreement with other reports [13]. An analysis of the anatomical basis for this mechanical limit of constriction has been described [13].…”

Section: Discussionsupporting

confidence: 90%

Reduced pupillary light reflexes in diabetic autonomic neuropathy

Smith

1983

Diabetologia

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Infrared television pupillometry was performed in 71 healthy and 66 insulin-treated diabetic subjects. Resting pupil diameter and the amplitude of the reflex response to standard light flashes were measured in background darkness. In the healthy subjects with small pupils (less than 6 mm) the size of the light reflex was found to depend on the diameter of the pupil in darkness, the former decreasing by 0.55 mm/mm decrease in diameter. A positive correlation was also found in the diabetic subjects with small pupils but the reflexes were much smaller for a given resting diameter than in healthy subjects. The majority of the diabetic patients with small pupils had autonomic neuropathy. It is suggested that impaired pupillary dilatation in diabetic subjects is due to a sympathetic neuropathy and the small light reflex response in some patients is due to parasympathetic dysfunction in addition.

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Section: Discussionsupporting

confidence: 90%

Reduced pupillary light reflexes in diabetic autonomic neuropathy

Smith

1983

Diabetologia

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“…Because the effect of threat on the light reflex amplitude is calculated as the safe – threat difference, any factor reducing the light reflex amplitude in the safe condition may mask a true effect of threat. We hypothesized that mechanical limitations of the iris, which come into play when the constricting pupil reaches a critical diameter smaller than 3.5–4 mm (Newsome & Loewenfeld, 1971), could have curtailed the light reflex amplitude in the safe condition for some subjects and thus could have masked a true effect of threat. Indeed, visual inspection of the raw data revealed 6 candidate subjects, whose pupillary diameters at the trough of the constriction were exceeding the 4‐mm “floor” criterion when they were tested with the brightest probes (50 and 140 cd m −2 ) in the safe condition of Phase 3.…”

Section: Resultsmentioning

confidence: 99%

Parametric exploration of the fear‐inhibited light reflex

et al. 2005

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The effect of various parameters on the mediation of the fear-inhibited light reflex was examined. The light reflexes of 16 healthy men were measured across four light probe intensities, either in the presence of white noise alone or when the white noise was associated with the threat of either an electric shock or an acoustic sound blast. The white noise alone did not affect the light reflex amplitude. Both types of threat were subjectively anxiogenic and inhibited the light reflex across all light probe intensities, the threat of shock being more potent than the threat of sound blast. Importantly, the effect of either type of threat on the light reflex amplitude was found to increase with increasing light probe intensity, suggesting that brighter light probes may become more relevant motivationally in the threat condition, thus attracting greater allocation of attentional/cognitive resources.

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“…Another explanation for the failure of dapiprazole to suppress the threat-induced increase in IPD is the possibility of the operation of a ceiling effect in the placebo-treated eye. Physiologicalpharmacological studies have determined that, for most human subjects, the upper end for linear pupillary dilatation (ceiling) is approximately 6-6.5 mm (Newsome and Loewenfeld, 1971;Szabadi, 1977;Longmore et al, 1987). Inspection of our data (Table 2 and Fig.…”

Section: Discussionmentioning

confidence: 98%

Effects of peripheral sympathetic blockade with dapiprazole on the fear-inhibited light reflex

et al. 2005

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Fear (e.g. associated with the threat of an electric shock) causes an increase in initial pupil diameter (IPD) and a decrease in the amplitude of the light reflex response. There is evidence for dissociation between the two responses to threat: only the reduction in light reflex response amplitude is sensitive to the anxiolytic drug diazepam. We examined the effects of peripheral sympathetic blockade with the alpha(1)-adrenoceptor antagonist dapiprazole on both responses to threat on the basis of the hypothesis that only the response of the IPD will be affected, whereas the response of the light reflex will remain unaffected. Twelve healthy volunteers (Experiment 1) and eight healthy volunteers with smaller pupils (Experiment 2) participated in one experimental session. Dapiprazole 0.5% (two drops of 20 microl, three times) was instilled in the subjects' right or left eye while the contralateral eye was treated with placebo eye drops (artificial tear, two drops of 20 microl, three times) according to a single-blind balanced design. Pupil diameter was monitored by infrared binocular television pupillometry. At the point of maximum dapiprazole-evoked miosis, the light reflex was elicited three times in each of three Safe blocks (no possibility of electric shock), alternating with three Threat blocks (possibility of electric shock). At the end of each Safe and Threat block, subjects rated their mood and feelings on the Visual Analogue Scales. In Experiment 1, dapiprazole caused significant miosis. Threat increased subjectively rated anxiety and inhibited the light reflex. The inhibition of the light reflex was unaffected by dapiprazole. The threat-induced increase in IPD was also unaffected by dapiprazole, probably due to a ceiling effect curtailing the threat-induced increase in IPD. In the smaller pupil group in Experiment 2, where the possible contribution of a ceiling effect was minimized, dapiprazole suppressed the threat-induced increase in IPD. The inhibition of the light reflex by threat is likely to reflect central parasympathetic inhibition and is unlikely to involve the peripheral sympathetic innervation of the iris. The threat-induced increase in IPD is likely to reflect mainly central sympathetic excitation. The different central autonomic mechanisms underlying the two pupillary responses to threat may explain the dissociation between the separate effects of threat on IPD and light reflex amplitude.

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Iris Mechanics II. Influence of Pupil Size on Details of Iris Structure

Cited by 31 publications

References 12 publications

Reduced pupillary light reflexes in diabetic autonomic neuropathy

Reduced pupillary light reflexes in diabetic autonomic neuropathy

Parametric exploration of the fear‐inhibited light reflex

Effects of peripheral sympathetic blockade with dapiprazole on the fear-inhibited light reflex

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