Speed of pupillary light response following topical pilocarpine or tropicamide

Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma

Purpose

To evaluate the biomechanical properties of the iris by evaluating iris movement during pupil constriction and to compare such properties between healthy and primary angle-closure glaucoma (PACG) subjects.

Methods

A total of 140 subjects were recruited for this study. In a dark room, the anterior segments of one eye per subject were scanned using anterior segment optical coherence tomography imaging during induced pupil constriction with an external white light source of 1700 lux. Using a custom segmentation code, we automatically isolated the iris segments from the AS-OCT images, which were then discretized and transformed into a three-dimensional point cloud. For each iris, a finite element (FE) mesh was constructed from the point cloud, and an inverse FE simulation was performed to match the clinically observed iris constriction in the AS-OCT images. Through this optimization process, we were able to identify the elastic modulus and permeability of each iris.

Results

For all 140 subjects (95 healthy and 45 PACG of Indian/Chinese ethnicity; age 60.2 ± 8.7 for PACG subjects and 57.7 ± 10.1 for healthy subjects), the simulated deformation pattern of the iris during pupil constriction matched well with OCT images. We found that the iris stiffness was higher in PACG than in healthy controls (24.5 ± 8.4 kPa vs. 17.1 ± 6.6 kPa with 40 kPa of active stress specified in the sphincter region; P < 0.001), whereas iris permeability was lower (0.41 ± 0.2 mm2/kPa s vs. 0.55 ± 0.2 mm2/kPa s; p = 0.142).

Conclusions

This study suggests that the biomechanical properties of the iris in PACG are different from those in healthy controls. An improved understanding of the biomechanical behavior of the iris may have implications for the understanding and management of angle-closure glaucoma.

Pupil responsiveness in cluster headache: a dynamic TV pupillometric evaluation

In this study the variations in pupil diameter induced by different stimuli (dark-light adaptation, light reflex, electric stimulation of the sural nerve) were investigated in episodic (in the active or remission phases) and in chronic cluster headache (CH) patients. Pupil size monitoring was performed with a monocular, infrared TV pupillometer, and sural nerve stimuli were applied after the pain threshold had been measured as the flexion reflex threshold of the biceps femoris muscle (RIII reflex). The results were compared with those obtained in patients with "peripheral" (third neuron) Horner's syndrome and in healthy sex- and age-matched controls. On the symptomatic side we found an impairment of pupil response to light flashes and nociceptive stimuli; similar findings were sometimes evident on the pain-free side, too. These results substantiate previous observations that in cluster headache a dysfunction of the integrative central nervous system pathways also exists intercritically and mostly bilaterally, involving both autonomic regulation and pain perception mechanisms.

The effect of anticholinergic drugs on the inner eye muscles

Using 12 healthy volunteers, we tested the para-sympatholytic effects on the eye. In a randomized crossover double-blind trial, hyoscine-N-butylbromide was tested against saline. Before (20 or 40 mg IV) and up to 45 min after the injection, pupillar light reaction, accommodation, visual acuity, and nyctometer values were measured. The range of accommodation diminishes according to dosage: 9-15 min after the injection, the inhibition is maximum; 45 min after the injection, only a small effect remains, even using the 40 mg dosage. Pupillary reaction is little affected by either dosage, and the pupil diameters at the end of the reaction are only slightly greater after the injection of either dosage than after placebo injection. The time constant of the reaction remains unchanged. Visual acuity and nyctometer values remain unchanged under the influence of hyoscine-N-butylbromide. The results are discussed with respect to the potential ability of a patient to meet the requirements of modern traffic. According to our findings, there are no ophthalmologically-based reasons for an emmetropic person to assume impaired driving abilities after a single injection of hyoscine-N-butylbromide of up to 40 mg. If the accommodative capacity of a patient is impaired whose hyperopia is not fully corrected, the ability to drive in modern traffic may be impaired. After a single dose of 20 mg hyoscine-N-butylbromide (i.e., 1 ampule Buscopan), the impairment of even these patients does not last longer than about 45 min.

Pilocarpine mydriasis in mice

In several rodent species pilocarpine and oxotremorine produce mydriasis, rather than the miosis which is characteristic of most other species. We have established that pilocarpine is a mydriatic drug in mice, a species in which the action has previously not been described, and that this effect occurs after local ocular, intraperitoneal (IP) or intracerebroventricular (ICV) application. Arecoline produces miosis or mydriasis (depending on dose) following direct ocular application but mild mydriasis after IP or ICV injection. Atropine also produces mydriasis in mice, and the effect of pilocarpine is additive with that produced by atropine and is not antagonized by antihistamines. Direct ICV pilocarpine injection produces mydriasis at doses equivalent to those used systemically. Pilocarpine mydriasis probably results from inhibition of parasympathetic activity.

Factors determining the potency of cholinomimetic miotic drugs and their effect upon the light reflex in man

1. Television pupillometry was used to measure the effect of six topically applied cholinomimetic drugs on the resting diameter and light reflex amplitude of the human pupil. Drug potency was obtained from dose response curves. 2. The tertiary amines arecoline, aceclidine and pilocarpine were considerably more effective miotics than the choline esters carbachol, methacholine and acetylcholine. 3. All the drugs which caused miosis also reduced light reflex amplitude proportionally. 4. The in vitro potency of these drugs was also measured on preparations of rabbit iris sphincter and guinea pig ileum. 5. Dose response relationships for pilocarpine in man and in vitro showed evidence of partial agonist activity on the rabbit iris only. 6. A comparison of the in vivo and in vitro results showed that three factors influenced the potency of topically applied miotics: accessibility to the iris; sensitivity to cholinesterase; and cholinoceptor agonist potency.

Abnormal pupillary responses in myasthenia gravis. A pupillographic study

Using an open-loop stimulus (Maxwellian view), the direct pupillary response to light and its derivative curves (velocity and accleration of pupillary reactions) were recorded by infrared video pupillography in seven patients with myasthenia gravis and in three normal subjects. Responses before and after intravenous injection of 5 mg edrophonium hydrochloride were determined. Five of the patients had never taken anticholinesterase drugs except for diagnostic injections of edrophonium while the other two patients had been treated with oral preparations of corticosteroids. Analyses of the pupillary responses showed reduced amplitude, amximal velocity, and maximal acceleration of pupillary constriction in the myasthenic patients. On the other hand, changes in parameters of pupillary dilatation were minimal. Abnormal values returned towards normal within five minutes after edrophonium injection in all patients except in one individual who was being treated with corticosteroids at the time of examination. These results suggest that involvement of the iris sphincter may be common in patients with myasthenia gravis and this can be demonstrated by analysing the pupillary reaction and its derivative curves in response to an open-loop stimulus.