Objective Principle Requirements Drugs and solution Procedure Observations Observation table Result and Interpretation Additional information Exercise

1. Mr. Vishal Balakrushna Jadhav
Assistant Professor (Pharmacology)
GES’s Sir Dr. M. S. Gosavi COPER, Nashik-5
ExperimentNo. 3
Study of mydriatic and miotic effects
on rabbit eye.

2. • Objective
• Principle
• Requirements
• Drugs and solution
• Procedure
• Observations
• Observation table
• Result and Interpretation
• Additional information
• Exercise
Overview of Discussion

3. To examine the effects of a miotic and mydriatic drugs on
the size of the pupil, light reflex, corneal reflex and
intraoculartension of the rabbit eye.
Objective

4. The Iris of the eye is composed of two types of muscle fibres,
the circular and the radial muscles. The circular fibres are
supplied by parasympathetic nerve fibres (cholinergic) and
innervates the constrictor pupillae. The radial ones are
innervated by sympathetic nerve fibres (adrenergic) and
innervates the dilator pupillae.
The stimulation of sympathetic and parasympathetic nerves
produces mydriasis and miosis respectively (as shown in
figure) and their paralysis produces opposite effects.
Drugs which simulate the effects of autonomic nervous system
can produce the above mentioned effects.
Principle

5. Fig. Autonomic control of pupil (A); and site of
action of mydriatics(B) and miotics(C)

6. Mydriatics show their either by disrupting parasympathetic
supply to the eye (e.g. atropine) or by over-activating the
sympathetic system (α1- selective action) leads to dilatation of
pupil by stimulating dilator muscles (e.g. phenylephrine). They
are used to reduce painful ciliary spasm, for diagnosing
Horner's syndrome, examining the retina and deeper
structures, for treating chronic simple glaucoma, corneal
ulcers and also used for retinoscopy particularly in children
and very old patients.
Miotics constrict the pupil (M3 selective action) by contracting
iris sphincter muscles (e.g. pilocarpine) or by inhibiting
acetylcholinesterase enzyme there by facilitating actions of
acetylcholine at transmitted sites (e.g. physostigmine). These
mechanisms increases outflow of aqueous humor and
decrease the intraocular pressure. These drugs are used
during cataract and anterior chamber surgeries, to treat wide
angle glaucoma, xerostomia (dry mouth).

7. 1. Rabbit
2. Scissors
3. Measuring scale
4. Droppers
5. Torch
6. Cotton wool.
Requirements

8. A. Normal saline
B. Mydriatic drugs:
Active Passive
Phenylephrine 20% Atropine sulphate 1.0%
C. Miotic drugs:
Active Passive
Pilocarpine 4.0% Phentolamine (not used)
D. Local anaesthetic:
Lignocaine hydrochloride 1-2%
Drugs and solutions

9.  Handle rabbit with care.
 Clip off eyelashes of both the eyes
 Use pouch method to instill drugs into eye.
Pinch lower eyelid to make a small pouch.
 Instill 1-2 drops of saline/drug in it using
dropper. Pull the lower eyelid upwards and
keep it in contact with conjunctiva for 1-2
minutes. You can also press medial canthus for
5 seconds after instillation of drug.
 Keep one eye (either right or left eye) as
control and the other as test. Apply saline in
the control eye and a drug in the test eye.
 Following parameters are measured at 5-15
minutes after instillation of drug (as shown in
fig.): 1. Size of pupil, 2. Light reflex, and 3.
Touch reflex (Corneal reflex).
Procedure

10. 1. Size of Pupil
Measure the diameter of both the pupils. This can be measured with a
pupilometer made up of cardboard or hard paper. Take a hard
paper, cut it approximately equal to a 6 inch ruler. Then cut holes in
it having increasing order of diameter in millimeters. You can start
with 1mm then mark upto 10 mm. You can also measure with the
help of a simple scale. It is difficult to force open eyes of rabbit.
Hence, with pupilometer it becomes easy to measure diameter.
Keep pupilometer close to eye through which you can see pupil,
match the hole in pupilometer with size of pupil and note down the
size in mm written on the matched hole.
2. Light Reflex
Light reflex is checked with a torch. A pencil torch is best suited for this
purpose. Always put the light from side (back) and bring it to the
front. Do not put the light from the front side of the rabbit. Observe
the changes in the diameter of pupil when light is put into eye. Note
any decrease or increase in pupillary diameter. Take 3 readings.

