Visual System - Optics

Question 1

What is refraction?

Answer 1

light passes from one medium into another (velocity and direction changes)

Question 2

What is the index of refraction?

Answer 2

n=speed of light in a vacuum/speed of light in a medium

Question 3

The angle of incidence is equal to?

Answer 3

angle of reflection

Question 4

The angle of incidence is > or < than what?

Answer 4

angle of refraction depending on the direction of the light

Question 5

What types of lenses are there?

Answer 5

convex

concave

Question 6

What is an application of converging lenses?

Answer 6

camera uses a lens to focus an image on film

Question 7

Emmetropia

Answer 7

adequate correlation between axial length and refractive power
parallel light rays fall on the retina

Question 8

Ametropia

Answer 8

mismatch between axial length and refractive power

parallel light rays don’t fall on the retina (myopia, hyperopia, astigmatism, presbyopia)

Question 9

What is myopia?

Answer 9

Parallel rays converge at a focal point anterior to the retina

Question 10

What are causes of myopia?

Answer 10

excessive long globe (more common)

excessive refractive power

Question 11

What are symptoms of myopia?

Answer 11

Blurred distance vision
Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
Headache

Question 12

List treatments of myopia.

Answer 12

correction with diverging lenses, with contact lens, by removing the lens to reduce refractive power of the eye

Question 13

What is hyperopia?

Answer 13

Parallel rays converge at a focal point posterior to the retina

Question 14

What are the causes of hyperopia?

Answer 14

excessive short globe (axial hyperopia) : more common

insufficient refractive power (refractive hyperopia)

Question 15

What are symptoms of hyperopia?

Answer 15

visual acuity at near tends to blur relatively early

asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis

Question 16

What is amblyopia?

Answer 16

eye fails to achieve normal visual acuity, even with prescription eyeglasses or contact lenses

Question 17

List treatments of hyperopia.

Answer 17

correction with converging lenses/with` +ve lens + cataract extraction/with contact lens/with intraocular lens

Question 18

What is astigmatism?

Answer 18

Parallel rays come to focus in 2 focal lines rather than a single focal point

Question 19

Astigmatism etiology

Answer 19

hereditary

Question 20

What is the cause of astigmatism?

Answer 20

refractive media is not spherical–>refract differently along one meridian than along meridian perpendicular to it–>2 focal points

Question 21

What are symptoms of astigmatism?

Answer 21

Asthenopic symptoms (headache , eyepain)
blurred vision
distortion of vision
head tilting and turning

Question 22

How to treat regular astigmatism?

Answer 22

Regular astigmatism : cylinder lenses with or without spherical lenses (convex or concave), Sx

Question 23

How to treat irregular astigmatism?

Answer 23

rigid cylinder lenses, surgery

Question 24

Near response triad?

Answer 24

Adaptation for Near Vision

Pupillary Miosis (Sphincter Pupillae) to increase depth of field
Convergence (medial recti from both eyes) to align both eyes towards a near object
Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision

Question 25

What is presbyopia?

Answer 25

Naturally occurring loss of accommodation (focus for near objects), distant vision intact

Question 26

Presbyopia onset from what age?

Answer 26

40

Question 27

Presbyopia is corrected by?

Answer 27

reading glasses (convex lenses) to increase refractive power of the eye

Question 28

What type of convex lenses are used for treatment of presbyopia?

Answer 28

reading glasses bifocals trifocals progressive power glasses

Question 29

What type of spectacle lenses are used for treatment of presbyopia?

Answer 29

Monofocal lenses : spherical lenses , cylindrical lenses | Multifocal lenses

Question 30

For who might contact lenses be helpful?

Answer 30

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

Question 31

What are disadvantages to contact lenses?

Answer 31

careful daily cleaning and disinfection , expense

Question 32

What are possible complications of contact lenses?

Answer 32

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

Question 33

Intraocular lenses

Answer 33

replacement of cataract crystalline lens | give best optical correction for aphakia , avoid significant magnification and distortion caused by spectacle lenses

Question 34

Types of surgical correction for optical issues

Answer 34

Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL