Lab 2 - Drugs and the ANS: The Eye as a Model

Question 1

What is typically used to treat inflammatory/allergic conditions that affect the cornea and the conjuctiva?

Answer 1

topical antiinflammatory agents (corticosteroids)

Question 2

How are acute eye infections treated?

Answer 2

Treated topically with anti-infective preparations (antibacterials, antifungals, antivirals) dependant upon the nature of the problem

Question 3

What is the difference in treatment for acute eye infections compared to severe ones?

Answer 3

In severe infection, systemic treatment is given in addition to topical therapy.

Question 4

What must happen to the pupil prior to eye surgery?

Answer 4

Dilation of the pupil (mydriasis) is a prerequisite for certain surgical procedures

Facilitating inspection of the retina and preventing the iris from adhering to the lens in inflammation (iritis).

Question 5

What is needed for removal of foreign and minor surgical procedures on eyes?

Answer 5

The removal of foreign bodies and minor surgical procedures require the instillation of local anaesthetics (cocaine derivatives).

Question 6

How can the pupil be pharmacologically dilated?

Answer 6

With antimuscarinic agents

e.g.

• atropine
• cyclopentolate
• tropicamide

With sympathomimetics

e. g.
* phenylephrine

Question 7

How can the pupil be pharmacologically constricted?

Answer 7

With muscarinic agonists

e. g.
* pilocarpine

They can be used to open up inefficient drainage channels in the trabecular meshwork and thus treat glaucoma.

Question 8

What is the scientific name for pupil dilation?

Answer 8

Mydriasis

Question 9

What is the scientific name for pupil constriction?

Answer 9

Miosis

Question 10

How can hronically sore eyes associated with reduced tear secretion be treated?

Answer 10

Chronically sore eyes associated with reduced tear secretion (e.g. Sjögren’s syndrome of rheumatoid arthritis) can be treated with topically applied agents (e.g. hypromellose and mucolytic agents) as can excessive lachrymation (e.g. zinc sulphate)

Question 11

What is the name given to opacity of the eye’s lens and what can cause this?

Answer 11

Cataract

May be caused by the administration of systemic steroids or by their prolonged application topically to the eye.

Question 12

What can administration of compounds such as ethanol do to the retina?

Answer 12

The retina may also be damaged by systemic administration of many compounds (e.g. chloroquine, quinine, thioridazine, ethanol).

Question 13

Label a horizontal cross-section of a human eye

Answer 13

Question 14

Where does aqueous humour come from?

Answer 14

Originates from the epithelium covering the ciliary body.

The area of which is greatly increased by the presence of ciliary processes which are heavily vascularised.

Question 15

What makes up the ciliary epithelium?

Answer 15

Two layers of ectodermal cells

Question 16

Explain how the ciliary epithelium forms aqueous humour and its circulation

Answer 16

The ciliary epithelium consists of two layers of ectodermal cells (containing ATPase and carbonic anhydrase)

Ciliary epithelium absorbs Na+ selectively from the stroma

It transports it into the intracellular clefts, which open on the aqueous humour side.

The aqueous humour passes through the narrow space between the iris and the lens into the anterior chamber.

From there it returns to the venous circulation through the pores of the corneo-scleral trabeculum in the antero-lateral wall of the anterior chamber and through the endothelium of the canal of Schlemm.

The hyperosmolality in the cleft causes water flow from the stroma producing continuous flow of aqueous humour.

Question 17

What is normal intraocular pressure?

Answer 17

15mmHg (range: 10-20)

Question 18

How is intraocular pressure maintained?

Answer 18

It is maintained mainly by the balance between the rate of aqueous humour production and the resistance to its return to the venous circulation

Question 19

What is glaucoma?

Answer 19

A state of glaucoma exists when the intraocular pressure increases such that there is damage to nerve fibres at the optic nerve head which results in progressive optic atrophy

Question 20

How is glaucoma categorised?

Answer 20

Primary Glaucoma:

There are three types and it can be diagnosed when there is no evidence of ocular or general cause of secondary glaucoma.

Secondary Glaucoma:

This is said to be present when an intraocular pressure of more than 20mm-Hg is found in the presence of an ocular disturbance which can reasonably be expected to lead to a raised pressure (e.g. trauma, intraocular neoplasms, neovascular formation, steroid administration).

Question 21

What percentage of the population are affected by glaucoma?

Answer 21

More than 1% of the population over the age of 40

Question 22

How is glaucoma treated?

Answer 22

Various pharmacological approaches are available for the treatment of glaucoma during an acute attack and for long-term management including:

• pilocarpine
• physostigmine
• timolol
• adrenaline
• carbonic anhydrase inhibitors

Alternatives to drugs in the treatment of glaucoma have also been introduced (e.g. laser trabecular surgery).

Question 23

What is the central opening of the iris known as?

Answer 23

The pupil

Question 24

What do changes in the size of the pupil control?

Answer 24

The amount of light entering the eye

Constantly and unconsciously changes size due to the ANS stimulating the muscle of the iris

Question 25

What are the muscles of the iris?

Answer 25

Sphnicter Pupillae

• circular muscle
• innervated by the parasympathetic fibres of the oculomotor nerve
• constriction of the pupil

Dilator Pupillae

• radial muscle
• innervated by sympathetic nerves
• dilation of the pupil

Question 26

Overall, how is the pupil controlled by the ANS?

Answer 26

Through joint innervation by parasympathetic and sympathetic nerves

Sympathetic system

• controlled by noradrenaline (NA)

Question 27

Other than the two muscles of the iris, what other muscle can be affected by the ANS?

Answer 27

Ciliary muscle

• within the ciliary body
• eye lens is suspended at its equator by fibres of the ciliary body
• the fibres pull on the lens and changes its shape

Question 28

What affects do actions of the ciliary muscle have on the lens of the eye?

Answer 28

Contraction of ciliary muscle

• tension from ciliary fibres on lens is reduced
• lens becomes fatter
• lens refracts light entering eye from near objects to a greater extent
• can focus on near objects
• “accomodation”

However, ciliary muscle is also innervated by parasympathetic nerves

Question 29

What is tropicamide?

Answer 29

Anti-cholinergic drug

Causes mydriasis (pupil dilation)

It is used to allow better examination of the lens, vitreous humor, and retina.

Question 30

What is pilocarpine?

Answer 30

Causes miosis (pupil constriction)

As eye drops it is used for:

• angle closure glaucoma until surgery can be performed
• ocular hypertension
• open angle glaucoma
• bringing about constriction of the pupil following its dilation.

Question 31

In the practical, what 3 measurements were taken once the drugs had been administered to the eyes?

Answer 31

• Point of Accomodation
• Pupillary Reflex (+ve or -ve)
• Size of the Pupil