Visual systems optics

Question 1

What is refraction based on?

Answer 1

light is passing through one medium into another

Question 2

How do you calculate index of refraction?

Answer 2

Speed of light in a vacuum divided by speed of light in medium

Question 3

What happens to the light as it reaches a new medium?

Answer 3

Some of the light reflects off the boundary and some of the light refracts through the boundary.

Angle of incidence = Angle of Reflection

Question 4

What are the two types of lens?

Answer 4

Convex

Concave

Question 5

What is a convex lens?

Answer 5

A converging lens (convex) takes light rays and brings them to a point.

Question 6

What is a concave lens?

Answer 6

A diverging lens (concave) takes light rays and spreads them outward.

Question 7

What is emmetropia?

Answer 7

Perfect eye

Adequate correlation between axial length and refractive power

Parallel light rays fall on the retina (no accommodation)

Question 8

What is ametropia?

Answer 8

Refractive error

Mismatch between axial length and refractive power
Parallel light rays don’t fall on the retina (no accommodation)

Near-sightedness (Myopia)
Farsightedness (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 the causes od myopia?

Answer 10

excessive long globe (axial myopia) : more common

excessive refractive power (refractive myopia)

Question 11

What are the 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

How do you treat myopia?

Answer 12

Correction with diverging lenses (negative lenses)

Correction with contact lens

Correction 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 the symptoms of hyperopia?

Answer 15

visual acuity at near tends to blur relatively early

nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently blur

blurred vision is more noticeable if person is tired , printing is weak or light inadequate

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

Question 16

How do you treat hyperopia?

Answer 16

Correction with converging (positive lenses)

Correction with positive lens + cataract extraction

Correction with contact lens

Correction with intraocular lens

Question 17

What is Astigmatism?

Answer 17

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

Question 18

What causes Astigmatism?

Answer 18

refractive media is not spherical

–>refract differently along one meridian than along meridian perpendicular to it

–>2 focal points (punctiform object is represent as 2 sharply defined lines)

Question 19

What are the symptoms of astigmatism?

Answer 19

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

Question 20

What is the treatment of astigmatism?

Answer 20

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

Irregular astigmatism : rigid cylinder lenses, surgery

Question 21

What is the near response triad?

Answer 21

Adaptation for near vision

Question 22

What comprises the near response triad?

Answer 22

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 23

What is presbyopia?

Answer 23

Naturally occurring loss of accommodation (focus for near objects)

Onset from age 40 years

Distant vision intact

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

Question 24

What is the treatment for presbyopia?

Answer 24

convex lenses in near vision
Reading glasses
Bifocal glasses
Trifocal glasses
Progressive power glasses

Question 25

What are the different types of spectacle lens?

Answer 25

Monofocal lenses : spherical lenses , cylindrical lenses

Multifocal lenses

Question 26

What are the features of contact lenses?

Answer 26

higher quality of optical image and less influence on the size of retinal image than spectacle lenses

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

Question 27

What are the disadvantages for contacts?

Answer 27

careful daily cleaning and disinfection , expense

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

Question 28

What are intraocular lenses?

Answer 28

replacement of cataract crystalline lens

give best optical correction for aphakia (absence of crystalline lens)

avoid significant magnification and distortion caused by spectacle lenses

Question 29

What are the different surgical corrections?

Answer 29

Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty

Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL

Question 30

What are the process of laser surgical correction?

Answer 30

Initial cutting of corneal flap

Cutting of corneal flap

Flipping of corneal flap

Photorefractive treatment (laser)

Corneal stroma reshaped post laser

Corneal flap back in position

Question 31

What is an ICL implant?

Answer 31

Add lens ontop of natural lens

Catarct inevitable

Intra-collamer lens

Question 32

How is cataract surgery conducted?

Answer 32

Remove natural lens with ultrasound tip that breaks it and sucks it up

Insertion of artificial lens