Intracameral Injection in Rats with Low Risk of Adverse Effects

Summary

This protocol describes a technique for intracameral injection in rats using a central corneal incision and a long tunnel into the anterior chamber. This injection method minimizes the risk of inducing inadvertent tissue damage and thereby improves precision and reproducibility.

Abstract

Intracameral injection is a standard administration routine in ophthalmology. The application of intracameral injection in rodents for research is challenging due to the limiting dimensions and anatomy of the eye, including the small aqueous humor volume, the lens curvature, and lens thickness. Potential damage during intracameral injections introduces adverse effects and experimental variability. This protocol describes a procedure for intracameral injection in rats, allowing precision and reproducibility.

Sprague-Dawley rats were used as experimental models. Since the lens position in rats protrudes into the anterior chamber, injecting from the periphery, as done in humans, is unfavorable. Therefore, an incision is created in the central corneal region using a 31 gauge 0.8 mm stiletto blade to form a self-sealing tunnel into the anterior chamber. An incision at an angle close to the flat allows to create a long tunnel, which minimizes the loss of aqueous humor and shallowing of the anterior chamber. A 34 gauge nanoneedle is inserted into the tunnel for injection. This enables penetration with minimal friction resistance and avoids touching the lens. Injection of trypan-blue allows visualization by slit microscopy the presence of the dye in the anterior chamber and exclude leakage. Bioavailability to the corneal endothelial layer is demonstrated by injection of Hoechst dye, which stained the nuclei of corneal endothelial cells after injection.

In conclusion, this protocol implements a procedure for accurate intracameral injection in rats. This procedure may be used for intracameral delivery of various drugs and compounds in experimental rat models, increasing the efficiency and reproducibility of ophthalmic research.

Introduction

The bioavailability of compounds delivered by topical administration to the surface of the eye is greatly limited, typically <5%¹. Compounds administered by eye drops are mainly eliminated by drainage, induced lacrimation, tear fluid turnover, and conjunctival absorption. In addition, the permeation of compounds through the ocular surface is highly restricted by the cornea-conjunctiva barrier^1,2,3. The cornea is composed of three main layers: the outermost epithelium, the intermediate stroma, and the innermost endothelium. The superficial corn....

Protocol

The experiments in the protocol were approved by the National Permit Committee - for animal science and comply with the ARVO Statement the use of animals in ophthalmic and vision research. Female Sprague-Dawley rats, aged 8-10 weeks, were used for the present study and were exposed to 12/12 h light-dark cycles. The animals were obtained from a commercial source (see Table of Materials).

1. Animal preparation

1. Prepare an anesthetic mixture .......

Discussion

Pre-clinical research models should provide a controlled and reproducible environment to ensure the reliability and applicability of findings. In ophthalmology research, eye injection models are commonly used in diverse research aspects ranging from establishing disease models, testing new treatments, and assessing tissue reactions and potential adverse effects.

Intracameral injections serve as a common technique in experimental ophthalmology, facilitating the direct delivery of compounds to t.......

Materials

Name	Company	Catalog Number	Comments
Alizarin Red	Alpha Aesar	042040.5
Buprenorphine	Richter pharma	102047
Dexamethasone 0.1%	Fisher Pharmaceutical	393102-0413
Hamilton glass syringe 10 μL	Hamilton Co.	721711
Hoeschst	Merck	B2261
Ketamine	Bremer pharma GMBH (medimarket)	17889
Ofloxacin 0.3% eye drops	Allergan	E92170
Oxybuprocaine Hydrochloride 0.4%	Fisher Pharmaceutical	N/A
Pentobarbital sodium 200 mg/mL	CTS	N/A
Slit microscope	Haag-streit bern	b-90019115
Sprague-Dawley Rats	Envigo	N/A
Stiletto blade 31 G 0.8 mm	Tecfen medical (skymed)	QKN2808
Surgical microscope	Zeiss	OPMI-6 CFC
Trypan Blue	Sartorius	03-102-1B
Xylazine	Eurovet Animal Health	615648