Effect of Drugs on Rabbit Eye

Aim: To study the Mydriatic effect of topically applied atropine on rabbit eyes.

Principle: A large number of drugs are used for their local action in the eye as eye drops or eye ointments. Most of these drugs belong to an antimicrobial, autonomic or local anaesthetic group. The eye is supplied by both sympathetic and parasympathetic nerves. The superior palpebral muscle and the dilator papillae of the iris have sympathetic supply. The sphincter pupillae of the iris has a parasympathetic supply that exercises dominant control. The ciliary muscle is also supplied by the parasympathetic nerve and when it contracts, the ciliary body is moved inwards and forwards. Because the lens bulges forward and the eye is accommodated for near vision. The opposite effect is produced by the relaxation of ciliary muscle resulting in paralysis of accommodation. When the pupil dilates, the iris folds back near the opening of the canal of schlemn and the drainage of aqueous humour is decreased thereby increasing intraocular pressure. constriction of the pupil, by opposite action, will increase drainage and reduce intraocular pressure.

Topically applied drugs can affect the eye by changing conjunctival congestion, papillary size, light reflex, corneal sensitivity and intraocular pressure. however, the effects of drugs on papillary size, light reflex and corneal reflex can be easily studied by the students. the pupillary size can be measured by placing a transparent plastic scale in front of the eye but as close as possible. Light reflex is elicited by directing the light of a torch towards the pupil. The sensitivity of the cornea is tested by gently touching the cornea with a fine cotton swab stick from the side and not from the front of the eye. This elicits corneal reflex which manifests as the blinking of the crystals.

Requirements:

Animal : Rabbit(2-5kg)

Drugs: Atropine (1%w/v) & Physostigmine (1%w/v)

Equipment: rabbit holder, pen torch

Procedure:

• Place the rabbit in the rabbit holder by keeping the head outside.
• Observe size of the pupil in both the eyes.
• Examine the effect of light reflex by holding the torch in front of the eye moving light beam to and fro
• Examine the corneal reflex by touching a side of the cornea with a cotton swab.
• Instil a few drops of atropine solution in the conjunctiva over a period of 8-10 min in the right eye of the rabbit would serve as the control. Instil normal saline in the left eye.
• Record the pupillary size, light reflex and corneal reflex after ten minutes of drug initialisation and tabulate the observation.
• Repeat the experiments with physostigmine and ephedrine.

Observation: