22 Questions
What type of receptor is present in the radial dilator pupillae muscle?
α1 receptor
Which of the following muscles receives parasympathetic supply and has M3 receptor?
Circular sphincter pupillae muscle
What is the effect of α1 receptor stimulation in the radial dilator pupillae muscle?
Mydriasis
Which of the following is NOT a layer of the eye?
Retinal pigment epithelium
What is the function of the ciliary muscle?
Accommodation
Which of the following receptors is present in the ciliary epithelium?
β2 receptor
Which type of receptor is involved in the contraction of radial dilator pupillae muscles?
α1
What is the effect of parasympathomimetic drugs on pupil size?
Decrease pupil size
Which of the following is responsible for the light reflex?
Sphincter circular pupillae muscle
What is the effect of sympatholytic drugs on pupil size?
Decrease pupil size
What is the nerve responsible for the afferent pathway of the corneal reflex?
Trigeminal nerve
What is the effect of parasympatholytic drugs on the light reflex?
Loss of light reflex
Which of the following can cause loss of corneal reflex?
All of the above
What is the most common symptom of Myasthenia Gravis?
Skeletal muscle weakness
What is the effect of sympathomimetic drugs on pupil size?
Increase pupil size
What is the target of the autoimmune attack in Myasthenia Gravis?
Nicotinic acetylcholine postsynaptic receptors
What is the effect of epinephrine on the eye?
Mydriasis
Which of the following is an indication for glaucoma surgery?
Progressive glaucoma
What is the effect of choline esters like carbachol?
Lacrimation and salivation
What should be avoided in an asthmatic patient?
Epinephrine
What is the effect of pilocarpine on the eye?
Miosis
What is the demographic most commonly affected by Myasthenia Gravis?
All of the above
Study Notes
Autonomic Nervous System and Eye
- The eye receives both sympathetic and parasympathetic innervation, which affects many characteristics of the eye.
- The eye consists of three layers: outer fibrous coat (cornea and sclera), middle pigmented layer (uveal tract: iris, ciliary body, and choroid), and inner nervous layer (retina).
Eye Structure
- Iris muscles consist of:
- Radial (dilator pupillae) muscles
- Circular (constrictor pupillae) muscles
- Ciliary body consists of:
- Muscle (accommodation)
- Epithelium (aqueous humor, intraocular pressure)
Autonomic Receptors in Eye
- Cholinergic (M3) receptors are present in:
- Circular sphincter pupillae muscle
- Ciliary muscle
- Lacrimal gland
- Adrenergic receptors:
- Alpha 1 (α1) receptors are present in radial dilator pupillae muscle
- Beta 2 (β2) receptors are present in ciliary epithelium
Effect of Autonomic Drugs on Eye
- Pupil size is controlled by smooth muscles of iris:
- Radial dilator pupillae muscles (sympathetic, α1) increase size (mydriasis)
- Sphincter circular pupillae muscles (parasympathetic, M3) decrease size (miosis)
- Pharmacology of pupil size:
- Parasympathomimetic (muscarinic agonist): Active miosis
- Parasympatholytic (muscarinic antagonist): Passive mydriasis
- Sympathomimetic (αlpha agonist): Active mydriasis
- Sympatholytic (αlpha antagonist): Passive miosis
Light Reflex
- Physiology:
- When shining light is directed to one eye, it causes miosis of both eyes
- Sphincter circular pupillae muscle (parasympathetic, M3) is responsible for light reflex
- Pharmacology:
- Parasympathomimetic (muscarinic agonist): Intact light reflex
- Parasympatholytic (muscarinic antagonist): Loss of light reflex
- Sympathomimetic (αlpha agonist): Intact light reflex
- Sympatholytic (αlpha antagonist): Intact light reflex
Corneal (Blinking) Reflex
- Physiology:
- Stimulation of cornea (foreign body) causes blinking or closure of both eyelids
- Afferent (ophthalmic division of trigeminal nerve) → CNS → efferent (facial nerve) → eyelid muscle
- Pharmacology:
- Parasympathomimetic (muscarinic agonist): Intact corneal reflex
- Parasympatholytic (muscarinic antagonist): Intact corneal reflex
- Sympathomimetic (αlpha agonist): Intact corneal reflex
- Sympatholytic (αlpha antagonist): Intact corneal reflex
Glaucoma
- Primary open-angle glaucoma:
- Unusual features: physical obstruction of the angle of the anterior chamber of the eye
- Indications for glaucoma surgery: progressive glaucoma
- Avoid timolol in asthmatic patients
Myasthenia Gravis
- Definition: an acquired, autoimmune disorder caused by an antibody-mediated blockade of neuromuscular transmission resulting in skeletal muscle weakness and rapid muscle fatigue
- Prevalence: affects both men and women, and occurs across all racial and ethnic groups, with a higher impact on young adult women (under 40) and older men (over 60)
This quiz covers the effect of autonomic drugs on the eye, including the structure and function of the iris, pupil, and other eye components.
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