1/2- refraction and drops Flashcards
(25 cards)
What are the refractive structures of the eye?
Lens and cornea, cornea does most of it
When do refractive errors occur?
When the length of the eye does not match the refractive power of the lens
What is prebyopia?
age related loss of accomodation. Lens becomes harder and less able to change shape. Cannot thicken so struggle to focus on close things
When does presbyopia usually manifest?
mid 40s-ability to accommodate at reading distances is lost
Emmetropia?
No refractive error
Hypermetropia?
insufficient refraction focuses the image behind the retina.
How do you correct hypermetropia?
Convex lens, supplements power (so positive number)
Myopia?
short sighted, image is focused before the retina
How is myopia corrected?
Concave lens, negative refractive so a - prescription to counteract over-refraction
What is an astigmatism?
Rugby ball shaped. abnormal corneal curvature
What is a mydriatic? When are they used?
An agent that induces dilation of the pupil. Used for diagnostic imaging. Tend to be either parasympathetic antagonists or sympathomimetics
Anticholinergic mydriatisc?
Atropine, cyclopentolate, tropicamide
When is atropine used as a mydriatic
amblyopia in kids
When/why is tropicamide used?
routine choice for dilation as short acting (40 mins)
S/E of anticholinergic drops?
blurring, photophobia, dry mouth, flushing
Can precipitate an AACG due to narrowing of drainage angle, so c/i in synechiae (adhesions)
What type of muscarinic receptors are predominant in the eye?
M3
S/E of phenylephrine drops?
contracts iris dilator muscle and can cause blurring, watering, photophobia, rebound miosis, headache,tach
C/I in elderly with cardiac disease
What main two dyes are used in ophthalmology?
fluorescein and indocyanine green
What is fluorescein used for?
Can show defects in the corneal epithelium or for angiography
What are the s/e of fluorescein
avoid during pregnancy and injection can turn you yellow (plus nausea, headache)
What is indocyanine useful for?
angiography of the choroid but again c/i in pregnancy
Causes of myopia?
Genetic (18p and 12q)
very close work in early decades -> changes in synthesis of mRNA and myopia
When does myopia usually present?
around 6- the compensation for the growing eye may not occur and so becomes worse. changes will continue until teens
Why should you avoid overcorrection in myopia?
Can make it worse,
