Mydriatic and Cycloplegic Agents

6/15/18

Outline

Mydriatic and — Autnonomic NS and the Eye: Brief Review

Cycloplegic — Mydriatics vs Mydriatic/Cycloplegics: Mechanisms Agents — Sympathomimetics vs Parasympatholytics

Dr. Ian Herring DVM, MS, DACVO — Mydriatics and Mydriatic/Cycloplegics in practice

Autonomic NS: Overview Autonomic NS: Overview

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Autonomic NS and the Eye

— Pupillary aperture

— AH production

— AH drainage

— Ocular blood flow

Iris Musculature – Autonomic Innervation Mydriasis vs Cycloplegia

— Mydriatics: pupillary dilation only — Adrenergic agonists/Sympathomimetics — Direct vs indirect acting — Mydriatic/Cycloplegics: mydriasis and ciliary muscle paralysis — Anticholinergics (anti-muscarinics)

Adrenergic (predominantly α1a) Muscarinic (predominantly m3)

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Sympathomimetics Cocaine — Achieve mydriasis via direct action on iris dilator m.

— Primarily α1 stimulation — Other mechanisms also likely — Indirect adrenergic agonist — No cycloplegia — Inhibits NE re-uptake into nerve terminus — Indirect acting agents — Cocaine (prevents NE reuptake) — Ophthalmic use — Hydroxyamphetamine (stimulates NE release) — Confirmation of Horner’s syndrome — Direct acting agents — Does not localize — Phenylephrine (α1 selective) — Epinephrine (non-selective)

Phenylephrine Hydroxyamphetamine — α1 agonist, direct acting — Indirect adrenergic agonist — 2.5, 10% solution — Stimulate NE release from nerve terminus — Clear solution — Becomes dark with oxidation due to exposure to light, — Ophthalmic uses heat (ineffective) — Diagnostic mydriasis — Primary uses — Usually in combination with 0.25% tropicamide — Adjunctive mydriatic — Horner’s localization — Decreased efficacy in darkly pigmented irides — Pre- vs Post-ganglionic — Neurolocalization in Horner’s syndrome — No cycloplegic effect

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Phenylephrine Phenylephrine

Side effects — Stinging, lacrimation, esp w/higher Mydriatic Effect in Companion Animals concentrations Dog Cat Horse — Tachycardia, arrythmia Mydriasis (sole Complete in 2 Ineffective Ineffective agent) hours — Hypertension w/reflex bradycardia Other May prolong May shorten duration — Keratoconjunctivitis effect of other of atropine mydriasis mydriatics — Rebound miosis — Rebound conjunctival hyperemia

Cholinergic (Muscarinic) Epinephrine Antagonists — Non-selective,α- andβ-adrenoceptor direct agonist — Agents — Tropicamide — O.1 – 2% topical ophthalmic solutions — Atropine — Generally ineffective as a mydriatic in companion animals — Homatropine — Scopalamine — Intracameral application — Cyclopentolate — 1:10,000 solution bolus — Non-selective muscarinic antagonists

— 1:1,000,000 in irrigating fluids — Mydriatic effect primarily via iris sphincter M3 blockade — Mydriatic and hemostatic effect — All possess mydriatic/cycloplegic effect — Should be preservative, bisulfite free — Vary in efficacy/potency and duration of action

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Tropicamide Tropicamide — Non-selective muscarinic antagonist

— 0.5 and 1% ophthalmic solution Mydriatic Effect in Companion Animals

— Rapid onset/short duration mydriasis Dog Cat Horse

— Ideal for diagnostic mydriasis Onset of maximal 30-60 min 1-2 hrs 1-5 hrs mydriasis — Cycloplegic effect is concentration dependent Duration of Up to 12 hrs 4-9 hrs 5-12 hrs — Short-lived compared to other M3 antagonists mydriatic effect — May decrease BAB permeability Other Variable IOP IOP increase increase

Tropicamide Atropine

Side effects — Non-selective muscarinic Ach antagonist — Transient stinging — 0.5, 1 and 2% ophthalmic solutions — IOP rise — 1% ointment — Cats, both glaucomatous and normal — Evidence of breed variability in dogs — Most potent mydriatic and cycloplegic available — Effect on STT — Iridal melanin binding depot action — Appears variable by species; further investigation .˙. extended duration of effect required

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Atropine Atropine

Side Effects — Salivation, vomiting Mydriatic Effect in Companion Animals — IOP elevation in angle-closure glaucoma Dogs Cats Horses Cattle — Diminished tear production Maximal 30-60 min 30-60 min 10-48 hours 60 min mydriasis — Mild HR elevation Duration of 5 days 2.5 – 3 days 14 days 7 days mydriasis — Diminished GI motility in horses — Periocular dermatitis

Atropine Homatropine

— Non-selective muscarinic antagonist

— 2 – 5% ophthalmic solutions

— Mydriatic/cycloplegic effects — May allow adequate mydriasis for fundic examination — 1/10 as potent as atropine without negating latanoprost hypotensive effect — N.B. These were normal dogs! — Incomplete mydriatic in companion animals

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Scopalamine Cyclopentolate

— Non-selective muscarinic antagonist — 0.5, 1, and 5% ophthalmic solutions

— 0.25% solution — Potent mydriatic/cycloplegic — Efficacy reduced by iridal pigmentation — Potent mydriatic/cycloplegic — Similar duration of mydiasis as atropine — Decreased duration of action compared to atropine ophthalmic in dogs, cats, horses

— Commonly employed for cycloplegic refraction in humans; intracameral application for intraop mydriasis

Questions?

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