11. 3. Corneal Reflex
It is tested with a fine cotton wool wick. Wick is made in such a manner
that there is no protruding part of cotton. Touch peripheral part of
cornea with tip of cotton wick. Always bring forward the cotton
wool from the side (back). Rabbit should not be able to see cotton
wool or your hand. Blinking represents presence of corneal reflex.
Do not forget to note down the 3 readings.
Precaution: Do not touch central part of cornea it can cause corneal
ulcers/opacities. This can lead to blindness as central part of cornea
is the main part of cornea used for visibility.

12. Observations
Fig. Normal Left and Right Eyes of Rabbit

13. Fig. Right Eye treated with saline
Fig. Left Eye treated with epinephrine and right eye treated with atropine

14. Fig. Left Eye treated with ephedrine and right eye treated with physostigmine
Fig. Left Eye treated with lignocaine and right eye treated with saline

15. Sr.
No.
Drug Pupil size
(mm)
IOP
(mm Hg)
Light
reflex
Corneal
reflex
1 Saline 6 15.7 Present Present
2 Pilocarpine 3 14.2 Present Present
3 Amphetamine 8 18.8 Present Present
4 Ephedrine 7 15.7 Present Present
5 Cocaine 8 14.2 Present Absent
6 Physostigmine 1 14.2 Present Present
7 Lignocaine 6 15.7 Present Absent
8 Atropine 10 15.7 Absent Present
9 Epinephrine 9 14.2 Present Present
10 Phenylephrine 10 15.4 Present Present
Observation table

16.  Effects of a miotics (parasympathetic drugs like
pilocarpine, physostigmine and atropine) and mydriatics
(sympathetic drugs like amphetamine, epinephrine and
phenylephrine) on the size of the pupil, light and corneal
reflexes, and intraocular tension of the rabbit eye were
examined in contrast to saline solution.
 Effect of local anaesthetics like cocaine and lignocaine on
light and corneal reflexes were examined in contrast to
saline solution.
Result and Interpretation

17. Active and passive miosis and mydriasis (Table 9.2)
When miosis occurs as a result of active contraction of the
sphincter pupillae (circular muscle of the iris), it is known as
active miosis. This usually occurs as a result of action of
cholinomimetics.
When miosis occurs as a result of (passive) relaxation of the
dilator pupillae (radial muscle of the iris), it is known as passive
miosis. It usually results from action of adrenergic blockers.
Similarly with mydriatics also, there is active and passive
mydriasis due to active contraction of the dilator pupillae or
relaxation of sphincter pupillae respectively.
Additional information

18. Table- Classification of active and passive miotics and mydriatics

19. Indications of Miotics
1. Cataract
2. Anterior chamber surgery
3. Wide angle glaucoma
4. To break adhesions between lens and iris
5. Reversal of mydriatic effects of anticholinergics
6. Xerostomia.
Indications of mydriatics
1. Fundoscopy for visualization of the periphery of retina.
2. Retinoscopy in those who are unable to relax their eyes, e.g. children,
very old patients.
3. To break and prevent adhesions between iris and lens in iridocyclitis
(alternate miotics and mydriatics)
4. Chronic simple glaucoma
5. Corneal ulcer/uveitis
6. Preoperative: Cataract surgery/ Vitrectomy/ Retinal surgery
7. Fluorescent fundus or Indocyamine green angiography.

20. Local anaesthetics (LAs)
LAs reversibly block impulse conduction along nerve axons and
other excitable membranes that utilizes the Na+ channels as
primary means of action potential generation.
Procaine is not a surface anaesthetic (poor penetration).
Cocaine is not used because of corneal sloughing
(protoplasmic poison).
LAs block corneal reflex in the rabbit eye.

21.  What is the difference between mydriasis induced by
adrenergic agents and anti cholinergic drugs ?
 Name some clinically used mydriatics and miotics.
 What are the therapeutic uses of mydriatics and miotics ?
 The stomach wash fluid taken from a case of poisoning
produced pinpoint pupil when instilled into the eye of a rabbit.
The intraocular tension was also found to be decreased. What
is your probable diagnosis ? Justify Your answer.
 Name the receptors subtype for the action of cholinergic and
adrenergic drugs on rabbit eye.
Exercise

22. 22
Thank you!