Principle
Antimuscarinic cause reversible paralysis of constrictor pupillae (circular muscle of iris) and ciliary muscle which leads to mydriasis cycloplegia and increase intraocular pressure. α1 receptor agonists cause contraction of dilator pupllae (radial muscle of iris) and produced mydriasis. α1 receptor agonists do not increase intraocular pressure.
Muscarinic agonists cause contraction of constrictor papillae (the circular muscle of iris) and the ciliary muscle and reduction of intraocular pressure.
Anticholinestrase agents inhibit cholinesterase enzyme and increase the concentration of Ach and thus exhibit muscarinic activity on the eye.
Equipment required
1) Schioetz-Tonometer
2) Pentorch
3) Dropper
Animal required
Rabbits.
Drug solution required
1) Mydriatics (antimuscarinics) Atropine sulphate 1%w/v
2) Mydriatics (α1 receptor agonist) Adrenaline hydrochloride
3) Miotics (Muscarinic receptor agonist) Pilocarpine nitrate 1% w/v
4) Miotic (antichoine esterase agent) Physostigmine sulphate 0.25% w/v
5) Local anaesthetic required for measuring intraocular pressure Lignocaine hydrochloride 4% w/v.
Procedure
1) Select 6 healthy albino rabbits weighing between 1.5-2 kg body weight and do the marking for the identification of each rabbit.
2) Observe the size of the pupil of each rabbit using a petorch.
3) Instill the eye drops of the following drugs as given below:
Name of the drug
|
Dose
|
Rabbit no.
|
Atropine sulphate
|
2-3 drops
|
1
|
Adrenaline hydrochloride
|
2-3 drops
|
2
|
Pilocarpine nitrate
|
2-3 drops
|
3
|
Physostigmine suphate
|
2-3 drops
|
4
|
Normal saline
|
2-3 drops
|
5
|
Lignocaine hydrochloride
|
2-3 drops
|
6
|
After 5 minutes
Pilocarpine nitrate
|
2-3 drops
|
6
|
4) Observe the size of the pupil of each rabbit at 30 minutes interval for a period of 2 Hrs (Rabbit No. 1-4)/
5) Adjust the schioetz-tonometer pointer on zero position.
6) Place the tonometer in a vertical position on the centre of the cornea (Rabbit no. 5-6).
7) Read the position of the pointer and calculate the tension in mm Hg (intraocular pressure) by the table.
Observation and conclusion
Atropine sulphate produces dilation of the pupil due to antimuscarinic activity. Adrenaline hydrochloride also produces dilation of the pupil because of α1 receptor stimulation.
Pilocarpine nitrate produces miosis of the pupil and reduces intraocular pressure due to muscarinic receptor activation.
Physostigmine suphate produces effect similar to pilocarpine.
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