Examination of the Nervous System
John W. Scadding, Nicholas A. Losseff in Clinical Neurology, 2011
The pupillary response to light depends on the integrity of the afferent pathways. As already described, the direct light response is impaired, with damage to the retina or optic nerve, and this can be shown by the presence of an afferent pupillary defect. The relevant optic nerve fibres responsible for the light reaction leave those responsible for the perception of light to terminate in the pretectal region of the midbrain, from whence a further relay passes to the Edinger–Westphal nucleus. Damage to this pretectal region is believed to be responsible for the Argyll Robertson pupil classically seen in neurosyphilis. The characteristics of these pupils are that they are small, irregular and unequal, and exhibit light–near dissociation (Figure 3.8). Light–near dissociation refers to the loss of pupillary reaction to light, with preservation of that to accommodation. Pupils resembling those of Argyll Robertson also occur occasionally in diabetes and in other conditions with autonomic neuropathy. Large pupils exhibiting light–near dissociation are characteristic of damage in the region of the superior colliculi, as may be produced by tumours of the pineal gland. These cause Parinaud’s syndrome in which there is pupillary light–near dissociation, with paralysis of upgaze and convergence.
Toxins in Neuro-Ophthalmology
Vivek Lal in A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Clinical features of methanol intoxication include nausea, vomiting and abdominal pain. The CNS effects of methanol result from accumulation of formic acid within the optic nerve and leads to flashes of light. It progresses further to scotomas and scintillations. Vision loss is probably caused by interruption of mitochondrial function in the optic nerve which results in hyperemia, edema and optic nerve atrophy. Pupillary response to light is compromised and subsequently lost. Confirmation of diagnosis is by serum methanol level with gas chromatography (>20 mg/dL). Serum levels peak after 60–90 min of ingestion, but these do not correlate with the level of toxicity. Accumulation of formate leads to decrease in pH (<7.2 is a severe intoxication). Imaging findings may be suggestive with bilateral enhancing optic nerves and putaminal necrosis.
Vision Impairment and Its Management in Older Adults
K. Rao Poduri in Geriatric Rehabilitation, 2017
The pupillary response also becomes less brisk with smaller pupillary size due to decreased reactivity of the dilator muscles letting less light into the eye. As the eye ages, the lens thickens and becomes heavier. This is due to nuclear sclerosis, which is the most common form of cataract in those over 65 years. Nuclear sclerosis occurs when the continual production of lens fibers compacts around the nucleus causing a hard lens. With aging, the lens proteins transform and precipitate causing the lens to become yellow or brown in color. This normal aging process can be hastened by ultraviolet exposure and leads to a myopic shift due to change in its refractive index. These changes cause light to be scattered through the lens causing less light to reach the retina and can dim the vision.
Reversible Bitemporal Hemihypokinetic Pupil Without Hemianopia: A New Chiasmal Sign
Published in Neuro-Ophthalmology, 2022
Jorge Alberto Martins Pentiado Junior, Eduardo Yukio Nakamura, Lucas Ravagnani da Silva, Patricia Approbato Marques, Natalia Oliveira da Silva, Ricardo Santos de Oliveira, Maria Lucia Habib Simao
Notably, hemihypokinesia and pupillary hemiakinesia have always been described in classical studies with pupillometry with the obligatory presence of a visual field defect proportional to the pupillary motor defect.3,4 However, several cases have been reported since the 1920s of hemihypokinesia and/or an RAPD without a corresponding visual field defect. These patients presented with structural damage exclusively affecting the brachium of the superior colliculus or its synapses in the pretectal nucleus/pretectal region (pretectal afferent pupillary pathway). Such dissociation is expected, as the afferent pupillomotor fibres are anatomically separate from the visual fibres at these locations.7,16 It is currently accepted that both an RAPD and hemihypokinesia can also occur with retrogeniculate lesions and without involving the classical pupillary reflex arc, as the pupillary light reaction is controlled by two systems: subcortical (pregeniculate) and cortical (suprageniculate neurons and visual cortex).7,16,17 Thus, the pupillary response encompasses the subcortical and cortical visual pathways with functions and interactions that are still not fully understood.
Scene through the eyes of an apex predator: a comparative analysis of the shark visual system
Published in Clinical and Experimental Optometry, 2018
Shaun P Collin
The ciliary zone in sharks comprises the iris, the ciliary body, ciliary folds, and the ciliary papilla. All are bathed in aqueous humour. Zonular fibres that hold the crystalline lens in place also occur but are considered to be condensations of the vitreous body.1958 The irideal mechanism responsible for the pupillary response consists of a dilator muscle controlled by the third cranial nerve and an antagonistic sphincter muscle. The iris controls the amount of light entering the eye, while the other ciliary structures move the lens during accommodation and secrete the aqueous humour, which ultimately controls intraocular pressure (which is 7.8-mmHg in Mustelus sp.).1960 It is not known whether the aqueous humour is drained by the trabecular meshwork or the unconventional uveo‐scleral pathway.
Evaluation of Pupil Fields Using a Newly Developed Perimeter in Glaucoma Patients
Published in Current Eye Research, 2019
Kazuko Totsuka, Ken Asakawa, Hitoshi Ishikawa, Nobuyuki Shoji
In the present study, we used the imo, which is smaller, lighter, and more portable than the conventional devices. The imo device can be used to perform measurements anywhere. Moreover, neither a dark room nor occlusion is required, nor does it cause any psychological or physical stress. The device also employs an eye-tracking system that can be used to remeasure points when subjects blink or move their eyes during the examination. During the test, targets were presented for 1 s at each of the 36 test points. Because there are fewer measurement points used with the imo test than those used for the conventional tests, the inspection time is shorter than that required to test the perimeter with conventional modalities. Targets were presented for 1 s to provide a dynamic range of the pupillary response. However, to prevent eye movements to the perimetry target, stimuli were presented for 300 msec or less. To overcome this problem, both pupil images were continuously monitored, and the images could be used for an eye-tracking system during the examination. The eye-tracking system allowed targets to be presented to the correct retinal locations.
Related Knowledge Centers
- Iris Sphincter Muscle
- Miosis
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- Oculomotor Nerve
- Optic Nerve
- Physiology
- Parasympathetic Nervous System
- Opiate
- Opioid
- Iris Dilator Muscle