P/P - Vision

Question 1

visual acuity

Answer 1

the sharpness or clarity of vision

Question 2

how is visual acuity tested?

Answer 2

Snellen chart

Question 3

what is the Snellen chart?

Answer 3

• chart that has several lines of letters
• number above each line refers to distance from which a person with normal vision would be able to read clearly the letters on the line

Question 4

the Snellen chart is always viewed from what distance?

Answer 4

6 metres

Question 5

what is the Snellen fraction?

Answer 5

viewing distance (m) / number (distance) marked on test type line

Question 6

what does visual acuity depend on?

Answer 6

ability of the cornea to refract or bend light, shape of the lens, sensitivity of retina, and ability of brain to interpret the info.

Question 7

during the Snellen test, what happens if the fraction is lower that 6/6?

Answer 7

diverging spehrical lenses of increasing dioptres are placed in front of the eye, ideally until the 6 line can be read.

Question 8

what is the Snellen tet used to test?

Answer 8

visual acuity

Question 9

the red and green duochrome rings are used to test for what during the Snellen test?

Answer 9

the accuracy of a correct by making use of chromatic abberation

Question 11

what is an astigmatism caused by?

Answer 11

uneven curvature of the cornea causing the light to be focused at more than one place in the eye.

can cause a blurring of vision

Question 12

when should astigmatism be tested for?

Answer 12

once refractive errors have been corrected, then each eye should be tested separately

Question 13

what chart is used to test for astigmatisms?

Answer 13

fan/Landolt’s chart

Question 14

the classification of colour blindness is based upon what?

Answer 14

Young-Helmholtz trichromacy theory

Question 15

what is a perimeter?

Answer 15

instrument that is used to measure visual fields

Question 16

how does the ANS change the pupil in bright conditions?

Answer 16

• acetylcholine is released from PS nerves
• binds to muscarinic (M3) receptors
• cayses circular muscles of iris to contract
• decreases pupil diameter

Question 17

how does the ANS change the pupil in low light conditions?

Answer 17

• noradrenaline released from sympathetic nerve endings
• binds to alpha-adrenoceptors
• radial muscles of iris contract
• increases pupil diameter

Question 18

contraction of the ciliary muscles to focus on near objects, is controlled by what?

Answer 18

PNS and acetylcholie

Question 19

what receptors are found in the dilator pupillae of the iris?

Answer 19

adrenoceptors

Question 20

what receptors are found in the sphincter pupillae of the iris?

Answer 20

muscarinic receptors

Question 21

why would dilating the pupil be helpful in opthalmoscopy?

Answer 21

allows more extensive examination of the retina and structures like macula and optic nerve

Question 22

mydriasis

Answer 22

dilation of the pupil

Question 23

what medicines are typically used to induce mydriasis?

Answer 23

tropicamide
phenylephrine

Question 24

what is the mechanism of action of tropicamide?

Answer 24

• muscarinic (M3) antagonist
• stops ACh binding to M3 receptors
• stops circular muscle contraction
• stops pupil constriction

Question 25

what is the mechanism of action of phenylephrine?

Answer 25

• alpha-adrenoceptor agonist
• binds to receptors and causes radial muscles of iris to contract
• increases pupil size

Question 26

what % of tropicamide is standard?

Answer 26

0.5%

Question 27

what % of phenylephrine is standard?

Answer 27

2.5%

Question 28

myopia

Answer 28

pupil constriction

Question 29

why might inducing myopia be useful?

Answer 29

reduces intraocular pressure, eg as a treatment for closed-angle glaucoma

Question 30

what % is the standard does of pilocarpine?

Answer 30

2%

Question 31

what medicines can be used to induce myopia?

Answer 31

pilocarpine