Neuro - Visual System pt. 2

Question 1

What is refraction?

Answer 1

when light passes through one medium to another, its velocity changes

Question 2

How is the index of refraction calculated?

Answer 2

index of refraction (n) = speed of light in a vacuum / speed of light in a more dense medium = c/v

Question 3

What are the basic types of lenses?

Answer 3

→ convex

→ concave

Question 4

What is a convex lens?

Answer 4

→ almond shaped
→ converging lens
→ bring light rays to a point

Question 5

What is a concave lens?

Answer 5

→ diverging lens

→ spreads light rays away

Question 6

What are some applications of lenses?

Answer 6

cameras, etc.

Question 7

What is emmetropia?

Answer 7

→ adequate correlation between axial length + refractive power
→ parallel light rays fall on the retina without accommodation

Question 8

What is ametropia?

Answer 8

→ refractive error
→ mismatch between axial length + refractive power
→ parallel light rays don’t fall on the retina (no accommodation)

Question 9

What are some examples of ametropia?

Answer 9

→ myopia (near-sightedness)
→ hyperopia (far-sightedness)
→ astigmatism
→ presbyopia

Question 10

What is myopia?

Answer 10

→ short-sightedness

→ parallel rays converge at a focal point anterior to the retina

Question 11

What are symptoms of myopia?

Answer 11

→ blurred distance vision
→ squint in an attempt to improve uncorrected visual acuity when gazing into distance
→ headache

Question 12

What are causes of myopia?

Answer 12

→ not clear, possible genetic factors
→ excessive long globe (axial myopia)
→ excessive refractive power (refractive myopia)

Question 13

What is myopia treatment?

Answer 13

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

Question 14

What is hyperopia?

Answer 14

→ long-sightedness

→ parallel rays converge at focal point posterior to the retina

Question 15

What are causes of hyperopia?

Answer 15

→ not clear, possible genetic factors
→ excessive short globe (axial hyperopia)
→ insufficient refractive power (refractive hyperopia)

Question 16

What are symptoms of hyperopia?

Answer 16

→ visual acuity at near tends to blur relatively early
→ nature of blur varies from inability to read fine print, to near vision is clear but suddenly and intermittently blurred
→ blurred vision is more noticeable if person is tired, printing is weak or light inadequate
→ eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis

Question 17

What is amblyopia?

Answer 17

uncorrected hyperopia > 5D

Question 18

How is hyperopia treated?

Answer 18

→ correction with converging lenses (positive lenses)
→ correction with positive lens + cataract extraction
→ correction with contact lenses
→ correction with intraocular lenses

Question 19

What is astigmatism?

Answer 19

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

Question 20

What are causes of astigmatism?

Answer 20

→ hereditary
→ 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 21

What are asthenopic symptoms?

Answer 21

→ fatigue
→ pain in or around the eyes
→ blurred vision
→ headache
→ occasional double vision

Question 22

What is asthenopia?

Answer 22

→ eye strain

→ non-specific disorder

Question 23

What are symptoms of astigmatism?

Answer 23

→ asthenopic symptoms
→ blurred vision
→ distortion of vision
→ head tilting + turning

Question 24

How do you treat regular astigmatism?

Answer 24

cylinder lenses with or without spherical lenses

Question 25

How do you treat irregular astigmatism?

Answer 25

→ rigid cylinder lenses

→ surgery

Question 26

What is the Near Response Triad?

Answer 26

how near vision is mediated by 3 separate but simultaneous pathways:
→ pupillary miosis
→ convergence
→ accommodation

Question 27

What is the Pupillary Miosis pathway?

Answer 27

→ sphincter pupillae muscle in iris contracts
→ causes the pupil to constrict
→ increases depth of field

Question 28

What is the Convergence pathway?

Answer 28

→ medial rectus muscle contract
→ both eyes adduct medially
→ aligns both eyes towards a near object

Question 29

What is the Accommodation pathway?

Answer 29

→ circular ciliary muscle

→ lens accommodates, increasing refractive power required to focus on a near object

Question 30

What is presbyopia?

Answer 30

→ naturally occurring loss of accommodation (focus for near objects) due to loss of lens elasticity
→ onset from age 40 years
→ distant vison intact

Question 31

How can presbyopia be corrected?

Answer 31

→ corrected by reading glasses (convex lenses) to increase refracting power of the eye
→ bifocal glasses
→ trifocal glasses
→ progressive power glasses

Question 32

What are the advantages of having contact lenses?

Answer 32

higher quality of optical image + less influence in size of retinal image than spectacle lenses

Question 33

What are the disadvantages of having contact lenses?

Answer 33

→ careful daily cleaning and disinfection
→ expense complication
→ infectious keratitis
→ giant papillary 
→ conjunctivitis
→ corneal vascularisation
→ severe chronic conjunctivitis

Question 34

What are the advantages of intraocular lenses?

Answer 34

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

Question 35

What are the different surgical options for correction?

Answer 35

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

Question 36

What is the method of laser surgical correction?

Answer 36

→ 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 37

What is the ICL?

Answer 37

→ Staar Intra-Collamer Lens

→ inserted into the eye for the correction of myopia + astigmatism