Eye practical Flashcards
Which parts of the eye is PNS innervated
Ciliary muscle and spinster pupillae for pupil constriction (mitosis) by the oculomotor nerve
What is used to treat allergy or inflammation of the cornea or conjunctiva?
Topical anti-inflammatory agents (corticosteroids)
What is used to treat acute eye infections?
Topical anti-infective agents e.g. antibacterials, antifungals, antivirals
Why is mydriasis helpful and what drugs can induce this
Helpful before surgery to examine the retina and stop the iris from adhering to the lens in inflammation (iritis). Able to use; antimuscarinic agents (e.g. atropine, cyclopentolate, tropicamide) and sympathomimetics (e.g. phenylephrine)
When is miosis useful and what drugs can induce this
Used when you need to open up inefficient drainage channels in the trabecular meshwork-glaucoma. Able to use pilocarpine (muscarinic agonist) or timolol (beta blocker)
Treatment for chronically sore eyes
Due to reduced tear secretion
Hypromellose and mycolytics
Treatment for excessive lachrymation
Topical agents e.g. zinc sulphate
Other preparations are used in diagnostic procedures and for locating damaged areas of the cornea due to injury or disease
fluorescein sodium, rose bengal
What can cause cataracts (opacity of lens)
Administration of systemic steroids or prolonged application topically to the eye
Describe the production and use of aqueous humour
Originates from epithelium covering the ciliary body. The ciliary epithelium contains two lares of ectodermal cells (contains ATPase and Carbonic anhydrase). It absorbs Na+ from the stroma and transports it to the intracelullar clefts, which open on the aqueous humour side. The aqueous humour moves 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.
What is the normal intraocular pressure
15-20mmHg; maintained by production of aqueous humour and it’s return to the venous circulation
What causes the continuous flow of aqueous humour?
The hyperosmolarity in the cleft causes water flow from the stroma
What is glaucoma?
intraocular pressure increases such that there is damage to nerve fibres at the optic nerve head which results in progressive optic atrophy
Definition of secondary glaucoma
When the intraocular pressure is above 20mmHg; found in the presence of an ocular disturbance which can account for the increased pressure e.g. trauma, intraocular neoplasms, neovascular formation, steroid administration).
Definition of primary glaucoma
Raised intraocular pressure of above 20 mmHg but there is no evidence of ocular or general cause of secondary glaucoma
What is the effect of tropicamide on the eye?
Dilation of pupils; inhibition of PNS, decreased contraction of ciliary muscles
Decreased accommodation for near vision-lens bulges
Loss of light reflex; inhibition of PNS stops ability to constrict pupil
What is the effect of pilocarpine on the eye?
Parasympatheticomimetic
Constriction of pupils; enhanced PNS
Increased accommodation, increased bulging of lens
Loss of light reflex; enhanced PNS-maximal constriction
How does the sympathetic nervous system influence ocular function?
Alpha 1 receptor on radial muscle stimulated-mydriasis
Beta receptors in the eye stimulate aqueous humour production
What is the purpose of using a sympathomimetic and a beta-blocker for the treatment of glaucoma?
A sympathomimetic is used as it relaxes the ciliary muscle and there is more drainage of intraocular fluid.
Beta blockers are used as the beta 2 receptors in the eye stimulate production of aqueous humour, they also reduce vasoconstrictor effects so the intraocular pressure is reduced. Must NOT give an asthmatic beta blockers as there are beta2 receptors in the lungs.
What may be adverse effects of using sympathomimetic or beta blocker drugs?
As the beta blocker can bind to beta receptors systematically, they can cause bradycardia. To reduce this effect, you can increase polarity to reduce the chance of it entering the systemic circulation
What is the effect of heroin on the eye?
Heroin acts on opiate receptors which are located on GABAnergic interneurones which inhibit CNIII which releases ACh normally. Heroin inhibits the inhibitory interneurones i.e. disinhibition; releases ACh causing pupillary constriction - pin point pupil
How do carbonic anhydrase inhibitors/beta blockers/prostaglandin analogues work?
Carbonic anhydrase inhibitors are useful as there are receptors on the epithelial cells in the ciliary body which produce aqueous humour so less sodium and water is brought in -> less aqueous humour produced. Beta blockers and alpha agonists e.g. adrenaline, cause vasoconstriction and so reduce the amount of aqueous humour flowing through.
Prostaglandin analogues increase drainage through the trabecular meshwork as it removes residue making drainage more effective.
