Related Experiment Video

Updated: Oct 23, 2026

Ex Vivo and In Vivo Animal Models for Mechanical and Chemical Injuries of Corneal Epithelium
07:10

Ex Vivo and In Vivo Animal Models for Mechanical and Chemical Injuries of Corneal Epithelium

Published on: April 6, 2022

Ultrastructural effects of topical beta-adrenergic antagonists and an alpha-adrenergic agonist on the rabbit cornea

S Polat1, N Ozdemir, M Soylu

  • 1Department of Histology and Embryology, University of Cukurova Medical Faculty, Adana, Turkey.

Ophthalmologica. Journal International D'Ophtalmologie. International Journal of Ophthalmology. Zeitschrift Fur Augenheilkunde
|April 15, 1999
PubMed

Insights

Topical antiglaucoma drugs like timolol and apraclonidine caused more rabbit corneal ultrastructural changes than levobunolol and betaxolol over six weeks. These findings highlight potential toxicity concerns for specific glaucoma treatments.

Area of Science:

  • Ophthalmology
  • Pharmacology
  • Cell Biology

Background:

  • Glaucoma treatment often involves topical medications.
  • Understanding the ocular surface toxicity of these drugs is crucial for patient safety.
  • Beta-adrenergic antagonists and alpha-adrenergic agonists are common classes of antiglaucoma drugs.

Purpose of the Study:

  • To evaluate the in vivo effects of specific beta-adrenergic antagonist and alpha-adrenergic agonist drugs on rabbit corneas.
  • To compare the ultrastructural toxicity of timolol, levobunolol, betaxolol, and apraclonidine on the cornea.
  • To assess corneal changes after 6 weeks of topical drug instillation.

Main Methods:

  • Twenty-four New Zealand albino rabbits were used.
  • Corneas were treated topically twice daily for 6 weeks with balanced salt solution (BSS), BSS with benzalkonium chloride (BAC), Timoptic 0.5%, Betagan 0.5%, Betoptic 0.5%, or Iopidine 1%.
  • Transmission electron microscopy was employed to examine corneal ultrastructure.

Main Results:

  • BSS group showed normal corneal ultrastructure.
  • BSS and BAC group exhibited slight epithelial and endothelial changes.
  • Groups treated with Timoptic (timolol), Betagan (levobunolol), Betoptic (betaxolol), and Iopidine (apraclonidine) showed epithelial alterations including loss of microvilli, increased glycogen, nuclear indentation, intercellular widening, and cytoplasmic vacuolization.
  • Endothelial changes included vacuolization and focal cytoplasmic lysis.
  • Basal lamina, stroma, and Descemet's membrane remained largely unaffected.
  • Timolol and apraclonidine demonstrated greater corneal toxicity compared to levobunolol and betaxolol.

Conclusions:

  • Topical antiglaucoma medications can induce significant ultrastructural changes in the rabbit cornea.
  • Timolol and apraclonidine appear to be more toxic to the rabbit cornea than levobunolol and betaxolol following 6 weeks of topical application.
  • These findings underscore the importance of considering drug-induced corneal toxicity in glaucoma management.

More Related Videos

Establishment of a Severe Dry Eye Model Using Complete Dacryoadenectomy in Rabbits07:43

Establishment of a Severe Dry Eye Model Using Complete Dacryoadenectomy in Rabbits

Published on: January 8, 2020

Fabrication and Surgical Application of Enriched Photo-crosslinked Gelatin–Riboflavin Hydrogels for Corneal Wound Repair in Rabbits05:56

Fabrication and Surgical Application of Enriched Photo-crosslinked Gelatin–Riboflavin Hydrogels for Corneal Wound Repair in Rabbits

Published on: April 24, 2026

Related Concept Videos

Adrenergic Antagonists: Pharmacological Actions of β-Receptor Blockers01:27

Adrenergic Antagonists: Pharmacological Actions of β-Receptor Blockers

β-receptor blockers significantly impact the cardiovascular system by counteracting catecholamine-induced sympathetic responses. These medications decrease heart rate, contractility, and cardiac output, potentially leading to cardiac depression, life-threatening bradycardia, and death. Therapeutically, β-blockers function as mild antihypertensives and are utilized in treating angina pectoris and cardiac arrhythmias. However, nonselective β-blockers inhibit β2-receptors in bronchial smooth...
Open Angle Glaucoma: Treatment01:27

Open Angle Glaucoma: Treatment

In open-angle glaucoma, the iridocorneal angle remains open, but the trabecular meshwork becomes stiff, slowing down the outflow of aqueous humor. This causes a buildup of aqueous humor in the anterior chamber, leading to a sudden increase in intraocular pressure. The treatment for open-angle glaucoma focuses on reducing the elevated intraocular pressure by either decreasing the secretion of aqueous humor or increasing its outflow.
Drugs such as carbonic anhydrase inhibitors, α2- and...
Adrenergic Receptors: β Subtype01:26

Adrenergic Receptors: β Subtype

β-adrenoceptors have varied sensitivities towards adrenaline, noradrenaline, and isoprenaline. The order of agonist potency is as follows:
Isoprenaline > Adrenaline > Noradrenaline
Neurotransmitter binding to these receptors causes activation of adenylyl cyclase resulting in increased concentrations of cAMP and modulation of calcium ion channels within the cell. They are further classified into β1, β2, and β3 subtypes.
β1-adrenoceptors: β1-adrenoceptors have equal affinities for...
Adrenergic Agonists: Direct-Acting Agents01:30

Adrenergic Agonists: Direct-Acting Agents

Drugs that mimic the action of endogenous catecholamines like noradrenaline and adrenaline are called adrenergic agonists or sympathomimetics. Based on their mechanism of action, sympathomimetics can be classified as direct-, indirect-, or mixed-acting sympathomimetics. Direct-acting adrenergic agonists activate adrenoceptors without affecting presynaptic neurons, making them independent of neuronal catecholamine-depleting agents like reserpine and guanethidine.
These agents can be classified...
Adrenergic Agonists: Therapeutic Uses01:30

Adrenergic Agonists: Therapeutic Uses

Adrenergic agonists have diverse therapeutic uses across various medical conditions and emergencies.
Emergency and Intensive Care Unit (ICU) applications: Pressor agents increase blood pressure, heart rate, and contractility in shock and organ failure situations. Dopamine can induce vasodilation and stimulate adrenoceptors. Endogenous catecholamines are effective in treating cardiogenic shock. α2-agonists like clonidine can reverse anesthesia-induced hypertension.
Allergies and anaphylaxis:...
Adrenergic Antagonists: ɑ and β-Receptor Blockers01:31

Adrenergic Antagonists: ɑ and β-Receptor Blockers

Third-generation β-blockers, such as labetalol and carvedilol, represent a significant advancement in managing cardiovascular conditions. Unlike conventional β-blockers, which can induce peripheral vasoconstriction, third-generation drugs block α1 adrenoceptors. This promotes vasodilation through several mechanisms, such as increased nitric oxide production, inhibition of calcium ion entry, opening of potassium ion channels, and antioxidant action. Labetalol, for instance, is clinically...