Visual System Optics

Question 1

What is refraction?

Answer 1

light passing through one medium to another, the velocity changes

Question 2

How can the ratio of the speed changes in refraction be written?

Answer 2

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

The denominator will ALWAYS be SMALLER and produce a unitless value greater or equal to 1

Question 3

What is a mediums index of refraction??

Answer 3

The ratio of the speed of light changing from the vacuum to the medium

Question 4

What happens when light reaches a new medium?

Answer 4

Some light reflects some light refracts

Creates an angle of Incidence = angle of reflection

Question 5

What two types of lenses are there?

Answer 5

Convex : converging lens takes light and brings them to a point. positive lens

Concave : diverging leans take lights rays and spreads them outward, negative lens

Question 6

What is Emmetropia?

Answer 6

Adequate correlation between axial length and refractive power

Parallel light fall on the retina with no accommodation

as it should be

Question 7

What is Ametropia?

Answer 7

Refractive error

Mismatch between axial length and refractive power

SO parallel rays do not fall on retina - no accommodation

Question 8

Give examples of Ametropia?

Answer 8

• near sightedness = myopia
• Farsightedness = Hyperopia
• Astigmatism
• Presbyopia

Question 9

What is myopia?

Answer 9

parallel rays converge at the focal point anterior to the retina

caused by:

• excessive long globe
• excessive refractive myopia ( more common )

Question 10

What are the symptoms of myopia?

Answer 10

Blurred distance vision

Squint to improve visual acuity when gazing into distance

Headache

Question 11

What three methods can be used to correct myopia?

Answer 11

Correction with diverging lens

Correction with contact lens

Correction by removing the lens to reduce refractive power of the eye

Question 12

What is hyperopia?

Answer 12

Parallel rays converge at focal point posterior to retina

Caused by:

• excessive short globe (axial hyperopia, more common)
• Insufficient refractive power (refractive hyperopia)

Question 13

What are the symptoms of hyperopia?

Answer 13

Visual acuity at near tends to blur relatively early

• blur could be inability to read to sometime blurring
• more noticeable if person is tired, light inadquate

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

Amblyopia – uncorrected hyperopia > 5D

Question 14

How to treat hyperopia?

Answer 14

Correcting with converging lens
or correction with a positive lens. + cataract extraction

Correction with contact lens
Correction with intraocular lens ( can be in anterior or posterior chamber )

Question 15

What is Astigatism?

Answer 15

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

Hereditary

Due to refractive media not spherical which changes refraction along one meridian than along the meridian perpendicular to it

• 2 focal points (punctiform object is represented as 2 sharply defined lines)

Question 16

What are the symptoms of astigmatism?

Answer 16

Asthenopic symptoms
Blurred vision
disrotrion of vision
head tilting and turning

Question 17

How to treat astigmatism?

Answer 17

to treat regular astigmatism : cylinder lenses or convex/concave

Irregular astigmatism : rigid cylinder lenses, surgery

Question 18

What are asthenopic symptoms?

Answer 18

headache

eyepain

Question 19

What is the near response triad?

Answer 19

The pathways that mediate near vision

These are three simultanoues pathways

–> pupillary miosis - pupil constricts increasing the depth of field of the optics of the eye

• this is mediated by the contraction of the circular sphincter pupillae muscles in iris

–> Convergence - medial recti both align both eyes towards a near object

–> accommodation - lens increases refractive power to focus on near object through circular ciliary muscle

Question 20

What if eyes have a shallow depth of field?

Answer 20

Lose focus easily even with slight object movement

when viewing a near object

Question 21

What is Presbyopia?

Answer 21

Naturally occuring loss of accommodation

onset from 40+

corrected by reading glasses

convex

to increase refractive power of eye

Question 22

Why is the age of onset for presbyopia 40?

Answer 22

As we age natural lens looses its elasticity and so ability to accommodate is lost

Vision is not as clear when at near

Question 23

What types of convex glasses can be given for presbyopia?

Answer 23

reading
bifocal
trifocal
progressive power glasses

Question 24

What spectacle glasses can be given for presbyopia correction?

Answer 24

Monofocal
Spherical
Cylindrical
Multifocal lenses

Question 25

Why may contact lenses be given?

Answer 25

higher quality of optical image, less influence on size of retinal image than spectacle image, can be a cosmetic decision, atheltic activities, occupations, irregular corneal astigmatism, high anisometropia, corneal disease

Question 26

What are the disadvantegs to contact lenses?

Answer 26

careful daily cleaning and disinfection expense complication infectious keratitis giant papillary conjuctivitis corneal vascularization severe chronic conjuctivitis

Question 27

Why may intraocular lenses be considered?

Answer 27

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

Question 28

What types of surgeries are avaible for correction?

Answer 28

Keratorefractive Intraocular surgery

Question 29

Give types of keratorefractive surgeries?

Answer 29

``` RK AK PRK LASIK IC thermokeratoplasty ```

Question 30

Give types of intraocular surgery?

Answer 30

clear lens extraction with or wihtout IOL Phakic IOL

Question 31

What are the steps used in surgical correction for LASIK?

Answer 31

- 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 - Treatment completed

Question 32

What is ICL surgery?

Answer 32

Intra - collamer lens inserted for the correction of myopia and astigmatism

Question 33

Why will a px need reading glasses after clear lens extraction + IOL treatment?

Answer 33

same as cataract extraction but also implantation of intra ocular artificial lens the px loses accommodation so will need glasses

Question 34

Which of the following is false for myopia? A) May be associated with large globe B) Light ray converges behind the retina C) May be associated with increased corneal curvature D) Unable to see objects clearly at distance without glasses or other optical correction

Answer 34

= false is B

Question 35

In accommodation which one of the following does not take place?: A) Relaxation of Circular Ciliary Muscle B) Relaxation of Zonules C) Thickening of Lens D) Increase of Lens Refractive Power

Answer 35

Relaxation of circular ciliary muscle does not happen