vision

Question 1

what is the index of refraction (n)

Answer 1

speed of light in vacuum/speed of light in medium (as denominator always smaller, value is unitless and greater or equal to 1)

Question 2

what 2 things change when light goes from one medium to another

Answer 2

velocity and direction

Question 3

what 2 things happen when light reaches a new medium

Answer 3

some reflects off boundary, and some refracts through boundary

Question 4

what is the angle of incidence equal to

Answer 4

angle of reflection

Question 5

what is angle of incidence > or < angle of refraction depending on

Answer 5

direction of light

Question 6

2 types of lenses, shape and what they do

Answer 6

converging (convex) brings light rays to a focal point (distance from lens to focal point is focal length); diverging (concave) spreads light rays from source (focal point) outwards (distance from focal point to lens is focal length)

Question 7

function of converging lens

Answer 7

focus an image

Question 8

what is emmetropia

Answer 8

adequate correlation between axial length and reflective power, so parallel light rays fall on retina with no accomodation

Question 9

what is ametropia

Answer 9

refractive error where there is a mismatch between axial length and refractive power, meaning light rays don’t fall on retina (no accomodation)

Question 10

4 types of ametropia

Answer 10

nearsightedness (myopia), farsightedness (hyperopia), astigmatism, presbyopia

Question 11

what happens in myopia

Answer 11

parallel rays converge at focal point anterior to retina

Question 12

2 causes of myopia

Answer 12

genetic factor: excessive long globe (axial; more common), excessive refractive power (refractive; lens is too convex)

Question 13

3 symptoms of myopia

Answer 13

blurred distance vision, squint in attempt to improve uncorrected visual acuity when gazing into distance (only get light that is straight so no need for refractive power), headache

Question 14

3 ways myopia is corrected

Answer 14

diverging lens, by making retina more convex, or by removing lens to reduce refractive power of eye (no longer done as many other issues)

Question 15

what happens in hyperopia

Answer 15

parallel rays converge at focal point posterior to retina

Question 16

2 causes of hyperopia

Answer 16

inherited: excessive short globe (axial; more common), insufficient refractive power (refractive)

Question 17

2 symptoms of hyperopia

Answer 17

visual acuity at near tends to blur relatively early, asthenopic symptoms

Question 18

when is blurred vision more noticeable

Answer 18

when tired, weak printing, or inadequate lighting

Question 19

asthenopic symptoms of hyperopia

Answer 19

eyepain, headache in frontal region, burning sensation in eyes, blepharoconjunctivitis

Question 20

what is ambylopia

Answer 20

uncorrected hyperopia > 5D, so vision is always blurry regardless of distance; lazy eye ir not corrected at childhood as brain doesn’t use that eye as blurred

Question 21

how is hyperopia corrected

Answer 21

converging lens, anterior chamber intraocular lens, posterior chamber intraocular lens

Question 22

what happens in astigmatism

Answer 22

parralel rays come to focus in 2 focal lines rather than one, as cornea dome different shape

Question 23

cause of astigmatism

Answer 23

hereditary; refractive media is not spherical so refracts differently along one meridian than along meridian perpendicular to it, creating 2 focal points on retina (punctiform object represented as 2 sharply defined lines)

Question 24

4 symptoms of astigmatism

Answer 24

asthenopic symptoms (eyepain, headache), blurred vision, distorted vision, head tilting and turning

Question 25

treatment of regular astigmatism

Answer 25

cylinder lenses with/without spherical lenses (convex or concave), so light pasing through vertical part will go straight, but light passing through side will hit convex/concave structure, creating joint focal point

Question 26

treatment of irregular astigmatism

Answer 26

rigid cylinder lenses, surgery

Question 27

what is the near response triad for

Answer 27

adaption for near vision

Question 28

3 things responsible for near response triad

Answer 28

pupillary miosis, convergence, accomodation

Question 29

what causes pupillary miosis and effect

Answer 29

sphincter pupillae to increase depth of field

Question 30

what causes convergence and effect

Answer 30

medial recti from both eyes to align both eyes towards a near object

Question 31

what causes accomodation and effect

Answer 31

circular ciliary muscle to increase refractive power of lens for near vision

Question 32

what is presbyopia

Answer 32

naturally occuring loss of accomodation (focus for near objects) after 40 years, with distant vision intact

Question 33

how is presbyopia corrected

Answer 33

reading glasses with convex lenses to increase refractive power of eye; also bi/tri focal glasses or progressive power glasses

Question 34

4 types of optical correction

Answer 34

spectacle lenses, contact lenses, intraocular lenses, surgical

Question 35

types of spectacle lenses

Answer 35

monofocal: spherical, cylindrical; multifocal

Question 36

contact lenses vs spectacle lenses

Answer 36

contact lenses have higher quality of optical image and less influence on size of retinal image

Question 37

indication for contact lenses

Answer 37

cosmetic, athletic activities, occupational, irregular corneal astigmatism, high anisometropia, corneal disease

Question 38

disadvantages of contact lenses

Answer 38

careful daily cleaning and disinfection, expense

Question 39

complication of contact lenses

Answer 39

infectious keratitis, giant papillary conjunctivitis, corneal vascularisation, severe chronic conjunctivitis

Question 40

what is intraocular lenses

Answer 40

replacement of cataract crystalline lens

Question 41

when are intraocular lenses used

Answer 41

best optical correction for aphakia, and avoid significant magnification and distortion caused by spectacle lenses

Question 42

2 types of surgical correction

Answer 42

keratorefractive, intraocular

Question 43

what is clear lens extraction with intraocular lens; what is lost and correction

Answer 43

same as cataract extraction, with implantation of artifical lens; lose accomodation so needs reading glasses

Question 44

accomodation mechanism for near vision

Answer 44

circular ciliary muscle in ciliary body contracts -> zonules between ciliary body and lens capsule attachment passively relax -> lens returns to natural convex shape due to innate elasticity -> refractive power of lens increases

Question 45

what mediates accomodation

Answer 45

efferent oculomotor nerve